657 - Siderophore deletion decreases the growth potential of E. coli containing the K1 antigen in low-iron murine peritoneal wash fluid

To test whether knocking out important iron acquisition proteins called siderophores and/or their receptors in E. coli K1 would decrease growth in murine neonatal peritoneal fluid.

Design/Methods: E. coli K1 knockouts were created using a combination of siderophores or siderophore receptors: Enterobactin (entF), Yersiniabactin (irp12), Salmochelin (iroB), Yersiniabactin receptor (fyuA), and Enterobacter-Salmochelin receptor (iroN). Specific knockouts tested were fyuA/entF, fyuA/iroB, fyuA/iroN, and irp12/entF/iroB. E. coli K1 and KO E. coli K1 were grown in murine adult (8-12 weeks) or neonatal (P4-6) PWF obtained from C57Bl/6 mice. Colony forming units (CFUs) were measured at 0, 2, 4, 6, 8, 10, and 24 hours following culture. Statistics were done with mix-effects analysis and Tukey’s test for multiple comparisons.

Results: As previously demonstrated, control E. coli K1 grew more slowly in adult PWF compared to neonatal PWF but growth was similar at 24 hours. All knockouts grew similarly to controls except for mutants containing entF, specifically fyuA/entF and irp12/entF/iroB. When in neonatal PWF, KO growth was not different from controls. However, when grown in adult PWF, KO growth was slower and did not reach control CFU at 24 hours (0hr control 37 vs KO 43 CFU, p=0.93; 2hr 867 vs 600, p=0.92; 4hr 3500 vs 4680, p=0.42; 6hr 17700 vs 7230, p=0.23; 8hr 135000 vs 10800, p=0.40; 10hr 766000 vs 11700, p=0.46; 24hr 1.47e7 vs 69700, p=0.04).

Conclusion(s): Knockout of these specific siderophores and their receptors in E. coli K1 does not decrease growth in the iron-rich environment of neonatal PWF, but KO of entF decreases growth rate and growth potential in the low-iron environment of adult PWF. These data suggest that targeting entF with vaccines or antibodies may be helpful to decrease severity of infections with E. coli K1 in low-iron but not high-iron environments.