A comparison of antibiotic resistance integrons in cattle from separate beef meat production systems at slaughter

Aims: To compare antibiotic resistance integrons in cattle from three separate grass-fed, grain-fed and certified organic cattle production systems at slaughter. Methods and Results: In this study 198 samples from three separate cattle production systems were tested by PCR for the presence of class 1 and class 2 integrons. Integron-containing bacteria were readily isolated from pen faeces and hide samples regardless of production system. Lower numbers of integron-containing bacteria were isolated from the remaining sample types. Ninety-one class 1 and 34 class 2 integron-containing bacteria were isolated. Characterization of the integrons demonstrated a high degree of similarity across the three production systems with aadA1 and aadA2 routinely present. Integrons harbouring the cassette array cmlA5-bla(OXA-10)-aadA1 and the putative insertion sequence IS1066 were isolated from organic and grass-fed cattle and have not been described previously. Conclusions: Integrons carrying antibiotic resistance genes were common in cattle from differing production systems at slaughter and the likelihood of presence appears unrelated to the production system. Significance and Impact of the Study: Similar integron arrays are present in different cattle production systems suggesting that their presence may be independent of production practices. This is the first report of two novel integron structures present in Aeromonas.