Herbicides alter the S. marcescens response to antibiotics. (2020)
Type of ContentElectronic Thesis or Dissertation
Thesis DisciplinePlant Biotechnology
Degree NameMaster of Science
PublisherUniversity of Canterbury
AuthorsFu, Qifanshow all
Exposure to herbicides and antibiotics has been associated with increased honeybee mortality and colony loss on a global scale. The focus of my research is on the recently discovered link between herbicides and the development of antibiotic resistance, which could conflict with efforts to halt honeybee decline and antibiotic stewardship.
In this study, I have tested whether exposure to sublethal herbicides changes antibiotic responses in Serratia marcescens, an important opportunistic pathogen responsible for honeybee mortality as well as in-hospital infection. S. marcescens was exposed to eighteen combinations chosen from three herbicide formulations and six antibiotics. The pattern of antibiotic response induced by herbicides varied in direction and intensity, which included increase, decrease or no change in antibiotic MIC. The most notable result was the 64-fold increase in ciprofloxacin MIC under exposure of Number 8 (glyphosate).
Two further experiments were conducted to determine the mechanism of the increased antibiotic tolerance induced by herbicides. In one experiment, herbicides were withdrawn from S. marcescens colonies with elevated ciprofloxacin MIC. Most of the resulting colonies did not survive under the same amount of ciprofloxacin, which indicate that persistent exposure of herbicides is necessary for the ciprofloxacin resistance phenotype. In the other experiment, a mutation assay using rifampicin as selection marker was performed to identify that none of the three herbicides promote mutation in S. marcescens. Combined with results from previous studies, it is likely that the elevated tolerance to antibiotics is physiological response such as efflux-pumps. However, further studies are needed to identify the exact mechanism.