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Ampicillin-resistant (Ampr) Salmonella enterica isolates (n = 344) representing 32 serotypes isolated from retail meats from 2002 to 2006 were tested for susceptibility to 21 other antimicrobial agents and screened for the presence of five beta-lactamase gene families (blaCMY, blaTEM, blaSHV, blaOXA, and blaCTX-M) and class 1 integrons. Among the Ampr isolates, 66.9% were resistant to five or more antimicrobials and 4.9% were resistant to 10 or more antimicrobials. Coresistance to other β-lactams was noted for amoxicillin-clavulanic acid (55.5%), ceftiofur (50%), cefoxitin (50%), and ceftazidime (24.7%), whereas less than 5% of isolates were resistant to piperacillin-tazobactam (4.9%), cefotaxime (3.5%), ceftriaxone (2%), and aztreonam (1.2%). All isolates were susceptible to cefepime, imipenem, and cefquinome. No Salmonella producing extended-spectrum beta-lactamases was found in this study. Approximately 7% of the isolates displayed a typical multidrug-resistant (MDR)-AmpC phenotype, with resistance to ampicillin, chloramphenicol, streptomycin, sulfonamide, tetracycline, plus resistance to amoxicillin-clavulanic acid, cefoxitin, and ceftiofur and with decreased susceptibility to ceftriaxone (MIC 4 μg/ml). Pulsed-field gel electrophoresis results showed that several MDR clones were geographically dispersed in different types of meats throughout the five sampling years. Additionally, 50% of the isolates contained blaCMY, 47% carried blaTEM-1, and 2.6% carried both genes. Only 15% of the isolates harbored class I integrons carrying various combinations of aadA, aadB, and dfrA gene cassettes. The blaCMY, blaTEM, and class 1 integrons were transferable through conjugation and/or transformation. Our findings indicate that a varied spectrum of coresistance traits is present in Ampr Salmonella strains in the meat supply of the United States, with a continued predominance of blaCMY and blaTEM genes in β-lactam-resistant isolates. [ABSTRACT FROM AUTHOR]

Background. Knowledge of the clinical features of infections caused by Escherichia coli strains that produce plasmid-mediated AmpC β-lactamase is limited. Of the several groups of plasmid-mediated AmpC β-lactamases, CMY-type β-lactamase is the most common in the United States. Methods. We prospectively identified patients infected or colonized with E. coli strains that produce CMY-type β-lactamase, and we collected clinical data over a 7-month period. A retrospective cohort study was performed to identify features associated with these cases. Patients with extended-spectrum β-lactamase-producing E. coli were used as a control group. Pulsed-field gel electrophoresis, plasmid analysis, and phylogenetic typing were performed. Results. Twenty-two patients with infection or colonization due to CMY-type β-lactamase-producing E. coli and 25 patients with infection or colonization due to extended-spectrum β-lactamase-producing E. coli were identified. The demographic characteristics of the patients were similar in both cohorts. Patients with CMY-type β-lactamase-producing E. coli were significantly more likely to have symptomatic infection than were patients with extended-spectrum β-lactamase-producing E. coli (Pp.028). The CMY-type β-lactamase was identified as CMY-2 or its variants. Ninety-four percent of the CMY-type β-lactamase-producing isolates belonged to E. coli phylogenetic groups B2 and D, which are associated with virulence. Many of the isolates shared similar plasmid profiles, whereas the pulsed-field gel electrophoresis profiles were diverse. Co-resistance to non-β-lactam antimicrobials was common. Conclusion. In Pittsburgh, Pennsylvania, CMY-type β-lactamase-producing E. coli strains are almost as common as extended-spectrum β-lactamase-producing E. coli strains, and they cause symptomatic infection in the majority of cases. [ABSTRACT FROM AUTHOR]