Revealing an abundance of microbial fecal contamination and multidrug resistant bacteria in the Mississippi Gulf Coast

Authors: MUKHERJEE, MAITREYEE - West Texas A & M University; CUTHBERT, ROBYN - West Texas A & M University; AITKEN, EMMA - University Of Southern Mississippi; GAY, KRISTY - University Of Southern Mississippi; MCKINNEY, KATONIA - University Of Southern Mississippi; Brooks, John

Submitted to: Water
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/20/2023
Publication Date: 6/24/2023
Citation: Mukherjee, M., Cuthbert, R., Aitken, E., Gay, K., McKinney, K., Brooks, J.P. 2023. Revealing an abundance of microbial fecal contamination and multidrug resistant bacteria in the Mississippi Gulf Coast. Water. 15(13):2339. https://doi.org/10.3390/w15132339 .
DOI: https://doi.org/10.3390/w15132339

Interpretive Summary: Water contamination, particularly bathing waters such as public beaches, is a well known problem along U.S. coasts. While the problem is typically associated with fecal indicator bacteria such as E. coli or other similar bacterial groups, the question whether these bacterial groups carry antimicrobial resistance adds another layer of public health concern. The Mississippi Gulf Coast provides for recreation, public use, travel, and economic purpose. Thus, it is important to understand the levels and potential for distribution of these bacterial groups and antimicrobial resistance. In this study, we collected and analyzed water samples from multiple beach coasts along the MS gulf coast over a period of 1 year. Fecal indicator bacteria such as E. coli and enterococci were measured. Overall, levels were above recommended EPA values for both bacterial groups. Antimicrobial resistance was detected against all tested antibiotics, ranging from below 10% to nearly 95%. Some isolates were resistant to more than 3 antibiotics. While not uncommon, it does demonstrate that resistance is widespread amongst many of these bacterial groups throughout the environment, particularly areas where the public interfaces often with potential sources.

Technical Abstract: Microbial pathogenic contamination within coastal recreational water sources together with the occurrence and distribution of antimicrobial resistance and multidrug resistance in such environments is a primary global emerging environmental and public health concern. The Mississippi Gulf Coast is an important resource for recreation, public use, travel, and economic purposes that has been greatly affected by microbial contamination related issues periodically in the past several years. Therefore, it is important to monitor, understand and mitigate the occurrence and distribution of pathogenic contamination and antimicrobial drug resistance within these coastal waters since collecting such data will help improve the state’s environmental and public health control measures and would serve as an important resource for keeping the coast clean and sustainable in future. In this study, we collected and analyzed surface ocean water samples from ten sites across the Mississippi Gulf Coast over a period of ten months to- 1) enumerate and isolate pathogenic bacterial population (Fecal Indicator Bacteria, FIBs) using EPA methods 1603 (E. coli) and 1600 (Enterococcus) and 2) Identify the patterns of antimicrobial drug-resistance and multidrug resistance utilizing the Kirby-Bauer disc diffusion method. Data collected over ten months suggest the prevalence of highly concerning levels of FIBs (both E. coli and Enterococcus) across the Mississippi Gulf Coast. The E. coli numbers ranged between 111.8 – 990.8 cfu ml-1, nine out the ten studied sites falling well beyond the water quality criteria set by EPA for recreational waters (126 E. coli cfu ml-1). The Enterococcus values ranged between 9.2-674.6 cfu ml-1, seven out of the ten sites falling beyond the EPA’s recommended values as well (35 Enterococcus cfu ml-1). Overall, across all sampling sites and sampling events, our study detected very high levels antimicrobial resistance within the E. coli isolates at an average of 94.9% for erythromycin, 82.8% for cephalothin, 54.3% for ampicillin, 34.9% for amoxycillin, and 6.9% for each of sulfamethoxazole and ciprofloxacin. Strikingly, resistance within the E. coli isolates to the last resort antibiotic was found to be 8.9% overall. For Enterococcus these numbers were 75.9% for ciprofloxacin, 75% for erythromycin, 61.4% for cephalothin, 38.6% for tetracycline, 7.8% for amoxycillin, 7.5% for ampicillin, and 2.6% for imipenem across all sites and sampling events. In addition to resistance to individual antibiotics, our study also found a remarkably high amounts of multidrug resistant ‘superbugs’ in the Mississippi Gulf Coast waters. On an average, at least 97.3% of the E. coli isolates and 95.8% of the Enterococcus isolates were resistant to at least one antibiotic. Within the E. coli isolates, 94.6% was resistant to =2 antibiotics, 64.5% belonged to the =3 category, 41.8% in the =4 category, 18.2% in the =5 category, 6.3% belonged to =5 antibiotics. Within the Enterococcus isolates, MDR patterns were as follows: 87.3% belonging to the =2 category, 66.4% belonging to the =3 category, 37.9% falling into the =4 category, 17.9% were in the =5 category, 8.4% in the =6 category, and 3.6% in the =7 antibiotics. Of the total 380 E. coli isolates, three were found to be resistant to a total of 7 different antibiotics. One out of the 266 Enterococcus isolates was resistant to all eight antibiotics we tested it for.