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1.  Use of the Bruker MALDI Biotyper for Identification of Molds in the Clinical Mycology Laboratory 
Journal of Clinical Microbiology  2014;52(8):2797-2803.
Matrix-assisted laser desorption ionization–time of flight mass spectrometry (MALDI-TOF MS) is increasingly used for the identification of bacteria and fungi in the diagnostic laboratory. We evaluated the mold database of Bruker Daltonik (Bremen, Germany), the Filamentous Fungi Library 1.0. First, we studied 83 phenotypically and molecularly well-characterized, nondermatophyte, nondematiaceous molds from a clinical strain collection. Using the manufacturer-recommended interpretation criteria, genus and species identification rates were 78.3% and 54.2%, respectively. Reducing the species cutoff from 2.0 to 1.7 significantly increased species identification to 71.1% without increasing misidentifications. In a subsequent prospective study, 200 consecutive clinical mold isolates were identified by the MALDI Biotyper and our conventional identification algorithm. Discrepancies were resolved by ribosomal DNA (rDNA) internal transcribed spacer region sequence analysis. For the MALDI Biotyper, genus and species identification rates were 83.5% and 79.0%, respectively, when using a species cutoff of 1.7. Not identified were 16.5% of the isolates. Concordant genus and species assignments of MALDI-TOF MS and the conventional identification algorithm were observed for 98.2% and 64.2% of the isolates, respectively. Four erroneous species assignments were observed using the MALDI Biotyper. The MALDI Biotyper seems highly reliable for the identification of molds when using the Filamentous Fungi Library 1.0 and a species cutoff of 1.7. However, expansion of the database is required to reduce the number of nonidentified isolates.
PMCID: PMC4136132  PMID: 24850347
2.  Validation of Antibiotic Susceptibility Testing Guidelines in a Routine Clinical Microbiology Laboratory Exemplifies General Key Challenges in Setting Clinical Breakpoints 
This study critically evaluated the new European Committee for Antimicrobial Susceptibility Testing (EUCAST) antibiotic susceptibility testing guidelines on the basis of a large set of disk diffusion diameters determined for clinical isolates. We report several paradigmatic problems that illustrate key issues in the selection of clinical susceptibility breakpoints, which are of general importance not only for EUCAST but for all guidelines systems, i.e., (i) the need for species-specific determinations of clinical breakpoints/epidemiological cutoffs (ECOFFs), (ii) problems arising from pooling data from various sources, and (iii) the importance of the antibiotic disk content for separating non-wild-type and wild-type populations.
PMCID: PMC4068562  PMID: 24777093
3.  Evaluation of the Bruker MALDI Biotyper for Identification of Gram-Positive Rods: Development of a Diagnostic Algorithm for the Clinical Laboratory 
Journal of Clinical Microbiology  2014;52(4):1089-1097.
Reported matrix-assisted laser desorption ionization–time of flight mass spectrometry (MALDI-TOF MS) identification rates of Gram-positive rods (GPR) are low compared to identification rates of Gram-positive cocci. In this study, three sample preparation methods were compared for MALDI-TOF MS identification of 190 well-characterized GPR strains: direct transfer, direct transfer-formic acid preparation, and ethanol-formic acid extraction. Using the interpretation criteria recommended by the manufacturer, identification rates were significantly higher for direct transfer-formic acid preparation and ethanol-formic acid extraction than for direct transfer. Reducing the species cutoff from 2.0 to 1.7 significantly increased species identification rates. In a subsequent prospective study, 215 clinical GPR isolates were analyzed by MALDI-TOF MS, and the results were compared to those for identification using conventional methods, with discrepancies being resolved by 16S rRNA and rpoB gene analysis. Using the direct transfer-formic acid preparation and a species cutoff of 1.7, congruencies on the genus and species levels of 87.4% and 79.1%, respectively, were achieved. In addition, the rate of nonidentified isolates dropped from 12.1% to 5.6% when using an extended database, i.e., the Bruker database amended by reference spectra of the 190 GPR of the retrospective study. Our data demonstrate three ways to improve GPR identification by the Bruker MALDI Biotyper, (i) optimize sample preparation using formic acid, (ii) reduce cutoff scores for species identification, and (iii) expand the database. Based on our results, we suggest an identification algorithm for the clinical laboratory combining MALDI-TOF MS with nucleic acid sequencing.
