The rpoS Gene Is Predominantly Inactivated during Laboratory Storage and Undergoes Source-Sink Evolution in Escherichia coli Species

The rpoS gene codes for an alternative RNA polymerase sigma factor, which acts as a general regulator of the stress response. Inactivating alleles of rpoS in collections of natural Escherichia coli isolates have been observed at very variable frequencies, from less than 1% to more than 70% of strains. rpoS is easily inactivated in nutrient-deprived environments such as stab storage, which makes it difficult to determine the true frequency of rpoS inactivation in nature. We studied the evolutionary history of rpoS and compared it to the phylogenetic history of bacteria in two collections of 82 human commensal and extraintestinal E. coli strains. These strains were representative of the phylogenetic diversity of the species and differed only by their storage conditions. In both collections, the phylogenetic histories of rpoS and of the strains were congruent, indicating that horizontal gene transfer had not occurred at the rpoS locus, and rpoS was under strong purifying selection, with a ratio of the nonsynonymous mutation rate (Ka) to the synonymous substitution rate (Ks) substantially smaller than 1. Stab storage was associated with a high frequency of inactivating alleles, whereas almost no amino acid sequence variation was observed in RpoS in the collection studied directly after isolation of the strains from the host. Furthermore, the accumulation of variations in rpoS was typical of source-sink dynamics. In conclusion, rpoS is rarely inactivated in natural E. coli isolates within their mammalian hosts, probably because such strains rapidly become evolutionary dead ends. Our data should encourage bacteriologists to freeze isolates immediately and to avoid the use of stab storage.     

The decoupling between genetic structure and metabolic phenotypes in Escherichia coli leads to continuous phenotypic diversity

To assess the extent of intra-species diversity and the links between phylogeny, lifestyle (habitat and pathogenicity) and phenotype, we assayed the growth yield on 95 carbon sources of 168 Escherichia strains. We also correlated the growth capacities of 14 E. coli strains with the presence/absence of enzyme-coding genes. Globally, we found that the genetic distance, based on multilocus sequence typing data, was a weak indicator of the metabolic phenotypic distance. Besides, lifestyle and phylogroup had almost no impact on the growth yield of non-Shigella E. coli strains. In these strains, the presence/absence of the metabolic pathways, which was linked to the phylogeny, explained most of the growth capacities. However, few discrepancies blurred the link between metabolic phenotypic distance and metabolic pathway distance. This study shows that a prokaryotic species structured into well-defined genetic and lifestyle groups can yet exhibit continuous phenotypic diversity, possibly caused by gene regulatory effects.     

The CTX-M-15-Producing Escherichia coli Clone O25b: H4-ST131 Has High Intestine Colonization and Urinary Tract Infection Abilities

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.     

Bilharziose intestinale chez des touristes québécois: aspects parasitologiques et diagnostiques.

Intestinal bilharziasis (or schistosomiasis) is becoming more and more frequent among Canadian travellers who come in contact with natural soft waters in tropical countries. The clinical signs accompanying contamination, the prodrome and the chronic phase are inconstant, but eosinophilia is often the warning sign, and specific seroparasitologic findings suggest the diagnostic investigation, Five tourists from Quebec became infected while travelling in Martinique. The clinical, parasitologic and serologic features that led to the diagnosis are described. The prodome (a flu-like syndrome with eosinophilia) is underlined. Treatment with niridazole was effective, as confirmed by the absence of Schistosoma mansoni eggs (or the presence of dead eggs) in specimens from rectal biopsies performed subsequently.