title: Induction of Antimicrobial Resistance in Escherichia coli and Non-Typhoidal Salmonella Strains after Adaptation to Disinfectant Commonly Used on Farms in Vietnam.
abstract: In Vietnam, commercial disinfectants containing quaternary ammonium compounds (QACs) are commonly used in pig and poultry farms to maintain hygiene during production. We hypothesized that sustained exposure to sub-bactericidal concentrations of QAC-based disinfectants may result in increased levels of antimicrobial resistance (AMR) among Enterobacteriacea due to the increase of efflux pump expression. To test this hypothesis we exposed six antimicrobial-susceptible Escherichia coli (E. coli) and six antimicrobial-susceptible non-typhoidal Salmonella (NTS) isolates to increasing concentrations of a commonly used commercial disinfectant containing a mix of benzalkonium chloride and glutaraldehyde. Over the 12-day experiment, strains exhibited a significant change in their minimum inhibitory concentration (MIC) of the disinfectant product (mean increase of 31% (SD ± 40)) (p = 0.02, paired Wilcoxon test). Increases in MIC for the disinfectant product were strongly correlated with increases in MIC (or decreases in inhibition zone) for all antimicrobials (Pearson's correlation coefficient 0.71-0.83, all p < 0.01). The greatest increases in MIC (or decreases in inhibition zone) were observed for ampicillin, tetracycline, ciprofloxacin, and chloramphenicol, and the smallest for gentamicin, trimethoprim/sulphamethoxazole. The treatment of 155 representative E. coli isolates from farmed and wild animals in the Mekong Delta (Vietnam) with phenyl-arginine beta-naphthylamide (PAβN), a generic efflux pump inhibitor, resulted in reductions in the prevalence of AMR ranging from 0.7% to 3.3% in these organisms, indicating a small contribution of efflux pumps on the observed prevalence of AMR on farms. These results suggest that the mass usage of commercial disinfectants, many of which contain QACs, is potentially a contributing factor on the generation and maintenance of AMR in animal production in Vietnam.
authors.affiliation: The Hospital for Tropical Diseases, Wellcome Trust Major Overseas Programme, Oxford University Clinical Research Unit, Ho Chi Minh City, Vietnam. nhungnt@oucru.org.
authors.forename: Nguyen T
authors.initials: NT
authors.lastname: Nhung
authors.affiliation: The Hospital for Tropical Diseases, Wellcome Trust Major Overseas Programme, Oxford University Clinical Research Unit, Ho Chi Minh City, Vietnam. thuyct@oucru.org.
authors.forename: Cao T
authors.initials: CT
authors.lastname: Thuy
authors.affiliation: The Hospital for Tropical Diseases, Wellcome Trust Major Overseas Programme, Oxford University Clinical Research Unit, Ho Chi Minh City, Vietnam. trungnv@oucru.org.|Department of Medical Microbiology, Academic Medical Center, University of Amsterdam, Amsterdam 1105 AZ, the Netherlands. trungnv@oucru.org.
authors.forename: Nguyen V
authors.initials: NV
authors.lastname: Trung
authors.affiliation: The Hospital for Tropical Diseases, Wellcome Trust Major Overseas Programme, Oxford University Clinical Research Unit, Ho Chi Minh City, Vietnam. jcampbell@oucru.org.|Centre for Tropical Medicine, Nuffield Department of Clinical Medicine, Oxford University, Old Road Campus, Roosevelt Drive, Oxford, OX3 7BN, UK. jcampbell@oucru.org.
authors.forename: James
authors.initials: J
authors.lastname: Campbell
authors.affiliation: The Hospital for Tropical Diseases, Wellcome Trust Major Overseas Programme, Oxford University Clinical Research Unit, Ho Chi Minh City, Vietnam. sbaker@oucru.org.|Centre for Tropical Medicine, Nuffield Department of Clinical Medicine, Oxford University, Old Road Campus, Roosevelt Drive, Oxford, OX3 7BN, UK. sbaker@oucru.org.
authors.forename: Stephen
authors.initials: S
authors.lastname: Baker
authors.affiliation: The Hospital for Tropical Diseases, Wellcome Trust Major Overseas Programme, Oxford University Clinical Research Unit, Ho Chi Minh City, Vietnam. gthwaites@oucru.org.|Centre for Tropical Medicine, Nuffield Department of Clinical Medicine, Oxford University, Old Road Campus, Roosevelt Drive, Oxford, OX3 7BN, UK. gthwaites@oucru.org.
authors.forename: Guy
authors.initials: G
authors.lastname: Thwaites
authors.affiliation: The Hospital for Tropical Diseases, Wellcome Trust Major Overseas Programme, Oxford University Clinical Research Unit, Ho Chi Minh City, Vietnam. hoant@oucru.org.|Centre for Tropical Medicine, Nuffield Department of Clinical Medicine, Oxford University, Old Road Campus, Roosevelt Drive, Oxford, OX3 7BN, UK. hoant@oucru.org.
authors.forename: Ngo T
authors.initials: NT
authors.lastname: Hoa
authors.affiliation: The Hospital for Tropical Diseases, Wellcome Trust Major Overseas Programme, Oxford University Clinical Research Unit, Ho Chi Minh City, Vietnam. jcampbell@oucru.org.|Centre for Tropical Medicine, Nuffield Department of Clinical Medicine, Oxford University, Old Road Campus, Roosevelt Drive, Oxford, OX3 7BN, UK. jcampbell@oucru.org.
authors.forename: Juan
authors.initials: J
authors.lastname: Carrique-Mas
keywords: adaptation; antimicrobials; disinfectant; efflux pumps