rpoS gene function is a disadvantage for Escherichia coli BJ4 during competitive colonization of the mouse large intestine

Abstract

The ability of Escherichia coli to survive stress during growth in different environments is, in large part, dependent on rpoS and the genes that comprise the rpoS regulon. E. coli BJ4 and an isogenic BJ4 rpoS mutant were used to examine the influence of the rpoS gene on E. coli colonization of the streptomycin-treated mouse large intestine. Colonization experiments in which the wild-type E. coli BJ4 and its rpoS mutant were fed individually as well as simultaneously to mice suggested that E. coli BJ4 does not face prolonged periods of nutrient starvation in the mouse large intestine and that the rpoS regulon is not expressed during long-term colonization after adaptation of the bacteria to the gut environment.

FIG. 1

Competitive growth and survival in minimal medium. E. coli BJ4 (▴) and E. coli BJ4 rpoS (■) were inoculated into minimal medium (0.2% glucose) and incubated with shaking (160 rpm) at 37°C for 20 days. Viable counts (CFU per milliliter) were determined at different time points by plating on selective medium.

FIG. 2

Sensitivity to stress challenges. E. coli BJ4 (▴) and E. coli BJ4 rpoS (■) were tested for their ability to resist (A) heat (57°C) and (B) oxidative stress in the presence of 15 mM H₂O₂.

FIG. 3

Individual mouse large intestine colonizing abilities. One set of three mice was fed 10¹⁰ CFU of the E. coli BJ4 wild-type strain (▴), and another set of three mice was fed 10¹⁰ CFU of E. coli BJ4 rpoS (■). At the indicated times, fecal samples were plated on selective medium.

FIG. 4

Competitive mouse large intestine colonizing abilities. E. coli BJ4 (▴) and E. coli BJ4 rpoS (■) were fed simultaneously to four sets of three mice as follows: (A) both at 10⁹ CFU; (B) both at 10⁴ CFU; (C) BJ4 at 10⁵ CFU and BJ4 rpoS at 10⁹ CFU; (D) BJ4 at 10⁹ CFU and BJ4 rpoS at 10⁵ CFU. Error bars represent the standard errors of the geometric means.

FIG. 5

Colonizing abilities of the complemented mutant BJ4 rpoS(pRH320). (A) Mice were fed 10⁹ CFU of E. coli BJ4 rpoS(pRH320). Symbols: ●, E. coli BJ4 rpoS(pRH320); ■, E. coli BJ4 rpoS segregants, i.e., without the plasmid. (B) Mice were fed simultaneously with E. coli BJ4 (▴) at 10⁹ CFU and E. coli BJ4 rpoS(pRH320) at 10⁵ CFU (●). ■, E. coli BJ4 rpoS segregants, i.e., without the plasmid. Fecal samples were plated on selective medium on the indicated days. Error bars represent the standard errors of the geometric means.