Genes Encoding the Virulence and the Antimicrobial Resistance in Enterotoxigenic and Shiga-toxigenic E. coli Isolated from Diarrheic Calves

Abstract

Calf diarrhea is one of the considerable infectious diseases in calves, which results in tremendous economic losses globally. To determine the prevalence of Shiga-toxigenic <i>E</i>. coli (STEC) and Enterotoxigenic <i>E</i>. coli (ETEC) incriminated in calf diarrhea, with special reference to Shiga- toxins genes (<i>stx</i>1 and <i>stx</i>2) and enterotoxins genes (<i>lt</i> and <i>sta</i>) that govern their pathogenesis, as well as the virulence genes; <i>eae</i>A (intimin) and <i>f</i>41(fimbrial adhesion), and the screening of their antibiogram and antimicrobial resistance genes; <i>aad</i>B, <i>sul</i>1, and <i>bla-</i>TEM, a total of 274 fecal samples were collected (April 2018-Feb 2019) from diarrheic calves at different farms in El-Sharqia Governorate, Egypt. The bacteriological examination revealed that the prevalence of <i>E. coli</i> in diarrheic calves was 28.8%. The serotyping of the isolated <i>E. coli</i> revealed 7 serogroups; O₂₆, O₁₂₈, O₁₁₁, O₁₂₅, O₄₅, O₁₁₉ and O₉₁. Furthermore, the Congo red binding test was carried out, where 89.8% of the examined strains (n = 71) were positive. The antibiogram of the isolated strains was investigated; the majority of <i>E. coli</i> serotypes exhibit multidrug resistance (MDR) to four antimicrobial agents; neomycin, gentamycin, streptomycin, and amikacin. Polymerase chain reaction (PCR) was used to detect the prevalence of the virulence genes; <i>stx</i>1, <i>stx</i>2 <i>lt</i>, <i>sta</i>, <i>f</i>41 and <i>eae</i>A, as well as the antibiotic resistance genes; <i>aad</i>B, <i>sul</i>1, and <i>bla</i>-TEM. The prevalence of STEC was 20.2% (n = 16), while the prevalence of ETEC was 30.4% (n = 24). Briefly, the Shiga toxins genes; <i>stx</i>1 and <i>stx</i>2, are the most prevalent virulence genes associated with STEC, which are responsible for the pathogenesis of the disease and helped by the intimin gene (<i>eae</i>A). In addition, the <i>lt</i> gene is the most prevalent enterotoxin gene accompanied by the ETEC strains, either alone or in combination with <i>sta</i> and/or <i>f</i>41 genes. The majority of pathogenic <i>E. coli</i> incriminated in calf diarrhea possesses the <i>aad</i>B resistance gene, followed by the <i>sul</i>1 gene. Enrofloxacin, florfenicol, amoxicillin-clavulanic acid, and ampicillin-sulbactam, are the most effective antimicrobial agents against the isolated STEC and ETEC strains.