PMCID: PMC3993486  PMID: 24452159
4.  Influence of Clinical Breakpoint Changes from CLSI 2009 to EUCAST 2011 Antimicrobial Susceptibility Testing Guidelines on Multidrug Resistance Rates of Gram-Negative Rods 
Journal of Clinical Microbiology  2013;51(7):2385-2387.
Multidrug resistance (MDR) rates of Gram-negative rods were analyzed comparing CLSI 2009 and EUCAST 2011 antibiotic susceptibility testing guidelines. After EUCAST 2011 was applied, the MDR rates increased for Klebsiella pneumoniae (2.2%), Enterobacter cloacae (1.1%), Pseudomonas aeruginosa (0.7%), and Escherichia coli (0.4%). A total of 24% of Enterobacteriaceae MDR isolates and 12% of P. aeruginosa MDR isolates were categorized as MDR due to breakpoint changes.
PMCID: PMC3697730  PMID: 23596246
5.  Identification of Gram-Positive Cocci by Use of Matrix-Assisted Laser Desorption Ionization–Time of Flight Mass Spectrometry: Comparison of Different Preparation Methods and Implementation of a Practical Algorithm for Routine Diagnostics 
Journal of Clinical Microbiology  2013;51(6):1834-1840.
This study compared three sample preparation methods (direct transfer, the direct transfer-formic acid method with on-target formic acid treatment, and ethanol-formic acid extraction) for the identification of Gram-positive cocci with matrix-assisted laser desorption ionization–time of flight mass spectrometry (MALDI-TOF MS). A total of 156 Gram-positive cocci representing the clinically most important genera, Aerococcus, Enterococcus, Staphylococcus, and Streptococcus, as well as more rare genera, such as Gemella and Granulicatella, were analyzed using a Bruker MALDI Biotyper. The rate of correct genus-level identifications was approximately 99% for all three sample preparation methods. The species identification rate was significantly higher for the direct transfer-formic acid method and ethanol-formic acid extraction (both 77.6%) than for direct transfer (64.1%). Using direct transfer-formic acid compared to direct transfer, the total time to result was increased by 22.6%, 16.4%, and 8.5% analyzing 12, 48, and 96 samples per run, respectively. In a subsequent prospective study, 1,619 clinical isolates of Gram-positive cocci were analyzed under routine conditions by MALDI-TOF MS, using the direct transfer-formic acid preparation, and by conventional biochemical methods. For 95.6% of the isolates, a congruence between conventional and MALDI-TOF MS identification was observed. Two major limitations were found using MALDI-TOF MS: the differentiation of members of the Streptococcus mitis group and the identification of Streptococcus dysgalactiae. The Bruker MALDI Biotyper system using the direct transfer-formic acid sample preparation method was shown to be a highly reliable tool for the identification of Gram-positive cocci. We here suggest a practical algorithm for the clinical laboratory combining MALDI-TOF MS with phenotypic and molecular methods.
PMCID: PMC3716085  PMID: 23554198
6.  Prosthetic Valve Endocarditis and Bloodstream Infection Due to Mycobacterium chimaera 
Journal of Clinical Microbiology  2013;51(6):1769-1773.
Prosthetic valve endocarditis (PVE) due to fast-growing nontuberculous mycobacteria (NTM) has been reported anecdotally. Reports of PVE with slowly growing NTM, however, are lacking. We present here one case of PVE and one case of bloodstream infection caused by Mycobacterium chimaera. Randomly amplified polymorphic DNA (RAPD)-PCR indicated a relatedness of the two M. chimaera strains. Both patients had heart surgery 2 years apart from each other. A nosocomial link was not detected.
