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1.  Prevalence and clonality of methicillin-resistant Staphylococcus aureus (MRSA) in the Atlantic Azores islands: predominance of SCCmec types IV, V and VI 
In order to obtain insights into the methicillin-resistant Staphylococcus aureus (MRSA) population structure in the Azores archipelago, 106 MRSA isolates were collected from patients attending an Azorean central hospital between January 2007 and February 2008. Antimicrobial resistance was determined for all isolates. Molecular typing was performed by pulsed-field gel electrophoresis (PFGE), spa typing, multilocus sequence typing (MLST), staphylococcal chromosome cassette mec (SCCmec) typing and the presence of Panton–Valentine leukocidin (PVL). The majority of the isolates (87%, n = 92) belonged to the EMRSA-15 clone (ST22, SCCmec-IVh), followed by the Pediatric clone (ST5-VI/IVc) (11%, n = 12). The Berlin clone (ST45-IVa) and a new clone (spa type t1839, ST1339 and SCCmec V variant) were represented by single isolates. All of the isolates carried SCCmec types IV, V or VI and a non-multiresistant antibiotic profile, resembling the currently emerging community MRSA. Moreover, PVL was described for the first time to be associated with the Pediatric clone carrying SCCmec type VI. We provided the first description of the population structure of MRSA in the Azores islands, which seems to be shaped by genetic events occurring locally, as well as by the regular population exchange between the islands, continental Portugal, the United Kingdom and the United States.
PMCID: PMC2854357  PMID: 20229224
2.  Cost-Effectiveness and Efficacy of spa, SCCmec, and PVL Genotyping of Methicillin-Resistant Staphylococcus aureus as Compared to Pulsed-Field Gel Electrophoresis 
PLoS ONE  2013;8(11):e79149.
Pulsed-field gel electrophoresis (PFGE) is a valuable molecular typing assay used for methicillin-resistant Staphylococcus aureus (MRSA) surveillance and genotyping. However, there are several limitations associated with PFGE. In Alberta, Canada, the significant increase in the number of MRSA isolates submitted to the Provincial Laboratory for Public Health (ProvLab) for PFGE typing led to the need for an alternative genotyping method. In this study, we describe the transition from PFGE to Staphylococcus protein A (spa), Staphylococcal cassette chromosome (SCCmec), and Panton-Valentine leukocidin (PVL) typing. A total of 1915 clinical MRSA isolates collected from 2005 to 2009 were used to develop and validate an algorithm for assigning PFGE epidemic types using spa, SCCmec, and PVL typing and the resulting data was used to populate a new Alberta MRSA typing database. An additional 12620 clinical MRSA isolates collected from 2010 to 2012 as part of ongoing routine molecular testing at ProvLab were characterized using the new typing algorithm and the Alberta MRSA typing database. Switching to spa, SCCmec, and PVL from PFGE typing substantially reduced hands-on and turn-around times while maintaining historical PFGE epidemic type designations. This led to an approximate $77,000 reduction in costs from 2010 to 2012. PFGE typing is still required for a small subset of MRSA isolates that have spa types that are rare, novel, or associated with more than one PFGE epidemic type.
PMCID: PMC3828336  PMID: 24244440
3.  Predominance of Community-Associated Methicillin-Resistant Staphylococcus aureus Strains Carrying Staphylococcal Chromosome Cassette mec Type IVA in South Korea▿  
Journal of Clinical Microbiology  2007;45(12):4021-4026.
Studies on the molecular epidemiologic characteristics of methicillin-resistant Staphylococcus aureus (MRSA) strains have demonstrated their genetic and geographical diversity. In addition, it has been reported that there are genetic differences between community-associated (CA) and health care-associated (HA) MRSA strains. Therefore, we investigated the major epidemiologic characteristics of CA MRSA isolates in South Korea and compared them with those of HA MRSA strains. Distributions of staphylococcal chromosome cassette mec (SCCmec) types and other molecular features, including the Panton-Valentine leukocidin (PVL) gene, were studied in 138 invasive MRSA isolates. Multiplex type IVA SCCmec was identified as the major CA MRSA infection type (53.1%), with a significantly higher prevalence than in HA MRSA (P < 0.001). One major group of type IVA strains carried a larger atypical class B mec element and new subtypes of ccrA2 (96% amino acid homology). The PVL gene was detected in one USA300-like isolate only. Seven major clone types determined by combinational grouping (genetic background SCCmec typing) showed representative patterns of antimicrobial susceptibilities. We concluded that less multi-drug-resistant strains of clone types B-I and D-1 (genetic background, B and D complexes; type IVA SCCmec) predominate in CA MRSA and that international PVL-positive strains have not spread in South Korea as yet.
PMCID: PMC2168574  PMID: 17942660
4.  Livestock-associated Methicillin-Resistant Staphylococcus aureus Sequence Type 398 in Humans, Canada 
Emerging Infectious Diseases  2010;16(4):587-594.
Recent emergence of infections resulting from this strain is of public health concern.
Rates of colonization with livestock-associated methicillin-resistant Staphylococcus aureus (MRSA) sequence type 398 have been high for pigs and pig farmers in Canada, but prevalence rates for the general human population are unknown. In this study, 5 LA-MRSA isolates, 4 of which were obtained from skin and soft tissue infections, were identified from 3,687 tested MRSA isolates from persons in Manitoba and Saskatchewan, Canada. Further molecular characterization determined that these isolates all contained staphylococcal cassette chromosome (SCC) mecV, were negative for Panton-Valentine leukocidin, and were closely related by macrorestriction analysis with the restriction enzyme Cfr91. The complete DNA sequence of the SCCmec region from the isolate showed a novel subtype of SCCmecV harboring clustered regularly interspaced short palindromic repeats and associated genes. Although prevalence of livestock-associated MRSA seems to be low for the general population in Canada, recent emergence of infections resulting from this strain is of public health concern.
