Is Caretta Caretta a Carrier of Antibiotic Resistance in the Mediterranean Sea?

Abstract

Sea turtles can be considered a sentinel species for monitoring the health of marine ecosystems, acting, at the same time, as a carrier of microorganisms. Indeed, sea turtles can acquire the microbiota from their reproductive sites and feeding, contributing to the diffusion of antibiotic-resistant strains to uncontaminated environments. This study aims to unveil the presence of antibiotic-resistant bacteria in (i) loggerhead sea turtles stranded along the coast of Sicily (Mediterranean Sea), (ii) unhatched and/or hatched eggs, (iii) sand from the turtles’ nest and (iv) seawater. Forty-four bacterial strains were isolated and identified by conventional biochemical tests and 16S rDNA sequencing. The Gram-negative Aeromonas and Vibrio species were mainly found in sea turtles and seawater samples, respectively. Conversely, the Gram-positive Bacillus, Streptococcus, and Staphylococcus strains were mostly isolated from eggs and sand. The antimicrobial resistance profile of the isolates revealed that these strains were resistant to cefazolin (95.5%), streptomycin (43.2%), colistin and amoxicillin/clavulanic acid (34.1%). Moreover, metagenome analysis unveiled the presence of both antibiotic and heavy metal resistance genes, as well as the mobile element class 1 integron at an alarming percentage rate. Our results suggest that Caretta caretta could be considered a carrier of antibiotic-resistant genes.

Antibiotic Resistance of Gram-Negative Bacteria from Wild Captured Loggerhead Sea Turtles

“…was found; however, some differences in terms of prevalence of some taxa were registered. In fact, Enterobacter, Citrobacter, Providentia and Shewanella were more frequently found in weak turtles; this result is in accordance with previous reports on the microbial composition of sea turtles injured by anthropogenic threats, or feeding on longlines bait and on marine debris [9,10,13,27,28]. The vulnerability of loggerhead turtles to be colonized in their gut by aerobic heterotrophic bacteria may be related to different stress conditions due to their illness or a debilitated health status that may result in an altered metabolic state [49].…”

“…Shewanella sp. was the most abundant isolate in our samples (31% and 30% in healthy and weak sea turtles), while Citrobacter and Aeromonas were the most abundant in other reports [10,13]. This difference could be ascribed to different health conditions or origin of sea turtles or to diverse microbial composition of Mediterranean Sea (the present survey was carried out one and four years before the cited reports).…”

“…The latter were the sea turtles with a problem (hook, plastic presence, gastrointestinal occlusion, collision with a boat) that needed a recovery period. A significant correlation was found among the different body measurements recorded To date, a few studies investigated the microbial community associated with Caretta caretta by using culture-dependent methods [9,10,[27][28][29] or metagenomic analysis [30][31][32], and even fewer studies were carried out on the antibiotic resistance of isolates [9,10,13,28]. All the latter studies collected samples from animals that needed to be recovered for several reasons (traumas, ingestion of fishing hooks, parasitosis, respiratory disorders) [9,10,13,28], or found dead along the seacoast [13].…”

“…Additionally, the isolation of ABR strains can be considered as a spoiling index of the habitat of these animals [11,12]. ABR from marine animals could enter into the food web by ingestion of contaminated meat or could be released during egg deposition of female animals [13].…”

“…Sea turtles have been proposed as sentinel species in the Western Mediterranean Sea and carriers of ABR strains in marine habitats [10,13], for their migratory lifestyle [14,15] and their tendency to bio-accumulate contaminants, toxins and pathogens [16]. The loggerhead sea turtle (Caretta caretta) is the most common sea turtle species in the Mediterranean Sea, where it can encounter different threats of anthropogenic origin and undergo severe diseases and infections [16][17][18][19][20][21][22][23].…”