Tetracycline Resistance Profile in Darwin Finches in the Galapagos Islands

Antimicrobial Resistance (AMR), which is the ability of microorganisms to withstand attack by antimicrobial drugs, has a worldwide impact. Thus, it is important to identify resistance mechanisms circulating in the environment. Among antimicrobials widely used in human and veterinary health, tetracycline is ideal due to its safety and has been categorized by the WHO as a critically important antimicrobial. Based on the fact that wild animals are bioindicators of environmental contamination and that wild birds are considered sentinels of AMR in the ecosystem, in the present study, we studied AMR patterns in Darwin finches (Geospiza spp.) in the Galapagos Islands, Ecuador. To this end, a total of 384 cloacal swabs from Darwin finches were collected from three zones of Santa Cruz Island (an urban, an agricultural, and a protected zone). Phenotypic antibiotic resistance was analyzed by the Kirby-Bauer disk diffusion method in Escherichia coli (n = 136) and Enterococcus spp. (n = 332) isolates. PCR was performed for the detection of the tetA gene in E. coli strains and of the tetM gene in Enterococcus isolates. Resistance for at least one of nine and one of eight antimicrobials was observed in 62.5% (85/136) and 28.6% (95/332) of E. coli and Enterococcus isolates, respectively. A high percentage of phenotypic resistance to tetracycline was identified for both bacteria. The tetA and tetM genes were identified in 83.7% (36/43) of E. coli strains and 75.4% (49/65) of Enterococcus spp. isolates, respectively. The highest percentages of AMR were observed in the agricultural zone. We also found the presence of multi-drug-resistant strains. These results show that Darwin finches might be proposed as sentinels of AMR in the Galapagos Islands.