Prevalence and molecular characteristics of antimicrobial resistance of Aeromonas hydrophila, Salmonella spp., Vibrio cholerae, fecal coliform, and Escherichia coli in hybrid red tilapia and cultured water
Authors:   , Thaotumpitak Varangkana 
Published: September 2023

Foodborne pathogens and antimicrobial resistant bacteria in tilapia and cultivation water has been emerged as a public health threat. This study aimed to determine the prevalence of indicator and pathogenic bacteria in hybrid red tilapia (Oreochromis spp.) and their cultivation water, and to characterize phenotypic and genotypic AMR, virulence genes, and extended-spectrum beta-lactamase (ESBL) production of Escherichia coli, Aeromonas hydrophila, Salmonella spp., and Vibrio cholerae. A total of 120 tilapia, which were comprised of carcass rinse (n=120), muscle (n=120), intestine (n=120), liver and kidney (n=120), and cultivation water (n=120) were collected from tilapia farms in Kanchanaburi province, Thailand during October 2019 and November 2020. The overall prevalence of fecal coliforms (74.8%) and E. coli (56.7%) were observed. The highest concentration of fecal coliforms (2.4 ± 4.0 × 104 MPN/g) and E. coli (1.2 ± 2.9 × 104 MPN/g) were mainly found in fish intestine. The prevalence of A. hydrophila, Salmonella, and V. cholerae were 2.5%, 32.0%, and 17.5%, respectively. A. hydrophila was only detected in carcass rinse and cultivation water, while Salmonella and V. cholerae were most detected in cultivation water. The detection of Salmonella was associated with fecal coliforms, E. coli, V. cholerae, relative humidity, and wind gust. The most common Salmonella serovars were Saintpaul (18.9%), Neukoelln (15.2%), and Escanaba (15.2%). Ducks reared nearby in the tilapia farm were postulated that they may be the source of Salmonella contamination in tilapia farms based on rep-PCR characterization. All E. coli isolates were absent of stx1 and stx2. All A. hydrophila isolates were positive for aero and hly. All Salmonella isolates were invA positive. All of V. cholerae isolates classified as non-O1/non-O139. The A. hydrophila (100%), Salmonella (100%), and E. coli (79.6%) isolates were resistance to at least one antimicrobial. The Salmonella (72.3%), E. coli (53.8%), and A. hydrophila (26.7%) were multidrug resistance. All V. cholerae isolates were susceptible to all tested antimicrobials. The predominant resistance in E. coli were ampicillin (63.1%), oxytetracycline (58.6%), and tetracycline (58.0%). The blaTEM (58.0%), qnrS (43.8%), and tetA (29.1%) were the common resistance genes of E. coli. The blaTEM-1 and blaCTX-M-55 were reported in this study. The A. hydrophila isolates was resistant to ampicillin (100%), oxytetracycline (26.7%), tetracycline (26.7%), and trimethoprim (26.7%). The A. hydrophila isolates were commonly found mcr-3 (20.0%), followed by floR, qnrS, sul1, sul2, and dfrA1 with the same resistance rates at 13.3%. The Salmonella isolates highly resisted to ampicillin (79.3%), oxolinic acid (75.5%), and oxytetracycline (71.8%). The qnrS (65.4%), tetA (64.9%), and blaTEM (63.8%) were predominant genes found in the Salmonella isolates. The V. cholerae isolates were mainly carried sul1 (12.0%), followed by catB, qnrS, tetA, tetB, strA, and dfrA1 with the same resistance rate at 4.0%. Class 1 integron was only examined in E. coli (19.5%) and A. hydrophila (6.7%). For ESBL-producing E. coli (3.9%) was detected. This study reported the emerging of colistin resistance gene (mcr-3) in tilapia in Thailand. In summary, tilapia and cultivation water are the potential reservoirs of important foodborne pathogens and AMR bacteria. Proper handling, personal hygiene, and fully cooked fish can promote food safety regarding tilapia consumption. To reduce pathogens and resistant bacterial transmission from tilapia to humans and the environment, implementation of One Health should be carried out with effective control and prevention of the dissemination of resistant bacteria.