Molecular studies of plasmids of multiply-resistantShigellaspp. in Hong Kong

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Abstract
One hundred and twoShigellaspp. isolated in two hospitals in Hong Kong were analysed for antibiotic resistances, resistance plasmids and plasmid profiles. Three quarters of the isolates wereS.flexneri. All isolates harboured plasmids, up to a maximum of ten within one strain. Plasmids of 220 kb encoding resistances to tetracycline, chloramphenicol and sulphonamide and probably also associated with invasivenes in the Sereny test were found in 80 strains and were transferable in 18% of cases. Resistance plasmids of 92 and 99 kb were found in 27 and 15 strains respectively and encoded resistances to ampicillin, tetracycline, chloramphenicol, kanamycin, sulphonamide, trimethoprim, cotrimoxazole and gentamicin; these plasmids were usually transferable. Four plasmids of 3·9, 2·8, 2·2 and 1·8 kb were commonly found inS. flexneristrains, but were rare in other species. In contrast, there was no predominant plasmid profile inS. sonnei. S. flexneriis endemic in Hong Kong and these plasmid studies suggest that the strains in circulation are derived from only a few clones.