PMCID: PMC3321955  PMID: 20350371
Methicillin-resistant Staphylococcus aureus; ST398; livestock associated; SCCmec; CRISPR; zoonoses; Canada; bacteria; expedited; research
5.  Characterization of Methicillin-Resistant Staphylococcus aureus Strains Recovered from a Phase IV Clinical Trial for Linezolid versus Vancomycin for Treatment of Nosocomial Pneumonia 
Journal of Clinical Microbiology  2012;50(11):3694-3702.
A total of 434 methicillin-resistant Staphylococcus aureus (MRSA) baseline isolates were collected from subjects enrolled in a prospective, double-blind randomized trial comparing linezolid versus vancomycin for the treatment of nosocomial pneumonia. Isolates were susceptibility tested by broth microdilution, examined for inducible clindamycin resistance by D-test, and screened for heterogeneous resistance to vancomycin (hVISA) by the Etest macromethod. All strains were subjected to Panton-Valentine leukocidin (PVL) screening, and SCCmec, pulsed-field gel electrophoresis (PFGE), and spa typing. Selected strains were evaluated by multilocus sequence typing (MLST). Clonal complexes (CCs) were assigned based on the spa and/or MLST results. Most strains were CC5 (56.0%), which originated from North America (United States) (CC5-MRSA-SCCmec II/IV; 70.0%), Asia (CC5-MRSA-II; 14.0%) and Latin America (CC5-MRSA-I/II; 12.3%). The second- and third-most-prevalent clones were CC8-MRSA-IV (23.3%) and CC239-MRSA-III (11.3%), respectively. Furthermore, the CC5-MRSA-I/II clone predominated in Asia (50.7% within this region) and Latin America (66.7%), followed by CC239-MRSA-III (32.8% and 28.9%, respectively). The European strains were CC8-MRSA-IV (34.5%), CC22-MRSA-IV (18.2%), or CC5-MRSA-I/II/IV (16.4%), while the U.S. MRSA isolates were CC5-MRSA-II/IV (64.4%) or CC8-MRSA-IV (28.8%). Among the U.S. CC8-MRSA-II/IV strains, 73.7% (56/76 [21.2% of all U.S. MRSA strains]) clustered within USA300. One strain from the United States (USA800) was intermediate to vancomycin (MIC, 4 μg/ml). All remaining strains were susceptible to linezolid, daptomycin, vancomycin, and teicoplanin. hVISA strains (14.5%) were predominantly CC5-MRSA-II, from South Korea, and belonged to a single PFGE type. Overall, each region had two predominant clones. The USA300 rate corroborates previous reports describing increased prevalence of USA300 strains causing invasive infections. The prevalence of hVISA was elevated in Asia, and these strains were associated with CC5.
PMCID: PMC3486224  PMID: 22972817
6.  Short Communication: Methicillin-Resistant Staphylococcus aureus Infections in Children and Young Adults Infected with HIV 
AIDS Research and Human Retroviruses  2009;25(12):1219-1224.
The epidemiology of methicillin-resistant Staphylococcus aureus (MRSA) infections, in particular with Panton-Valentine leukocidin (PVL)-positive strains, has not been well characterized in children and young adults with HIV infection. It is not known if PVL-positive strains of MRSA cause an increased morbidity in this population compared to PVL-negative strains. The purpose of this study was to retrospectively analyze the epidemiology of PVL-positive and PVL-negative MRSA infections in children and young adults with HIV from 2000 to 2007. Molecular typing was performed by polymerase chain reaction (PCR) for detection of the PVL genes. Staphylococcus Cassette Chromosome (SCC) mec and spa typing were performed on all PVL-positive isolates. The number of HIV patients with MRSA infection increased significantly between 2000 and 2007 (p = 0.0015). Twenty seven (87%) of the 31 MRSA isolates were from skin and soft tissue infections (SSTI). Clindamycin resistance was observed in 19% of the MRSA isolates. PVL-positive isolates bearing the type IV SCC mec element comprised 16 of 31 (52%) MRSA isolates. All the PVL-positive isolates belonged to the USA300 pulsed-field type. There was no difference in the mean CD4 count and HIV viral load between patients with PVL-positive and PVL-negative MRSA infections. PVL-positive MRSA infections were associated with more SSTI (p = 0.043) but not with increased morbidity or a higher risk of complications compared to PVL-negative MRSA infections in children and young adults with HIV.
