The Effect of Complex Environments on the Selection Towards Multidrug Resistance

Abstract

ABSTRACT. Background. Notwithstanding the lack of clinical evidence, cycling antibiotics has been advocated for as an effective method in reducing the selection for antibiotic resistance. Objective. This study was designed to evaluate the effectiveness of cycling antibiotics in reducing the selection for multidrug resistance in E. coli. Methods. Evolving E. coli in a daily rotation between Ampicillin, Ciprofloxacin, and Chloramphenicol in different cycling regimes while introducing a cycle with no antibiotic pressure, all in a 96 well-plate for 20 days. Each day the plate is read in a plate reader before transferred to the following cycle. By the end of day 20, the evolved strains were transferred to a MIC of different antibiotics to evaluate the whether they evolved multi-drug resistance. Results. Resistance evolved in both rotating and non-rotating regimes in Ampicillin and Chloramphenicol. However, in Ciprofloxacin alone, no resistance evolves, while rotating it with other antibiotics sometimes selected for resistance. Evolved strains showed similar resistance profile in other antibiotics that were used to assess the presence of multidrug resistance. Conclusion. The results of our study carried diverse outcomes – cycling showed that it could lower the rate of resistance in some cases, and in other cases have no significant effect. Many aspects should be considered regarding the results, such as the cycling method, the order of antibiotics used in the cycle, and the type of antibiotic being cycled.