PMCID: PMC3716099  PMID: 23536407
7.  Change of Antibiotic Susceptibility Testing Guidelines from CLSI to EUCAST: Influence on Cumulative Hospital Antibiograms  
PLoS ONE  2013;8(11):e79130.
We studied whether the change in antibiotic susceptibility testing (AST) guidelines from CLSI to EUCAST influenced cumulative antibiograms in a tertiary care hospital in Switzerland.
Antibiotic susceptibilities of non-duplicate isolates collected within a one-year period before (period A) and after (period B) changing AST interpretation from CLSI 2009 to EUCAST 1.3 (2011) guidelines were analysed. In addition, period B isolates were reinterpreted according to the CLSI 2009, CLSI 2013 and EUCAST 3.1 (2013) guidelines.
The majority of species/drug combinations showed no differences in susceptibility rates comparing periods A and B. However, in some gram-negative bacilli, decreased susceptibility rates were observed when comparing CLSI 2009 with EUCAST 1.3 within period B: Escherichia coli / cefepime, 95.8% (CLSI 2009) vs. 93.1% (EUCAST 1.3), P=0.005; Enterobacter cloacae / cefepime, 97.0 (CLSI 2009) vs. 90.5% (EUCAST 1.3), P=0.012; Pseudomonas aeruginosa / meropenem, 88.1% (CLSI 2009) vs. 78.3% (EUCAST 1.3), P=0.002. These differences were still evident when comparing susceptibility rates according to the CLSI 2013 guideline with EUCAST 3.1 guideline. For P. aeruginosa and imipenem, a trend towards a lower antibiotic susceptibility rate in ICUs compared to general wards turned into a significant difference after the change to EUCAST: 87.9% vs. 79.8%, P=0.08 (CLSI 2009) and 86.3% vs. 76.8%, P=0.048 (EUCAST 1.3).
The change of AST guidelines from CLSI to EUCAST led to a clinically relevant decrease of susceptibility rates in cumulative antibiograms for defined species/drug combinations, particularly in those with considerable differences in clinical susceptibility breakpoints between the two guidelines.
PMCID: PMC3815097  PMID: 24223893
8.  Standardisation of disk diffusion results for antibiotic susceptibility testing using the sirscan automated zone reader 
BMC Microbiology  2013;13:225.
Standardisation of disk diffusion readings could improve reproducibility and accuracy of antibiotic susceptibility testing (AST). This study evaluated accuracy, reproducibility, and precision of automated inhibition zone reading using the “Sirscan automatic” zone reader (i2a, Perols Cedex, France).
In a first step we compared Sirscan results with manual calliper measurements for comparability and accuracy. Sirscan readings were checked and adjusted on-screen as recommended by the manufacturer. One hundred clinical bacterial isolates representing a broad spectrum of organisms routinely isolated in a clinical laboratory were tested, and zone diameter values and interpretation according to EUCAST guidelines were compared. In a second step we analysed, whether fully automated zone reading can decrease standard deviation of diameter measurements and, thus, improve reproducibility and precision of the disk diffusion method. Standard deviations of manual measurements, on-screen adjusted Sirscan measurements, and fully automated Sirscan readings were compared for 19 repeat independent measurements of inhibition zones of S. aureus ATCC 29213, E. coli ATCC 25922, and P. aeruginosa ATCC 27853 (EUCAST quality control strains).
On-screen adjusted Sirscan and calliper measurements displayed high comparability. No significant differences were detected comparing the results of both reading methods. Standard deviations of inhibition zone diameters were significantly lower for fully automated Sirscan measurements compared with both adjusted Sirscan readings and the manual method, resulting in better reproducibility and precision of the automated readings.
