ARS | Publication request: CEPHALOSPORIN RESISTANCE AMONG BOVINE SALMONELLA ENTERICA SEROTYPES

Submitted to: Proceedings of the International Conference on Emerging Infectious Diseases
Publication Type: Abstract Only
Publication Acceptance Date: February 20, 2006
Publication Date: March 20, 2006
Citation: Frye, J.G., Cray, P.J., Jackson, C.R., Rose, M. 2006. Cephalosporin resistance among bovine salmonella enterica serotypes [abstract]. Proceedings of the International Conference on Emerging Infectious Diseases. 114:85.

Technical Abstract: Background: Extended-spectrum *-lactamases (ESBLs) are important resistance mechanisms which affect *-lactam antibiotics, including cephalosporins. Extended-spectrum 3rd generation cephalosporins are considered drugs of choice for serious Salmonella infections. The emergence of ESBL-producing organisms may affect therapy outcome. Detection of ESBL producers is difficult; while extended-spectrum cephalosporins are hydrolyzed, their MIC’s may remain within the susceptible range. Methods: Salmonella isolates were collected from cattle at slaughter from 2000-2004 (n = 3985) and screened for decreased susceptibility or resistance to ceftriaxone (MIC > 32 µg/ml) prior to selection for ESBL testing on Trek Diagnostic System’s ESBF1 plate using a semi-automated broth micro-dilution technique. QC strain E. coli ATCC 25922 was used and CLSI guidelines were followed. ESBL confirmation required a >3 two-fold decrease in MIC for at least one of the antimicrobials tested in combination with clavulanic acid (CA) versus the MIC in the absence of CA. Antimicrobials tested were ceftazidime +/- CA and cefotaxime +/- CA. Isolates were also screened for the blaCMY-2 blaTEM, blaSHV, and blaCTX-M group I-IV genes by use of PCR. Results: A total of 97 Salmonella isolates exhibited decreased susceptibility or resistance to ceftriaxone. Thirteen serotypes were identified including 58 S. Newport, 14 S. Agona, and 8 S. Typhimurium including var 5- isolates. None of the isolates were confirmed as ESBL producers. All isolates were susceptible to the 4th generation cephalosporin cefepime. In addition, all isolates were susceptible to ciprofloxacin and meropenem. The blaCMY-2 gene was detected in 68 isolates and the blaTEM gene was detected in 12 isolates. Conclusions: These data indicate that the majority of bovine Salmonella isolates with decreased susceptibility or resistance to ceftriaxone contain the blaCMY-2 gene. Phenotypic ESBL testing suggests that the isolates do not produce ESBL. However, further analysis is required to identify all genes responsible for reduced resistance to 3rd generation cephalosporins.