Characterisation, prevalence and antibiogram of Aeromonas hydrophila in turtles: insights into virulence factors, antimicrobial resistance genes and innate immunity

Abstract

ABSTRACT Bacterial infection poses a significant threat to the health and survival of turtles, both in their natural habitats and in captivity. Notably, the presence and interactions of bacteria, such as those belonging to the Aeromonas genus, have been identified for their adverse impact on turtle health and ecosystem dynamics. This study investigated the prevalence, antibiotic susceptibility, virulence factors, and antimicrobial resistance genes of Aeromonas hydrophila in Trachemys scripta elegans (Red-eared Slider) and Chelonia mydas (Green Turtle). The study also examined the innate immunity of T. scripta elegans and C. mydas. Buccal and cloacal swabs from 39 turtles were collected and examined alongside 45 water samples to try to isolate and amplify A. hydrophila. Polymerase chain reaction (PCR) amplifications were then sequenced to identify the presence of specific genes associated with virulence, and antimicrobial resistance. The findings revealed that A. hydrophila had a prevalence rate of 35.9% in all examined turtle species, with 14 water samples accounting for 31% of the total samples. Buccal samples from Green and Red-eared turtles showed a higher rate of A. hydrophila isolates than cloacal samples. Sensitivity to norfloxacin (85.71%), gentamycin (71.42%), and ceftriaxone (64.28%) was observed, whereas resistance to amoxicillin (64.28%), ampicillin (57.14%), and rifamycin (57.14%) was apparent. Antibiotic resistance genes, including blaTEM and blaSHV, in A. hydrophila isolates, were present in 42.86% and 28.5% of the samples, respectively. PCR analysis confirmed the genetic identity of A. hydrophila, and five virulence genes were detected: AHCYTOEN (100%), followed by aerolysin (92.8%), alt and act (85.7%), and lipase (78.5%). Genetic sequences of the isolates had a 99% identity with the reference strains in GenBank. Furthermore, the study found the innate immunity of turtles to be robust due to serum lysozyme activity, bactericidal killing assay (BKA), total leukocyte count, heterophil/lymphocyte ratio, and packed cell volume (PCV%), all of which help to protect them from infections. Overall, this research highlights the need for continued monitoring and management of antibiotic resistance in aquatic ecosystems.