Plasmid profiles and factors associated with toxigenicity in 51 strains of non-O1 isolated from water samples collected in Bangladesh were analysed. Eleven (21·5%) strains were found to harbour at least one plasmid of 1·7–115 Mda; seven of these strains shared a 115-Mda plasmid. Six of 13 strains tested gave positive cytotoxic and enterotoxic responses. However, two non-cytotoxic strains were enterotoxigenic. Only three of the six cytotoxic and enterotoxic strains caused haemagglutination of human erythrocytes which indicated that toxin production and haemagglutinating activity were unrelated in these non-O1 strains. Conjugal transfer assays demonstrated that the 115-Mda plasmid harboured by some of the toxigenic non-O1 strains carried genes coding for antibiotic resistance and cytotoxin production but not for enterotoxin production. However, this plasmid was also carried by non-toxigenic strains. Some other strains carrying no plasmids or only small-mol.-wt plasmids, were found to be toxigenic. Therefore, toxin production is not plasmid-mediated in all non-O1 strains. Regardless of their pathogenic potential, non-O1 strains possessed the capacity to grow in conditions of iron limitation and, under these conditions, synthesis of at least two new outer-membrane proteins was induced.


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