Graduation Year

2022

Document Type

Thesis

Degree

M.S.

Degree Name

Master of Science (M.S.)

Degree Granting Department

Biology (Integrative Biology)

Major Professor

Valerie Harwood, Ph.D.

Committee Member

Kathleen Scott, Ph.D.

Committee Member

Paul-Camilo Zalamea, Ph.D.

Keywords

Antibiotic resistance, Fecal indicators, Marine beach, multiple-antibiotic resistance

Abstract

As antibiotic resistance in the environment continues to rise there is an increased concern that infections may become harder to treat as bacteria acquire genes for multidrug resistance. Recreational beach waters in the Tampa Bay area are routinely monitored by the Florida Department of Environmental Protection for the presence of fecal indicator bacteria (FIB) such as Escherichia coli and enterococci. Exceedances of beach action values (BAV) 235 CFU/100 mL (E. coli) and 70 CFU/100 mL (enterococci) indicate the presence of fecal contamination which is associated with an increased risk of disease for beachgoers. Antibiotic-resistant E. coli and Enterococcus spp. have been studied in recreational beach waters but have not been as thoroughly researched in sand. This study investigated the frequency and concentration of antibiotic-resistant E. coli and Enterococcus spp. in water and sand from three recreational bay beaches in the Tampa, Florida area that have historically elevated BAV.

The frequency and concentration of ampicillin-resistant E. coli and erythromycin-resistant Enterococcus spp. in water and sand (swash zone, and 2.5 meters away from the swash zone) at these beaches was compared to the frequency of multi-drug resistant E. coli and Enterococcus spp.. Each beach was sampled three times from March 2021 to June 2021. E. coli was isolated on Media with and without ampicillin (16 µg/mL) and enterococci with and without erythromycin (4 µg/mL) selecting for intermediate resistance. Thirty percent of all E. coli isolates showed intermediate phenotypic resistance to ampicillin and were significantly higher in both concentration (P < 0.05) and proportion (P < 0.05) 2.5 meters away from the swash zone. Of the isolates that expressed ampicillin resistance, 97% were confirmed to species and then subjected to susceptibility testing to seven antibiotics. Twenty-one percent of ampicillin-resistant E. coli isolates showed multiple-antibiotic resistance (i.e. resistance to three or more antibiotics). Multidrug-resistant E. coli were observed to be significantly higher 2.5 meters away from the swash zone (P < 0.05).

Forty-one percent of all enterococci isolates showed intermediate phenotypic resistance to erythromycin and were significantly higher in both concentration (P < 0.1) and proportion (P < 0.05) 2.5 meters away from the swash zone (P < 0.05). Of the isolates that expressed erythromycin resistance, 83% of were confirmed to the genus Enterococcus and subjected to susceptibility testing to six antibiotics. Fifty-four percent of Enterococcus spp. isolates showed multidrug resistant patterns. These results express that sand does serve as a source for single and multidrug-resistant E. coli and Enterococcus spp. that could potentially infect beach recreators.

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