Potentially zoonotic shiga toxin-producing Escherichia coli serogroups in the faeces and meat of food-producing animals in Ibadan, Nigeria

Shiga toxin-producing Escherichia coli (STEC) are major food-borne pathogens associated with gastroenteritis and sometimes fatal haemolytic uraemic syndrome complication. Farm animals are asymptomatic carriers of STEC and contaminated meat is an important vehicle for zoonotic transmission from animals to humans. This study investigated the presence, virulence traits and antimicrobial susceptibility of seven potentially human pathogenic STEC serogroups (O157, O26, O91, O103, O111, O128 and O145) in the faeces and meat of food-producing animals in Ibadan, Nigeria. One hundred and fifty-four (7.3%) of 2133 samples were positive for STEC serogroups. The pathogens were detected in the faeces of cattle (15.2%), sheep (10.7%), goats (7.5%) and pigs (5.6%) as well as in beef (3.8%), goat-meat (1.7%) and pork (4.0%). All seven investigated STEC serogroups were found in cattle, all except O145 were found in sheep, three serogroups (O157, O26 and O111) were found in goats and three (O157, O111 and O128) in pigs. The rate of detection of each of the serogroups in all 2133 samples was: O157 (5.0%), O26 (0.2%), O91 (0.3%), O103 (0.3%), O111 (1.0%), O128 (0.2%) and O145 (0.1%). Of all 154 isolates, 11.0% had shiga toxin type 1 gene (stx(1)), 25.3% had stx(2) and 41.6% had stx(1)/stx(2); intimin gene (eaeA) was detected in 56.5% and enterohaemolysin gene (hlyA) in 75.3%. Among the O157 isolates, 24.5% were negative for stx genes but positive for eaeA and/or hlyA while 7.6% were negative for all four virulence genes. Fourteen different combinations of virulence genes were encountered but stx(1)/stx(2)/eaeA/hlyA combination was the most predominant. The percentage resistance of the isolates to the tested antimicrobial agents was: ampicillin (82.5%), chloramphenicol (42.9%), ciprofloxacin (22.1%), enrofloxacin (25.3%), nalidixic acid (37.7%), neomycin (24.0%), norfloxacin (20.8%), streptomycin (50.7%) and tetracycline (75.3%). One hundred and forty-eight (96.1%) of all 154 isolates were resistant to at least one of the tested antimicrobial agents while 69.5% were categorised as multi-drug resistant. Potentially pathogenic multi-drug resistant STEC isolates were recovered from the meat production chain in Nigeria. Unhygienic practices that predominate during slaughter and processing were observed to have contributed to faecal contamination and presence of STEC in meat.