PMCID: PMC2858900  PMID: 20001313
7.  A correlative analysis of epidemiologic and molecular characteristics of methicillin-resistant Staphylococcus aureus clones from diverse geographic locations with virulence measured by a Caenorhabditis elegans host model 
Methicillin-resistant Staphylococcus aureus (MRSA) strains from different geographic areas have different genetic backgrounds, suggesting independent clonal evolutions. To better understand the virulence of MRSA strains and the relationship to their clonal and geographic origins, we undertook an analysis of epidemiologic, molecular, and virulence characteristics of a large number of MRSA isolates from geographically diverse origins, in a Caenorhabditis elegans infection model. A total of 99 MRSA isolates collected between 1993 and 2010 at the Geneva University Hospitals from diverse global origins were characterized with Panton–Valentine leukocidin (PVL), toxic shock syndrome toxin (TSST), accessory gene regulator (agr) group, staphylococcal cassette chromosome mec (SCCmec), S. aureus protein A (spa), multilocus sequence typing (MLST), and pulsed-field gel electrophoresis (PFGE) typing. Epidemiologic data were provided from clinical records. The bacterial virulence was tested in a C. elegans host model. The inter-relationships of epidemiological/molecular characteristics in association with nematocidal activities were analyzed with univariate and two-factor analysis of variance (ANOVA). Community-associated MRSA (CA-MRSA) strains were more virulent than hospital-associated MRSA (HA-MRSA), with higher nematocidal activities in CA-MRSA strains (0.776 vs. 0.506, p = 0.0005). All molecular characteristics (PVL, TSST, spa, SCCmec, MLST, and PFGE types) showed a significant association with nematocidal activities on univariate analysis (p < 0.005). PVL was not a significant predictor after adjusting for genomic backgrounds using spa, MLST, or PFGE typing. The dominant CA-MRSA strains in North America showed higher nematocidal activities than strains from other regions (p < 0.0001). Strains with global origins containing distinct genetic backgrounds have different virulence in the C. elegans model. Nematocidal activities were most highly correlated with SCCmec, spa, MLST, and PFGE typing, suggesting that genomic background rather than a single exotoxin characteristic was the most discriminating predictor of virulence.
PMCID: PMC3545200  PMID: 22898726
8.  Outbreak in Alberta of community-acquired (USA300) methicillin-resistant Staphylococcus aureus in people with a history of drug use, homelessness or incarceration 
The USA300 strain of community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) can cause severe infection and is increasingly recognized as a cause of community outbreaks. In 2004, an outbreak was identified in the Calgary Health Region (CHR).
MRSA isolates were identified with standard methods at a central regional laboratory and typed via pulsed-field gel electrophoresis (PFGE). Isolates were tested by PCR for mecA, Panton–Valentine leukocidin (PVL), SCCmec, and spa genes. Cases were defined as such if a clinical isolate of the USA300 strain was noted between January 1 and September 30, 2004, and the patient had lived or traveled in CHR within 2 years before symptom onset. Demographic, clinical and risk data on all such cases were collected from several sources for statistical analysis. A case was defined as high-risk if the patient had a history of drug use, homelessness or incarceration.
Of 40 isolates with the USA300 PFGE pattern, all tested positive for PVL, SCCmec type IVa and spa type 008. Almost all infections (39/40, 98%) involved skin and soft tissues, except for 1 death from necrotizing hemorrhagic pneumonia; a notable proportion (38%) required hospital admission or intravenous antimicrobial therapy. The outbreak centred on the high-risk population in CHR (70%; risk ratio 169.4, 95% confidence interval 86.1–333.0).
People with histories of illicit drug use, homelessness or recent incarceration were at highest risk for infection with CA-MRSA. The emergence and spread of this virulent strain has important implications for treatment and public health in Canada.
PMCID: PMC1490001  PMID: 16804118
9.  Changing Epidemiology of Methicillin-Resistant Staphylococcus aureus in Iceland from 2000 to 2008: a Challenge to Current Guidelines ▿ †  
Journal of Clinical Microbiology  2010;48(11):4221-4227.
The epidemiology of methicillin-resistant Staphylococcus aureus (MRSA) is continuously changing. Iceland has a low incidence of MRSA. A “search and destroy” policy (screening patients with defined risk factors and attempting eradication in carriers) has been implemented since 1991. Clinical and microbiological data of all MRSA patients from the years 2000 to 2008 were collected prospectively. Isolates were characterized by pulsed-field gel electrophoresis (PFGE), sequencing of the repeat region of the Staphylococcus protein A gene (spa typing), staphylococcal cassette chromosome mec (SCCmec) typing, and screening for the Panton-Valentine leukocidin (PVL) gene. Two hundred twenty-six infected (60%) or colonized (40%) individuals were detected (annual incidence 2.5 to 16/100,000). From 2000 to 2003, two health care-associated outbreaks dominated (spa types t037 and t2802), which were successfully controlled with extensive infection control measures. After 2004, an increasing number of community-associated (CA) cases without relation to the health care system occurred. A great variety of clones (40 PFGE types and 49 spa types) were found, reflecting an influx of MRSA from abroad. The USA300 and Southwest Pacific (SWP) clones were common. SCCmec type IV was most common (72%), and 38% of the isolates were PVL positive. The incidence of MRSA in Iceland has increased since 1999 but remains low and has been stable in the last years. The search and destroy policy was effective to control MRSA in the health care setting. However, MRSA in Iceland is now shifting into the community, challenging the current Icelandic guidelines, which are tailored to the health care system.
PMCID: PMC3020889  PMID: 20844224
10.  Extensive Dissemination of Methicillin-Resistant Staphylococcus aureus (MRSA) between the Hospital and the Community in a Country with a High Prevalence of Nosocomial MRSA 
PLoS ONE  2013;8(4):e59960.
