Antibiotic resistance vector transport, reservoir amplification and attenuation
Alvarez, Pedro J.; Ward, C. H.; Gonzalez, Ramon
Doctor of Philosophy
Microbial antibiotic resistance is an emerging environmental pollution problem with deleterious effects on water supplies and human health. Currently, little is known about the role of environmental factors in the maintenance, propagation and attenuation of antibiotic resistance. This study investigated the effects of antibiotic exposure concentrations, nutrient availability, and microbial growth rate on resistance dynamics, as well as, the porous medium transport characteristics of antibiotic resistance vectors. Exposure to high antibiotic concentrations increased, (1) the percentage of resistant bacterial strains in soil, (2) the persistence of resistant strains in soil and (3) the relative abundance of resistance genes in bacteria; and decreased the Shannon Weaver diversity index. Rich growth medium enhanced resistance plasmid maintenance and stability even in the absence of selective pressure of the antibiotic possibly be alleviating the metabolic burden imparted on the carrier bacteria by the resistance plasmids. The growth rate exerted a strain-specific response on resistance dynamics, with higher plasmid instability (i.e., increased loss) observed at higher growth rates (Pseudomonas aeruginosa), but no such effect observed for an Eschericha coli strain. Resistance vector plumes may be enhanced by: (1) groundwater conditions conducive to plasmid coagulation and colloid formation of approximately 1 mum, and (2) high concentrations of resistant bacteria that exhibit fast initial deposition, and strong blocking behavior after matrix deposition. The results of this research suggest that decreasing environmental antimicrobial concentrations will be conducive to the attenuation of microbial antibiotic resistance, but may not be sufficient in completely eliminating the resistance reservoirs, thus additional control methods may be needed to minimize the impact of these pollutants. The results should also provide insight to improve regulatory and sustainability decision-making processes related to the use of antibiotic in animal agriculture.
Public health; Environmental science; Environmental engineering