Mechanisms of carbapenem resistance among a collection of Enterobacteriaceae clinical isolates in a Texas city

Department of Medicine, San Antonio Military Medical Center, Fort Sam Houston, Texas 78234, USA.
Diagnostic microbiology and infectious disease (Impact Factor: 2.46). 04/2010; 66(4):445-8. DOI: 10.1016/j.diagmicrobio.2009.11.013
Source: PubMed


Fourteen Enterobacteriaceae isolates with ertapenem MIC >2 mg/mL were analyzed to identify mechanisms of resistance. All isolates produced extended-spectrum beta-lactamase or AmpC beta-lactamase with variable, but decreased, expression of outer membrane proteins. One Enterobacter cloacae produced derepressed AmpC beta-lactamase, 1 Escherichia coli expressed plasmid-mediated AmpC beta-lactamase, and 1 E. cloacae produced a carbapenemase.

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    • "A total of 30 cases received an aminoglycoside, 20% (6/30) of cases as monotherapy and 80% (24/30) as combination therapy [8-13,16,19,22,40,42,47,48,55,64-68]. There was no significant difference in treatment failure rates between those who received aminoglycoside monotherapy compared to combination therapy (0% vs. 17%; p= 0.6). "
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    ABSTRACT: Enterobacteriaceae other than Escherichia spp. and Klebsiella spp. are recognisable for their increasing resistance. Plasmid-mediated beta-lactamases, including extended-spectrum beta-lactamases (ESBLs), plasmid-mediated AmpC beta-lactamases (pAmpCs) and the newly emerged KPC, play an important role in beta-lactam resistance. In this study, we investigated the genetic characteristics of plasmid-mediated beta-lactamases amongst non-Escherichia, non-Klebsiella Enterobacteriaceae that were non-susceptible to at least a broad-spectrum cephalosporin. A total of 143 (23.9%) of 598 isolates during the 6-month study period met the screening criteria, amongst which 142 (99.3%) and 99 (69.2%) isolates carried ESBL and pAmpC genes, respectively. Resistance genotypes were described. bla(KPC) was not detected in isolates with reduced susceptibility to carbapenems. This study provides an insight into plasmid-mediated resistance determinants amongst cephalosporin-non-susceptible Enterobacteriaceae other than Escherichia spp. and Klebsiella spp.
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