HOST MUTATIONS (MIAA AND RPSL) REDUCE TETRACYCLINE RESISTANCE MEDIATED BY TET(O) AND TET(M)

The effects of mutations in host genes on tetracycline resistance medi ated by the Tet(O) and Tet(M) ribosomal protection proteins, which ori ginated in Campylobacter spp, and Streptococcus spp., respectively, we re investigated by using mutants of Salmonella typhimurium and Escheri chia coli, The miaA, miaB, and miaAB double mutants of S. typhimurium specify enzymes for tRNA modification at the adenosine at position 37, adjacent to the anticodon in tRNA, In S. typhimurium, this involves b iosynthesis of N-6-(4-hydroxyisopentenyl)-2-methylthioadenosine (ms(2) io(6)A). The miaA mutation reduced the level of tetracycline resistanc e mediated by both Tet(O) and Tet(M), but the latter showed a greater effect, which was ascribed to the isopentenyl (i(6)) group or to a com bination of the methylthioadenosine (ms(2)) and i(6) groups but not to the ms(2) group alone (specified by miaB). In addition, mutations in E. coli rpsL genes, generating both streptomycin-resistant and strepto mycin-dependent strains, were also shown to reduce the level of tetrac ycline resistance mediated by Tet(O) and Tet(M), The single-site amino acid substitutions present in the rpsL mutations were pleiotropic in their effects on tetracycline MICs, These mutants affect translational accuracy and kinetics and suggest that Tet(O) and Tet(M) binding to t he ribosome may be reduced or slowed in the E. coli rpsL mutants in wh ich the S12 protein is altered. Data from both the miaA and rpsL mutan t studies indicate a possible link between stability of the aminoacyl- tRNA in the ribosomal acceptor site and tetracycline resistance mediat ed by the ribosomal protection proteins.