Prevalence and Antimicrobial Characteristics of Shiga Toxin-Producing Escherichia coli Isolates from Pork in Korea

Shiga toxin-producing Escherichia coli (STEC) strains are important food-borne pathogens that can be transmitted through the consumption of food products derived from pigs. Moreover, antimicrobial resistance in STEC has been a matter of increasing concern. The aim of this study was to investigate the prevalence and antimicrobial characteristics of STEC isolates from pork in Korea. We isolated 131 isolates of E. coli from 334 pork samples collected from slaughterhouses and retail markets from 2008 to 2009. Among the 131 isolates, 6 (4.58%) were confirmed to belong to 6 different serotypes of STEC. All six STEC isolates contained stx1 and eaeA virulence genes, and four of them additionally carried the hly gene. The minimum inhibitory concentration (MIC) of 15 antibiotics (amoxicillin/clavulanic acid, ampicillin, cephalothin, cefoxitin, ceftiofur, gentamicin, neomycin, streptomycin, nalidixic acid, ciprofloxacin, colistin, chloramphenicol, florfenicol, tetracycline and sulfamethoxazole/trimethoprim) toward the STEC isolates was determined. As a result, three strains were associated with high MICs for florfenicol and chloramphenicol (64 mu g/mL). Furthermore, all three strains were found to contain the florfenicol-resistant gene (floR) but not the chloramphenicol-resistant gene (cat). Sequence alignment and BLAST analysis of the polymerase chain reaction products of the floR gene indicated that they contained sequences with homology to the floR gene of E. coli or Salmonella enterica serovar, Heidelberg. This is the first report on the detection of floR in STEC isolated from pork obtained from retail markets in Korea.