Author ORCID Identifier

https://orcid.org/0000-0001-7066-7140

Year of Publication

2020

Degree Name

Doctor of Philosophy (PhD)

Document Type

Doctoral Dissertation

College

Engineering

Department/School/Program

Civil Engineering

First Advisor

Dr. Gail Brion

Abstract

Currently, the world is engaged in a battle against very small parts of our environment that develop and share genes for resistance to multiple environmental conditions. Pathogenic infections caused by antibiotic-resistant bacteria have been impacting animal and human health and life. Increasing incidences of methicillin- resistant Staphylococcus aureus (MRSA) infections transmitted through the environment are rising faster than the discovery of new antibiotics. Multi-drug resistant S. aureus infections in healthy individuals without prior hospitalization have been increasing all around the world.

Many people carry S. aureus in their nose and on their skin, common niches for the bacteria to co-grow with other staphylococci, like S. epidermidis. These bacteria are carried into the environment in wastes, where they can spread and interact with other lifeforms. This highlights the need for more understanding of the possible sources, fate, and potential interactions of S. aureus in the environment in order to manage related risks. Although, many investigations have been conducted on S. aureus infections in clinical settings, only a limited number of studies have focused on this organism in the environment. Understanding S. aureus prevalence, presence, and evolution in water systems could be a potential step for controlling possible future disease impacts.

Wastewater treatment plants have been suspected as one of the potential sources for spreading S. aureus in the environment. A rise in antimicrobial resistance genes in bacteria in urban water systems downstream of wastewater treatment plants has been documented. However, comprehensive studies required to understand the mechanisms and factors used by this opportunistic pathogen to survive and spread beyond its normal niche on skin into the environment. This is partly due to a lack of methods that can isolate S. aureus from other microorganisms in complex environmental samples, and a tendency to use only limited genetic information.

The current study created a better enrichment and isolation method and assessed the prevalence and fate of S. aureus in engineered wastewater systems, and in streams receiving the waste. The types, characteristics, virulence factors, and mobile genetic elements of S. aureus were investigated in sewage and in sediment samples from an urban creek. In addition, the presence and types of metal and antibiotic-resistant genes were studied and compared with reference clinical isolates of S. aureus. Our results suggest the use of an intermediate bacterium as one possible transmission route that S. aureus has to impact the resistance status of other environmental microorganisms in natural waters. Genes from S. aureus were found in another species of staphylococci bacteria that survived treatment and carried these into the creek. In light of finding this route of transmission, multiple recommendations for treatment system upgrades were considered to break the bridge for transferring resistant genes between bacteria in wastewater treatment plants and those in the natural environment.

Digital Object Identifier (DOI)

https://doi.org/10.13023/etd.2020.452

Funding Information

1) National Science Foundation

EAGER : The Role of Engineered Systems in Adaptation of Staphylococcus aureus

09/01/2017 - 10/31/2017

2) Kentucky Water Resources Research Institute (KWRRI)

FY2018-2019 USGS Student Research Enhancement Grant : Assessment of MRSA presence in suburban WWTPs effluent in Lexington, Kentucky

2018-2019

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