Multicenter evaluation of rapid antimicrobial susceptibility testing by VITEK®2 directly from positive blood culture

STUDY OBJECTIVE

To compare the antimicrobial susceptibility testing (AST) performance of positive blood cultures (PBC) VITEK®2 off-label use (D0) and traditional VITEK®2 workflow using isolated colonies after overnight (D1).

METHODS

Patient samples with monomicrobial Gram-negative rod or Gram-positive cocci in clusters bacteremia were tested on D0 and compared to D1 AST results in 7 laboratories in France.

RESULTS

Overall, categorical and essential agreement rates were 98.4% and 96.7%, respectively. Very major discrepancy and major discrepancy rates for Enterobacterales and Staphylococci satisfied the NF EN ISO 20776-2 (2007) criteria for sepsis-relevant drugs. Very major discrepancies were >3% for amoxicillin-clavulanate (4.9%, 6/122), piperacillin-tazobactam (7.5%, 4/53) and meropenem (33%,1/3) for Enterobacterales and gentamicin for Staphylococci (4.6%, 4/87).

CONCLUSION

Direct AST from PBC broths by VITEK®2 for Enterobacterales and Staphylococci is reliable and fast and may positively influence antimicrobial stewardship.

Multicenter Clinical Evaluation of ETEST Eravacycline for Susceptibility Testing of Enterobacteriaceae and Enterococci

Eravacycline (ERV) (brand name Xerava [Tetraphase]) is a new tetracycline-class antibacterial that has been approved by the U.S. Food and Drug Administration (FDA) and the European Medicines Agency (EMA) for treatment of complicated intra-abdominal infections (cIAIs). ETEST is a gradient diffusion method that represents a simple alternative to the broth microdilution (BMD) method for performing antimicrobial susceptibility testing (AST). A multicenter evaluation of the performance of the new ETEST ERV (bioMérieux) in comparison with BMD was conducted following FDA and International Standards Organization (ISO) recommendations, using FDA- and EUCAST-defined breakpoints. Clinical isolates of Enterobacteriaceae (n = 542) and Enterococcus spp. (n = 137) were included. Based on the BMD reference method, 92 Enterobacteriaceae isolates and 9 enterococcal isolates were nonsusceptible to ERV according to the FDA breakpoints, while 7 Escherichia coli isolates and 3 Enterococcus sp. isolates were classified as ERV resistant according the EUCAST breakpoints. Referring to FDA performance criteria, the ETEST ERV demonstrated 99.4% and 100.0% essential agreement (EA), 98.0% and 94.9% categorical agreement (CA), very major error (VME) rates of 5.4% and 33.33%, and major error (ME) rates of 1.3% and 3.1% with clinical and challenge isolates, respectively, of Enterobacteriaceae and Enterococcus spp. According to EUCAST breakpoints, E. coli and Enterococcus sp. isolate results also met ISO acceptance criteria for EA and CA (EA of 99.0% and 100.0%, respectively, and CA of 100.0% for both), without any VMEs or MEs. In conclusion, we report that ETEST ERV represents an accurate tool for performing ERV AST of Enterobacteriaceae and Enterococcus sp. isolates.

656. Sulbactam-Durlobactam MIC Determination: Comparative Evaluation of the New ETEST® SUD to the CLSI 2021 Broth Microdilution Method

Background

Species belonging to the Acinetobacter baumannii-calcoaceticus (ABC) complex, such as A. baumannii, A. pittii and A. nosocomialis, are a major cause of hospital acquired infections and outbreaks with increasing occurrence of multidrug-resistance. Sulbactam-durlobactam (SUD), a combination of one active β-lactam antibiotic (sulbactam) with a new β-lactamase inhibitor (durlobactam), is currently being tested in a phase 3 clinical trial by Entasis Therapeutics for the treatment of serious infections caused by ABC, including multidrug-resistant strains. At the same time, an ETEST^® SUD (sulbactam-durlobactam - MIC range 0.004/4-64/4 µg/mL) has been developed and calibrated versus the broth microdilution reference method (BMD) as described by the Clinical and Laboratory Standards Institute (CLSI). This test is intended to determine the MIC of sulbactam-durlobactam for species of the ABC complex. The aim of this study was to perform a first comparative study of ETEST SUD with the CLSI BMD method on a panel of 263 isolates.

