Graduation Year
2022
Document Type
Dissertation
Degree
Ph.D.
Degree Name
Doctor of Philosophy (Ph.D.)
Degree Granting Department
Biology (Integrative Biology)
Major Professor
Valerie J. Harwood, Ph.D.
Committee Member
Mya Breitbart, Ph.D.
Committee Member
Kathleen Scott, Ph.D.
Committee Member
Andrew Kramer, Ph.D.
Keywords
MST, FIB, norovirus, QMRA, coliphages, adenovirus
Abstract
Although an often-overlooked issue, fecal pollution at recreational beaches should concerneveryone. Worldwide more than 80% of wastewater is discharged into rivers or the ocean without any treatment. Untreated and inefficiently treated wastewater can introduce diseasecausing microorganisms into the aquatic environment. Fecal-borne pathogens can also originate in animal waste, and humans can be exposed to these pathogens from poorly managed animal feces that make their way into the aquatic environment. Exposure to waterborne pathogens in recreational waters is a public health hazard, as it facilitates the transmission of waterborne illness, and surface waters serve as natural reservoirs of antibiotic resistant bacteria and their genes. To ensure safe swimming conditions the World Health Organization (WHO) recommends the use of sanitary inspections, routine monitoring, and quantitative microbial risk assessment (QMRA).
The use of fecal indicator bacteria (FIB) is essential for beach management. It is expensive and logistically challenging to try to measure all disease-causing microorganisms present in environmental waters. Therefore, we rely on compliance monitoring of FIB (e.g., enterococci) to help protect people from the health risks associated with swimming in polluted waters. FIB monitoring is based on standardized methodology, and the connection of FIB levels to gastrointestinal illness in swimmers is derived from epidemiology studies. Nevertheless, one of the major drawbacks of using FIB is that we are unable to differentiate sources of fecal contamination. FIB are present in the gut of numerous warm, and even cold-blooded animals, and can persist in extra-intestinal sources like sediments and vegetation. Due to the specific nature of the association of many pathogens with their host (for example, viruses that specifically infect humans), there is an increased risk when fecal contamination comes from humans and certain animals such as cattle (for example, Salmonella, Yersinia enterocolitica, Listeria monocytogenesis, and Crytosporidium are often found in manure:). For this reason, methods to detect host-associated microorganisms, collectively termed microbial source tracking (MST) markers are used to identify microbial contamination from feces of key animal groups that may contaminate recreational waters. For example, quantitative real-time PCR assays that target the human-specific HF183 Bacteriodes 16S rRNA genetic marker is often used to detect human faecal pollution in surface waters. Epidemiological studies are the gold standard when it comes to determining the human health risk associated with exposure to polluted waters. However, these studies are expensive and logistically difficult to perform. Quantitative microbial risk assessment (QMRA) is a framework that uses mathematical models to estimate the risk of infection and disease when a population is exposed to microorganisms in the environment. In this sense, QMRA is a powerful tool that can be used to improve beach management, as it helps us understand the impact that certain microorganisms in the environment will have on the health of swimmers. Together, effective monitoring to characterize water quality, accurate identification of sources of pollution, and estimation of risk posed to swimmers are paramount to support management strategies to protect human health and the environment.
In chapter two of this dissertation, the relationships among microbial indicators of fecal pollution, MST marker genes, and pathogens were analyzed in Costa Rican coastal waters. We found that regardless of season, Jacó rivers were implicated as sources of human fecal contamination based on percent exceedance of recreational water quality guidelines (RWQC), high MST marker concentrations, and occurrence of diverse waterborne pathogens. We compared and evaluated exceedance of RWQC and performance of indicator microorganisms and MST markers with respect to pathogen detection and determined that the US EPA enterococci statistical threshold value (STV) criterion had the highest positive (78%) and negative (96%) predictive value of all indicators in ocean samples. We concluded that no one fecal indicator or MST sewage marker best correlated with pathogens; rather, the use of multiple fecal indicators and MST markers maximized pathogen correlations. We recommend a fecal pollution toolbox approach, containing at least one viral indicator for pathogen prediction at tropical beaches, as the use of viral indicators maximized pathogen correlations in both river and ocean data.
Chapter three describes a second study at the polluted beach in Costa Rica, wherein indicators, MST markers and pathogens were measured in river and ocean samples. QMRA was performed to estimate the risk of gastroenteritis from swimming in rivers in three subwatersheds at the beach. We determined that median risk from pathogens in river samples was above the USEPA benchmark of 36 illnesses per 1000 recreators (it ranged from 0.345 to 0.577). Risk of gastrointestinal illness varied at a localized scale within three different subwatersheds at the beach. Norovirus genogroup I (NoVGI) followed by adenoviruses contributed the most to risk of gastrointestinal illness in all subwatersheds. We found that FIB exceedances were higher during rainy season, but risk was greater in the dry compared to rainy season, due largely to the increased frequency of detection of NoVGI (the main driver of risk) in dry season (100% vs 41%). We concluded that substantial viral log10 reduction (3.8 – 4.1 dry; 2.7 -3.2 rainy) are needed to ensure safe swimming conditions in Jacó rivers.
Lastly, chapter four is a field study in which we explored the extent of ampicillin resistance and multidrug resistance of the FIB E. coli and Enterococcus spp. in Costa Rican wastewater and surface waters. E. coli were more frequently resistant to ampicillin (18%) than were Enterococcus spp (4%). Forty two percent of E. coli isolates and 45% of Enterococcus isolates in this study were multidrug-resistant (resistant to more than 3 antibiotic classes). E. coli isolates that were resistant to a combination of 6 different classes of antibiotics were found frequently and exclusively in the hospital wastewater. E. coli isolated from the hospital wastewater were more likely to be resistant (∼ 40% of isolates) to gentamicin, cefotaxime, and ciprofloxacin versus those isolated from residential wastewater, the treated (but not disinfected) effluent and the estuary where the wastewater treatment plant discharges (<25% of isolates). Enterococcus isolates were frequently resistant to tetracycline (>50% of isolates), erythromycin (∼ 25% of isolates) and ciprofloxacin (∼10% to 25% of isolates). Our results indicate that although wastewater from hospital and residential water can be important sources of antibiotic resistant bacteria, those bacteria are also present in high frequency in the estuary, and highlight the importance of disinfection of the treated effluent prior to its release into the environment.
Clean water is considered an essential human right by the United Nations. Not surprisingly, clean water is a prominent need described on the worldwide sustainable development agenda. The sustainable development goal to “ensure availability and sustainable management of water and sanitation for all”, reminds us of the importance of water and sanitation in the global development agenda. Clean water and sanitation for all is an ambitious goal as millions of people worldwide collect their drinking water directly from surface waters and billons lack basic or managed sanitation services. A lack of progress on eliminating wastewater pollution impedes achieving many of the sustainable development goals. Furthermore, to achieve the water and sanitation-related sustainable development goals and address antibiotic resistance, sustainable management of water resources is necessary and more likely to be attainable by focusing efforts in areas where sanitation is lacking. Results of this research serve as a baseline for future reference that can help improve coastal management of tropical polluted beaches.
Scholar Commons Citation
González-Fernández, Adriana, "Anthropogenic Fecal Pollution Affects Microbial Water Quality and Multidrug Resistance in Tropical Aquatic Environments" (2022). USF Tampa Graduate Theses and Dissertations.
https://digitalcommons.usf.edu/etd/10389
