Absence of co-localization between pathovar-associated virulence factors and extended-spectrum ß-lactamase (blaCTX-M) genes on a single plasmid.

Extended-spectrum ß-lactamases (ESBLs) were reported in virulent food-borne Escherichia coli clones, and numerous genes encoding ESBLs and virulence factors (VFs) are plasmid-mediated. We investigated the plasmidic co-localization of ESBL genes and pathovar-associated VF genes isolated in 18 E. coli isolates from faecal samples of diseased cattle. From the rare ESBL-producing E. coli among the various pathovars, no plasmid co-localization was found between VF and blaCTX-M genes on a single plasmid. However, a link between replicon types and VFs was highlighted: EspP was associated with IncFIB and ToxB with IncB/O. Associations of IncF alleles to VF or CTX-M-types were also identified: CS31A was linked to the allele FIB38 and CTX-M-14 to IncFII2. Also, as illustrated here, IncFII and IncFIB were carried by two different plasmids in a single cell.

Assessment of Adhesins as an Indicator of Pathovar-Associated Virulence Factors in Bovine Escherichia coli.

The CS31A, F17, and F5 adhesins are usually targeted by serology-based methods to detect pathogenic Escherichia coli associated with calf enteritis. However, the virulence traits of the selected isolates are still poorly described. Here, from a set of 349 diarrheagenic E. coli isolates from cattle, we demonstrated a 70.8% concordance rate (Cohen's kappa, 0.599) between serology- and PCR-based approaches for the detection of adhesins under field conditions. A 79% to 82.4% correspondence between the two methods was found for fimbrial adhesins, whereas major discrepancies (33%) were observed for CS31A-type antigens. Various F17A variants were found, such as F17Ac (20K) (50%), F17Aa (FY) (18.9%), F17Ab (8.1%), and F17Ad (111K) (5.4%), including a high proportion (17.6%) of new F17A internal combinations (F17Aab, F17Aac, and F17Abc) or untypeable variants. In addition, the highest proportion of pathovar-associated virulence factor (VF) genes was observed among E. coli isolates that produced F5/F41 adhesins. A specific link between the heat-stable toxins related to the enterotoxigenic E. coli (ETEC) pathovar and adhesins was identified. STa was significantly linked to F5/F41 and EAST1 to CS31A adhesins (P < 0.001), respectively, whereas NTEC was associated with F17 adhesin (P = 0.001). Clustering between phylogroups according to the adhesin types was also observed. Also, few Shiga toxin-producing E. coli (STEC) or enteropathogenic E. coli (EPEC) pathovars were identified. Finally, no statistically significant difference was observed in the occurrence of extended-spectrum beta lactamase (ESBL) production according to the adhesins expressed by the isolates (P = 0.09). Altogether, this study gives new insights into the relationship between adhesins, VF, and antimicrobial resistance in calf enteritis and supports the need for further standardization of methodologies for such approaches.