According to the EARS-Net surveillance data, Portugal has the highest prevalence of nosocomial methicillin-resistant Staphylococcus aureus (MRSA) in Europe, but the information on MRSA in the community is very scarce and the links between the hospital and community are not known. In this study we aimed to understand the events associated to the recent sharp increase in MRSA frequency in Portugal and to evaluate how this has shaped MRSA epidemiology in the community. With this purpose, 180 nosocomial MRSA isolates recovered from infection in two time periods and 14 MRSA isolates recovered from 89 samples of skin and soft tissue infections (SSTI) were analyzed by pulsed-field gel electrophoresis (PFGE), staphylococcal chromosome cassette mec (SCCmec) typing, spa typing and multilocus sequence typing (MLST). All isolates were also screened for the presence of Panton Valentine leukocidin (PVL) and arginine catabolic mobile element (ACME) by PCR. The results showed that ST22-IVh, accounting for 72% of the nosocomial isolates, was the major clone circulating in the hospital in 2010, having replaced two previous dominant clones in 1993, the Iberian (ST247-I) and Portuguese (ST239-III variant) clones. Moreover in 2010, three clones belonging to CC5 (ST105-II, ST125-IVc and ST5-IVc) accounted for 20% of the isolates and may represent the beginning of new waves of MRSA in this hospital. Interestingly, more than half of the MRSA isolates (8/14) causing SSTI in people attending healthcare centers in Portugal belonged to the most predominant clones found in the hospital, namely ST22-IVh (n = 4), ST5-IVc (n = 2) and ST105-II (n = 1). Other clones found included ST5-V (n = 6) and ST8-VI (n = 1). None of the MRSA isolates carried PVL and only five isolates (ST5-V-t179) carried ACME type II. The emergence and spread of EMRSA-15 may be associated to the observed increase in MRSA frequency in the hospital and the consequent spillover of MRSA into the community.
PMCID: PMC3617237  PMID: 23593155
11.  Molecular Characterization of Methicillin-Resistant Staphylococcus aureus with Emergence of Epidemic Clones of Sequence Type (ST) 22 and ST 772 in Mumbai, India▿  
Journal of Clinical Microbiology  2010;48(5):1806-1811.
A total of 412 methicillin-resistant Staphylococcus aureus (MRSA) strains isolated between October 2006 and June 2009, representing a mixed hospital- and community-associated patient population from Mumbai, India, were evaluated. MRSA was characterized by multiplex PCR amplification of the Panton-Valentine leukocidin (PVL) gene and the mecA gene, staphylococcal cassette chromosome mec (SCCmec) typing, and multilocus sequence typing (MLST). PCR results were compared with patient risk factors (CDC guidelines) and antimicrobial susceptibility profiles. A total of 395 MRSA strains were mecA positive, and 224 were PVL gene positive. A total of 97 mecA-positive strains were SCCmec III (25%), 136 were SCCmec IV (34%), and 162 were SCCmec V (41%). All SCCmec III strains were multidrug resistant, and all patients had risk factors. Of the SCCmec IV and V strains, 73% were multidrug susceptible and 72% of the associated patients had no risk factors. The multidrug susceptibility and absence of patient risk factors in 72% of cases with SCCmec IV and SCCmec V MRSA demonstrate the presence of community-associated MRSA (CA-MRSA) in Mumbai. Twenty-one percent of these patients had risk factors, signifying CA-MRSA infiltration into hospitals. MLST showed clonal expansion of multidrug-susceptible sequence type (ST) 22 (SCCmec IV) and ST 772 (SCCmec V), both of which feature in Asian studies and may be slowly replacing the multidrug-resistant ST 239 (SCCmec III) in hospitals. The PVL gene-positive methicillin-sensitive S. aureus (MSSA) strains were ST 30 and were postulated to be related to the penicillin-resistant S. aureus phage type 80/81, notorious for its virulence in the 1950s.
PMCID: PMC2863868  PMID: 20351212
12.  Invasive Infection Caused by a Community-Associated Methicillin-Resistant Staphylococcus aureus Strain Not Carrying Panton-Valentine Leukocidin in South Korea▿  
Journal of Clinical Microbiology  2009;48(1):311-313.
Panton-Valentine leukocidin (PVL)-negative, SCCmec type IVa strains are the most common strains of methicillin-resistant Staphylococcus aureus (MRSA) circulating in the community in South Korea. This report describes five elderly patients presenting in 2006 to 2007 with invasive community-associated MRSA infection caused by a PVL-negative, SCCmec type IVa strain with sequence type 72 and spa type t324.
PMCID: PMC2812302  PMID: 19889903
13.  Trends in Methicillin-Resistant Staphylococcus aureus Anovaginal Colonization in Pregnant Women in 2005 versus 2009▿  
Journal of Clinical Microbiology  2010;48(10):3675-3680.
In 2005, the prevalence of methicillin-resistant Staphylococcus aureus (MRSA) anovaginal colonization in pregnant women at our center (Columbia University Medical Center) was 0.5%, and MRSA-colonized women were less likely to carry group B streptococcus (GBS). In this study, our objectives were to identify changing trends in the prevalence of MRSA and methicillin-susceptible S. aureus (MSSA) anovaginal colonization in pregnant women, to assess the association between MRSA and GBS colonization, and to characterize the MRSA strains. From February to July 2009, Lim broths from GBS surveillance samples were cultured for S. aureus. MRSA strains were identified by resistance to cefoxitin and characterized by MicroScan, staphylococcal cassette chromosome mec (SCCmec) typing, pulsed-field gel electrophoresis (PFGE), spa typing, and Panton-Valentine leukocidin PCR. A total of 2,921 specimens from different patients were analyzed. The prevalences of MSSA, MRSA, and GBS colonization were 11.8%, 0.6% and 23.3%, respectively. GBS colonization was associated with S. aureus colonization (odds ratio [OR], 1.9; 95% confidence interval [95% CI], 1.5 to 2.4). The frequencies of GBS colonization were similar in MRSA-positive (34.2%) versus MRSA-negative patients (21.8%) (P = 0.4). All MRSA isolates from 2009 and 13/14 isolates from 2005 were SCCmec type IV or V, consistent with community-associated MRSA; 12/18 (2009) and 0/14 (2005) isolates were the USA300 clone. Levofloxacin resistance increased from 14.3% (2005) to 55.6% (2009) (P = 0.028). In conclusion, the prevalence of MRSA anovaginal colonization in pregnant women in New York City, NY, remained stable from 2005 to 2009, and USA300 emerged as the predominant clone with a significant increase in levofloxacin-resistant isolates.
