This research is the first known study to characterize spatially explicit patterns of Antibiotic Resistance (ABR) in top-level marine predators. A total of 134 viable bacteria samples were isolated from cloacal swabs of seven shark species and one teleost species and then stratified by geographic location. Samples were collected using sterile rayon-tipped culturettes and transported to the LSU-SVM for classification and antibiotic resistance analyses using the Kirby-Bauer method. Samples were characterized by Gram-stain and morphology and placed into three groups: 1) Gram-negative rods, 2) Gram-positive cocci, or 3) Gram-positive rods.
Prevalence rates were calculated for each study site as the number of isolates resistant to at least one drug divided by the total number of isolates in each location. Prevalence rates for each study location were: 1) Belize: 75%, 2) Florida Keys: 86.5%, 3) Coastal Louisiana: 62%, 4) Louisiana Offshore-sharks: 52%, 5) Louisiana Offshore-redfish: 91.7%, and 6) Massachusetts: 87.5%. High prevalence rates in Massachusetts prompted the removal of penicillin from analysis to evaluate potential intrinsic resistance, as the majority of Massachusetts isolates were Gram-negative and resistance to penicillin was assumed. Rates dropped dramatically with the removal of penicillin.
Spatial variation existed between locations allowing for intra-specific comparisons between sharks in Belize and Florida to evaluate potential geographic differences that might influence ABR patterns. Inter-specific comparisons between redfish and sharks from Louisiana offshore waters demonstrated significantly higher levels in redfish, which may be due to older age and longer exposure in redfish populations.
Florida demonstrated the highest prevalence in sharks and the Louisiana redfish had the highest ABR prevalence of all populations sampled. Both results suggest that top-level predatory fishes can serve as sentinels for ABR in the marine environment, and that multiple species should be sampled. Additionally, spatial variation was documented and future work on ABR surveillance of marine fishes should incorporate geographically stratified data collection and spatial analyses. A color atlas is provided with maps of prevalence rates, intrinsic prevalence rates, multi-drug resistance rates, and a 10-map series of categorical maps showing the spatial patterns of resistance for five important antibiotic drugs.