Antibiotic susceptibility pattern of Escherichia coli strains with verocytotoxic E. coli-associated virulence factors from food and animal faeces

There is limited information available on the antibiotic susceptibility patterns of enterohemorrhagic Escherichia coli (EHEC) or Verocytotoxin-producing E. coli (VTEC). Therefore in vitro antibiotic activities of 13 antibiotic substances against 60 E. coli isolates (from food or animal and one human faecal isolate) with VTEC-associated virulence factors were determined. The isolates harboured at least one of the following virulence factors: vtx1 and/or vtx2 gene, eae gene (EHEC or EPEC) or EHEC hly A gene. There was no relationship between serotype, virulence factor and resistance pattern. All strains were susceptible to quinolones, gentamicin, trimethoprim/sulfamethoxazole and nitrofurantoin. Resistant isolates were observed for cephalothin, tetracycline and in one case for cefazolin. Minimal inhibition concentrations at which 90% of the strains were inhibited were 8 μg ml−1 for ampicillin, 8/4 μg ml−1 for ampicillin/sulbactam, >16 μg ml−1 for cephalothin, 8 μg ml−1 for tetracycline and 8 μg ml−1 for chloramphenicol. No multi-drug-resistance was observed. Cephalothin and tetracycline show the potential for an increased resistance rate as a high number of isolates was intermediate resistant. The resistance profile of E. coli with VTEC-AVF investigated in this study reveals a high percentage of susceptible isolates compared to E. coli isolates in general and is similar to profiles published for EHEC or VTEC strains.