Molecular characterisation of antibiotic resistant bacteria isolated from farmed catfish and humans in Vietnam

Nguyen, K 2012, Molecular characterisation of antibiotic resistant bacteria isolated from farmed catfish and humans in Vietnam, Doctor of Philosophy (PhD), Applied Sciences, RMIT University.

Document type: Thesis
Collection: Theses

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Title Molecular characterisation of antibiotic resistant bacteria isolated from farmed catfish and humans in Vietnam
Author(s) Nguyen, K
Year 2012
Abstract Antibiotics have significantly contributed to the decline of mortality rates from bacterial infectious diseases. However, bacterial resistance and multiple resistance are emerging problems that globally threaten the effectiveness of antimicrobial therapy in human medicine. Furthermore, the overuse and inappropriate use of antimicrobial agents in animal husbandry and aquaculture have contributed to the development of resistance in human pathogens. In Vietnam, the rapid development of the catfish industry has contributed significantly to the national economy but in some instances this industry has also contributed to the possible development of antibiotic resistance in bacteria associated with catfish production.

This project aimed to determine the extent of antibiotic resistance in catfish commensal isolates and human E. coli in Vietnam. Furthermore, molecular characterisation of antibiotic resistance and the roles of integrons in dissemination of resistance genes of catfish and human isolates were conducted.

A total of 365 catfish commensal microflora comprising of 157 E. coli, 116 Pseudomonas spp., 92 Aeromonas spp. and 72 human E. coli isolates were included in this study. Antibiotic susceptibility testing was conducted against 14 antimicrobial agents and revealed high levels of resistance to ampicillin, amoxicillin, tetracycline, trimethoprim/sulfamethoxazole and streptomycin in both catfish and human isolates. In addition, the values of the multiple antibiotic resistance (MAR) index indicated that catfish and human E. coli isolates are exposed to high risk sources of contamination, where antibiotics are commonly used.

In this study, class 1 integrons were detected in 72.7% of catfish E. coli, and in 32.8% and 28.3% of catfish Pseudomonas and Aeromonas isolates, respectively, but no class 2 integrons were found in catfish isolates. On the contrary, one class 2 integron was observed from 72 human E. coli isolates, however, the prevalence of class 1 integrons was lower in human collection.

PCR amplification of cassette arrays carried by class 1 and class 2 integrons revealed the predominance of genes conferring resistance to trimethoprim and streptomycin. Gene cassette arrays of dfrA1-aadA5 and dfrA12-orfF-aadA2 are the most prevalent among catfish and human isolates, indicating the possible transmission of antibiotic resistance genes via class 1 integrons among commensal flora in the environment.

Studies on plasmids contain in catfish and human isolates showed the predominance of large plasmids (the sizes > 55kb), from 50% - 70% in catfish Pseudomonas and Aeromonas isolates to 90% in catfish and human E. coli. In addition, transmission of class 1 integrons was demonstrated by transformation and conjugation, confirming their significant roles in dissemination of antibiotic resistances.

In this study, plasmid-mediated quinolone resistance genes were also determined in ciprofloxacin resistant isolates. A total of 15 isolates (34%) contained PMQR genes of which aac(6’)-Ib-cr were detected in eight E. coli isolates from all sources, and qnrS were observed in seven catfish isolates. The prevalence of PMQR genes was higher among catfish isolates than human isolates, implying the possible reservoirs of PMQR determinants of aquatic environments in Vietnam.

This study provided evidence of the dissemination of antibiotic resistance in bacteria isolated from environmental and clinical sources in Vietnam.
Degree Doctor of Philosophy (PhD)
Institution RMIT University
School, Department or Centre Applied Sciences
Keyword(s) Catfish
antibiotic resistance
E. coli
Pseudomonas spp.
Aeromonas spp.
antibiotic resistant bacteria
class 1 integrons
class 2 integrons
gene cassette
untypical class 1 integrons
plasmid-mediated quinolone resistant (PMQR) determinants
qepA genes
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Created: Mon, 24 Sep 2012, 09:43:42 EST by Brett Fenton
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