PMCID: PMC2953117  PMID: 20686089
14.  Differentiation of Clonal Complex 59 Community-Associated Methicillin-Resistant Staphylococcus aureus in Western Australia▿ ‡ 
Clonal complex 59 (CC59) community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) strains were characterized using pulsed-field gel electrophoresis, spa typing, multilocus sequence typing, diagnostic DNA microarrays, and PCRs targeting staphylococcal cassette chromosome mec (SCCmec) elements and Panton-Valentine leukocidin (PVL). Six distinct groups within CC59 were characterized. At least seven different variants of SCCmec elements were identified (IVa [2B], IVb [2B], IVd [2B], IV variant [2B], IVa [2B&5], V variant [5C2], and V [5C2&5]). (The structural type is indicated by a Roman numeral, with a lowercase letter indicating the subtype, and the ccr complex and the mec complex are indicated by an Arabic numeral and an uppercase letter, respectively. Where there is an extra ccr element, this is indicated by “&” and an Arabic numeral designating the ccr type.) The first group is similar to the American sequence type 59 (ST59) MRSA-IV CA-MRSA strain USA1000. The second group includes a PVL-negative ST87 strain with an SCCmec element of subtype IVb (2B). The third group comprises PVL-variable ST59 MRSA-IV strains harboring multiple SCCmec IV subtypes. PVL-negative ST59 MRSA strains with multiple or composite SCCmec elements (IVa [2B&5]) form the fourth group. Group 5 corresponds to the internationally known “Taiwan clone,” a PVL-positive strain with a variant SCCmec element (V [5C2&5]). This strain proved to be the most common CC59 MRSA strain isolated in Western Australia. Finally, group 6 encompasses the ST59 MRSA-V variant (5C2). The differentiation of CC59 into groups and strains indicates a rapid evolution and spread of SCCmec elements. Observed differences between groups of strains as well as intrastrain variability within a group facilitate the tracing of their spread.
PMCID: PMC2863625  PMID: 20211891
15.  High-Density Livestock Production and Molecularly Characterized MRSA Infections in Pennsylvania 
Environmental Health Perspectives  2014;122(5):464-470.
Background: European studies suggest that living near high-density livestock production increases the risk of sequence type (ST) 398 methicillin-resistant Staphylococcus aureus (MRSA) colonization. To our knowledge, no studies have evaluated associations between livestock production and human infection by other strain types.
Objectives: We evaluated associations between MRSA molecular subgroups and high-density livestock production.
Methods: We conducted a yearlong 2012 prospective study on a stratified random sample of patients with culture-confirmed MRSA infection; we oversampled patients from the Geisinger Health System with exposure to high-density livestock production in Pennsylvania. Isolates were characterized using S. aureus protein A (spa) typing and detection of Panton-Valentine leukocidin (PVL) and scn genes. We compared patients with one of two specific MRSA strains with patients with all other strains of MRSA isolates, using logistic regression that accounted for the sampling design, for two different exposure models: one based on the location of the animals (livestock model) and the other on crop field application of manure (crop field model).
Results: Of 196 MRSA isolates, we identified 30 spa types, 47 PVL-negative and 15 scn-negative isolates, and no ST398 MRSA. Compared with quartiles 1–3 combined, the highest quartiles of swine livestock and dairy/veal crop field exposures were positively associated with community-onset-PVL-negative MRSA (CO-PVL-negative MRSA vs. all other MRSA), with adjusted odds ratios of 4.24 (95% CI: 1.60, 11.25) and 4.88 (95% CI: 1.40, 17.00), respectively. The association with CO-PVL-negative MRSA infection increased across quartiles of dairy/veal livestock exposure (trend p = 0.05).
Conclusions: Our findings suggest that other MRSA strains, beyond ST398, may be involved in livestock-associated MRSA infection in the United States.
Citation: Casey JA, Shopsin B, Cosgrove SE, Nachman KE, Curriero FC, Rose HR, Schwartz BS. 2014. High-density livestock production and molecularly characterized MRSA infections in Pennsylvania. Environ Health Perspect 122:464–470;
PMCID: PMC4014753  PMID: 24509131
16.  Panton–Valentine Leukocidin-Positive Methicillin-Resistant Staphylococcus aureus Infections in Children With Cancer 
Pediatric blood & cancer  2009;53(7):1216-1220.
New strains of methicillin-resistant Staphylococcus aureus (MRSA) which frequently carry the Panton–Valentine leukocidin (PVL) genes have been recognized to cause invasive infections in otherwise healthy children and adults. However, the epidemiology of PVL-positive MRSA infections has not been described in children or adults with cancer.
The epidemiology of MRSA infections in patients with cancer was retrospectively studied from 2000 to 2007. Molecular typing was performed by polymerase chain reaction (PCR) for the detection of the PVL genes. Staphylococcus cassette chromosome (SCC) mec and spa typing was performed on all PVL-positive isolates.
