Emergence of Multidrug-Resistant Escherichia coli Harbouring the CS31A Virulence Factor in Neonatal Calf Diarrhoea in Central France

<i>Escherichia coli</i> is a significant cause of Neonatal Calf Diarrhoea (NCD). Its extensive antigenic diversity, coupled with the ability to acquire antimicrobial resistance determinants, hampers treatment effectiveness and compromises the control measures. This study investigated the link between the presence of multidrug-resistant (MDR) <i>E. coli</i> and virulence factors (VFs) in NCD from central France (Departments of Cantal, Haute-Loire, Loire, and Puy-de-Dôme), between 2016 and 2022. <i>E. coli</i> was identified at TERANA Laboratories, France, using API 20E (BioMérieux^®) and MALDI-TOF Mass Spectrometry. Virulence factors, namely adhesins, were assessed with the slide agglutination method, and antimicrobial susceptibility testing was conducted across various antimicrobial classes. Out of 2367 <i>E. coli</i> strains isolated from cases of NCD, a high percentage were resistant to aminopenicillins (88.8%), aminoglycosides (89.1%), tetracyclines (79.7%), quinolones (48.4%), and sulphonamides (42.4%). More than half (58.6%) carried VFs, and 84.9% exhibited MDR profile, of which 61.34% (1233/2010) also harboured VFs. The adhesin CS31A-producing <i>E. coli</i> was the most prevalent, followed by the fimbrial adhesins F5 and F17 (60.8%, 20.0%, and 8.3%, respectively), all of which were associated with a high prevalence of MDR strains (79.1-93.9%). The highest occurrence of MDR profiles was observed in <i>E. coli</i> strains carrying CS31A and in those lacking VFs, both groups showing co-resistance to aminopenicillins, aminoglycosides, and tetracyclines or sulphonamides. The calf production sector may act as a reservoir for MDR <i>E. coli</i> strains, regardless of the presence of VFs, posing a major threat to public health and safety.