TYPING OF SEQUENTIAL BACTERIAL ISOLATES BY PULSED-FIELD GEL-ELECTROPHORESIS

We typed 39 sets of multiple bacterial isolates of the same species fr om patients by pulsed-field gel electrophoresis of genomic DNA (PFGE). Isolates were cultured from different sites or over a 2-week or longe r interval. Staphylococcus aureus, Enterococcus faecalis, Pseudomonas aeruginosa, Escherichia coli, Klebsiella pneumoniae, and Enterobacter cloacae were tested. Excluding E. cloacae, 28 of 32 sets of isolates ( 87%) demonstrated only identical or highly related PFGE types. Four of the seven sets of E. cloacae showed different types. For species othe r than E. cloacae, our results suggest that patients are usually colon ized and infected with a single strain of these bacterial pathogens. U nlike all of the other tested species, E. cloacae PFGE typing differen ces suggested the presence of multiple strains causing colonization an d infection.