A total of 88 MRSA isolates from clinically distinct infectious episodes were collected from 88 patients with cancer during the 8-year study period. Infections were predominant in the skin and soft tissues (SSTI; P =0.0003). PVL-positive isolates, bearing the type IV SCCmec element, encoding the gene for methicillin resistance, increased significantly during this period (P =0.043) and comprised 35 of 88 (40%) MRSA isolates. Of these 35 isolates, 32 belonged to spa type 8 and were USA300 genotype. Patients infected with PVL-positive strains did not have more SSTI (P =0.166) or bacteremia (P =0.510) as compared to patients with PVL-negative strains. A greater percentage of PVL-positive isolates were susceptible to ciprofloxacin (P =0.006).
PVL-positive MRSA infections are not associated with a higher morbidity as compared to PVL-negative MRSA infections in children with cancer.
PMCID: PMC3075015  PMID: 19731325
cancer; children; methicillin-resistant Staphylococcus aureus; Panton-Valentine leukocidin
17.  Population Structure of Staphylococcus aureus Strains Isolated from Intensive Care Unit Patients in The Netherlands over an 11-Year Period (1996 to 2006) ▿  
Journal of Clinical Microbiology  2009;47(12):4090-4095.
The genetic background and the presence of several virulence factors of Staphylococcus aureus isolates from intensive care unit (ICU) patients from 14 hospitals in The Netherlands isolated from 1996 until 2006 were investigated. In total, 936 methicillin-susceptible S. aureus (MSSA) and 7 methicillin-resistant S. aureus (MRSA) isolates were collected. The genetic background was determined by spa typing and multilocus sequence typing (MLST). The virulence determinants Panton-Valentine leukocidin (PVL), toxic shock syndrome toxin 1 (TSST-1), and collagen adhesion (CNA) were detected with real-time PCR assays. On the MRSA isolates, mobile resistance staphylococcal cassette chromosome mec (SCCmec) typing was performed. Among the MSSA isolates, 313 different spa types were observed. A genetic background common to MRSA clones, e.g., MLST clonal complex 1 (CC1), CC5, CC8, CC22, CC30, and CC45, was observed among 62% of the isolates. The remaining isolates were associated with MSSA-related MLST CCs. MLST CC1, CC25, and CC30 were continuously present, and other MLST CCs fluctuated over time. Two percent of the MSSA isolates harbored PVL, 21% had TSST-1, and 46% were positive for CNA. There were no changes in the prevalence of the virulence factors over time. Four MRSA isolates were typed as ST8-MRSA-IV (where ST is the MLST sequence type and IV is the SCCmec type), two were ST5-MRSA-II, and one was ST228-MRSA-I. All MRSA isolates were PVL, CNA, and TSST-1 negative except for the two ST5-MRSA-II isolates, which were TSST-1 positive. No changes in the S. aureus genetic background and the prevalence of the virulence factors PVL, CNA, and TSST-1 were observed in ICU patients in The Netherlands over time.
PMCID: PMC2786662  PMID: 19812275
18.  Community-associated and healthcare-associated methicillin-resistant Staphylococcus aureus virulence toward Caenorhabditis elegans compared 
Virulence  2012;3(7):576-582.
Community-associated (CA) methicillin-resistant Staphylococcus aureus (MRSA) strains have emerged as major human pathogens. CA-MRSA virulence appears to be distinct from healthcare-associated (HA) MRSA with several factors [α-hemolysin (Hla), Panton-Valentine leukocidin (PVL), α-type phenol soluble modulins (PSMα) and SCCmec IV] postulated to enhance virulence or fitness. Using the Caenorhabditis elegans infection model, we compared the virulence of clinical and laboratory isolates of CA-MRSA and HA-MRSA and explored the contribution of CA-MRSA associated virulence factors to nematode killing. All CA-MRSA strains were highly pathogenic to nematodes, while HA-MRSA strains demonstrated variable nematode killing. Nematode killing by isogenic mutants of hla or the loci for PVL, PSMα, PSMβ, PSMδ or SCCmec IV was not different than the parental strains. These results demonstrate that CA-MRSA is highly virulent, shows some strains of HA-MRSA are equally virulent toward nematodes and suggests CA-MRSA virulence in C. elegans is not linked to a single virulence factor.
PMCID: PMC3545934  PMID: 23076331
community-associated methicillin-resistant Staphylococcus aureus; healthcare-associated methicillin-resistant Staphylococcus aureus; Caenorhabditis elegans; virulence factors; multilocus sequence type
19.  Molecular features of heterogeneous vancomycin-intermediate Staphylococcus aureus strains isolated from bacteremic patients 
BMC Microbiology  2009;9:189.
Heterogeneous vancomycin-intermediate Staphylococcus aureus (hVISA) bacteremia is an emerging infection. Our objective was to determine the molecular features of hVISA strains isolated from bacteremic patients and to compare them to methicillin resistant S. aureus (MRSA) and methicillin sensitive S. aureus (MSSA) blood isolates.
We assessed phenotypic and genomic changes of hVISA (n = 24), MRSA (n = 16) and MSSA (n = 17) isolates by PCR to determine staphylococcal chromosomal cassette (SCCmec) types, Panton-Valentine leukocidin (PVL) and the accessory gene regulator (agr) loci. Biofilm formation was quantified. Genetic relatedness was assessed by PFGE. PFGE analysis of isolates was diverse suggesting multiple sources of infection. 50% of hVISA isolates carried SCCmec type I, 21% type II; 25% type V; in 4% the SCCmec type could not be identified. Among MRSA isolates, 44% were SCCmec type I, 12.5% type II, 25% type V, 12.5% were non-typable, and 6% were SCCmec type IVd. Only one hVISA isolate and two MSSA isolates carried the PVL. Biofilm formation and agr patterns were diverse.
hVISA isolates were diverse in all parameters tested. A considerable number of hVISA and MRSA strains carried the SCCmec type V cassette, which was not related to community acquisition.
