Antimicrobial resistance and resistance genes in recent <em>Enterobacter</em> isolates from NSW  — ASN Events
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  3. Antimicrobial resistance and resistance genes in recent Enterobacter isolates from NSW 

Antimicrobial resistance and resistance genes in recent Enterobacter isolates from NSW  (#421)

Lupeoletalalelei Isaia 1 2 3 , Andrew N Ginn 1 2 3 , Sally R Partridge 1 2 3 , Jon R Iredell 1 2 3
  1. Centre for Infectious Diseases and Microbiology, Sydney, NSW, Australia
  2. The University of Sydney, Sydney, NSW, Australia
  3. Westmead Millenium Institute, Sydney, NSW, Australia

Emerging antimicrobial resistance is a global concern, with multi-resistant organisms causing difficulties in the management and treatment of severe infections. Enterobacter species are among the most commonly isolated Enterobacteriaceae implicated in clinical infections. We investigated the prevalence of antibiotic resistance in 1466 Enterobacter isolates (mainly from urine and blood) from the Centre for Infectious Diseases and Microbiology, Westmead, January 2012–April 2015. Minimum inhibitory concentrations were determined using the Phoenix™ Automated Microbiology System and results interpreted using Clinical and Laboratory Standards Institute guidelines. A subset (n=550) of these Enterobacter isolates were screened for genes commonly responsible for reduced susceptibility to β-lactams (extended-spectrum β-lactamase (ESBL), carbapenemase and plasmid-borne AmpC genes) or aminoglycosides (encoding common aminoglycoside modifying enzymes and 16S rRNA methylases) by multiplex PCR-reverse line blot with additional simplex PCR.

 

Enterobacter spp. are naturally resistant to ampicillin, amoxicillin, amoxicillin-clavulanate, first-generation cephalosporins and cefoxitin, due to intrinsic chromosomal AmpC genes. Resistance to third-generation cephalosporins was also common (ceftriaxone 40%, ceftazidime 34%), 15% of isolates were non-susceptible to carbapenems and 12% of isolates were resistant to gentamicin.

 

ESBL genes were found in ~30% isolates tested but, unlike other local Enterobacteriaceae, ESBL-type blaSHV genes were more common than blaCTX-M genes. Carbapenemase genes were found in ~20% of isolates, mostly blaIMP, although the globally-circulating blaNDM was also found. Common gentamicin resistance genes (aac(3)-II, aac(6') and aadB) were found in ~30% of isolates tested. The local epidemiology of antibiotic resistance genes in Enterobacter spp. thus appears to be similar to that in local Escherichia coli and Klebsiella pneumoniae, but differences in the proportions of genes found suggest subtly different gene pools.

 

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