Comparison of the antimicrobial tolerance of oxytetracycline-resistant heterotrophic bacteria isolated from hospital sewage and freshwater fishfarm water in Belgium

The aim of this study was to investigate the relationship between antimicro bial tolerance and taxonomic diversity among the culturable oxyretracycline -resistant (Ot(r)) heterotrophic bacterial population in two Belgian aquati c sites receiving wastewater either from human medicine or from aquaculture . The study of Ot(r) heterotrophs and mesophilic Aeromonas spp. allowed com parison of tolerance data at the inter-genus as well as at the intragenus l evel. In total, 354 independently obtained Ot(r) isolates were subjected to antimicrobial tolerance testing and identified by GLC analysis of their ce llular fatty acid methyl esters (FAMEs), by API 20E profiling and/or by Flu orescent Amplified Fragment Length Polymorphism (FAFLP) DNA fingerprinting. In general, Ot(r) hospital heterotrophs displayed a higher frequency (84%) of ampicillin (Amp) tolerance compared to the Ot(r) heterotrophs from the freshwater fishfarm site (22%). FAME results indicated that this effect was linked to the predominance of intrinsically ampicillin-resistant Ot(r) Aer omonas strains over representatives of Acinetobacter and Escherichia coli w ithin the hospital strain set. Among the Ot(r) mesophilic Aeromonas strain set, the global tolerance profiles of the two sites only differed in a high er number of kanamycin (Kan) -tolerant strains (43%) for hospital aeromonad s in comparison with the fishfarm aeromonads (8%). To some extent, this fin ding was correlated with the specific presence of Aeromonas caviae DNA hybr idisation group (HG) 4. Collectively, these results suggest that the profil es for Amp and Kan tolerance observed in both sites arose from taxonomic di fferences in the culturable Ot(r) bacterial population at the generic or su bgeneric level. In addition, our identification data also revealed that Ent erobacter sp., Stenotrophomonas maltophilia, and A. veronii biovar sobria H G8 may be considered potential indicator organisms to assess microbial tole rance in various compartments of the aquatic environment.