The characterization, occurrence, and mobility of antibiotic resistant bacteria, antibiotic resistance genes, and plasmids isolated from urban wastewater treatment plants.
Throughout the decades, there has been an increase in the prevalence and the spread of antibiotic resistance genes (ARGs) within the bacterial populations found in various environments. The continual use of antibiotics has contributed to a higher state of resistance in microorganisms and is recognized as a threat to global public health. The spread of ARGs within a bacterial population is still poorly understood, although, wastewater treatment plants (WWTPs) have been recognized as ‘hotspots’ for the dissemination and proliferation of ARGs. More research is required to further our understanding of the occurrence and mobility of antibiotic resistant bacteria (ARB), ARGs, and plasmids within densely populated microbial environments such as in WWTPs. The first objective investigated the presence of tetracycline resistant and tetracycline sensitive bacteria and characterized them based on identity, morphology, and antibiotic resistance patterns. It was found that tetracycline resistant and sensitive populations differed greatly in composition. In addition, isolates that were resistant to tetracycline were more likely to carry resistances to other antibiotics, unlike sensitive ones. The knowledge acquired from this research will shed light upon resistance patterns and routes that can occur in a complex WWTP microbial population. The second objective investigated the presence, host range, and characterization of plasmids found in both antibiotic resistant and sensitive isolates. The members belonging to the phylum Enterobacteriaceae were found to be the main carriers of plasmids. Numerous plasmids with conjugative properties, type secretion systems, antibiotic resistance genes, and virulence factors were identified among the selected cultures. The genetic information obtained will contribute to the understanding of the role plasmids play in the mobility, host range, metabolic function, virulence, and the spread of ARGs. The last objective monitored the conjugative transfer of two novel plasmids, pNT36-3, and pNT36-4, between two environmental strains of Escherichia coli NT36 and EB-G3. Furthermore, the effects of subinhibitory concentrations of antibiotics on plasmid transfer are also examined. In the presence of 1 μg/mL of carbenicillin, the plasmid transfer rate significantly increased while decreasing in the presence of other antibiotics. Understanding the environmental conditions, host requirements, and occurrence of plasmid transfer will bring about great insight in understanding gene transfer between environmental bacteria.