May Megan K.

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May
First Name
Megan K.
ORCID
0000-0003-4816-0380

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  • Thesis
    Characterizing bacterial antibiotic resistance, prevalence, and persistence in the Marine Environment
    (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 2019-02) May, Megan K.
    Antibiotics are naturally occurring chemicals in bacteria that were recently discovered and utilized by humans. Despite a relatively short time of use, anthropogenic use of antibiotics has increased natural levels of antibiotic resistance, which has caused a looming antibiotic resistance crisis, where antibiotics may not work. Understanding resistance patterns is critical to allow for continued therapeutic use of antibiotics. While resistance is often thought of in hospitals, antibiotics and antibiotic resistance genes from human activity are disposed of into nature where they are able to interact with naturally occurring antibiotics and resistance. In this dissertation, I examine the ocean as an understudied region of the environment for antibiotic resistance. The ocean represents an area of human activity with recreation and food consumption and it is an enormous region of the planet that is affected by both land and sea activities. In Chapter 2, I explore the policies that have contributed to the antibiotic resistance crisis. I offer explanations of market and political failures that contributed to the situation, areas for growth in terms of assessing scientific knowledge, and finally, recommendations for mitigating antibiotic resistance. In Chapters 3 and 4, I collected individual bacterial cultures from Cape Cod, MA beaches to assess the phenotypic response to antibiotic resistance. I show that 73% of Vibrio-like bacteria and 95% of heterotrophic bacteria (both groups operationally defined) are resistant to at least one antibiotic. These results indicate that antibiotic resistance is prevalent and persistent on beaches over both spatial and temporal scales. In Chapter 5, I used metagenomics to assess the abundance and types of resistance genes at coastal impacted Massachusetts sites. I found that, even in sites that seem distinct in terms of anthropogenic impact, prevalence of resistance remained the same. Finally, in Appendix A, I examined part of the TARA Ocean dataset for prevalence of antibiotic resistance genes across the world’s ocean. Here, I found that there are distinctions between different ocean biomes based upon antibiotic, metal, and mobile genetic elements. This dissertation has increased the understanding of temporal and spatial dynamics of antibiotic resistance in the coastal and open ocean.
  • Dataset
    Supplementary Information: Antibiotic resistance in Vibrio-like bacteria is common on Cape Cod, MA beaches
    ( 2018-10-23) May, Megan K. ; Gast, Rebecca J.
    Antibiotic resistance (AR) is a natural process, enhanced by anthropogenic antibiotic use. Natural environments, like the ocean, act as reservoirs of resistance; but until recently, little research has examined their dynamics. Six beaches on Cape Cod, MA, with varying human impacts, were sampled over one year on nine occasions. Vibrio-like bacteria were isolated from wet sand, dry sand, and water from each beach and tested for sensitivity to five antibiotics (amoxicillin/clavulanic acid, ciprofloxacin, doxycycline, oxytetracycline, and trimethoprim) using the disk diffusion method. 73% of isolates showed resistance to at least one antibiotic, and resistance was persistent over time, space, and sample type. Isolates commonly exhibited trimethoprim, ciprofloxacin, and/or amoxicillin resistance. 16S ribosomal DNA amplicon-based community structure varied along with the dominant operational taxonomic unit (OTU). Permutational multivariate analysis of variance (PERMANOVA) indicate that resistance patterns, prevalence, and bacterial community composition were often related to month of sampling. Seasonal environmental variables also explain AR and community structure data. Distance based linear models (DistLM) using arcGIS land use variables reflecting homogeneity in land use. Estimates of Vibrio-like resistant bacteria range from 57 to 980 cells per ml water, accounting for 0.00057-0.0098% of the total bacteria encountered with beach water contact. These results illustrate that resistance to antibiotics by Vibrio- like bacteria is widespread on local recreational marine beaches. Although these resistant bacteria are a small percentage of the total bacteria, they may represent a potential public health issue through the introduction of resistance genes into human microbiomes during recreation or shellfish consumption.