Experimental Transfer of Tetracycline Resistance Genes from Fish-derived Bacteria to Escherichia coli

To determine whether the tetracycline resistance genes tet (34), tet (M), and tet (S) can be transferred among bacteria, we used a filter mating experiment allowing intimate cell-cell contact between donor and recipient. The tet(34) gene, conveyed on a chromosome of Vibrio species (No. 6 and SW-42) was not transferred to Escherichia coli JM109, suggesting that it is not transferred among bacterial species. The tet (M) gene was transferred from three Vibrio strains (4-E, SW-18, and SW-38) to E. coli at frequencies of $8.5{\times}10^{-5}\;to\;2.1{\times}10^{-6}$. The tet(S) gene was transferred from Lactococcus garvieae KHS98032 to E. coli at a frequency of $1.8{\times}10^{-6}$. Transconjugated recipients showed increased minimum inhibitory concentrations against oxytetracycline. Although the donors possess the Tn916-Tn1545 transposons, they were not detected in transformed recipients, suggesting that the transfer of tet(M) and tet(S) is mediated by elements or mechanisms. Two ribosomal protect protein genes were also transmissible from marine bacteria to E. coli, suggesting gene hopping among marine, terrestrial, and human environments.