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Background: E. coli is a major cause of neonatal sepsis. After ingestion, E. coli translocates the neonatal gut causing bacteremia. E. coli virulence depends on iron acquisition mechanisms, including siderophore systems. Lactoferrin (LF) protects against neonatal sepsis through immunomodulatory and antimicrobial effects which include iron chelation. However, it is not known whether siderophores in neonatal E. coli strains have an impact on LF’s effects on bacterial invasion and survival in intestinal epithelium.

Objective: To investigate the effects of human LF and the siderophore aerobactin on intestinal invasion and survival of septicemia-producing neonatal E. coli.

Design/Methods: Neonatal E. coli septicemia isolates RS218 and SCB34, and the nonpathogenic laboratory strain DH5α were first compared in their ability to grow in liquid media with 1 mg/mL human lactoferrin (LF) by measuring optical density over 20 h at 37°C. A deletion mutant in SCB34 lacking the aerobactin siderophore receptor gene iutA (ΔiutA) was also tested. Invasion of T84 intestinal epithelial cells was compared between SCB34 and ΔiutA using a gentamicin protection assay, substituting amikacin due to the strain’s resistance profile. Invasion was assessed in the presence of 1 mg/mL LF at the time of infection, and also after overnight incubation of T84 cells with 1 mg/mL LF.

Results: RS218, SCB34 and ΔiutA grew similarly without LF, but significantly less in the presence of LF (Fig. 1, P<0.001). This effect was greatest on DH5α. Invasion and recovery of live bacteria from within T84 intestinal cells was no different between SCB4 and ΔiutA when LF was added at the time of infection, confirming that E. coli does not undergo substantial growth prior to invasion in this model (not shown). Conversely, LF pretreatment of T84 cells prior to E. coli invasion significantly reduced the recovery of live SCB34 (Fig. 2, P=.012). Moreover, invasion by ΔiutA in LF-untreated T84 cells was significantly reduced compared to SCB34 (P=.016), but did not significantly decrease in the presence of LF.

Conclusion(s): LF significantly impairs growth of neonatal E. coli clinical isolates but does not completely abolish it. While LF also decreased neonatal E. coli invasion, the effect was independent of the function of the siderophore aerobactin, which by itself is necessary for invasion. The iron-dependent mechanisms determining host-E. coli interactions are potential therapeutic targets against neonatal sepsis.

Presented at the 2021 PAS Virtual Conference


Infectious Disease | Pediatrics

Human Lactoferrin and the Siderophore Aerobactin Independently Impact Intestinal Invasion by Neonatal Escherichia coli Bacteremia Isolates