Antibiotic-resistant Escherichia coli is one of the most serious problems in pig production. This study aimed to determine the antibiotic susceptibility and genotypes profiles of diarrhoeagenic E. coli that causes diarrhea in piglets. Thirty-seven pathogenic E. coli strains were used in this study. These were isolated from rectal swabs of diarrheic piglets from farms in Thailand from 2018 to 2019. Escherichia coli isolates were highly resistant to amoxicillin (100%), followed by oxytetracycline (91.9%), enrofloxacin (89.2%), trimethoprim/sulfamethoxazole (86.5%), amoxicillin: clavulanic acid (81.1%), colistin and gentamicin (75.7%), ceftriaxone and ceftiofur (64.9%), ceftazidime (35.1%) and 97.3% showed multidrug-resistance (MDR). There were 8 (21.6%) mcr-1 carriers, 10 (27.0%) mcr-3 carriers and 10 (27.0%) co-occurrent mcr-1 and mcr-3 isolates. The phenotype-genotype correlation of colistin resistance was statistically significant (performed using Cohen’s kappa coefficient (κ = 0.853; p < 0.001)). In addition, PCR results determined that 28 of 37 (75.7%) isolates carried the int1 gene, and 85.7% int1-positive isolates also carried the mcr gene. Genetic profiling of E. coli isolates performed by ERIC-PCR showed diverse genetics, differentiated into thirteen groups with 65% similarity. Knowledge of the molecular origins of multidrug-resistant E. coli should be helpful for when attempting to utilize antibiotics in the pig industry. In terms of public health awareness, the possibility of transmitting antibiotic-resistant E. coli from diarrheic piglets to other bacteria in pigs and humans should be of concern.

Background: Enterotoxigenic Escherichia coli (ETEC) is one of the most important pathogens causing neonatal and post-weaning diarrhea (PWD) in piglets. The F4+ETEC is particularly problematic in pig farms. Here, we present a simple extraction for producing crude F4 fimbriae to be exploited as an antigenic determinant for effective vaccination. Results: The SDS-PAGE and LC-MS/MS analysis revealed that the crude F4 fimbriae extract contains a major band of molecular weight around 24 kDa, corresponding to the size of the major subunit (FaeG) of F4 fimbriae together with several minor bands of different molecular weights. Crude F4 fimbriae extracts (150 µg/dose) were used to immunize 3 four-weeks old piglets. The antiserum was collected and evaluated the level of F4-specific antibodies by ELISA. It was clear that the level of serum pig IgG and pig IgA antibodies against F4 were significantly higher than that against other E. coli strains (F18+ETEC, F41+ETEC and F4-F18-F41-EC) and unvaccinated control (p < 0.01). Moreover, the pig IgG antibody level against other E. coli strains was also detected at considerably higher level than that of the unvaccinated control (p < 0.05). Conclusions: Our results therefore demonstrated that the crude F4 fimbriae obtained from simple extraction not only induce specific immunity against F4+ E. coli but also stimulate cross-immunity against other E. coli strains. The result suggested that crude F4 fimbriae extract from our method can be used for future vaccine development against porcine diarrheal diseases caused by E. coli.