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1.  Daptomycin exposure precedes infection and/or colonization with daptomycin non-susceptible enterococcus 
Background
Daptomycin non-susceptible enterococci (DNSE) are emerging as an important cause of healthcare-associated infection, however little is known about the epidemiology of DNSE. At the University of Iowa Hospitals and Clinics (UIHC) an increase in the frequency of patients infected and/or colonized with DNSE has occurred. The goals of this study were to evaluate potential factors associated with the development of DNSE colonization and/or infection and to compare the characteristics of patients with prior daptomycin exposure to those without prior daptomycin exposure.
Methods
The study is a retrospective case-series involving all patients with DNSE infection and/or colonization at UIHC, a 734-bed academic referral center, from June 1, 2005 to June 1, 2011.
Results
The majority of patients with DNSE colonization and/or infection had prior daptomycin exposure (15 of 25; 60%), a concomitant gastrointestinal process (19 of 25; 76%), or were immunosuppressed (21 of 25; 84%). DNSE infection was confirmed in 17 of 25 (68%) patients, including 9 patients with bacteremia. Twelve of 17 (71%) patients with DNSE infection had prior daptomycin exposure, including 7 of 9 (78%) patients with bacteremia. Compared to patients without prior daptomycin exposure, patients with prior daptomycin exposure were less likely to harbor E. faecalis (0% vs. 33%; p = 0.019). A high proportion of patients (10 of 25; 40%) died during their hospitalizations. Most enterococcal isolates were E. faecium (86%), and were vancomycin-resistant (72%). Molecular typing revealed a diverse population of DNSE.
Conclusions
Prior daptomycin exposure, immunosuppression, and/or a concomitant gastrointestinal process, may be associated with the development of DNSE. PFGE revealed a diverse population of DNSE, which along with both increasing numbers of DNSE detected yearly and increasing annual rates of daptomycin usage, suggests the emergence of DNSE under antimicrobial pressure.
doi:10.1186/2047-2994-1-19
PMCID: PMC3436660  PMID: 22958379
Enterococcus; Daptomycin; Resistance; Non-Susceptible; DNSE
2.  Activity of Ceftaroline and Epidemiologic Trends in Staphylococcus aureus Isolates Collected from 43 Medical Centers in the United States in 2009▿ 
A Staphylococcus aureus surveillance program was initiated in the United States to examine the in vitro activity of ceftaroline and epidemiologic trends. Susceptibility testing by Clinical and Laboratory Standards Institute broth microdilution was performed on 4,210 clinically significant isolates collected in 2009 from 43 medical centers. All isolates were screened for mecA by PCR and evaluated by pulsed-field gel electrophoresis. Methicillin-resistant S. aureus (MRSA) were analyzed for Panton-Valentine leukocidin (PVL) genes and the staphylococcal cassette chromosome mec (SCCmec) type. All isolates had ceftaroline MICs of ≤2 μg/ml with an MIC50 of 0.5 and an MIC90 of 1 μg/ml. The overall resistance rates, expressed as the percentages of isolates that were intermediate and resistant (or nonsusceptible), were as follows: ceftaroline, 1.0%; clindamycin, 30.2% (17.4% MIC ≥ 4 μg/ml; 12.8% inducible); daptomycin, 0.2%; erythromycin, 65.5%; levofloxacin, 39.9%; linezolid, 0.02%; oxacillin, 53.4%; tetracycline, 4.4%; tigecycline, 0%; trimethoprim-sulfamethoxazole, 1.6%; vancomycin, 0%; and high-level mupirocin, 2.2%. The mecA PCR was positive for 53.4% of the isolates. The ceftaroline MIC90s were 0.25 μg/ml for methicillin-susceptible S. aureus and 1 μg/ml for MRSA. Among the 2,247 MRSA isolates, 51% were USA300 (96.9% PVL positive, 99.7% SCCmec type IV) and 17% were USA100 (93.4% SCCmec type II). The resistance rates for the 1,137 USA300 MRSA isolates were as follows: erythromycin, 90.9%; levofloxacin, 49.1%; clindamycin, 7.6% (6.2% MIC ≥ 4 μg/ml; 1.4% inducible); tetracycline, 3.3%; trimethoprim-sulfamethoxazole, 0.8%; high-level mupirocin, 2.7%; daptomycin, 0.4%; and ceftaroline and linezolid, 0%. USA300 is the dominant clone causing MRSA infections in the United States. Ceftaroline demonstrated potent in vitro activity against recent S. aureus clinical isolates, including MRSA, daptomycin-nonsusceptible, and linezolid-resistant strains.
doi:10.1128/AAC.00315-11
PMCID: PMC3165333  PMID: 21709080
3.  Prevalence and Genetic Relatedness of Methicillin-Susceptible Staphylococcus aureus Isolates Detected by the Xpert MRSA Nasal Assay ▿  
Journal of Clinical Microbiology  2011;49(8):2996-2999.
Methicillin-susceptible Staphylococcus aureus (MSSA) isolates lacking mecA yet testing positive on the Xpert MRSA assay were recovered from culture for 7.7% of 248 Xpert-positive nasal samples. These “false-positive” Xpert results may be attributed to staphylococcal cassette chromosome (SCC) elements without the mecA gene. Pulsed-field gel electrophoresis (PFGE) analysis revealed a diverse population of MSSA strains.
doi:10.1128/JCM.00046-11
PMCID: PMC3147776  PMID: 21677066
4.  Characterization of blaKPC-containing Klebsiella pneumoniae isolates detected in different institutions in the Eastern USA 
Background
The emergence of blaKPC-containing Klebsiella pneumoniae (KPC-Kp) isolates is attracting significant attention. Outbreaks in the Eastern USA have created serious treatment and infection control problems. A comparative multi-institutional analysis of these strains has not yet been performed.