Our results indicate that fully automated zone reading can further improve standardisation of AST by decreasing standard deviation and, thus, improve precision of inhibition zone diameter results.
PMCID: PMC3852248  PMID: 24099061
Inhibition zone diameter; Kirby-Bauer; Automation
9.  Meningoencephalitis with Subdural Empyema Caused by Toxigenic Clostridium perfringens Type A 
Journal of Clinical Microbiology  2012;50(10):3409-3411.
We report a clinical case of meningoencephalitis with subdural empyema in an immunocompromised farmer caused by toxigenic Clostridium perfringens type A, which was identified by 16S RNA gene analysis of cerebrospinal fluid and subdural empyema. In immunocompromised patients, C. perfringens should be considered a potential pathogen of sepsis.
PMCID: PMC3457414  PMID: 22895036
10.  Practical Approach for Reliable Detection of AmpC Beta-Lactamase-Producing Enterobacteriaceae ▿  
Journal of Clinical Microbiology  2011;49(8):2798-2803.
In this prospective study all Enterobacteriaceae isolates (n = 2,129) recovered in the clinical microbiology laboratory during October 2009 to April 2010 were analyzed for AmpC production. Clinical and Laboratory Standards Institute (CLSI) cefoxitin and cefotetan susceptibility breakpoints and CLSI critical ESBL diameters were used to screen for potential AmpC producers. In total, 305 isolates (211 potential AmpC producers and 94 AmpC screen-negative isolates as a control group) were further analyzed by multiplex PCR for the detection of plasmid-encoded ampC beta-lactamase genes and by ampC promoter sequence analysis (considered as the gold standard). Cefoxitin and cefotetan were assessed as primary screening markers. The sensitivities of cefoxitin and cefotetan for the detection of AmpC production were 97.4 and 52.6%, respectively, and the specificities were 78.7 and 99.3%, respectively. As a phenotypic confirmation test, the Etest AmpC and the cefoxitin-cloxacillin double-disk synergy method (CC-DDS) were compared. The sensitivities for the Etest AmpC and the CC-DDS method were 77.4 and 97.2%, respectively, and the specificity was 100% for both methods. The results of the Etest AmpC were inconclusive for 10 isolates. With the CC-DDS method 2 inconclusive results were observed. Based on this study, we propose a comprehensive diagnostic flow chart for the detection of AmpC production consisting of a simple phenotypic screening and a single phenotypic confirmation test with inconclusive results being resolved by molecular analysis. For the proposed flow chart using (i) cefoxitin as a screening marker for AmpC production, (ii) the CC-DDS method as phenotypic confirmation, and (iii) molecular methods in case of inconclusive results, the sensitivity and specificity for AmpC detection would have been 97.4 and 100%, respectively, with respect to the studied isolates. The phenotypic methods used in the AmpC algorithm are simple to perform and easy to implement in the diagnostic laboratory.
PMCID: PMC3147735  PMID: 21632895
11.  Detection of Methicillin-Resistant Staphylococcus aureus (MRSA) in Specimens from Various Body Sites: Performance Characteristics of the BD GeneOhm MRSA Assay, the Xpert MRSA Assay, and Broth-Enriched Culture in an Area with a Low Prevalence of MRSA Infections ▿  
Journal of Clinical Microbiology  2010;48(11):3882-3887.
