Bacteriocin synthesis in uropathogenic and commensal Escherichia coli: colicin E1 is a potential virulence factor

Abstract

Background: Bacteriocin production is an important characteristic of E. coli strains of human origin. To date, 26 colicin and 9 microcin types have been analyzed on a molecular level allowing molecular detection of the corresponding genes. The production incidence of 29 bacteriocin types and E. coli phylogroups were tested in a set of 361 E. coli strains isolated from human urinary tract infections (UTI) and in 411 control strains isolated from feces of patients without bacterial gut infection.

Results: Production of 17 and 20 individual bacteriocin types was found in the UTI and control strains, respectively. Microcin H47 encoding determinants were found more often among UTI strains compared to controls (37.9% and 27.0% respectively, p = 0.02) and strains producing microcin H47 belonged predominantly to phylogroup B2 when compared to other bacteriocin producers (67.4% and 36.7%, respectively; p < 0.0001). Producers of 3 or more identified bacteriocin types were more common in the UTI group (20.0% compared to 12.4% in controls, p = 0.03). In the UTI strains, there was a markedly higher number of those producing colicin E1 compared to controls (22.1% to 10.2%, respectively, p = 0.0008). Moreover, colicin E1 production was more common in the UTI bacteriocinogenic strains with multi-producer capabilities. As shown by Southern blotting, pColE1 DNA was not recognized by the ColIa probe and vice versa suggesting that pColE1 was independently associated with pColIa in UTI strains.

Conclusion: E. coli strains isolated from human urinary tract infections showed increased incidence of microcin H47 and colicin E1 production, respectively. Moreover, colicin E1 itself appears to be a potentially important virulence factor of certain uropathogenic E. coli strains.

Figure 1

Detection of DNA encoding colicins E1 and Ia in 6 plasmid DNA samples (out of 12 randomly picked and analyzed colicin E1 producers). Panel A: an agarose gel with total plasmid DNA stained with ethidium bromide; panel B: Southern blot analysis of the same plasmid DNA samples with colicin E1 probe; panel C: Southern blot analysis with colicin Ia probe. The 1 kb DNA ladder (New England Biolabs, Ipswitch, MA) was used as the DNA marker (panel A, lane 13). Lanes 1 and 2, plasmid DNA isolated of strain B399 (digested with EcoRI and undigested, respectively). Lanes 3 and 4, strain B954 (producer of colicins E1, Ia, and microcin V); lanes 5 and 6, strain B961; lanes 7 and 8, strain B2041; lanes 9 and 10, strain B953; lanes 11 and 12, strain B830. Strains B399, B954, B2041 and B830 were all producers of colicins E1, Ia, and microcin V. Strain B961 produced colicins E1, Ia, E7, K and microcin V. Strain B953 produced colicins E1, Ia, and microcins V and H47. Please note that patterns of undigested plasmid DNA were different in panel B and C, respectively, indicating that colicin Ia and E1 genes are located on separate plasmids.