Methods
We analysed 42 KPC-Kp recovered during 2006–07 from five institutions located in the Eastern USA. Antimicrobial susceptibility tests, analytical isoelectric focusing (aIEF), PCR and sequencing of bla genes, PFGE and rep-PCR were performed.
Results
By in vitro testing, KPC-Kp isolates were highly resistant to all non-carbapenem β-lactams (MIC90s ≥ 128 mg/L). Among carbapenems, MIC50/90s were 4/64 mg/L for imipenem and meropenem, 4/32 mg/L for doripenem and 8/128 for ertapenem. Combinations of clavulanate or tazobactam with a carbapenem or cefepime did not significantly lower the MIC values. Genetic analysis revealed that the isolates possessed the following bla genes: blaKPC-2 (59.5%), blaKPC-3 (40.5%), blaTEM-1 (90.5%), blaSHV-11 (95.2%) and blaSHV-12 (50.0%). aIEF of crude β-lactamase extracts from these strains supported our findings, showing β-lactamases at pIs of 5.4, 7.6 and 8.2. The mean number of β-lactamases was 3.5 (range 3–5). PFGE demonstrated that 32 (76.2%) isolates were clonally related (type A). Type A KPC-Kp isolates (20 blaKPC-2 and 12 blaKPC-3) were detected in each of the five institutions. rep-PCR showed patterns consistent with PFGE.
Conclusions
We demonstrated the complex β-lactamase background of KPC-Kp isolates that are emerging in multiple centres in the Eastern USA. The prevalence of a single dominant clone suggests that interstate transmission has occurred.
doi:10.1093/jac/dkn547
PMCID: PMC2640158  PMID: 19155227
carbapenemases; ESBLs; Enterobacteriaceae; PFGE; rep-PCR
5.  Methicillin-Resistant Staphylococcus aureus (MRSA) Strain ST398 Is Present in Midwestern U.S. Swine and Swine Workers 
PLoS ONE  2009;4(1):e4258.
Background
Recent research has demonstrated that many swine and swine farmers in the Netherlands and Canada are colonized with MRSA. However, no studies to date have investigated carriage of MRSA among swine and swine farmers in the United States (U.S.).
Methods
We sampled the nares of 299 swine and 20 workers from two different production systems in Iowa and Illinois, comprising approximately 87,000 live animals. MRSA isolates were typed by pulsed field gel electrophoresis (PFGE) using SmaI and EagI restriction enzymes, and by multi locus sequence typing (MLST). PCR was used to determine SCCmec type and presence of the pvl gene.
Results
In this pilot study, overall MRSA prevalence in swine was 49% (147/299) and 45% (9/20) in workers. The prevalence of MRSA carriage among production system A's swine varied by age, ranging from 36% (11/30) in adult swine to 100% (60/60) of animals aged 9 and 12 weeks. The prevalence among production system A's workers was 64% (9/14). MRSA was not isolated from production system B's swine or workers. Isolates examined were not typeable by PFGE when SmaI was used, but digestion with EagI revealed that the isolates were clonal and were not related to common human types in Iowa (USA100, USA300, and USA400). MLST documented that the isolates were ST398.
Conclusions
These results show that colonization of swine by MRSA was very common on one swine production system in the midwestern U.S., suggesting that agricultural animals could become an important reservoir for this bacterium. MRSA strain ST398 was the only strain documented on this farm. Further studies are examining carriage rates on additional farms.
doi:10.1371/journal.pone.0004258
PMCID: PMC2626282  PMID: 19145257
6.  Evaluation of Etest and Disk Diffusion Methods Compared with Broth Microdilution Antifungal Susceptibility Testing of Clinical Isolates of Candida spp. against Posaconazole▿  
Journal of Clinical Microbiology  2007;45(6):1974-1977.
We performed Etest, disk diffusion, and broth microdilution susceptibility testing of 2,171 clinical isolates of Candida spp. against posaconazole. By using provisional breakpoints for comparison purposes only, the categorical agreement between the agar-based methods and broth microdilution results ranged from 93 to 98%, with <1% very major errors. The essential agreement (within 2 well dilutions) between the Etest and broth microdilution methods was 94%. These agar-based methods hold promise as simple and reliable methods for determination of the posaconzole susceptibilities of Candida spp.
doi:10.1128/JCM.02087-06
PMCID: PMC1933029  PMID: 17301284
7.  Evaluation of Disk Diffusion and Etest Compared to Broth Microdilution for Antifungal Susceptibility Testing of Posaconazole against Clinical Isolates of Filamentous Fungi▿  
Journal of Clinical Microbiology  2007;45(4):1322-1324.
We performed Etest, disk diffusion, and broth microdilution susceptibility testing of posaconazole against 146 clinical isolates of filamentous fungi. By using provisional breakpoints for comparison purposes only, categorical agreement between the results of the agar-based methods and those of broth microdilution were 96 to 98%, with no very major errors. These agar-based methods hold promise as simple and reliable methods for determining the posaconazole susceptibilities of filamentous fungi.
doi:10.1128/JCM.02450-06
PMCID: PMC1865846  PMID: 17267623

Results 1-7 (7)