Associação entre fatores de virulência e resistência antimicrobiana de Escherichia coli enterotoxigênicas isoladas de leitões com diarreia no Brasil

Abstract

Background: Enterotoxigenic Escherichia coli (ETEC) is the etiologic agent of post weaning colibacillosis, one of the most important diseases in pig farming. The pathogenesis of the disease is associated with two virulence factors (VF), fimbriae and enterotoxins. In veterinary medicine, the use of antibiotics can lead to the selection of resistant bacteria. The association of VF and antibiotic resistance is an important mechanism for bacterial survival under adverse conditions. This study aimed to determine the VF and antimicrobial susceptibility of ETEC isolates from piglets with diarrhea and analyze the association between these factors. Materials, Methods & Results: A total of 185 rectal swabs were collected from weaned piglets in Brazilian farms of the states of Rio Grande do Sul, Santa Catarina, Paraná, Minas Gerais and Goiás. The isolation of ETEC was carried out on blood and MacConkey Agar and characterization by biochemical tests and detection by PCR of fimbrial genes F4, F45, F6, F18 and F41, and toxins genes LT, STa, STb and STx2e. Antimicrobial susceptibility profiles were determined by Agar diffusion test for amoxicillin, ampicillin, ceftiofur, ciprofloxacin, colistin, doxycycline, enrofloxacin, florfenicol, gentamicin, neomycin, norfloxacin, oxytetracycline, streptomycin, tetracycline, lincomycin + spectinomycin and sulfamethoxazole + trimethoprim. The association between VF and antimicrobials resistance results was determined by Chi-square and Fisher test (P ≤ 0.05). A total of 376 isolates were analyzed. The frequencies of fimbriae and toxins amplified were: F4 (31.6%), F18 (18.9%), F5 (4.2%) and toxins STa (43.1%), STb (24.7%), LT (21.8%) and STx2e (5.3%). Antibiotic resistance was higher to tetracycline (96.3%), florfenicol (95.2%), oxytetracycline (93.62%) and doxycycline (90.7%). Lowest levels of resistance were to ceftiofur (2.1%), colistin (9.8%), lincomycin + spectinomicin (15.4%) and neomycin (23.1%). The association of VF and resistance was significant for fimbriae F4 and streptomycin and sulfamethoxazole + trimethoprim; F5 and enrofloxacin, ciprofloxacin and norfloxacin; F18 and amoxicillin, ampicillin, doxycycline, enrofloxacin, norfloxacin, ciprofloxacin and sulfamethoxazole + trimethoprim. Among the toxins LT and tetracycline, streptomycin and florfenicol; STa and amoxicillin, ampicillin, oxytetracycline, enrofloxacin and sulfamethoxazole + trimethoprim; STb and colistin and streptomycin. Discussion: Resistance to all antimicrobials was observed, with higher levels for tetracyclines and lower to ceftiofur and lincomycin + spectinomycin. Several studies have reported ETEC virotype variation which can be influenced by management differences in pig farms. The presence of VF and acquisition of antimicrobial resistance mechanisms might be related to evolutionary factors, infection pressure and intensive use of antibiotics. E. coli is considered one of the most versatile bacterial species and its diversity in adaptability is due to its genomic plasticity, influencing the capacity to colonize numerous host species. This is possible by mechanisms such as gain or loss of genes through lateral transfer of plasmids, transposons and integrons, which vary regarding the environment to which they are exposed. More studies are needed to correlate genetically the interaction of antimicrobial resistance and virulence genes to elucidate if the virulence expression is affected by chromosomal mutations that lead to specific resistance or/ and both determinants are inserted into the same mobile genetic element, such as a conjugative plasmid.