Resistance to third-generation cephalosporins in human non-typhoidal Salmonella enterica isolates from England and Wales, 201012

To identify the mechanism(s) underlying cefotaxime resistance in 118 of 21641 (0.55) non-typhoidal Salmonella enterica isolates collected from humans throughout England and Wales from January 2010 to September 2012. Non-duplicate isolates (n118) resistant to cefotaxime (MICs 1 mg/L) were screened by PCR for genes encoding CTX-M extended-spectrum beta-lactamases (ESBLs) and associated ISEcp1-like elements, and for genes encoding acquired AmpC, SHV, TEM, VEB, PER and GES beta-lactamases. Sequencing was used to identify specific alleles in selected isolates. Carbapenem resistance was sought by ertapenem disc screening. Seventy-nine isolates (0.37 of all referred S. enterica) produced ESBLs, 37 isolates (0.17) produced CMY-type AmpC enzymes, and 1 isolate had both enzyme types; the mechanism of cefotaxime resistance in 3 isolates could not be identified. Group 1 CTX-M genes were identified in 57 isolates belonging to 22 serotypes, with CTX-M-1 (n11), -15 (n9) and -55/57 (n8) the most prevalent alleles among the 29 (51) investigated. CTX-M-2 (n5), -14 (n5), -8 (n1) and -65 (n1) were also identified. TEM-52 was identified in two isolates and SHV-12 in seven isolates. There was no evidence of carbapenem resistance. ESBL and AmpC genes were detected in both domestically acquired and travel-associated salmonellae. Eighty-nine isolates (75) were multidrug resistant (resistant to at least three antimicrobial classes) and 42 (36) had decreased susceptibility to ciprofloxacin (MICs 0.251 mg/L), with a further 13 (11) isolates resistant (MICs 1 mg/L). The prevalence of CTX-M and acquired AmpC genes in human non-typhoidal S. enterica from England and Wales is still low, but has increased from 0.03 in 200103 to 0.49 in 201012. Resistance to third-generation cephalosporins requires monitoring as it may reduce therapeutic options.