Kinetics of Targeted Phage Rescue in a Mouse Model of Systemic Escherichia coli K1

Abstract

Escherichia (E.) coli K1 strains remain common causative agents of neonatal sepsis and meningitis. We have isolated a lytic bacteriophage (ΦIK1) against E. coli strain IHE3034 and tested its specificity in vitro, as well as distribution and protective efficacy in vivo. The phage was shown to be specific to the K1 capsular polysaccharide. In the lethal murine model, a high level of protection was afforded by the phage with strict kinetics. A single dose of 1 x 10⁸ phage particles administered 10 and 60 minutes following the bacterial challenge elicited 100 % and 95 % survival, respectively. No mice could be rescued if phage administration occurred 3 hours postinfection. Tissue distribution surveys in the surviving mice revealed that the spleen was the primary organ in which accumulation of active ΦIK1 phages could be detected two weeks after phage administration. These results suggest that bacteriophages have potential as therapeutic agents in the control of systemic infections.

Figure 1

Morphology of ΦIK1 shows typical characteristics of Podoviridae. Bar represents 100nm.

Figure 2

In vitro kinetics of the ΦIK1-IHE3034 interaction in different MOIs. Lines A (medium control), B (bacterium growth control), and H (medium control) are control fields. In rows C, D, E, F, and G the final concentration of phages are 10⁵, 10⁴, 10³, 10², and 10¹, respectively. In columns 1-3, 4-6, 7-9, and 10-12 bacterial end concentrations were 10⁶, 10⁵, 10⁴, and 10³ respectively. Accordingly ratios are presented PFU: CFU.

Figure 3

In the phage rescue experiment, survival of IHE3034 infected BALB/c mice strongly depended on the elapsed time between the injection of bacterium suspension (1 x 10⁸ CFU/mouse) and ΦIK1 (1 x 10⁸ PFU / mouse). Phage administration occurred 10 min (G10M), 1 h (G1H), 2 h (G2H), and 3 h (G3H) postinfection, while the IHE3034 and the ΦIK1 suspensions were used as positive (GBC) and negative (GPC) controls, respectively. The obtained survival curves were statistically compared by the logrank (Matel-Cox) test using the GraphPad Prism 6.0 software.

Figure 4

Detection of active phages in the surviving mice two weeks after bacterial challenge and phage rescue. Results are subdivided according to the organs (X axis). In each subsection (1-12) the summarized results of the GPC, G10M G1H, and G2H are presented as columns. G3H and GBC were not drafted as no mice survived in G3H, while no phage was administered to GBC (STable 1.).