Transfer Among Erwinia spp. and Other Enterobacteria of Antibiotic Resistance Carried on R Factors

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RESUMO

Antibiotic resistance carried on R factors was transferred by conjugation from Escherichia coli B/r and Shigella flexneri 1a to Erwinia spp. Tetracycline resistance (TetR) carried on R factor R100 drd-56 was transferred from E. coli B/r to strains of Erwinia amylovora, E. aroideae, E. atroseptica, E. chrysanthemi, E. cytolytica, E. dissolvens, E. herbicola, E. nigrifluens, and E. nimipressuralis, but not to strains of Erwinia carotovora, E. carnegieana, E. dieffenbachiae, E. oleraceae, and E. quercina. Multiple antibiotic resistance (chloramphenicol, streptomycin, tetracycline; ChlR-StrR-TetR) carried on R factor SR1 was transferred from a clinical isolate of S. flexneri 1a to strains of E. aroideae, E. chrysanthemi, E. herbicola, and E. nigrifluens, but not to strains of other Erwinia spp. The frequency of this transfer was low with receptive cultures of Erwinia spp. and E. coli (F− strain). Antibiotic resistance in the exconjugants showed varying degrees of stability in the presence or absence of acridine orange, depending on the strain tested. The frequencies of segregation to drug susceptibility in the presence of acridine orange, though low, suggest that the elements exist as plasmids in the majority of the Erwinia exconjugants. Multiple antibiotic resistance (ChlR-StrR-TetR) was found to segregate into various resistance classes (ChlR-StrR, StrR-TetR, TetR, StrR, and none) in these exconjugants. The exconjugants of E. amylovora, E. herbicola, and E. nigrifluens, to which R100 drd-56 was transferred from E. coli B/r, were sensitive to the male (F)-specific phage M13. There was a positive correlation between the susceptibility of exconjugants to the F-specific phage M13 and their ability to transfer R100 drd-56 to the recipient cultures of Escherichia coli, Erwinia herbicola, Salmonella typhimurium, and Shigella dysenteriae. Exceptions were, however, noted with Erwinia dissolvens and E. nimipressuralis exconjugants harboring R100 drd-56; these exconjugants, although not susceptible to M13, transferred R100 drd-56 to the recipient cultures. The frequency of transfer of R100 drd-56 and the levels of resistance to tetracycline in Erwinia exconjugants were found to differ markedly depending upon the strain employed. Transfer of multiple antibiotic resistance (ChlR-StrR-TetR) from Erwinia exconjugants was not obtained in preliminary trials with an E. coli F− strain as the recipient culture.

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