Pathogenicity island markers in commensal and uropathogenic Escherichia coli isolates

Uropathogenic isolates of Escherichia coli (UPEC) contain blocks of DNA, termed pathogenicity islands (PAIs), that contribute to their virulence. Two multiplex PCR assays were developed to detect eight PAI markers among 50 commensal E. coli and 100 UPEC isolates. In total, 40% of commensal isolates and 93% of UPEC carried PAIs. Despite this difference, the distribution of various PAIs showed the same pattern in both groups, with the most prevalent being PAI IV536 (38% commensal vs. 89% UPEC), followed by PAI I-CFT073 (26% vs. 73%), PAI IICFT073 (14% vs. 46%), PAI IIJ96 (8% vs. 34%), PAI I-536 (8% vs. 33%) and PAI II536 (4% vs. 20%). PAI III536 was detected only in UPEC (2%), while PAI I-J96 was not detected in any isolate. Although the mean number of PAIs per isolate was higher among UPEC (2.97) than in commensal (0.98) isolates, there were no statistical differences among group B2 E. coli from the two origins; however, commensal isolates from groups D and B1 appeared to be less virulent than pathogenic isolates. Regardless of their phylogenetic group, nearly all the commensal and UPEC isolates with the same number of PAIs had the same PAI combinations. Although group B2 E. coli are uncommon among commensal intestinal flora, they are highly virulent when present, suggesting that the intestinal flora may act as a reservoir for bacteria that can cause urinary tract infection.