Antibiotic Resistance and Virulence Profiles of Gram-Negative Bacteria Isolated from Loggerhead Sea Turtles (Caretta Caretta) of the Island of Maio, Cape Verde

Abstract Background: Several studies detected high levels of antibiotic-resistance in loggerhead sea turtles (Caretta caretta) and pointed this species as prime reservoirs of antibiotic-resistant bacteria and carriers of potentially pathogenic bacteria. This study aimed to characterize, for the first time, the Gram-negative aerobic microbiota of the Cape Verdean loggerhead subpopulation. Cloacal, oral and egg content swab samples from 33 nesting loggerheads (n = 99) of the Island of Maio were analysed regarding the presence of Gram-negative bacteria and their antibiotic resistance and virulence profiles. Results: Shewanella putrefaciens (27.78%), Morganella morganii (22.22%) and Vibrio alginolyticus (22.22%) were the most prevalent species isolated from the animals under study. A low incidence of antibiotic-resistant bacteria (26%) was detected, and no multidrug-resistant isolates were identified. Non-Enterobacteriaceae isolates presented the most complex virulence profiles, revealing the ability to produce hemolysins (100%), DNases (89%), lipases (79%), proteases (53%), lecithinases (21%), gelatinases (16%), and also biofilms (74%). Moreover, higher virulence indices were obtained for turtles with high parasite intensities compared with apparently healthy animals, and a positive correlation between antibiotic resistance and virulence was observed. Conclusions: Results suggest that this loggerhead population may be less exposed to antimicrobial compounds, probably due to the low anthropogenic impact observed in both their nesting (the Island of Maio) and foraging sites. Nevertheless, the presence of potentially pathogenic bacteria expressing virulence factors may threat both sea turtles’ and humans’ health.