Methods

The panel consisted of 204 A. baumannii, 29 A. pittii, 30 A. nosocomialis, including 24 SUD-resistant strains, and one CLSI QC strain. BMD was performed using the 2021 CLSI guidelines. ETEST SUD was evaluated using the standard ETEST procedure for Acinetobacter spp. (inoculum 0.5 McFarland, Mueller Hinton medium, incubation at 35°C for 20-24h). For each method, the MIC was read at complete inhibition of visible growth. To determine category agreement (CA) and error rates, the sulbactam-durlobactam provisional breakpoint of 4 µg/mL was applied.

Results

The QC strain MICs were in the expected range with reproducible results. The essential MIC agreement [EA, ±1 dilution] was 97.7% without any tendency to over- or underestimate the MIC when compared to BMD. The CA was 98.5%. Two Very Major Errors, both within the EA, and two Major Errors, one within the EA, were observed.

Conclusion

In this study, the ETEST SUD was found to be equivalent to the CLSI reference method. MIC end points were easy to read. With a 15-dilution range and simplicity of use, ETEST SUD could represent a valuable tool for MIC determination and could be an alternative to BMD.

For Research Use Only. The performance characteristics of this product have not been established yet.

Disclosures

All Authors: No reported disclosures

Performance of the VITEK®2 advanced expert system™ for the validation of antimicrobial susceptibility testing results

Time to reporting antimicrobial susceptibility testing (AST) results to physicians plays an essential role in antibiotic stewardship programs. Expert software has been developed for facilitating the microbiologists' AST review process. The reliability of the VITEK®2 Advanced Expert™ software to effectively alert the microbiologist in detection of atypical and inconsistent AST results was assessed at the Labor Berlin-Charité Vivantes services. The results demonstrated a confidence rate of 99.3% in reporting fully consistent AST results to physicians.

1227. Plazomicin Susceptibility Testing using ETEST® MIC for Enterobacterales

Background

Plazomicin (PLZ) approved by FDA in June of 2018, is an aminoglycoside class antibacterial indicated for the treatment of adults with complicated urinary tract infections (cUTI) including pyelonephritis caused by Enterobacterales. It is used in patients who have limited or no alternative treatment options, e.g. CRE and MDRO patients. The drug has bactericidal activity, it is active against organisms producing ESBL, Carbapenemase and aminoglycoside-modifying enzymes. The purpose of this study was to compare ETEST® PLZ bioMérieux to the broth microdilution reference method (BMD) for Citrobacter freundii, Enterobacter cloacae, Escherichia coli, Klebsiella oxytoca and pneumoniae, Morganella morganii, Providencia stuartii, Proteus mirabilis and vulgaris and Serratia marcescens isolates.

Methods

A total of 598 isolates were tested by ETEST® (PLZ) and BMD at four clinical trial sites.

Isolates were subcultured on tryptic soy or Columbia agar plates supplemented with 5% sheep blood. Suspensions of the isolates were prepared in 0.85% saline, which were used to inoculate BMD and Mueller Hinton agar for ETEST®. Results were read after 16-20 hours incubation at 35°C +2°C in ambient air. QC organisms were tested with each run following CLSI QC guidelines.

Results were analyzed using FDA breakpoints for PLZ (Susceptible <2 µg/mL, Intermediate 4 µg/mL, Resistant >8 µg/mL).

Performance was evaluated using FDA performance criteria, EA and CA (≥ 90%), major error rate (≤3.0%) and very major error rate (≤2.0%).

Results

Conclusion

ETEST® PLZ clinical performance met the FDA acceptance criteria and was found useful for determining Plazomicin MIC of Enterobacterales, including ESBL, CRE (MBL, KPC, Oxa-48), high level AmpC and aminoglycoside resistant strains. Percent susceptibility of Plazomicin is at 80% among the 598 isolates tested, the mode MIC is 0.5 ug/ml as Susceptible.

Disclosures

Tom Armstrong, BS, bioMérieux (Employee) Laurine Blanchard, PhD, bioMérieux (Employee) Michael Kresken, PhD, bioMérieux (Scientific Research Study Investigator, Research Grant or Support) Gilles Zambardi, biomerieux (Employee) Marion Pompilio, BioMérieux (Employee)

1222. Fosfomycin Susceptibility Testing using the new ETEST®FO

Background

Fosfomycin (FO) is a bactericidal antibiotic with a broad spectrum of activity against a wide range of Gram-positive and Gram-negative bacteria. Oral FO is mainly used in the treatment of urinary tract infections, particularly those caused by E. coli and E. faecalis. In order to determine MICs to FO, the ETEST® FM is already available but the reading can be difficult especially with E. coli. To resolve this issue, a new ETEST® with FO, called ETEST® FO, has been developed (not FDA cleared, yet). The purpose of this study is to compare this new strip to the agar dilution reference method (AD) on a panel of E. coli and E. faecalis.

