Occurrence, Mobility, Characterization, and Fate of Antibiotic Resistant Bacteria, Genes and Plasmids Isolated from Urban Wastewater Treatment Plants

Candidate: Amir Tehrani

Supervisor: Dr. Kimberly Gilbride

Abstract:
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 are 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, mobility, and fate of antibiotic resistant bacteria (ARB), ARGs, and plasmids within densely populated microbial environments such as the WWTP. The main goal of this study is to address the frequency, fate, and transfer of ARB, ARGs, and plasmids of three urban in Toronto, Ontario.

The first set of experiments that were conducted was to investigate the presence of tetracycline-resistant and tetracycline-sensitive bacteria and characterize them based on identity, morphology, and antibiotic resistance profiles. One of the key findings was that the tetracycline-resistant and sensitive population differed greatly in composition. The genus Stenotrophomonas was found to be most common among the resistant cultures and Acinetobacter was found most common among the sensitive. Furthermore, bacteria that were already antibiotic resistant were more likely to carry resistances to other antibiotics as well.

The second set of experiments investigated the presence, host range, and characterization of plasmids found in both antibiotic resistant and sensitive isolates within each population. The members belonging to the phylum Enterobacteriaceae were found to be mainly carriers of plasmids. Numerous plasmids with conjugative properties, type secretion systems, antibiotic resistance, and virulence factors were identified among the sequenced annotations.

The last set of experiments monitors the conjugative properties of two characterized plasmids, pNT36-3, and pNT36-4, between two environmental strains of Escherichia coli NT36 and EB-G3. Furthermore, the effects of lower concentrations of antibiotics on plasmid transfer rates are also examined. It was found that in the presence of 1 μg/mL of carbenicillin, the plasmid transfer rate significantly increased. Overall, these series of studies performed help contribute to our understanding of the occurrence, mobility, and fate of ARGs and ARB in the environment.