Gentamicin-resistant Kiebsiella aerogenes as a clinically-significant source of transferable antibiotic resistance

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Abstract
Of 108 epidemiologically-distinct strains of gentamicin-resistant Klebsiella aerogenes collected from 12 hospitals in six countries, 86 (80%) transferred multiple antibiotic resistance to Escherichia coli K12. For 77 (90%) of the successful donors the resistances were conferred by single plasmids with molecular weights of between 25 and 130 megadaltons. Forty-eight per cent of the donors transferred resistance to chloramphenicol, tetracycline, sulphamethoxazole, ampicillin/carbenicillin, in addition to resistance to at least two aminoglycosides and to one or more cephalosporins. Resistances to chloramphenicol, tetracycline, ampicillin/carbenicillin, sulphamethoxazole, gentamicin and trimethoprim were transferable in 89, 75, 74, 74, 67 and 58%, respectively, of strains that were resistant to these agents. Six ‘epidemic’ plasmids conferring extensive multiple resistance were found in 21 different serotypes from patients in single hospitals in London, Munich and Sydney. Three of these plasmids conferred resistances to gentamicin, trimethoprim and sulphamethoxazole. The frequency of transferable resistance and the intrageneric spread of single plasmids suggests that Klebsiella species serves as an important source of multiple resistance for this and other more pathogenic species.