Methods

A total of 39 isolates comprising 20 E. coli (ESBL or CPE) and 19 E. faecalis (VRE or VSE) were tested by ETEST® FO and Agar dilution. The isolates were sub-cultured on Columbia agar plates supplemented with 5% sheep blood before testing. After incubation, suspensions of the isolates were prepared in 0.85% saline. These suspensions were used to inoculate both AD and ETEST^® plates. Results were read after 16-20 hours incubation at 35°C +2°C in ambient air. Following CLSI QC guideline, 4 QC organisms were tested. Results were analyzed using the FDA/CLSI breakpoints for FO (S < 64µg/mL, I=128 µg/mL, R> 256 µg/mL). Performance was evaluated using FDA performance criteria, essential agreement (EA, ≥ 90%), category agreement (CA, ≥ 90%), major error rate (ME, ≤3.0%) and very major error rate (VME, ≤2.0%).

Results

All the QC strains MICs were within the CLSI ranges. For the panel results, see the table below:

Performance for ETEST^® FO on E. coli and E. faecalis

Conclusion

This first and preliminary study shows that ETEST® FO can potentially meet the FDA acceptance criteria and could be a valuable tool for determining FO MIC for E. coli harboring various resistance mechanisms and E. faecalis including VRE. Moreover, in comparison with the current ETEST FM strip, this new strip brings a real reading improvement and resolve the issue for E. coli. The clinical study phase will determine the product’s performance.

Disclosures

Marion Pompilio, BioMérieux (Employee) Gilles Zambardi, biomerieux (Employee)

A simple phenotypic test for detecting the contribution of outer membrane permeability to carbapenem resistance

Introduction. The worldwide emergence of carbapenem resistance in Gram-negative bacteria makes the development of simple tests mandatory to identify antimicrobial resistance mechanisms. Enzymatic and membrane barriers are the prominent resistance mechanisms described in these bacteria. Several tests are currently used to detect carbapenemase activities.Aim. However, a simple test for the identification of membrane-associated mechanisms of resistance is not yet available and this mechanism is often inferred after the exclusion of a carbapenemase in carbapenem-resistant Gram-negative bacteria.Methodology. Different media (liquid and solid) containing a membrane permeabilizer were tested to identify the existence of a membrane barrier. Here, polymyxin B nonapeptide (PMBN) was selected to bypass the role of impermeability in clinical carbapenem-resistant Enterobacteriaceae, including Escherichia coli, Enterobacter cloacae , Klebsiella pneumoniae and Klebsiella aerogenes isolates. In parallel, the expression of porins (OmpC and OmpF types) was checked in the various bacterial strains in order to search for a correlation between the restoration of susceptibility and the expression of porin.Results. Using a large number of clinical isolates, PMBN associated with a carbapenem allowed us to detect porin-deficient isolates with a sensitivity ranging from 89 to 93 % and a specificity ranging from 86 to 100 %.Conclusion. This paves the way for a diagnostic assay allowing the detection of this membrane-associated mechanism of resistance in Enterobacteriaceae.

644. Comparative Evaluation of ETEST® ERV bioMérieux with the CLSI Broth Microdilution Method for Eravacycline MIC Determination

Background

Eravacycline (XERAVA™) is a novel, FDA and EMA-approved fully-synthetic fluorocycline antibiotic developed by Tetraphase Pharmaceuticals Inc. for the treatment of complicated intra-abdominal infections (cIAI) including those caused by multidrug-resistant (MDR) pathogens that have been highlighted as urgent public health threats by the US CDC and the WHO.

The new ETEST ERV strip (MIC range 0.002 – 32 µg/mL) has been developed by bioMérieux and calibrated vs. the broth microdilution reference method (BMD) as described by the Clinical and Laboratory Standards Institute (CLSI) to determine the minimal inhibitory concentration (MIC) of eravacycline against Enterobacterales and Enterococci. The aim of the study was to compare ETEST ERV to the CLSI BMD method on a panel of 166 strains comprising 131 Enterobacterales and 35 Enterococci.

