First description of an oxyimino-cephalosporin-resistant, ESBL-carrying Escherichia coli isolated from meat sold in Denmark

Sir, Gram-negative bacteria expressing extended-spectrum blactamases (ESBLs) have emerged globally and this has limited the treatment strategies available for bacterial infections. Very few studies have demonstrated the presence of resistant ESBL-expressing Escherichia coli in foods and food animals. In a Spanish study from 2003, the prevalence of resistant ESBLexpressing E. coli was 2.8% in isolates tested from sick animals and the genes were identified as CTX-M-, SHVand TEM-type. In a Danish study from 2000 to 2002 on E. coli and Salmonella isolates no ESBLs were detected. In a study of 34 resistant ESBL-expressing Salmonella from the Netherlands from 2001 to 2002 from poultry, poultry products and patients, a high prevalence of blaTEM-52, CTX-M-type ESBLs and the Ambler class C ACC-1 was found among the tested isolates of animal origin. Nine unrelated isolates of animal origin, one Salmonella and eight E. coli, from the UK tested as ESBL-resistant. All E. coli isolates contained ampC promoter mutations and the Ambler class C CMY-2 was detected in the Salmonella isolate tested. As part of the continuous surveillance of antimicrobial resistance in food animals, foods and humans in Denmark (DANMAP), E. coli isolates are obtained from meat sold at retail in Denmark. A total of 732 samples were positive for isolation of E. coli; only one isolate per sample was investigated. MICs of 17 antimicrobials were determined according to CLSI guidelines. The b-lactams tested included ampicillin (MIC >32 mg/L); cefalotin (MIC >64 mg/L), a first-generation cephalosporin; and ceftiofur (MIC >8 mg/L), a third-generation cephalosporin that is used only in veterinary practice. Furthermore, sensitivity to b-lactamase inhibitors was tested using amoxicillin in combination with clavulanic acid (MIC = 8/4 mg/L). Among these 732 E. coli isolates obtained from poultry, beef and pork from 2004 (Table 1) the first resistant ESBL-expressing E. coli isolated from food products sold in Denmark was identified (7633094-7). This resistant ESBL-expressing E. coli was isolated from sliced beef (Goulash) imported from Germany, and was also resistant to quinolones [nalidixic acid (MIC >128 mg/L) and ciprofloxacin (MIC >4 mg/L)], sulphonamides (MIC > 1024 mg/L), tetracycline (MIC >32 mg/L) and trimethoprim (MIC >32 mg/L). Using primers previously designed for TEM-type genes, a 957 bp amplicon was obtained from E. coli 7633094-7 and by sequencing was identified as blaTEM-52. 2 This was the first E. coli isolated in Denmark from meat containing blaTEM-52. Previously, blaTEM-52 has been found in high prevalence among E. coli from patients in Canadian hospitals. Recently, bacterial isolates containing blaTEM-52 have been detected in Salmonella enterica serovars Blockley, Thomsen, London, Enteritidis, Paratyphi B, Virchow and Typhimurium from poultry and patients in the Netherlands and from patients in Scotland. Using E. coli MT102 and S. enterica serovar Typhimurium JEO3817 and serovar Dublin JEO66 as recipients, cephalosporin resistance was transferred by conjugation, indicating that blaTEM-52 was located on a mobile DNA element. Only resistance to b-lactams was transferred in these experiments. These results show the importance of monitoring the prevalence of antimicrobial resistance not only in food animals but also in meat sold at retail. Both locally produced and imported meat should be examined, especially since global trade is expected to increase in the future. National programmes to limit the selection for resistance will have to be combined with international measures and regulations to ensure that consumers are not exposed to unnecessary hazards from antimicrobial-resistant bacteria in food bought at retail. Furthermore, since resistance genes, as identified in this study, are located on mobile DNA elements, resistance may be transferred in the human gut to virulent human adapted strains, resulting in reduced antimicrobial treatment options and prolonged hospitalization.