Serotype-related enterotoxigenicity inEscherichia coliO6.H16 and O148.H28

The ability of certain Escherichia coli strains to produce enterotoxin is determined by transmissible plasmids. It is therefore possible that any E. coli strain might be able to acquire such a plasmid and that the correlation between enterotoxigenicity and serotype might be random. However, recent studies show that the enterotoxigenic strains so far describe belong to a restricted range of serotypes. Enterotoxigenic strains of E. coli O6.H16 and E. coli O148.H28 have been associated with outbreaks of diarrhoea in several countries, therefor strains of E. coli belonging to these serotypes were selected for further study. Twenty-three strains of E. coli O6.H16 and 14 strains of E. coli O148.H28 were examined; 20 strains of E. coli O6.H16 and all 14 strains of E. coli O148.H28 were enterotoxigenic but strains of E. coli O6 wit flagellar antigens other than H16 and strains of E. coli O148 wit flagellar antigens other than H28 were not enterotoxigenic. The examination of single colony subcultures derived from the E. coli O6.H16 strains showed that in some strains loss of enterotoxigenicity had occurred in a proportional of colonies.