Methods

Quality control was performed with the CLSI QC strains E.coli ATCC 25922 and E.faecalis ATCC 29212. The ETEST ERV strip was applied on a Mueller–Hinton agar plate previously seeded with a 0.5 McF bacterial suspension. After incubation for 16–20H at 35°C, the reading was performed using the bacteriostatic mode i.e.,80% of growth. The FDA-approved breakpoints were applied (S≤0.5µg/mL for Enterobacterales and S ≤0.064 µg/mL for Enterococci).

Results

The MIC essential agreement was 99.4% at ±1 dilution for the whole panel and the category agreement was 96.4% with 4.8% Major Errors (1 E. coli, 2 K. pneumoniae, 1 K.aerogenes, 1 C. koseri, 1 E. faecalis), all at ±1 dilution around the single breakpoint. No Very Major Error (VME) was observed.

Conclusion

In this study, the new ETEST ERV strip has been found to be substantially equivalent to the CLI reference method. MIC end-points appear easier to read in comparison to the reference method. With a 15-dilution MIC range and simplicity of use, ETEST ERV could represent a valuable tool for MIC determination and an alternative to the BMD reference method. ETEST ERV will undergo clinical studies to seek IVD FDA clearance and CE marking. For Research Use Only. The performance characteristics of this product have not yet been established.

Disclosures

All authors: No reported disclosures.

Phylogenetic Distribution of CRISPR-Cas Systems in Antibiotic-Resistant Pseudomonas aeruginosa

Pseudomonas aeruginosa is an antibiotic-refractory pathogen with a large genome and extensive genotypic diversity. Historically, P. aeruginosa has been a major model system for understanding the molecular mechanisms underlying type I clustered regularly interspaced short palindromic repeat (CRISPR) and CRISPR-associated protein (CRISPR-Cas)-based bacterial immune system function. However, little information on the phylogenetic distribution and potential role of these CRISPR-Cas systems in molding the P. aeruginosa accessory genome and antibiotic resistance elements is known. Computational approaches were used to identify and characterize CRISPR-Cas systems within 672 genomes, and in the process, we identified a previously unreported and putatively mobile type I-C P. aeruginosa CRISPR-Cas system. Furthermore, genomes harboring noninhibited type I-F and I-E CRISPR-Cas systems were on average ~300 kb smaller than those without a CRISPR-Cas system. In silico analysis demonstrated that the accessory genome (n = 22,036 genes) harbored the majority of identified CRISPR-Cas targets. We also assembled a global spacer library that aided the identification of difficult-to-characterize mobile genetic elements within next-generation sequencing (NGS) data and allowed CRISPR typing of a majority of P. aeruginosa strains. In summary, our analysis demonstrated that CRISPR-Cas systems play an important role in shaping the accessory genomes of globally distributed P. aeruginosa isolates.

IMPORTANCE

P. aeruginosa is both an antibiotic-refractory pathogen and an important model system for type I CRISPR-Cas bacterial immune systems. By combining the genome sequences of 672 newly and previously sequenced genomes, we were able to provide a global view of the phylogenetic distribution, conservation, and potential targets of these systems. This analysis identified a new and putatively mobile P. aeruginosa CRISPR-Cas subtype, characterized the diverse distribution of known CRISPR-inhibiting genes, and provided a potential new use for CRISPR spacer libraries in accessory genome analysis. Our data demonstrated the importance of CRISPR-Cas systems in modulating the accessory genomes of globally distributed strains while also providing substantial data for subsequent genomic and experimental studies in multiple fields. Understanding why certain genotypes of P. aeruginosa are clinically prevalent and adept at horizontally acquiring virulence and antibiotic resistance elements is of major clinical and economic importance.

