Cattle are a major reservoir of Shiga toxin-producing Escherichia coli. This study investigated the occurrence of seven major STEC serogroups including O157, O145, O103, O121, O111, O45 and O26 among 578 STEC isolates previously recovered from 559 cattle. The isolates were characterized for serotype and major virulence genes. Polymerase chain reaction revealed that 41.7% (241/578) of isolates belonged to STEC O157, O145, O103, O121, O45 and O26, and 33 distinct serotypes. The 241 isolates corresponded to 16.5% (92/559) of cattle that were STEC positive. The prevalence of cattle that tested positive for at least one of the six serogroups across the five farms was variable ranging from 2.9% to 43.4%. Occurrence rates for individual serogroups were as follows: STEC O26 was found in 10.2% (57/559); O45 in 2.9% (16/559); O145 in 2.5% (14/559); O157 in 1.4% (8/559); O121 in 1.1% (6/559); and O103 in 0.4% (2/559). The following proportions of virulence genes were observed: stx1, 69.3% (167/241); stx2, 96.3% (232/241); eaeA, 7.1% (17/241); ehxA, 92.5% (223/241); and both stx1 and stx2, 62.2% (150/241) of isolates. These findings are evidence that cattle in South Africa carry STEC that belong to six major STEC serogroups commonly incriminated in human disease. However, only a subset of serotypes associated with these serogroups were clinically relevant in human disease. Most STEC isolates carried stx1, stx2 and ehxA but lacked eaeA, a major STEC virulence factor in human disease.

This study investigated occurrence and antimicrobial resistance profiles of Campylobacter spp. isolates in beef cattle on five cow-calf operations in South Africa. A total of 537 fecal samples from adult beef cattle (n = 435) and rectal swabs from calves (n = 102) were screened for Campylobacter jejuni, Campylobacter coli, and Campylobacter upsaliensis by culture and polymerase chain reaction. Furthermore, 86 Campylobacter spp. isolates including 46 C. jejuni,24 C. coli, and 16 C. upsaliensis were tested for antimicrobial resistance against a panel of 9 antimicrobials. Overall, Campylobacter spp. was detected in 29.7% of cattle. Among the 158 Campylobacter spp.-positive cattle, 61.8% carried C. jejuni, 25% carried C. coli, and 10% carried C. upsaliensis. Five animals (3.1%) had mixed infections: three cows carried C. jejuni and C. coli concurrently, one cow had both C. jejuni and C. upsaliensis, and one cow harbored C. coli and C. upsaliensis. Antimicrobial resistance profiling among 86 Campylobacter spp. isolates revealed that 52.3% of the isolates were resistant to one or more antimicrobials. Antimicrobial resistance was observed in 46.7% of C. jejuni isolates, 35.6% of C. coli, and 17.8% of C. upsaliensis. Thirty-six percent of isolates were resistant to clindamycin, 19.7% to nalidixic acid, 18.6% to tetracycline, and 17.4% to erythromycin. Lower resistance rates were recorded for azithromycin (8.1%), florfenicol (3.4%), gentamicin (4.8%), and telithromycin and ciprofloxacin (5.8%). Multidrug resistance (MDR) was observed in 32.5% of isolates. Significantly higher levels of MDR were detected among C. jejuni (36.9%) and C. coli (33.3%) isolates in comparison to C. upsaliensis (18.7%). Two main multiresistance patterns were detected: nalidixic acid/clindamycin (17.8%) and tetracycline/clindamycin (14.2%). To the best of our knowledge, this is the first study which has shown that beef cattle on cow-calf operations in South Africa constitute an important reservoir and a potential source of clinically relevant and antimicrobial resistant Campylobacter spp. strains.

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