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Bacterial conjugation is one of the most important mechanisms for spread of antibiotic resistance among bacteria. We have previously demonstrated that cefotaxime (CTX) exposure up-regulates expression of Type-IV conjugation transfer genes, and that this leads to increased transfer of a  bla  CTX–M–  1  encoding IncI1 resistance plasmid pTF2 in  Escherichia coli . To elucidate the underlying mechanisms, a search for genes that are essential for the up-regulated expression of the transfer ( tra ) genes in the presence of CTX was undertaken. We constructed a reporter gene-fusion strain MG1655/pTF2 Δ traF : lacZ  where the promoter region of the  traF -gene of the plasmid pTF2 was fused with a  lacZ  on the native plasmid. Random mutagenesis mediated by Tn5 transposon was carried out in the strain, and seven genes ( rfaH ,  yhiN ,  waaP ,  waaQ ,  gnd ,  pgl , and IS Ecp1 ) were identified where insertion prevented CTX-induced up regulation of  traF . Site-specific mutagenesis was carried out, and for all seven mutants, gene deletions abolished the CTX induced up-regulation of  traF , and the increased conjugation transfer of the plasmid in the presence of CTX was no longer observed. In addition, the deletion of the genes also abolished CTX induced expression of the  bla  CTX–M–  1  gene. Our results suggested that through CTX induced induction of the identified genes,  bla  CTX–M–  1  expression increased, which led to up-regulation of  traF  and plasmid transfer. These data reveal that a number of chromosomally encoded genes contribute to the antibiotic induced up-regulation of the conjugation machinery of plasmids, and such genes may be future targets to prevent antibiotic induced spread of resistance plasmids.

Identification of Genes Essential for Antibiotic-Induced Up-Regulation of Plasmid-Transfer-Genes in Cephalosporin Resistant Escherichia coli