Role of the culture medium in porin expression and piperacillin-tazobactam susceptibility in Escherichia coli

The continuing emergence of the multidrug resistance phenotype in Gram-negative bacteria makes the development of rapid susceptibility tests mandatory. To achieve this goal, proprietary specific media for bacterial growth can be used but may have some adverse effects. In this study, we dissected the role of media on porin, efflux pump and β-lactamase expression. Depending on the medium used, we observed a change in piperacillin-tazobactam susceptibility for some isolates, such as increases in MIC values. No significant alteration in efflux activity or in β-lactamase production was detected after changing the incubation medium. The ratio of piperacillinase:nitrocefinase showed no specific alteration, indicating that the various media did not affect significantly the relative enzymic affinity for the substrates. In contrast, osmotic variation was able to modulate both porin expression and OmpC : OmpF balance, thus modulating the antibiotic uptake. This study suggests that porin expression may be impacted by a susceptibility testing medium, which may modify the antibiotic diffusion into the bacteria, thus affecting MIC results.

Meropenem/colistin synergy testing for multidrug-resistant Acinetobacter baumannii strains by a two-dimensional gradient technique applicable in routine microbiology

OBJECTIVES

Precise assessment of potential therapeutic synergy, antagonism or indifference between antimicrobial agents currently depends on time-consuming and hard-to-standardize in vitro chequerboard titration methods. We here present a method based on a novel two-dimensional antibiotic gradient technique named Xact™.

METHODS

We used a test comprising a combination of perpendicular gradients of meropenem and colistin in a single quadrant. We compared test outcomes with those obtained with classical chequerboard microbroth dilution testing in a study involving 27 unique strains of multidrug-resistant Acinetobacter baumannii from diverse origins.

RESULTS

We were able to demonstrate 92% concordance between the new technology and classical chequerboard titration using the A. baumannii collection. Two strains could not be analysed by Xact™ due to their out-of-range MIC of meropenem (>128 mg/L).

CONCLUSIONS

The new test was shown to be diagnostically useful, easy to implement and less labour intensive than the classical method.

Comparative evaluation of a novel chromogenic medium (chromID OXA-48) for detection of OXA-48 producing Enterobacteriaceae

Comparative evaluation of the recently developed chromogenic culture medium chromID OXA-48 (bioMérieux) with chromID CARBA (bioMérieux) and SUPERCARBA showed that chromID OXA-48 and SUPERCARBA media have the highest sensitivity for detection of OXA-48 producing Enterobacteriaceae (91% and 93%) comparatively to chromID CARBA (21 %). The chromID OXA-48 has the highest specificity, with 100%, as compared to 53% and 68% for the SUPERCARBA and chromID CARBA media for detecting those OXA-48 producers.

Evaluation of Etest® strips for detection of KPC and metallo-carbapenemases in Enterobacteriaceae

The performance of Etest KPC and MBL strips (bioMérieux) was evaluated as compared to other phenotypic tests for detecting carbapenemases of the KPC-type and metallo-β-lactamases, respectively, on 133 well-characterized enterobacterial isolates. KPC and meropenem-containing MP/MPI Etest had high sensitivity (>92 %) and specificity (>97 %).

Performance of chromID® CARBA medium for carbapenemases-producing Enterobacteriaceae detection during rectal screening

Chromogenic chromID® CARBA medium was compared with CDC method and MacConkey agar with imipenem for its performance in detecting carbapenemase-producing Enterobacteriaceae (CPE) during a faecal screening surveillance program. Double rectal swabs were collected from patients hospitalized in the ICU. One swab was inoculated onto the solid media chromID® CARBA and MacConkey agar with imipenem, while the other was tested according to CDC protocol. Suspected colonies from all procedures were identified to species level and tested for their susceptibility to carbapenems by phenotypic tests. All carbapenem non-susceptible isolates were tested by the modified Hodge test (MHT) and synergy tests. Positive results were confirmed by PCR testing for carbapenemase gene detection. Performance of all three procedures applied was statistically analyzed as compared to MHT and PCR results for the presence of carbapenemase-encoding genes. Out of 177 rectal samples tested, 86 samples were found to contain one or more CPE verified by molecular detection of carbapenemase encoding genes among isolated Enterobacteriaceae. Sensitivity of chromID® CARBA was 96.5 % in clinical samples. Specificity was 91.2 % at the reading level and 100.0 % after Gram staining. chromID® CARBA performed with high accuracy among the phenotypic methods applied, giving early results.

