Multicenter evaluation of the new Vitek 2 Neisseria-Haemophilus identification card.

The new Neisseria-Haemophilus identification (NH) card for Vitek 2 was compared with 16S rRNA gene sequencing (16S) as the reference method for accurate identification of Neisseria spp., Haemophilus spp., and other fastidious gram-negative bacteria. Testing was performed on the Vitek 2 XL system with modified software at three clinical trial laboratories. Reproducibility was determined with nine ATCC quality control strains tested 20 times over a minimum of 10 days at all three sites. A challenge set of 30 strains with known identifications and 371 recent fresh and frozen clinical isolates were also tested. Expected positive and negative biochemical reactions were also evaluated for substrate reproducibility. All microorganisms were tested on the NH card, and all clinical and stock isolates were saved for 16S testing. All reproducibility tests yielded expected results within a 95% confidence interval. For challenge microorganisms, there was 98% overall correct identification, including 8% low discrimination, 2% incorrect identification, and 0% unidentified. For clinical strains, there was 96.5% overall correct identification, including 10.2% low discrimination, 2.7% incorrect identification, and 0.8% unidentified. The 2.7% (10/371) of clinical isolates that gave an incorrect identification consisted of 7 isolates correct to genus and 3 strains incorrect to genus. There were an additional 27 strains (primarily Neisseria species) for which the 16S identification result was different from the NH card result. These were all unclaimed species by the system. The new NH card met all performance criteria within a 95% confidence interval compared to identification of clinical isolates by 16S.

Multicenter evaluation of the Vitek 2 anaerobe and Corynebacterium identification card.

The new anaerobe and Corynebacterium (ANC) identification card for Vitek 2 was compared with a 16S rRNA gene sequencing (16S) reference method for accuracy in the identification of corynebacteria and anaerobic species. Testing was performed on a Vitek 2 XL system with modified software at three clinical trial laboratories. Reproducibility was determined with nine ATCC quality control strains that were tested 20 times over a minimum of 10 days at all three sites. A challenge set of 50 well-characterized strains and 365 recent fresh and frozen clinical isolates were included in the study. The expected positive and negative biochemical well reactions were also evaluated for substrate reproducibility. All strains were tested with the ANC card, and clinical isolates were saved for 16S rRNA gene sequencing. All reproducibility tests yielded expected results within a 95% confidence interval, except for that with Corynebacterium striatum ATCC 6940, for which identification failed at one trial site. For the challenge isolates, there was 98% correct identification, 5% low discrimination, and 2% incorrect identification, and 0% were unidentified. For clinical strains, there was 95.1% correct identification, 4.9% low discrimination, and 4.6% incorrect identification, and 0.3% were unidentified. The 4.6% (17/365) of clinical isolates that were incorrectly identified consisted of 14 isolates that were correct at the genus level and three that were incorrect at the genus level. The new ANC card met all performance criteria within a 95% confidence interval compared to the identification performance by 16S rRNA gene sequencing.

Methicillin-resistant Staphylococcus aureus with reduced susceptibility to vancomycin in Canada.

This study defines the characteristics of decreasing vancomycin susceptibility in multiple isolates of methicillin-resistant Staphylococcus aureus (MRSA) recovered from a hospitalized patient in Canada over a period of 6 months. The MICs of the isolates increased during therapy with vancomycin. The patient fractured her right hip while in the United States. She was started on treatment with vancomycin. The MICs of successive isolates increased from < or =1 to 4 mg/L over 6 months. Then, an isolate tested at 8 mg/L initially and 4 mg/L with confirmatory E-test (AB BIODISK, Solna, Sweden). One month later, MRSA was still present in her wound, and therapy was changed to linezolid with rifampin. Subsequent cultures were negative for MRSA. Susceptibility testing was performed on the BD Phoenix (Becton Dickinson Diagnostic Systems, Sparks, MD), Dade Microscan (Dade Behring Microscan, Sacramento, CA), Pasco MIC (Becton Dickinson, Sparks, MD), Vitek 2 (bioMerieux, St. Louis, MO), and Sensititre (Trek Diagnostic Systems, Cleveland, OH) systems, and by E-test. Molecular typing (pulsed-field gel electrophoresis [PFGE]) was used to verify the relatedness of the isolates. Transmission electron microscopy (TEM) was used to assess the cell wall thickness of isolates with differing MICs. Population analysis was performed to assess for vancomycin hetero-resistance. MICs of 4 mg/L were only obtained with BD Phoenix, E-test, and broth microdilution. All isolates were identical by PFGE. The most resistant isolate had a thicker cell wall on TEM. Vancomycin hetero-resistance was observed in the resistant isolates. This is the first strain of MRSA with reduced susceptibility to vancomycin reported in Canada. The breakpoints for vancomycin susceptibility have been revised in light of such observations.

Bacterial contamination of health care workers' pagers and the efficacy of various disinfecting agents.

Health care workers in our facility were surveyed, and their pagers were cultured before and after disinfection with various agents. All pagers were contaminated with bacteria, including the pathogens Staphylococcus aureus, Pseudomonas aeruginosa, Acinetobacter baumannii, Klebsiella spp. and methicillin-resistant S. aureus. Disinfection reduced bacterial contamination. No risk factors for pager contamination with pathogens were identified.

Susceptibility of human isolates of Salmonella typhimurium DT 104 to antimicrobial agents used in human and veterinary medicine.

Multiple antibiotic resistance is frequently observed among strains of Salmonella typhimurium DT104. We examined the antibiotic resistance patterns of 240 human isolates submitted from central and northern Alberta to our laboratory for confirmatory testing during 1996-1999. Broth microdilution MIC panels included antibiotics proposed by the Canadian National Enteric Disease Surveillance Committee for human and animal isolates. Seven different susceptibility patterns were observed. The two most common patterns accounted for 83% of isolates; 48% were susceptible to all antibiotics tested and 35% were resistant to ampicillin, tetracycline, chloramphenicol and amoxicillin-clavulanate. All strains were susceptible to enrofloxacin and trovafloxacin with variable resistance to kanamycin and chloramphenicol. There were more susceptible isolates observed in 1996 and 1997 than in 1998 and 1999, but multiple resistant isolates were found throughout the study period.