Emergence of colistin resistance and characterization of antimicrobial resistance and virulence factors ofAeromonas hydrophila,Salmonellaspp., andVibrio choleraeisolated from hybrid red tilapia cage culture

Abstract

Background Tilapia is a primary aquaculture fish in Thailand, but little is known about the occurrence of antimicrobial resistance (AMR) in Aeromonas hydrophila, Salmonella spp., and Vibrio cholerae colonizing healthy tilapia intended for human consumption and the co-occurrence of these AMR bacteria in the cultivation water. Methods This study determined the phenotype and genotype of AMR, extended-spectrum β-lactamase (ESBL) production, and virulence factors of A. hydrophila, Salmonella spp., and V. cholerae isolated from hybrid red tilapia and cultivation water in Thailand. Standard culture methods such as USFDA’s BAM or ISO procedures were used for the original isolation, with all isolates confirmed by biochemical tests, serotyping, and species-specific gene detection based on PCR. Results A total of 278 isolates consisting of 15 A. hydrophila, 188 Salmonella spp., and 75 V. cholerae isolates were retrieved from a previous study. All isolates of A. hydrophila and Salmonella isolates were resistance to at least one antimicrobial, with 26.7% and 72.3% of the isolates being multidrug resistant (MDR), respectively. All A. hydrophila isolates were resistant to ampicillin (100%), followed by oxytetracycline (26.7%), tetracycline (26.7%), trimethoprim (26.7%), and oxolinic acid (20.0%). The predominant resistance genes in A. hydrophila were mcr-3 (20.0%), followed by 13.3% of isolates having floR, qnrS, sul1, sul2, and dfrA1. Salmonella isolates also exhibited a high prevalence of resistance to ampicillin (79.3%), oxolinic acid (75.5%), oxytetracycline (71.8%), chloramphenicol (62.8%), and florfenicol (55.3%). The most common resistance genes in these Salmonella isolates were qnrS (65.4%), tetA (64.9%), blaTEM (63.8%), and floR (55.9%). All V. cholerae isolates were susceptible to all antimicrobials tested, while the most common resistance gene was sul1 (12.0%). One isolate of A. hydrophila was positive for int1, while all isolates of Salmonella and V. cholerae isolates were negative for integrons and intSXT. None of the bacterial isolates in this study were producing ESBL. The occurrence of mcr-3 (20.0%) in these isolates from tilapia aquaculture may signify a serious occupational and consumer health risk given that colistin is a last resort antimicrobial for treatment of Gram-negative bacteria infections. Conclusions Findings from this study on AMR bacteria in hybrid red tilapia suggest that aquaculture as practiced in Thailand can select for ubiquitous AMR pathogens, mobile genetic elements, and an emerging reservoir of mcr and colistin-resistant bacteria. Resistant and pathogenic bacteria, such as resistance to ampicillin and tetracycline, or MDR Salmonella circulating in aquaculture, together highlight the public health concerns and foodborne risks of zoonotic pathogens in humans from cultured freshwater fish.

Distribution of bacteria and antimicrobial resistance in retail Nile tilapia (Oreochromis spp.) as potential sources of foodborne illness

“…None of these isolates was an ESBL producer, and all isolates were negative for colistin resistance genes. However, mcr-1 and mcr-3 were widely reported in fish in Thailand and Vietnam, addressing fish could represent a novel source of clinically important resistant bacteria [ 13 , 69 , 70 ].…”

“…The predominant resistance genes, bla TEM , sul1 , and tetA , were commonly reported in fish populations worldwide. For example, sul genes were the most abundant resistance genes in non - cholera Vibrio isolates from fish in South Africa, while bla TEM and tet genes were mainly presented in Salmonella in tilapia farms in Thailand [ 10 , 13 ]. In addition, the co-occurrence of bla TEM and tetA has been previously observed in E .…”

“…However, Salmonella exhibited high resistance to quinolones. For example, three-quarters and one-thirds of Salmonella isolated from a tilapia farm resisted oxolinic acid and enrofloxacin, respectively [ 13 ]. DNA gyrase and topoisomerase IV, which comprise four essential subunits, including gyr A, gyr B, par C, and par E, are the primary targets of quinolones, acting to inhibit bacterial replication.…”

Molecular characterization of Aeromonas hydrophila detected in Channa marulius and Sperata sarwari sampled from rivers of Punjab in Pakistan

“…These isolates were resistant to β-lactams and sulfonamides (100%), oxytetracycline (90%), and streptomycin (62.22%), but completely susceptible to cefotaxime. In a recent study, Thaotumpitak, [80] identified six antimicrobial resistance genes in A. hydrophila isolated from hybrid red tilapia cultured in cages in Thailand, including blaTEM, sul1, sul3, qnrA, qnrB, and tetA. All A. hydrophila isolates were resistant to ampicillin, oxytetracycline, tetracycline, trimethoprim, and oxolinic acid.…”

Genomic characterization of antimicrobial resistance in 61 aquatic bacterial isolates

“…20,24 Phenotypic resistance is reported but is variably detected in Aeromonas spp. 25 Eighteen isolates harbored genes predicted to confer tolerance to biocides and metals, or loci encoding resistancenodulation-division (RND)-type efflux pumps. These stress genotypes were limited to 6 species (Table 2).…”