Heterogeneity within apparently pure cultures of Escherichia coli freshly isolated from significant bacteriuria

Pyrolysis mass spectrometry (PyMS), a highly discriminatory method for comparison of isolates, was used to assess the homogeneity of colonies taken from apparently pure cultures of Escherichia coli in 10 urine specimens. Ten randomly selected colonies were subcultured from each urine for comparison. For six urines, the set of 10 single-colony isolates proved indistinguishable by PyMS. However, for four urines there was clear heterogeneity. For two urines, one of the isolates was distinct, and the remaining nine indistinguishable. One urine yielded seven indistinguishable isolates, and three further individually distinct isolates. One urine yielded two clusters of indistinguishable isolates, one comprising seven and the other three isolates. Thus, significant heterogeneity (as measured by PyMS) occurs in apparently pure cultures of E. coli from urinary tract infection. The nature of this heterogeneity remains to be established, as does the significance, if any, of this phenomenon in urinary tract infection.