Universal surveillance upon patient admission is important in reducing the transmission of methicillin-resistant Staphylococcus aureus (MRSA) and associated disease in hospitals. High costs for the health care system in conjunction with MRSA have promoted the development of rapid screening methods to detect MRSA carriers. This study compared two real-time PCR methods, the BD GeneOhm MRSA assay (BDGO) and the Xpert MRSA assay, with broth-enriched culture to define their performance characteristics and rapidity in an area with low MRSA prevalence. In total, 414 swabs from the nose and 389 swabs from the groin from 425 patients were tested. Of those 425 patients, 378 had swabs from both the nose and groin in parallel. Two hundred thirty-one and 194 patients were randomly assigned to the BDGO group and the Xpert MRSA group, respectively. In general, sensitivity, specificity, and negative predictive value (NPV) were high for the BDGO (100%, 98.5%, and 100%, respectively) and the Xpert MRSA (100%, 98.2%, and 100%, respectively), irrespective of whether or not nasal and inguinal specimens were considered alone or combined. In contrast, the positive predictive value (PPV) was lower: before the resolution of discrepant results, the PPVs for nasal and inguinal specimens alone and combined were 87.5%, 86.7%, and 82.4% for the BDGO and 91.7%, 66.7%, and 92.9% for the Xpert MRSA, respectively. After the resolution of discrepant results, PPVs were 93.8%, 93.3% and 94.1% for the BDGO and 91.7%, 88.9% and 92.9% for the Xpert MRSA, respectively. With the BDGO, 4 of 16 carriers were each identified by nasal or inguinal swabs alone, whereas in the Xpert MRSA group, 4 of 13 carriers were exclusively identified by nasal swabs and 2 of 13 were identified by inguinal swabs alone. Both PCR methods showed no significant difference in the number of discrepant results (odds ratio, 0.70 [P = 0.789]), but specimens from wounds and other body sites (axilla, vagina, and throat) produced discrepancies more often than nasal and groin specimens (odds ratios, 4.724 [P = 0.058] and 12.163 [P < 0.001], respectively). The facts that no false-negative PCR results were detected and increased PPVs were found after the resolution of discrepant results point to PCR as the actual gold standard. Since both sensitivity and NPV were exceptionally high for PCR, backup cultures may, therefore, be unnecessary in an area with low prevalence and with a preemptive isolation strategy but may still be useful for PCR-positive specimens because of the lower PPV for both methods and the possibility of susceptibility testing. The median time for analysis, including extraction, hands-on time, and actual PCR was 2 h 20 min for the Xpert MRSA versus 5 h 40 min for the BDGO. Concerning reporting time, including administration and specimen collection, the Xpert MRSA was faster than the BDGO (7 h 50 min versus 17 h).
PMCID: PMC3020866  PMID: 20861339
12.  Rapid Detection of Methicillin-Resistant Staphylococcus aureus (MRSA) in Diverse Clinical Specimens by the BD GeneOhm MRSA Assay and Comparison with Culture▿  
Journal of Clinical Microbiology  2010;48(3):981-984.
The efficacy of the BD GeneOhm methicillin-resistant Staphylococcus aureus (MRSA) assay was assessed by analyzing nasal swabs and swabs from other body sites for the presence of MRSA in a low-prevalence area. From 681 patients with a high risk for MRSA carriage, 1,601 specimens were collected and transported in Amies agar. After discordant analysis, the sensitivity, specificity, positive predictive value, and negative predictive value of the BD GeneOhm MRSA assay were 84.3%, 99.2%, 88.4%, and 98.9%, respectively, compared to culture.
PMCID: PMC2832448  PMID: 20071545
13.  Septicemia Caused by Tick-borne Bacterial Pathogen Candidatus Neoehrlichia mikurensis 
Emerging Infectious Diseases  2010;16(7):1127-1129.
We have repeatedly detected Candidatus Neoehrlichia mikurensis, a bacterium first described in Rattus norvegicus rats and Ixodes ovatus ticks in Japan in 2004 in the blood of a 61-year-old man with signs of septicemia by 16S rRNA and groEL gene PCR. After 6 weeks of therapy with doxycycline and rifampin, the patient recovered.
PMCID: PMC3358111  PMID: 20587186
Candidatus Neoehrlichia mikurensis; septicemia; human infection; 16S rRNA gene PCR; therapy; tick-borne pathogen; bacteria; dispatch
14.  Urinary Tract Infection Caused by Eikenella corrodens▿ 
PMCID: PMC1828998  PMID: 17122012

Results 1-14 (14)