Treated wastewater effluent as a potential source of virulent and antibiotic resistant Yersinia species in receiving surface water.
Khumalo, Gcinile Zamantungwa.
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Yersinia enterocolitica is a potentially pathogenic bacterium transmitted through the faecal-oral route. Typical symptoms include those associated with gastrointestinal disease, although infection can also lead to more serious and invasive illnesses, particularly in sensitive populations. Previous studies have detected Y. enterocolitica in surface water in various parts of the world, and studies have reported the intake of untreated water to be one of the potential risk factors for Y. enterocolitica infection. This study investigated the antibiotic resistant patterns and the virulence determinants of the previously identified Y. enterocolitica in treated wastewater effluents and the receiving rivers. In addition, the antibiogram and virulence factors of these isolates were determined in order to establish the possible effects posed by these isolates to the users of receiving surface waters. Finally, the genetic relatedness of the isolates was established by Random Amplified Polymorphic DNA (RAPD-PCR). The antibiotic susceptibility assays revealed that the isolates were resistant to ampicillin (100%), amoxicillin (98%), cefuroxime (96%), cefalothin (90%), streptomycin (93%), chloramphenicol (100%), tetracycline (100%) and trimethoprim (100%). The calculated multiple antibiotic resistance (MAR) indices of the Y. enterocolitica isolates ranged from 0.5-0.66, suggesting high multi-antibiotic resistance among the isolates. A high prevalence (59%) of class 2 integrin was found among the isolates, with 26 and 6% of the isolates in possession of class1 and class 3, respectively. The integrase genes detection showed that the isolates possessed 3 classes of integrons, detected in 59%, 26% and 6% of the isolates, respectively. The virulence determinant assays using crystal violet staining showed that only 21% (15/70) of the isolates could retain the purple colour suggesting that they may be the virulent strain of Y. enterocolitica. The negative MBL activity suggests that the tested isolates do not demonstrate any hydrolytic activity for the degradation of cephalosporins. Virulence gene detection via PCR showed that the most abundant gene is the ystA (56%) followed by ail (34%), both chromosomally located. The plasmid located genes were detected in 3% of the isolates for both Vir/Lcr and yadA. The genotypic characterization of the tested isolates revealed two main clusters (A and B), with cluster A comprising the majority of the isolates (68%) and include the Y. enterocolitica positive control, whilst cluster B grouped 31% of the isolates. had 31% similarity to the control.