Search

This study aimed to investigate AMR profiles of Aeromonas hydrophila, Salmonella spp., and Vibrio cholerae isolated from Nile tilapia (Oreochromis spp.) (n = 276) purchased from fresh markets and supermarkets in Bangkok, Thailand. A sample of tilapia was divided into three parts: fish intestine (n = 276), fish meat (n = 276), and liver and kidney (n = 276). The occurrence of A. hydrophila, Salmonella, and V. cholerae was 3.1%, 7.4%, and 8.5%, respectively. A high prevalence of these pathogenic bacteria was observed in fresh market tilapia compared to those from supermarkets (p < 0.05). The predominant Salmonella serovars were Paratyphi B (6.4%), followed by Escanaba (5.7%), and Saintpaul (5.7%). All isolates tested positive for the virulence genes of A. hydrophila (aero and hly), Salmonella (invA), and V. cholerae (hlyA). A. hydrophila (65.4%), Salmonella (31.2%), and V. cholerae (2.9%) showed multidrug resistant isolates. All A. hydrophila isolates (n = 26) exhibited resistant to ampicillin (100.0%) and florfenicol (100.0%), and often carried sul1 (53.8%) and tetA (50.0%). Salmonella isolates were primarily resistant to ampicillin (36.9%), with a high incidence of blaTEM (26.2%) and qnrS (25.5%). For V. cholerae isolates, resistance was observed against ampicillin (48.6%), and they commonly carried qnrS (24.3%) and tetA (22.9%). To identify mutations in the quinolone resistance determining regions (QRDRs), a single C248A point mutation of C248A (Ser-83-Tyr) in the gyrA region was identified in six out of seven isolates of Salmonella isolates. This study highlighted the presence of antimicrobial-resistant pathogenic bacteria in Nile tilapia at a selling point. It is important to rigorously implement strategies for AMR control and prevention., Competing Interests: The authors have declared that no competing interests exist., (Copyright: © 2024 Sripradite et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.)

Aeromonas hydrophila, a widely distributed human pathogen causing a variety of diseases, can be isolated from clinical and environmental sources. Analysis in Thailand of 110 isolates of Aeromonas hydrophila by randomly amplified polymorphic DNA-PCR (RAPD-PCR) revealed one specific RAPD pattern group (G) that was associated only with strains from environmental sources. Cytotoxic activity, adhesion to epithelial cells and exoenzyme secretions of A. hydrophila were also investigated. A comparison of isolates with pattern group G with a set of isolates derived from human blood showed low induction of cytotoxicity from those with RAPD pattern group G suggesting low virulence of these strains.

A group of seven sucrose-negative Aeromonas strains (referred to as group Au) isolated from the internal organs of septicaemic farmed frogs (Rana rugulosa) in Thailand was subjected to a polyphasic taxonomic study including fluorescent amplified fragment length polymorphism (FAFLP) and ERIC-PCR fingerprinting, 16S rDNA sequencing, microplate DNA-DNA hybridizations and extensive phenotypic characterization. Comparison of FAFLP and ERIC-PCR fingerprints indicated that the group Au isolates belonged to the species Aeromonas hydrophila DNA hybridization group (HG) 1 in which they represent a genotypic subgroup closely affiliated to A. hydrophila subsp. hydrophila and subsp. dhakensis. One representative of the Au group exhibited > or = 99.0% 16S rDNA sequence similarity with the type strains of the two A. hydrophila subspecies. DNA-DNA hybridization with type and reference strains of all known Aeromonas taxa revealed that the Au group represented a homogeneous taxon that exhibited the highest relatedness with members of the two A. hydrophila subspecies, ranging from 75 to 93%. Phenotypic characterization on the basis of 152 features further revealed that the Au group isolates differed from A. hydrophila subsp. hydrophila or subsp. dhakensis in a total of 13 biochemical properties. Of these, assimilation of L-glycine and isobutyrate as sole carbon source, acid production from salicin and D-sucrose, and aesculin hydrolysis were of diagnostic value. From the results of this study, it can be concluded that the Aeromonas frog isolates of the Au group represent a new subspecies of A. hydrophila, for which the name Aeromonas hydrophila subsp. ranae subsp. nov. is proposed. Its type strain is Au-1D12(T) (=LMG 19707(T) = CCUG 46211(T)).