The CTX-M-15-producing Escherichia coli clone O25b: H4-ST131 has high intestine colonization and urinary tract infection abilities - PubMed (original) (raw)

The CTX-M-15-producing Escherichia coli clone O25b: H4-ST131 has high intestine colonization and urinary tract infection abilities

Sophie Vimont et al. PLoS One. 2012.

Abstract

Increasing numbers of pyelonephritis-associated uropathogenic Escherichia coli (UPEC) are exhibiting high resistance to antibiotic therapy. They include a particular clonal group, the CTX-M-15-producing O25b:H4-ST131 clone, which has been shown to have a high dissemination potential. Here we show that a representative isolate of this E. coli clone, referred to as TN03, has enhanced metabolic capacities, acts as a potent intestine- colonizing strain, and displays the typical features of UPEC strains. In a modified streptomycin-treated mouse model of intestinal colonization where streptomycin was stopped 5 days before inoculation, we show that TN03 outcompetes the commensal E. coli strains K-12 MG1655, IAI1, and ED1a at days 1 and 7. Using an experimental model of ascending UTI in C3H/HeN mice, we then show that TN03 colonized the urinary tract. One week after the transurethral inoculation of the TN03 isolates, the bacterial loads in the bladder and kidneys were significantly greater than those of two other UPEC strains (CFT073 and HT7) belonging to the same B2 phylogenetic group. The differences in bacterial loads did not seem to be directly linked to differences in the inflammatory response, since the intrarenal expression of chemokines and cytokines and the number of polymorphonuclear neutrophils attracted to the site of inflammation was the same in kidneys colonized by TN03, CFT073, or HT7. Lastly, we show that in vitro TN03 has a high maximum growth rate in both complex (Luria-Bertani and human urine) and minimum media. In conclusion, our findings indicate that TN03 is a potent UPEC strain that colonizes the intestinal tract and may persist in the kidneys of infected hosts.

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Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Figure 1

Figure 1. Intestinal colonization.

Intestinal competition tests were performed in streptomycin-pre-treated CD1 mice. Competitive indexes (CIs) are given for day 1 and day 7 post-inoculation. The CI index is a ratio of ratios, in which the ratio between resistant (TN03) and sensitive (K-12 MG1655, IAI1 or ED1a) strains at post-inoculation time points is divided by this same ratio at the initial inoculation time. Horizontal bars represent median log10 CI ratios and compared to a ratio of null effect (0, that is log10 1.0) using a Wilcoxon signed-rank test.

Figure 2

Figure 2. Maximum growth rate in four media.

Four E. coli strains: K-12 MG1655 (white), HT7 (light grey), CFT073 (grey) and TN03 (dark grey) were grown in four different media: Luria Bertani (LB), urine, minimum medium with gluconate and minimum medium with glucose. Boxplots represent distribution of maximal growth rates (MGRs) calculated during the three repetitions of culture assays with the smooth spline function from R network. Black bars inside each boxplot represent medians. Dots located far from the box represent outliers. Links between boxplots with asterisks represent significant differences between two strains tested by Welch test for observed mean comparison. * p<0.05.

Figure 3

Figure 3. Experimental model of UTI.

C3H/HeN mice were infected with the HT7, CFT073, or TN03 strains directly by transurethral inoculation of the bacteria (108 cfu in 50 µl sterile PBS). At day 1, day 2 and day 7 post infection, bladders (A) and kidneys (B) were harvested and their bacterial burdens determined. Horizontal bars represent median log10 bacterial counts. Statistical differences between strains at each post-infection time point were performed using the Kruskal-Wallis equality-of-populations rank test.

Figure 4

Figure 4. Expression of pro-inflammatory mediators in kidneys infected by UPEC.

Expression of MIP-2, KC, IL-1ß, IL-6, MCP-1, RANTES and TNF-α in the day 2 and day 7 post-infection kidneys following the transurethral inoculation of the CFT073 and TN03 UPEC isolates. mRNA expression of each inflammatory marker was calculated using the −ΔΔCT method. Values are expressed as the relative fold increase in kidneys of each mRNA level of proinflammatory mediator in comparison with that measured in naive mice. Horizontal bars represent the median values. Statistical differences between the strains were determined at each time point using the Kruskal-Wallis equality-of-populations rank test.

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Grants and funding

This work was funded in part by a grant from the French National Research Agency under reference ANR-08-MIE-030 (to GA, and AV). AV was in receipt of a “Contrat Hospitalier de Recherche Translationnelle” (CHRP, INSERM-APHP, 2010). A.B. was supported by a “Bourse Médico-Scientifique” from the “Fondation pour la Recherche Médicale”. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

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