Abstract
Summary Nine multiple antibiotic resistant Escherichia coli strains were isolated from commercially available meat. All isolates contained plasmids and were resistant to 7 or more antibiotics. Four isolates contained conjugal R-plasmids that transferred resistance to Escherichia coli K12 711. Two of the isolates also transferred R-plasmids to Salmonella typhimurium KS 294 and KS 296 recipients. Three E. coli isolates contained smaller mobilizable plasmids which were cotransferred along with the R-plasmid. Heat curing of R-plasmids confirmed they encoded for tetracycline, streptomycin, kanamycin and neomycin resistance. The frequencies of plasmid transfer were highest at 37°C and declined with decreasing temperature. Two isolates displayed conjugal transfer of antibiotic resistance at 10°C in broth. The highest transfer frequency occurred in the pH range 6.5 to 7.0. The influence of varying NaCl concentration on R-plasmid transfer also showed high variability among isolates from different sources. Conjugal transfer under anaerobic conditions was also highly varible among E. coli isolates from different sources.
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