Nosocomial urinary tract infection with a slowly growing, fastidious Escherichia coli.

Escherichia coli recovered from a nosocomially acquired urinary tract infection required 48 h of incubation on blood agar and did not grow on other routine clinical laboratory media. This bacterium dissociated readily into three colony types, all of which were confirmed as E. coli by DNA hybridization studies. Preliminary studies indicate a prolonged lag phase that could not be corrected by the addition of a variety of peptones and yeast extracts. Better growth was achieved by the addition of 10% horse serum.