PMCID: PMC2749053  PMID: 19732456
20.  National Surveillance of Methicillin-Resistant Staphylococcus aureus in China Highlights a Still-Evolving Epidemiology with 15 Novel Emerging Multilocus Sequence Types 
Journal of Clinical Microbiology  2013;51(11):3638-3644.
The global spread of methicillin-resistant Staphylococcus aureus (MRSA) is a serious problem, particularly in mainland China. In order to better understand the national molecular epidemiology and resistance profiles of hospital-associated MRSA (HA-MRSA) in China, a laboratory-based multicenter surveillance study was conducted. Sixty-nine hospitals in 45 large cities in 27 provinces were involved, and a total of 1,141 HA-MRSA isolates were collected during the 6-month study period in 2011. All MRSA isolates were characterized by multilocus sequence typing (MLST), staphylococcal cassette chromosome mec (SCCmec) typing, spa typing, detection of the Panton-Valentine leukocidin (PVL) locus (lukS-PV and lukF-PV), and antibiogram analysis. ST239-III-t030, ST239-III-t037, and ST5-II-t002 were the predominant HA-MRSA clones (overall prevalence rates, 57.1%, 12.9%, and 8.1%, respectively), although the prevalence rates of these major clones varied markedly in different administrative regions. Of note, 6.6% of the HA-MRSA isolates were found to belong to ST59, which had typical community-associated MRSA (CA-MRSA) features, including carriage of SCCmec type IV or V and PVL and less antimicrobial resistance than other major HA-MRSA clones. Moreover, among 36 MLST sequence types (STs) identified, 15 STs, accounting for 3.5% of total isolates, were novel. A novel ST designated ST2590, which is a single-locus variant of ST5-II-t002, was identified in three hospitals in two large cities, with a total of 17 isolates. To further monitor trends in HA-MRSA prevalence, epidemic clonal shifts, clone emergence, and transmission between community and health care settings, longitudinal national MRSA surveillance is required.
PMCID: PMC3889745  PMID: 23985906
21.  Presence and Molecular Epidemiology of Virulence Factors in Methicillin-Resistant Staphylococcus aureus Strains Colonizing and Infecting Soldiers▿  
Journal of Clinical Microbiology  2009;47(4):940-945.
Methicillin-resistant Staphylococcus aureus (MRSA) has emerged as an important cause of skin and soft-tissue infections (SSTI). The understanding of the molecular epidemiology and virulence of MRSA continues to expand. From January 2005 to December 2005, we screened soldiers for MRSA nasal colonization, administered a demographic questionnaire, and monitored them prospectively for SSTI. All MRSA isolates underwent molecular analysis, which included pulsed-filed gel electrophoresis (PFGE) and PCR for Panton-Valentine leukocidin (PVL), the arginine catabolic mobile element (ACME), and the staphylococcal cassette chromosome mec (SCCmec). Of the 3,447 soldiers screened, 134 (3.9%) had MRSA colonization. Of the 3,066 (89%) who completed the study, 39 developed culture-confirmed MRSA abscesses. Clone USA300 represented 53% of colonizing isolates but was responsible for 97% of the abscesses (P < 0.001). Unlike colonizing isolates, isolates positive for USA300, PVL, ACME, and type IV SCCmec were significantly associated with MRSA abscess isolates. As determined by multivariate analysis, risk factors for MRSA colonization were a history of SSTI and a history of hospitalization. Although various MRSA strains may colonize soldiers, USA300 is the most virulent when evaluated prospectively, and PVL, ACME, and type IV SCCmec are associated with these abscesses.
PMCID: PMC2668321  PMID: 19213694
22.  A Panton-Valentine Leucocidin (PVL)-Positive Community-Acquired Methicillin-Resistant Staphylococcus aureus (MRSA) Strain, Another Such Strain Carrying a Multiple-Drug Resistance Plasmid, and Other More-Typical PVL-Negative MRSA Strains Found in Japan 
Journal of Clinical Microbiology  2005;43(7):3356-3363.
Community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) was collected from children with bullous impetigo in 2003 and 2004. One strain collected in 2003 was Panton-Valentine leucocidin (PVL) positive. In 2004, a multiple-drug-resistant PVL+ CA-MRSA strain was isolated from an athlete with a cutaneous abscess. These strains were analyzed by multilocus sequence typing, spa typing, agr typing, coagulase typing, staphylococcal cassette chromosome mec (SCCmec) typing, PCR assay for 30 virulence genes, drug susceptibility testing, pulsed-field gel electrophoresis, and for plasmids. The two Japanese PVL+ CA-MRSA strains belonged to the globally extant (“pandemic”) sequence type 30 (ST30) with SCCmec IV. A transmissible, multiple-drug resistance plasmid emerged in such ST30 strains. The PVL− CA-MRSA strains (“domestic” CA-MRSA) accumulated for bullous impetigo, exhibiting new genotypes. Hospital-acquired MRSA of ST91 (but not pandemic ST5) shared common features with the PVL− CA-MRSA strain.
