Concurrent transfer and recombination between plasmids encoding for heat-stable enterotoxin and drug resistance in porcine enterotoxigenicEscherichia coli

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Abstract
The frequency of and genetic mechanisms for simultaneous transfer of genes encoding for tetracycline and sulpha-streptomycin resistance, heat-labile (LT) and heat-stable (ST-mouse) enterotoxin production in porcine enterotoxigenicEscherichia coli toEscherichia coli K12 were investigated. SevenE.coli strains of 0-group 149 were studied by conjugation and transformation experiments. All strains transferred tetracycline-resistance plasmids at a high frequency. No interaction was observed between these plasmids and those encoding for LT production. However, most tetracycline-resistant recipient cells were ST-mouse+ following recombination events between plasmids encoding for colicin B and ST-mouse production and plasmids encoding for tetracycline resistance. Alternatively, when selecting for sulpha or streptomycin resistance a majority of the transconjugants were also ST-mouse+, as plasmids coding for sulpha and streptomycin were mobilized by the colicin B and ST-mouse encoding plasmid. Since the simultaneous transfer of genes encoding for drug resistance, colicin B and ST-mouse production are common events in vitro, they might also occur frequently in vivo during antibiotic selective pressure.