Virulence and other phenotypic characteristics of urinary isolates of cysteine-requiring Escherichia coli.

Urinary isolates of cysteine-requiring Escherichia coli were found to be generally lacking in virulence factors commonly associated with uropathogenic strains. The proportion of auxotrophic strains showing type-1 fimbriation, haemolysin production, motility and sensitivity to normal human serum was significantly less than that of a comparable number of urinary isolates of prototrophic E. coli, although the proportion in both groups possessing K1 antigen was similar. Furthermore, the biotyping and serogrouping of these and other strains from systemic infections demonstrated a high degree of phenotypic diversity. This is further evidence that infection with these auxotrophs results from a combination of decreased host resistance and a physiological condition conducive to the random selection of these auxotrophs in vivo.