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Detection of Listeria monocytogenes in food is currently based on enrichment methods. When L. monocytogenes is present with other Listeria species in food, the species compete during the enrichment process. Overgrowth competition of the nonpathogenic Listeria species might result in false-negative results obtained with the current reference methods. This potential issue was noted when 50 food samples artificially spiked with L. monocytogenes were tested with a real-time PCR assay and Canada's current reference method, MFHPB-30. Eleven of the samples studied were from foods naturally contaminated with Listeria species other than those used for spiking. The real-time PCR assay detected L. monocytogenes in all 11 of these samples; however, only 6 of these samples were positive by the MFHPB-30 method. To determine whether L. monocytogenes detection can be affected by other species of the same genus due to competition, an L. monocytogenes strain and a Listeria innocua strain with a faster rate of growth in the enrichment broth were artificially coinoculated at different ratios into ground pork meat samples and cultured according to the MFHPB-30 method. L. monocytogenes was detected only by the MFHPB-30 method when L. monocytogenes/L. innocua ratios were 6.0 or higher. In contrast, using the same enrichments, the real-time PCR assay detected L. monocytogenes at ratios as low as 0.6. Taken together, these findings support the hypothesis that L. monocytogenes can be outcompeted by L. innocua during the MFHPB-30 enrichment phase. However, more reliable detection of L. monocytogenes in this situation can be achieved by a PCR-based method mainly because of its sensitivity. [ABSTRACT FROM AUTHOR]

Abstract: From 2116 Klebsiella pneumoniae strains isolated between January 2001 and December 2002 in Nova Scotia, Canada, 25 (1.18%) showed a reduced susceptibility to cefoxitin or extended-spectrum cephalosporins. Narrow-spectrum β-lactamase genes (bla SHV-11, bla SHV-1, bla SHV-26, bla SHV-32, bla SHV-36, and bla SHV-40) were the most prevalent. Four new variants were identified (bla LEN-17, bla OKP-B-13, bla OKP-B-14, and bla OKP-A-11), representing the 1st description of bla OKP in the Americas. Among the extended-spectrum β-lactamase (ESBL) genes, bla SHV-2, bla SHV2a, bla SHV-12, and bla CTX-M-15 were detected (ESBL prevalence of 0.14%). Nineteen strains were resistant to cefoxitin (MIC, 32 to >256 μg/mL). Nevertheless, an AmpC-like activity was detected in only 1 strain, which expressed CMY-2. The combined effects of narrow-spectrum β-lactamase production and decreased or nonexpression of OmpK35/36 porins did not account for the cefoxitin resistance observed in some of these strains. [Copyright &y& Elsevier]

Summary: Objective: To characterize the mechanism of glycopeptide resistance and to determine the genetic relatedness among strains by pulsed-field gel electrophoresis (PFGE) in vancomycin-resistant Enterococcus faecium from Argentina. Materials and methods: A total of 189 vancomycin-resistant single-patient isolates of Enterococcus faecium recovered between January 1997 and December 2000 from 30 hospitals in Argentina were studied. Minimum inhibitory concentrations were determined by the agar dilution method and van genes were detected by PCR. PFGE was used for molecular typing. Results: All isolates except three (vanB) were of genotype vanA. For 189 vancomycin-resistant Enterococcus faecium, SmaI-PFGE indicated 35 clonal types. Most of the isolates (56%) belonged to the same clonal type 1, which was present in 19 hospitals and dominant in 17. Conclusions: The emergence of vancomycin-resistant Enterococcus faecium in Argentina seems to be related to the intra- and inter-hospital dissemination of an epidemic clone carrying the vanA element. [Copyright &y& Elsevier]