Rapid clinical bacteriology and its future impact

Clinical microbiology has always been a slowly evolving and conservative science. The sub-field of bacteriology has been and still is dominated for over a century by culture-based technologies. The integration of serological and molecular methodologies during the seventies and eighties of the previous century took place relatively slowly and in a cumbersome fashion. When nucleic acid amplification technologies became available in the early nineties, the predicted "revolution" was again slow but in the end a real paradigm shift did take place. Several of the culture-based technologies were successfully replaced by tests aimed at nucleic acid detection. More recently a second revolution occurred. Mass spectrometry was introduced and broadly accepted as a new diagnostic gold standard for microbial species identification. Apparently, the diagnostic landscape is changing, albeit slowly, and the combination of newly identified infectious etiologies and the availability of innovative technologies has now opened new avenues for modernizing clinical microbiology. However, the improvement of microbial antibiotic susceptibility testing is still lagging behind. In this review we aim to sketch the most recent developments in laboratory-based clinical bacteriology and to provide an overview of emerging novel diagnostic approaches.

Methicillin-resistant Staphylococcus aureus expressing low-level methicillin resistance may not be detected by the VITEK2® system

Low-level methicillin-resistant Staphylococcus aureus may be difficult to detect with the VITEK® 2 system (VK2). Here, we suggest that S. aureus exhibiting VK2-oxacillin MIC of 1 or 2 mg/L and a negative cefoxitin screen should be tested for the presence of mecA or its gene product.

Clinical impact of rapid oxacillin susceptibility testing using a PCR assay in Staphylococcus aureus bactaeremia

OBJECTIVES

The aim of this work was to establish the clinical impact of rapid oxacillin susceptibility testing in nosocomial Staphylococcus aureus bacteraemia.

METHODS

This study was performed in 145 critically ill patients infected by S. aureus. Patients were randomly assigned to one of two groups: patients for whom susceptibility testing was performed using a rapid same day multiplex PCR assay for detection of the staphylococcal mecA (mean delay of response: 6 h) and those for whom testing was accomplished using traditional overnight techniques (21 h).

RESULTS

The results of this study showed no significant difference between the two groups in terms of age, Simplified Acute Physiologic Score, severity of infection, severity of underlying disease and clinical outcome (control vs. PCR): unfavourable outcome of infection, 12.32 vs. 12.5%; 95% CI for the difference = -11.49 to 11.09 (P = 0.975); unfavourable general outcome, 16.43 vs. 20.83%; 95% CI for the difference = -17.35 to 8.50 (P = 0.497). For the oxacillin-susceptible S. aureus bactaeraemia, results were: unfavourable outcome of infection = 13.04 vs. 11.11%; 95% CI for the difference = -11.38 to 16.18 (P = 0.767); unfavourable general outcome = 13.04 vs. 20.37%; 95% CI for the difference = -22.12 to 8.07 (P = 0.331).

CONCLUSION

This study seemed to demonstrate that rapid oxacillin susceptibility testing using a PCR assay did not have a major impact on the care and outcome of patients with S. aureus bactaeremia.

[Biological diagnosis of whooping cough: contribution of gene amplification]

An upsurge in pertussis infections, despite mandatory vaccination in France since 1966, has occurred again in developed countries due to progressive loss of vaccinal immunity and wider circulation of the causal bacterium, Bordetella pertussis. Unfortunately, the classical culture method is insufficiently sensitive and serology can only confirm diagnosis retrospectively. New techniques are needed for rapid diagnosis, and subsequent treatment and preventive measures. One new method, gene amplification using polymerase chain reaction (PCR), has been particularly useful in detecting Bordetella pertussis. PCR is highly specific and more sensitive than culture. It is thus quite useful in case of atypical clinical presentations and in previously treated or vaccinated patients. Less restrictions on sample transportation and preservation make PCR a technique which general practitioners can use for rapid easy diagnosis of pertussis.

European multicentre evaluation of a commercial system for identification of methicillin-resistant Staphylococcus aureus

A commercial system for the rapid detection of methicillin-resistant Staphylococcus aureus, the BBL Crystal MRSA test (C-MRSA ID; Becton Dickinson, USA), was evaluated prospectively and compared with a polymerase chain reaction test for the presence of the mecA gene. Ten European centres tested a total of 676 isolates of Staphylococcus aureus from blood cultures. The system correctly identified 661 (97.8%) isolates within 4 h. All but three mecA gene-negative isolates (99.4% specificity) yielded a negative C-MRSA ID reaction, and 158 of 170 mecA gene-positive isolates were accurately detected (92.9% sensitivity). After repeated testing of discrepant results, sensitivity and specificity increased to 99% and 100%, respectively.

