Thermosensitive transfer of antimicrobial resistances and citrate utilization and cotransfer of hydrogen sulfide production from an Escherichia coli isolate

Abstract

A hydrogen-sulfide producing, citrate-positive strain of Escherichia coli isolated from urinary tract infection was found to be resistant to chloramphenicol (Cm), tetracycline (Tc), streptomycin (Sm), trimethoprim (Tmp), sulfamethoxazole (Smx), and cotrimoxazole (Tmp/Smx). The strain contained 7 plasmids of molecular sizes 120, 35, 5.0, 3.2, 3.0, 2.6, and 2.4 megadaltons (Md), as detected by agarose gel electrophoresis of plasmid DNA. Thermosensitive transfer of Cm, Tc, and citrate utilization occurred conjugally to E. coli K-12 recipient strains at a frequency of approximately 10 −6 per donor cell after an 18 hour incubation. The transconjugants were also resistant to Sm and Smx and produced hydrogen-sulfide. Two plasmids of about 120 Md, pNH222, and 35 Md, pNH223, were detected in these transconjugants. Transformation or 1-hour conjugal transfer experiments at 26°C with selection for Cm or Tc yielded only the 120 Md species. Plasmid pNH222 showed one way incompatibility with F plasmids, a characteristic shown previously to be typical of Inc HI1 plasmids. Transformation experiments with selection for Sm yielded transformants with one plasmid species, (pNH223), 35 Md in size, which carried the gene(s) for H 2S production but not for raffinose fermentation. The fact that characteristics such as citrate utilization and hydrogen sulfide production, used in the identification of enteric bacteria, can be transmitted to E. coli by plasmids is of important taxonomic significance.