Host range and transfer efficiency of incompatibility group HI plasmids.

HI plasmids are distinguished by their thermosensitive mode of conjugation (transfer efficiency is optimal at 22-30 degrees C) and their capacity to encode multiple antibiotic resistance. These traits have implicated HI plasmids as potential vectors in the dissemination of antibiotic resistance among pathogenic and indigenous bacterial species in water and soil environments. We compared the transfer efficiency of HI plasmids with that of plasmids from 13 other incompatibility groups at 37, 24, and 14 degrees C in intragenic conjugations between laboratory strains of Escherichia coli K-12 under in vitro conditions. Only the HI plasmids and a representative plasmid from incompatibility groups M, N, P alpha, T, and W were observed to be transmissible at 14 degrees C. These plasmids, along with HI plasmids and the related HII representative, were tested for their host range and transfer proficiency to Enterobacteria species and some other Gram-negative organisms of environmental significance at 24 and 14 degrees C. Notable differences in the host range of HI plasmids compared with plasmid representatives from the other enterobacterial groups were not evident at 24 degrees C. At 14 degrees C, R478 (HI2) displayed the broadest host range and transfer proficiency among the test plasmids. The ability of several plasmid groups, including HI, to transfer at 14-24 degrees C to Vibrio cholerae non 01, Salmonella typhi, and the fish pathogens Aeromonas salmonicida, Vibrio anguillarum, and Yersinia ruckeri needs to be corroborated by in situ studies.