Roles of serine accumulation and catabolism in the colonization of the murine urinary tract by Escherichia coli CFT073

Abstract

A D-serine deaminase (DsdA) mutant of uropathogenic Escherichia coli strain CFT073 has a hypercolonization phenotype in a murine model of urinary tract infection (UTI) due to increased virulence gene expression by an unknown mechanism (B. J. Haugen et al., Infect. Immun. 75:278-289, 2007). DsdC is a D-serine-dependent activator of dsdXA transcription. DsdC may regulate the virulence genes responsible for hypercolonization. The loss of DsdA leads to increased intracellular accumulation of D-serine. In this study we show that deletion of the genes encoding L-serine deaminases SdaA and SdaB resulted in a mutant that accumulates higher intracellular levels of L-serine than CFT073. CFT073 sdaA sdaB has a mild competitive colonization defect whereas a CFT073 dsdA sdaA sdaB triple mutant shows a greater loss in competitive colonization ability. Thus, the inability to generate serine-specific catabolic products does not result in hypercolonization and the ability to catabolize serine represents a positive physiological trait during murine UTI. CFT073 dsdC and CFT073 dsdC dsdA mutants continue to outcompete the wild type in the UTI model. These results confirm that loss of DsdA activity results in the hypercolonization phenotype and that DsdC does not play a direct role in the elevated-colonization phenotype. Interestingly, a CFT073 dsdA mutant with deletions of D-serine transporter genes dsdX and cycA shows wild-type colonization levels of the bladder but is attenuated for kidney colonization. Thus, D-serine acts as a signal for hypercolonization and virulence gene expression by CFT073 dsdA, whereas overall catabolism of serine represents a positive Escherichia coli fitness trait during UTI.

FIG. 1.

Bladder and kidney colonization of mice with wild-type (wt) CFT073 and CFT073 sdaA sdaB. Mice were transurethrally inoculated with a 1:1 ratio of CFT073 lacZYA and CFT073 sdaA sdaB (A) or CFT073 lacZYA and CFT073 dsdA sdaA sdaB (B). Each data point represents the competitive index that is the ratio of recovered mutant CFU/g tissue to recovered wild-type CFU/g tissue for the designated organ tissue from one mouse 48 h postinoculation. Horizontal bars represent the median values of ratios for the organ type, which were equal to 0.28 (P = 0.020) and 0.502 (P = 0.042) (A) and 0.034 (P < 0.001) and 0.084 (P = 0.091) (B) for the bladder and kidney, respectively.

FIG. 2.

Bladder and kidney colonization of mice with wild-type (wt) and CFT073 dsdA dsdC. Mice were transurethrally inoculated with a 1:1 ratio of CFT073 lacZYA and CFT073 dsdA dsdC. Each data point represents the competitive index that is the ratio of recovered mutant CFU/g tissue to recovered wild-type CFU/g tissue for the designated organ tissue from one mouse 48 h postinoculation. Horizontal bars represent the median values of ratios for the organ type, which are 4.0 and 4.4 for the bladder and kidney, respectively (P < 0.004 and P < 0.005, respectively).

FIG. 3.

Bladder and kidney colonization of mice with wild-type (wt) and CFT073 dsdC. Mice were transurethrally inoculated with a 1:1 ratio of CFT073 lacZYA and CFT073 dsdC-STOP (A) or the same strains carrying a plasmid carrying dsdC (B). Each data point represents the competitive index that is the ratio of recovered mutant CFU/g tissue to recovered wild-type CFU/g tissue for the designated organ tissue from one mouse 48 h postinoculation. Horizontal bars represent the median values of ratios for the organ type, which were equal to 15 (P < 0.002) and 9.0 (P < 0.032) (A) and 2.3 (P = 0.54) and 3.6 (P = 0.68) (B) for the bladder and kidney, respectively.

FIG. 4.

Bladder and kidney colonization of mice with wild-type (wt) and CFT073 cycA dsdXA. Mice were transurethrally inoculated with a 1:1 ratio of CFT073 lacZYA and CFT073 cycA dsdXA. Each data point represents the competitive index that is the ratio of recovered mutant CFU/g tissue to recovered wild-type CFU/g tissue for the designated organ tissue from one mouse 48 h postinoculation. Horizontal bars represent the median values of ratios for the organ type, which were equal to 0.69 (P = 0.56) and 0.12 (P = 0.015) in the bladder and kidney, respectively.