Allelic Variation Contributes to Bacterial Host Specificity

Understanding the molecular parameters that regulate cross-species transmission and host adaptation of potential pathogens is crucial to control emerging infectious disease. Although microbial pathotype diversity is conventionally associated with gene gain or loss, the role of pathoadaptive nonsynonymous single-nucleotide polymorphisms (nsSNPs) has not been systematically evaluated. Here, our genome-wide analysis of core genes within Salmonella enterica serovar Typhimurium genomes reveals a high degree of allelic variation in surface-exposed molecules, including adhesins that promote host colonization. Subsequent multinomial logistic regression, MultiPhen and Random Forest analyses of known/suspected adhesins from 580 independent Typhimurium isolates identifies distinct host-specific nsSNP signatures. Moreover, population and functional analyses of host-associated nsSNPs for FimH, the type 1 fimbrial adhesin, highlights the role of key allelic residues in host-specific adherence in vitro. Together, our data provide the first concrete evidence that functional differences between allelic variants of bacterial proteins likely contribute to pathoadaption to diverse hosts

Initial adherence of EPEC, EHEC and VTEC to host cells

Initial adherence to host cells is the first step of the infection of enteropathogenic Escherichia coli (EPEC), enterohaemorrhagic Escherichia coli (EHEC) and verotoxigenic Escherichia coli (VTEC) strains. The importance of this step in the infection resides in the fact that (1) adherence is the first contact between bacteria and intestinal cells without which the other steps cannot occur and (2) adherence is the basis of host specificity for a lot of pathogens. This review describes the initial adhesins of the EPEC, EHEC and VTEC strains. During the last few years, several new adhesins and putative colonisation factors have been described, especially in EHEC strains. Only a few adhesins (BfpA, AF/R1, AF/R2, Ral, F18 adhesins) appear to be host and pathotype specific. The others are found in more than one species and/or pathotype (EPEC, EHEC, VTEC). Initial adherence of EPEC, EHEC and VTEC strains to host cells is probably mediated by multiple mechanisms

Isolation of Clostridium perfringens from three neonatal calves with haemorrhagic abomasitis.

peer reviewedBraxy-like disease with sudden death and acute haemorhagic abomasitis was diagnosed in three Belgian Blue calves : one two-day-old and one one month-old calves, in good condition with no clinical signs noted a few hours prior to death, and another two day-old calf, which had shown problems of abomasal dilatation and regurgitation prior to death. Histologically, the abomasal wall were oedematous and emphysematous. A pure and abundant growth of Clostridium perfringens was obtained in anaerobic conditions from the abomasal wall of the three Belgian Blue calves. No bacterial growth was obtained in aerobic conditions. The calf with digestive disorders was also positive for BVD virus by immunofluorescence in the abomasal wall and in the spleen.Un syndrome "Braxy-like", avec mort subite et abomasite aiguë hémorragique, a été observé chez trois veaux de la race Blanc-Bleu belge: deux veaux âgés de deux jours et un mois, en bonne santé et sans signes cliniques apparents quelques heures avant la mort, et un veau âgé de deux jours, avec une dilatation de la caillette et des problèmes de régurgitation peu de temps avant la mort. A l'examen histologique, la paroi des caillettes était oedématiée et emphysémateuse. Une culture pure et abondante de Clostridium perfringens a été obtenue en conditions anaérobies à partir de la paroi des caillettes de ces trois veaux. Les résultats des cultures bactériennes en conditions aérobies étaient négatifs. Le veau présentant des troubles digestifs était aussi positif par immunofluorescence pour le virus BVD à hauteur de la paroi de la caillette et de la rate

Putative Adhesins of Enteropathogenic and Enterohemorrhagic Escherichia coli of Serogroup O26 Isolated from Humans and Cattle ▿

Enterohemorrhagic Escherichia coli (EHEC) strains are responsible for food poisoning in developed countries via consumption of vegetal and animal food sources contaminated by ruminant feces, and some strains (O26, O111, and O118 serogroups) are also responsible for diarrhea in young calves. The prevalence of 27 putative adhesins of EHEC and of bovine necrotoxigenic E. coli (NTEC) was studied with a collection of 43 bovine and 29 human enteropathogenic (EPEC) and EHEC strains and 5 non-EPEC/non-EHEC (1 bovine and 4 human) O26 strains, using specific PCRs. Four “groups” of adhesins exist, including adhesins present in all O26 strains, adhesins present in most O26 strains, adhesins present in a few O26 strains, and adhesins not present in O26 strains. The common profile of EHEC/EPEC strains was characterized by the presence of loc3, loc5, loc7, loc11, loc14, paa, efa1, iha, lpfAO26, and lpfAO113 genes and the absence of loc1, loc2, loc6, loc12, loc13, saa, and eibG genes. Except for the lpfAO26 gene, which was marginally associated with bovine EHEC/EPEC strains in comparison with human strains (P = 0.012), none of the results significantly differentiated bovine strains from human strains. One adhesin gene (ldaE) was statistically (P < 0.01) associated with O26 EHEC/EPEC strains isolated from diarrheic calves in comparison with strains isolated from healthy calves. ldaE-positive strains could therefore represent a subgroup possessing the specific property of producing diarrhea in young calves. This is the first time that the distribution of putative adhesins has been described for such a large collection of EHEC/EPEC O26 strains isolated from both humans and cattle

Clinical Signs, Reproduction of Attaching/Effacing Lesions, and Enterocyte Invasion after Oral Inoculation of an O118 Enterohaemorrhagic Escherichia Coli in Neonatal Calves

Attaching and effacing (AE) lesions are produced among others by enteropathogenic Escherichia coli and enterohaemorrhagic E. coli (EHEC), which differs from the former by the production of cytotoxins active on various cell cultures, the verocytotoxins, or shigacytotoxins. EHEC are associated with diarrhoea and dysentery in humans and in ruminants, mainly calves from two to eight weeks of age. Clinical signs and/or lesions have been reproduced experimentally with EHEC strains belonging to serotypes O5:K4/Nm, O26:K-:H11, O111:Nm, and O157:H7 which are isolated from cattle and/or humans. The purpose of this work was to develop an experimental model of infection in newborn calves with a bovine EHEC strain isolated from a calf which of died of diarrhoea, and belonging to the O118:H16 serotype, which is also common to both cattle and humans. The bovine O118:H16 EHEC strain was able to colonize the gut of three newborn calves, and to induce diarrhoea twenty-four hours after challenge and to produce AE lesions in the small and/or large intestines. AE lesions were detected microscopically and ultrastructurally in the small intestine of one calf and in the whole intestinal track of two calves. Internalization of bacteria and also of pedestal-bacteria complex inside of the enterocyte was observed in two of the three calves. The significance of this stage is unknown but may be related to the invasion of the calf by the bacteria. The challenge strain was isolated from the mesenteric lymph nodes of the same two calves but not from other organs or from heart blood. No blood was observed in the faeces of any of the three calves, nor were any lesions in the internal organs, which may have been related to the production of a verotoxin whose role is still unknown in cattle