Tetracycline Resistance Gene Maintenance under Varying Bacterial Growth Rate, Substrate and Oxygen Availability, and Tetracycline Concentration

Abstract

Neither amplification nor attenuation of antibiotic resistance genes (ARG) in the environment are well understood processes. Here, we report on continuous culture and batch experiments to determine how tetracycline (TC), aerobic vs anaerobic conditions, bacterial growth rate, and medium richness affect the maintenance of plasmid-borne TC resistance (Tet(R)) genes. The response of E. coli (a model resistant strain excreted by farm animals) versus Pseudomonas aeruginosa (a model bacterium that could serve as a reservoir for ARGs in the environment) were compared to gain insight into response variability. Complete loss of the Tet(R) RP1 plasmid (56 kb) occurred for P. aeruginosa in the absence of TC, and faster loss was observed in continuous culture at higher growth rates. In contrast, E. coli retained its smaller pSC101 plasmid (9.3 kb) after 500 generations without TC (albeit at lower levels, with ratios of resistance to 16S rDNA genes decreasing by about 2-fold). A higher rate of ARG loss was observed in P. aeruginosa when grown in minimal growth medium (M9) than in richer Luria broth. Faster ARG loss occurred in E. coli under anaerobic (fermentative) conditions than under aerobic conditions. Thus, in these two model strains it was observed that conditions that ease the metabolic burden of plasmid reproduction (e.g., higher substrate and O2 availability) enhanced resistance plasmid maintenance; such conditions (in the presence of residual antibiotics) may be conducive to the establishment and preservation of ARG reservoirs in the environment. These results underscore the need to consider antibiotic concentrations, redox conditions, and substrate availability in efforts to evaluate ARG propagation and natural attenuation.

Effects of electron acceptors on removal of antibiotic resistant Escherichia coli, resistance genes and class 1 integrons under anaerobic conditions

“…However, these substances were absent in the synthetic wastewater, making either the oxygen diffused from the cathode or the anode electrode the possible electron acceptor available to the E. coli. The lower removal of ARGs under the condition of high DO together with high current mode was also in agreement with the previous finding that high DO concentration was beneficial for the persistence of tetracycline resistance plasmids in E. coli (Rysz et al, 2013).…”

Anaerobic Membrane Bioreactor Effluent Reuse: A Review of Microbial Safety Concerns

“…The results of this work showed that when normalized against 16S rRNA gene copies, the concentrations of sulfonamide and trimethoprim resistance genes were 1-2 log lower in an AnMBR system than in its aerobic counterpart. These observations, along with those of Wang et al [73], reinforce the concept that ARG abundances can be effectively reduced by anoxic or anaerobic conditions [83]. Furthermore, the work of Harb et al [74] is an example of how the combination of anaerobic digestion can be complimented by the advantages of MBR-based treatment for overall improved ARG removal capacity.…”

Abundance and distribution of Macrolide-Lincosamide-Streptogramin resistance genes in an anaerobic-aerobic system treating spiramycin production wastewater

“…As for gene acquisition by horizontal transfer, the relative abundances of mobile elements (intI1 and ISCR1) in anaerobic sludge were approximately two orders lower than those in aerobic sludge (Table A7), which means gene transfer in anaerobic sludge may not be as significant as that in aerobic sludge. Similarly, Rysz et al (2013) reported that higher oxygen availability enhanced resistance plasmid (another sort of mobile element) maintenance in pure cultured bacteria because aerobic condition eased the metabolic burden of plasmid reproduction. Less accumulation of ARGs in anaerobic sludge than in aerobic sludge suggests the merit of employing anaerobic digestion in treating antibiotic production wastewater, though the mechanism requires more study.…”