Virulence Genes and Antimicrobial Susceptibilities of Haemolytic and Non-Haemolytic Escherichia coli Isolated from Post-Weaning Piglets in Central Thailand

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The purpose of this study was to compare the existence of virulence genes in haemolytic Escherichia coli (HEC) and non-haemolytic E. coli (NHEC) isolated from weaner pigs in Thailand, and to determine their susceptibility to 10 antimicrobial agents. A total of 304 E. coli isolates were obtained from 90 piglets with diarrhoea and 110 healthy piglets. Of these, 74 HEC were isolated from 70 pigs with diarrhoea and 4 were isolated from 4 healthy pigs, while 190 and 40 NHEC were recovered from 110 healthy and 20 pigs with diarrhoea, respectively. A ten digoxigenin (DIG)-labeled probe system was utilized for detecting genes encoding virulence-associated toxins and proteins in these isolates, and the minimal inhibitory concentration values against 10 antimicrobials were determined by means of the agar dilution technique. In total 70.3% of the HEC contained exotoxin genes lth, estp, or stx2e, whereas 2.6% of the NHEC hybridized with gene probes for estp or stx2e. Over 90% of the isolates were resistant to most agents other than colistin and halquinol. The MIC90 of the HEC to halquinol and colistin were 4 and 8 times greater than those of the NHEC, respectively. The result represented the first characterization of resistant pathogenic E. coli distributing in the Thai pig industry. Amongst the HEC there appeared to be an association between the presence of some exotoxin genes, including lth, estp and stx2e, and reduced antimicrobial susceptibility.