Graduate Thesis Or Dissertation
 

Antibiotic Resistance in Septic Sludge and Receiving Environments of Ho Chi Minh City, Vietnam

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  • Approximately ninety percent of urban Vietnamese households are connected to septic tanks, from which up to three-quarters of the sludge is reported to be dumped into waterways in residential areas. Vietnam has a considerable prevalence of antibiotic misuse and resultant antibiotic-resistant bacteria (ARB) in the human microbiome. Due to the high excretion rate of antibiotics in their parent and similar forms after ingestion, a significant concentration of these pharmaceuticals may exist in wastewater, including septic tank effluents. The dissemination of these drugs into the environment poses a human health risk if pathogenic bacteria become resistant to antibiotic treatments. This study investigated the prevalence of antibiotic-resistant bacteria and genes in areas prone to receiving septic tank sludge in Ho Chi Minh City, Vietnam (HCMC) in winter of 2018. We collected sludge and soil samples (n = 24 and 55, respectively) from residential septic systems and environmental reservoirs (i.e. canals, rivers, and parks) in twelve districts of HCMC. Soil and sludge samples were also tested against a library of 13 antibiotic-resistant genes (ARGs). This analysis revealed that the integrase-1 gene (indicating multiple resistance and anthropogenic impact) was of high prevalence in sludge and soil, as well as genes conferring resistance to sulfonamides, erythromycin, trimethoprim, chloramphenicol, and tetracycline. We quantified concentrations of the fecal indicator bacteria Escherichia coli in soil and found that concentrations did not vary significantly between districts of the city (p > 0.05, one-way ANOVA). The susceptibility of E. coli isolated from sludge and soil (n = 104 and 129, respectively) against nine antibiotics was tested. A total of 65.4% (n = 68) of sludge isolates and 41.9% (n = 54) of soil isolates were found to be multi-drug resistant (phenotypically resistant to three or more classes of antibiotics). The resistance rates of soil and sludge isolates to ampicillin, tetracycline, sulfamethoxazole/trimethoprim, ciprofloxacin, and gentamicin were found to be significantly different between the two sample types (p < 0.05, Fisher’s exact test). In a temporal microcosm study of multidrug- and non-resistant E. coli isolates from our environmental samples, populations of multi-drug resistant bacteria were generally shown to decline at a slower rate than non-resistant strains. Temperature was found to play the most significant role in E. coli inactivation (p < 0.001, three-way ANOVA), followed by the inoculum level of resistance and presence of a background microbial community (p < 0.01, three-way ANOVA).
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  • UNC, Chapel Hill, North Carolina
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  • Navab-Daneshmand Lab Group
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  • This research was funded by the Evans Family Fellowship within Oregon State University's Humanitarian Engineering Program.
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  • Ongoing Research
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  • 2018-08-31 to 2019-03-28

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