Rapid diagnosis of Mycobacterium tuberculosis infections by an ELISA-like detection of polymerase chain reaction products

A polymerase chain reaction (PCR) assay was developed for the detection in clinical samples of mycobacteria belonging to the Mycobacterium tuberculosis complex. PCR products were detected with a simple and rapid colormetric method. With this method, 50 fg of M. tuberculosis DNA were detectable with the repetitive DNA-sequence-derived primers, corresponding to 10 genome equivalents. Detection of M. tuberculosis in 258 clinical samples by PCR was compared with detection by culture. PCR was positive for 56 of 57 culture-positive and Ziehl-Neelsen-staining-positive (ZN) samples, 11 of 18 culture-positive and ZN-negative samples. The presence of groEL DNA sequences was also investigated by PCR for all the specimens with the same revelation protocol. Three of the eight false-negative samples with the repetitive element-derived primers were found to contain groEL DNA sequences specific for the Mycobacterium genus. Among the 183 culture-negative samples, 30 were positive by PCR. When clinical data were known, the diagnosis of tuberculosis was established for the patients from whom those samples had been obtained. The results show that the rapid and simplified PCR assay described here is slightly more sensitive than culture and can be used in routine clinical practice.

[Comparison of different phenotypic methods with polymerase chain reaction (PCR) for the detection of resistance to oxacillin in coagulase negative staphylococci]

The mecA gene which confers the oxacillin resistance has been searched by PCR in 290 (124 positives, 166 negatives) coagulase-negative staphylococci (CNS) belonging to twelve species. The results were compared with the oxacillin MIC values obtained by agar dilution (4% NaCl) or by the ATB STAPH method (Api-bioMérieux; 0%, 2%, 5% NaCl) and growth inhibitory diameters obtained by agar diffusion with an oxacillin disk placed at 30 degrees C without NaCl, or at 35 degrees C in presence of 2% or 5% NaCl. Sensitivity of oxacillin resistance detection depends upon the salt concentration and the method used. The optimum concentration is 2%. With this concentration, the Api ATB test appears as the more performant (sensitivity: 89.8%). Search for the mecA gene by PCR represents a very interesting method that detects 96.9% of the oxacillin-resistant CNS strains.

Nosocomial infection with Candida albicans in a pancreatic transplant recipient investigated by means of restriction enzyme analysis

Restriction enzyme analysis (REA) of total DNA was used in order to investigate the possible transmission of Candida albicans from the grafted pancreas in a woman with a kidney-pancreas transplant. A strain of Candida albicans was recovered from the pancreas-transplant preservation medium cultured routinely before transplantation. Four infecting isolates and one vulval isolate were recovered from the recipient in the early post-operative stage. In addition, 12 unrelated control strains were studied for comparison. By means of EcoRI and HinfI, restriction patterns of the isolates recovered from the preservation medium and from the patient were found to be identical (100% similitude according to Jaccard's coefficient) apart from that of the strain isolated from the vulva. HinfI gave two characteristic fragments of 5.9 and 4.6 kb. In contrast, the 12 control strains generated 12 different patterns. The percentage of similarity between the patterns of the infecting strains and those of the control and the vulval strains was less than 60%. These findings provide evidence of transmission of the infecting strain via the pancreas transplant and the nosocomial nature of infection.

Laboratory diagnosis of oxacillin resistance in Staphylococcus aureus by a multiplex-polymerase chain reaction assay

A polymerase chain reaction (PCR) test was developed in which the mecA gene responsible for the intrinsic resistance to oxacillin in Staphylococcus aureus and the gyrA gene, always present in this species, were amplified in one operation. Among the 468 clinical isolates tested, the results obtained for 454 of the isolates (97%) were consistent with those of MIC determination. Discrepant results were noted for strains with low-level oxacillin resistance (MICs, 4-8 micrograms/ml) and mecA gene negative. For these strains, susceptibility to oxacillin was restored in the presence of a beta-lactamase inhibitor, which suggested a resistance by penicillinase hyperproduction. In contrast, all of the high-level resistant strains (MICs, > 8 micrograms/ml) carried the mecA gene. The presence of this gene has frequently been associated with resistance to gentamicin, tetracycline, erythromycin, lincomycin, and pefloxacin. The PCR assay described in this study can be accomplished with ease and total confidence in the clinical microbiologic laboratory for a rapid and effective establishment of antistaphylococcal chemotherapy.