Effects of tylosin and chlortetracycline on the proliferation of antibiotic-resistant bacteria in a simulated river water ecosystem
Abstract number: P608
Muñoz-Aguayo J., Lang K., Singer R.
Objective: The objective of this study was to examine the effects of varied concentrations of chlortetracycline (CTC) and tylosin tartrate salt (TYL) on the selection of resistance in aerobic bacterial populations in a simulated river water ecosystem.
Methods: Six replicates of a 10-day experiment using river water in continuous flow chemostats were conducted. In each replicate, 1 chemostat served as the control to which no antibiotic was added. In the first two replicates, TYL was added at concentrations of 100 ng/L and 10 mg/L. In replicate 3, TYL was added at concentrations of 10 mg/L and 50,000 mg/L, and in replicates 4 through 6, TYL was added at concentrations of 10 mg/L, 1000 mg/L and 50,000 mg/L. The amount of TYL present in the chemostats from samples taken on days 0, 3, 7 and 10 was quantified with a commercially available competitive enzyme-linked immunosorbent assay. The viable bacterial count was determined by plate count from days 0 through 10 using 1/10-strength LB agars with and without 16 mg/ml of TYL and Columbia CNA agars with and without 16 mg/ml of TYL. The presence of the erm (B) gene in the bacteria within the chemostats was assessed on days 0 through 10 by extracting DNA from a chemostat sample followed by PCR using previously published primers. Results of the TYL replicates were compared to the CTC replicates that were conducted previously.
Results: There was no significant difference among treatment groups in the total bacterial load within the chemostats when assessed on LB agar plates (89 log10 CFU/ml). Although the chemostats with higher levels of TYL had lower bacterial loads on Columbia CNA agar and Columbia CNA agar with 16 mg/ml of TYL, there was no difference among chemostats in the proportion of the total bacterial load that grew on CNA agar with 16 mg/ml of TYL. No differences among chemostats were observed when bacteria were grown on LB agar with 16 mg/ml of TYL. The gene erm (B) was detected on many days of the replicates, mainly in the high TYL concentration chemostats.
Conclusions: Low concentrations of TYL in this in vitro experiment did not select for increased levels of resistant bacteria. This is identical to the observation in the CTC experiment. Whereas high doses of CTC did select for tetracycline-resistant bacterial populations, high doses of TYL did not appear to have this effect. These results question the biological significance of low tylosin concentrations observed in the environment.
|Session name:||18th European Congress of Clinical Microbiology and Infectious Diseases|
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