PMCID: PMC1169136  PMID: 16000460
23.  Recombination between ccrC Genes in a Type V (5C2&5) Staphylococcal Cassette Chromosome mec (SCCmec) of Staphylococcus aureus ST398 Leads to Conversion from Methicillin Resistance to Methicillin Susceptibility In Vivo▿ †  
Various types of the staphylococcal cassette chromosome mec (SCCmec) are known to confer methicillin resistance on the human pathogen Staphylococcus aureus. Such cassettes are not always stably maintained. The present studies were aimed at identifying the mechanism underlying the in vivo conversion of methicillin-resistant S. aureus (MRSA) to methicillin-susceptible S. aureus (MSSA) derivatives as encountered in two patients suffering from pneumonia and an umbilicus infection, respectively. All MRSA and MSSA isolates identified belong to multilocus sequence type (MLST) 398, have spa type t034, and are Panton-Valentine leukocidin positive. Sequencing of 27,616 nucleotides from the chromosomal SCCmec insertion site in orfX to the hsdR gene for a restriction enzyme revealed a type V (5C2&5) SCCmec. Sequence comparisons show that parts of the cassette are highly similar to sequences within SCCmec elements from coagulase-negative staphylococci, indicating a possible common origin. The cassette investigated contains ccrC-carrying units on either side of its class C2b mec gene complex. In vivo loss of the mec gene complex was caused by recombination between the recombinase genes ccrC1 allele 8 and ccrC1 allele 10. In vitro, the SCCmec was very stable, and low-frequency MRSA-to-MSSA conversion was only observed when MRSA isolates were cultivated at 41°C for prolonged periods of time. In this case also, loss of the mec complex was due to ccrC gene recombination. Interestingly, the MRSA and MSSA isolates studied displayed no detectable differences in competitive growth and virulence, suggesting that the presence of the intact type V (5C2&5) SCCmec has no negative bearing on staphylococcal fitness under the conditions used.
PMCID: PMC2812175  PMID: 19995931
24.  Prevalence and Molecular Characterization of Methicillin-Resistant Staphylococcus aureus ST398 Resistant to Tetracycline at a Spanish Hospital over 12 Years 
PLoS ONE  2013;8(9):e72828.
Methicillin-resistant Staphylococcus aureus (MRSA) ST398, associated with livestock animals, was described in 2003 as a new lineage infecting or colonizing humans. We evaluated the prevalence and molecular characteristics of MRSA ST398 isolated in the Hospital Universitari de Bellvitge from January 2000 to June 2011. Tetracycline resistant (Tet-R) MRSA isolates from single patients (pts) were screened by SmaI-pulsed field gel electrophoresis (PFGE). Nontypable MRSA strains by SmaI (NTSmaI)-MRSA were further analysed by ApaI-PFGE, spa, SCCmec, agr, MLST typing, and by DNA microarray hybridization. Among 164 pts harboring Tet-R MRSA, NTSmaI-MRSA ST398-agrI was found in 33 pts (20%). Although the first pt was detected in 2003, 22/33 pts (67%) were registered in the 2010–2011 period. Ten pts (30%) were infected and cancer was the most frequent underlying disease. In one case, death was due to MRSA-ST398-related infection. Five pulsotypes (A–E) were detected using ApaI-PFGE, with type A accounting for 76% of the strains. The majority of the studied isolates presented spa type t011 (70%) and SCCmec type V (88%). One strain was spa negative both by PCR and microarray analysis. Forty-nine percent of the studied isolates showed resistance to 3 or more antibiotic classes, in addition to beta-lactams. Ciprofloxacin resistance was 67%. Tet-R was mediated by tet(M) and tet(K) in 26 isolates. All isolates lacked Panton-Valentine Leukocidin production, as well as other significant toxins. This study displays the molecular features of MRSA-ST398 clone and shows the increase in tetracycline resistance together with arise in MRSA-ST398 isolates infecting or colonizing patients in our clinical setting.
PMCID: PMC3764106  PMID: 24039806
25.  Emergence of Virulent Methicillin-Resistant Staphylococcus aureus Strains Carrying Panton-Valentine Leucocidin Genes in The Netherlands 
Journal of Clinical Microbiology  2005;43(7):3341-3345.
Methicillin-resistant Staphylococcus aureus (MRSA) strains carrying the Panton-Valentine leucocidin (PVL) genes have been reported worldwide and are a serious threat to public health. The PVL genes encode a highly potent toxin which is involved in severe skin infections and necrotizing pneumonia, even in previously healthy individuals. We assessed the prevalence of PVL-positive MRSA in The Netherlands for two periods of time: (i) 1987 through 1995 and (ii) 2000 and 2002, and determined their characteristics by using multilocus sequence typing and staphylococcal chromosome cassette (SCCmec) typing. It was found that up to 15% of all MRSA isolates detected in The Netherlands harbored the PVL genes. Most PVL-positive MRSA isolates were obtained from severe soft tissue infections in relatively young individuals. The first PVL-positive MRSA described in The Netherlands, isolated in 1988, was a single-locus variant of the “Berlin” epidemic MRSA clone. The 20 PVL-positive MRSA isolates studied in 2000 and 2002 consisted of five different sequence types (STs) that belonged to four clonal complexes. One of the STs, ST80, is considered to be a widespread European clone and was the most predominant ST (60%) in this study, while ST37 had never been found to be associated with PVL-positive MRSA. Most isolates harbored SCCmec type IV, a supposed marker for community-acquired MRSA. The number and type of virulence-associated genes varied among the different STs.
PMCID: PMC1169179  PMID: 16000458

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