Expression of colonization factor antigen I fimbriae by enterotoxigenic Escherichia coli; influence of growth conditions and a recombinant positive regulatory gene

Enterotoxigenic Escherichia coli (ETEC) may spontaneously lose the positive regulatory cfaR gene and thereby the capacity to express colonization factor antigen I (CFA/I). A recombinant plasmid harbouring the cfaR gene was transformed into cfaR‐negative mutant ETEC strains. CFA/I expression of wild‐type and cfaR‐transformed ETEC cultivated in different liquid media was quantified. At 37°C, a high level of CFA/I expression from wild‐type and cfaR‐transformed strains was observed after growth in CFA broth. Transformation enhanced CFA/I expression only marginally. The transformant cultures showed a considerable variation in CFA/I expression which was paralleled by the proportion of individual bacteria producing CFA/I. This heterogeneity could be explained by a variable tendency to structural CFA/I gene loss among individual cfaR‐transformed bacteria.