Characterization of transferable R plasmids from Aeromonas hydrophila.

Abstract

The properties and DNA structures of 14 transferable R plasmlds detected in Aeromonas hydrophila strains isolated from various areas were compared. Eight of nine R plasmids with resistance mazkers to tetracycline (TC) and sulfonamide (SA) were classified into the incompatibility (lnc.) Group A-C complex. One R plasmid was classified into Inc. Group C. Two R plasmids with resistance to chloramphenicol (CM), streptoanycin (SM), and SA were classified into Inc. Group U. The remaining R plasmids, pES10 and pES15 encoded with CM, SM, TC, kanamycinand SA, were not classified into any of the tested Inc. Groups. Rplasmids with resistance markersto either TC and SA or CM, SM and SA did not restrict DNA phage T1 growth; however, pES10 and pES15 restricted phage T1 growth. This restriction and modification system was similar to that of R plasmid N-3.1) The endonuclease digestion patterns of the DNA's were identical in R plasmids with the same resistance markers. The DNA of R plasmids with resistance to TC and SA showed a high homology to cach other when compazed by Southern blot hybridization.2) R plasmid DNAs encodcd with CM, SM, and SA showed homology with the probe of pAR323) detected from A. salmonicida. A. hydrophila strains carrying R plasmids having the identical DNA structure are widely distributed in freshwater fish culture ponds in various areas.