Convergent acquisition of antibiotic resistance determinants amongst the Enterobacteriaceae isolates of the Mhlathuze River, KwaZulu-Natal (RSA)

The Mhlathuze River has become a major reservoir for antibiotic-resistant microbes and a wide pool of antibiotic resistant genes with the environmental isolates exists in this water system. The ability of commensal organisms to carry resistant genes of clinical importance and their ability to transfer such genes to other bacteria are of greater concern than phenotypic measurements. Forty-three Enterobacteriaceae isolates, which were capable of resisting more than 4 different classes of antibiotics, were used for the molecular characterisation of antibiotic resistances. It was found that 58% of these multiple antibiotic-resistant isolates possess the Class 1 integron. Amongst these 25 isolates with positive detection of the Class 1 integron, the beta-lactamase gene (pse) was the most common, being present in 44% of these integrons. The aminoglycoside-resistant gene was detected in 16% of these integrons and 24% of Class 1 integrons contained two genes coding for sulphonamide resistance and for quaternary ammonium compounds resistance. A high degree of genotypic diversity and the lack of correlation between antimicrobial resistance patterns and molecular types of the isolates suggest convergent acquisition of resistance determinants by genetically unrelated strains rather than epidemic spread of resistant isolates in the community. Of the tested environmental isolates, 56% transferred their plasmids as well as their antibiotic resistance profiles to the recipient cells. The possibility of transmission of resistant genes between bacteria (especially pathogenic) which invade human and animal populations within this river poses a health risk to the communities who are dependent on this river for water consumption.