School of Public Health

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The collections in this community comprise faculty research works, as well as graduate theses and dissertations.

Note: Prior to July 1, 2007, the School of Public Health was named the College of Health & Human Performance.

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Author: search.filters.author.Malayil, Leena

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    Coupled DNA-labeling and sequencing approach enables the detection of viable-but-non-culturable Vibrio spp. in irrigation water sources in the Chesapeake Bay watershed
    (Springer Nature, 2021-06-22) Malayil, Leena; Chattopadhyay, Suhana; Mongodin, Emmanuel F.; Sapkota, Amy R.
    Nontraditional irrigation water sources (e.g., recycled water, brackish water) may harbor human pathogens, including Vibrio spp., that could be present in a viable-but-nonculturable (VBNC) state, stymieing current culture-based detection methods. To overcome this challenge, we coupled 5-bromo-2′-deoxyuridine (BrdU) labeling, enrichment techniques, and 16S rRNA sequencing to identify metabolically-active Vibrio spp. in nontraditional irrigation water (recycled water, pond water, non-tidal freshwater, and tidal brackish water). Our coupled BrdU-labeling and sequencing approach revealed the presence of metabolically-active Vibrio spp. at all sampling sites. Whereas, the culture-based method only detected vibrios at three of the four sites. We observed the presence of V. cholerae, V. vulnificus, and V. parahaemolyticus using both methods, while V. aesturianus and V. shilonii were detected only through our labeling/sequencing approach. Multiple other pathogens of concern to human health were also identified through our labeling/sequencing approach including P. shigelloides, B. cereus and E. cloacae. Most importantly, 16S rRNA sequencing of BrdU-labeled samples resulted in Vibrio spp. detection even when our culture-based methods resulted in negative detection. This suggests that our novel approach can effectively detect metabolically-active Vibrio spp. that may have been present in a VBNC state, refining our understanding of the prevalence of vibrios in nontraditional irrigation waters.
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    COUPLING DNA LABELING AND NEXT-GENERATION SEQUENCING TECHNIQUES TO CHARACTERIZE METABOLICALLY-ACTIVE BACTERIA IN NONTRADITIONAL IRRIGATION WATER
    (2019) Malayil, Leena; Sapkota, Amy R; Maryland Institute for Applied Environmental Health; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Bacteria are ubiquitous in irrigation water resources and can include pathogens that may compromise food safety and public health. However, only a small fraction of total bacterial community members in water can be identified through standard culture-based laboratory methods. 16S rRNA and shotgun sequencing techniques have improved the identification of non-culturable bacteria in water resources. Nevertheless, because sequencing approaches are nucleic-acid based, they are unable to differentiate between the proportion of bacterial communities identified that are live and metabolically-active versus those that are represented by free, relic DNA, not present in viable cells. To bridge this knowledge gap, my dissertation research coupled DNA-labeling (using 5-bromo-2’- deoxyuridine (BrdU) and propidium monazide (PMA)) with next-generation sequencing approaches to identify and comprehensively characterize metabolically-active bacteria in multiple nontraditional irrigation water sources in the Mid-Atlantic region. My aims were as follows: 1) To characterize the metabolically-active fraction of bacterial communities, as well as antibiotic resistance genes and virulence gene profiles in nontraditional irrigation water sources; 2) To evaluate culture-dependent and -independent methods in the detection of metabolically-active pathogenic and non-pathogenic Vibrio species in four nontraditional irrigational water sources; and 3) To track metabolically-active bacterial communities from rooftop-harvested rainwater to irrigated produce in Maryland. Overall, we identified diverse metabolically-active bacterial communities in all nontraditional water sources. Notably, we observed the presence of viable bacteria of importance to both human and/or animal health (Actinobacterium spp., Flavobacterium spp., Aeromonas spp. Pseudomonas spp. and Vibrio spp.). Interestingly, diverse antimicrobial resistance and virulence genes were predominantly found in non-BrdU-treated samples, indicating that these genes can persist in relic DNA and could be transferred to other environmental bacteria through transformation events. We also source-tracked viable bacteria, including Sphingomonas spp., Enterobacter spp., Enterococcus spp, and Citrobacter spp. from rooftop-harvested irrigation water to produce. In summary, this work provides the first description of total, viable, and metabolically-active bacterial communities in different nontraditional irrigation water sources. These data can be used to improve risk characterization of these water sources, and ultimately inform the selection of appropriate cost-effective remediation methods to treat these waters prior to irrigation activities in order to prevent foodborne outbreaks.