Induction of Antimicrobial Resistance in Escherichia coli and Non-Typhoidal Salmonella Strains after Adaptation to Disinfectant Commonly Used on Farms in Vietnam.

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 (PAßN), 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.

Antimicrobial usage in chicken production in the Mekong Delta of Vietnam.

Antimicrobials are used extensively in chicken production in Vietnam, but to date no quantitative data are available. A 2012-2013 survey of 208 chicken farms in Tien Giang province, stratified by size (10-200 chickens; >200-2000), was carried out to describe and quantify the use of antibacterial antimicrobials (usage per week per chicken and usage per 1000 chickens produced) in the Mekong Delta and to investigate factors associated with usage. Twenty-eight types of antimicrobial belonging to 10 classes were reported. Sixty-three per cent of all commercial formulations contained at least two antimicrobials. On 84% occasions, antimicrobials were administered with a prophylactic purpose. The overall adjusted quantities of antimicrobials used/week/chicken and per 1000 chickens produced (g) were 26.36 mg (SE ± 3.54) and 690.4 g (SE ± 203.6), respectively. Polypeptides, tetracyclines, penicillins and aminoglycosides were the antimicrobials used by most farms (18.6% farms, 17.5%, 11.3% and 10.1% farms, respectively), whereas penicillins, lincosamides, quinolones, and sulphonamides/trimethoprim were quantitatively the most used compounds (8.27, 5.2, 3.16 and 2.78 mg per week per chicken, respectively). Factors statistically associated with higher levels of usage (per week per chicken) were meat farms (OR = 1.40) and farms run by a male farmer (OR = 2.0). All-in-all-out farming systems (correlated with medium farms) were associated with reduced levels of antimicrobial usage (OR = 0.68). Usage levels to produced meat chickens were considerably higher than those reported in European countries. This should trigger the implementation of surveillance programmes to monitor sales of antimicrobials that should contribute to the rational administration of antimicrobials in order to preserve the efficacy of existing antimicrobials in Vietnam.

High prevalence of antibiotic resistance in commensal Escherichia coli among children in rural Vietnam.

BACKGROUND: Commensal bacteria represent an important reservoir of antibiotic resistance genes. Few community-based studies of antibiotic resistance in commensal bacteria have been conducted in Southeast Asia. We investigated the prevalence of resistance in commensal Escherichia coli in preschool children in rural Vietnam, and factors associated with carriage of resistant bacteria. METHODS: We tested isolates of E. coli from faecal samples of 818 children aged 6-60 months living in FilaBavi, a demographic surveillance site near Hanoi. Daily antibiotic use data was collected for participating children for three weeks prior to sampling and analysed with socioeconomic and demographic characteristics extracted from FilaBavi's re-census survey 2007. Descriptive statistics were generated, and a logistic regression model was used to identify contributions of the examined factors. RESULTS: High prevalences of resistance were found to tetracycline (74%), co-trimoxazole (68%), ampicillin (65%), chloramphenicol (40%), and nalidixic acid (27%). Two isolates were resistant to ciprofloxacin. Sixty percent of isolates were resistant to three or more antibiotics. Recent sulphonamide use was associated with co-trimoxazole resistance [OR 3.2, 95% CI 1.8-5.7], and beta-lactam use with ampicillin resistance [OR 1.8, 95% CI 1.3-2.4]. Isolates from children aged 6-23 months were more likely to be resistant to ampicillin [OR 1.8, 95% CI 1.3-2.4] and co-trimoxazole [OR 1.5, 95% CI 1.1-2.0]. Associations were identified between geographical areas and tetracycline and ampicillin resistance. CONCLUSIONS: We present high prevalence of carriage of commensal E. coli resistant to commonly used antibiotics. The identified associations with recent antibiotic use, age, and geographical location might contribute to our understanding of carriage of antibiotic resistant commensal bacteria.

Decreased Streptococcus pneumoniae susceptibility to oral antibiotics among children in rural Vietnam: a community study.

BACKGROUND: Streptococcus pneumoniae is the most significant bacterial cause of community-acquired pneumonia among children under five years worldwide. Updated resistance information of S. pneumoniae among children is essential to adjust the recommendations for empirical treatment of community-acquired pneumonia, which will have immense implications for local and global health. This study investigated the prevalence of antibiotic resistance in isolated strains of S. pneumoniae and relationship with antibiotic use and demographic factors of children under five in rural Vietnam in 2007. METHODS: In Bavi district, 847 children 6 to 60 months were selected from 847 households. The main child-caregivers in the households were interviewed weekly using structured questionnaires to collect information of daily illness symptoms and drug use for the selected child over a four-week period (from March through June 2007). In the 3rd week, the children were invited for a clinical examination and to collect nasopharyngeal samples for S. pneumoniae identification. Etest and disk diffusion were used to test antibiotic susceptibility. RESULTS: Of 818 participating children, 258 (32%) had ongoing respiratory infections, 421 (52%) carried S. pneumoniae, and 477 (58%) had used antibiotics within the previous three weeks. Of the 421 isolates, 95% were resistant to at least one antibiotic (401/421). Resistance to co-trimoxazole, tetracycline, phenoxymethylpenicillin, erythromycin and ciprofloxacin was 78%, 75%, 75%, 70% and 28%, respectively. Low resistance was noted for amoxicillin (4%), benzylpenicillin (4%), and cefotaxime (2%). The intermediate resistance to amoxicillin was 32%. Multidrug-resistance was seen in 60%. The most common pattern was co-resistance to co-trimoxazole, tetracycline and erythromycin. The proportion of children carrying resistant bacteria was higher among the children who had used antibiotics in the previous three weeks. CONCLUSIONS: Resistance to commonly used antibiotics and multidrug-resistance of S. pneumoniae in the area is remarkably high. High-dose amoxicillin is the only investigated oral antibiotic that can possibly be used for treatment of community-acquired pneumococcal infections. Strategies to promote appropriate prescribing and dispensing of effective antibiotics should be immediately implemented for the benefit of local and global health.