The effects of sub-MIC ciprofloxacin exposure on antibiotic susceptibility and virulence factors in Pseudomonas aeruginosa ATCC 9027

Abstract

Exposure to antibiotics below their minimum inhibitory concentration (sub-MIC) is known to be a selection pressure for the development of antibiotic resistance. In this work, we aimed to provide more understanding of how antibiotic resistance and cross-resistance developed in Pseudomonas aeruginosa under sub-MIC exposure to Ciprofloxacin. Fully susceptible P. aeruginosa ATCC 9027 was serially exposed to sub-MIC level of ciprofloxacin for 14 days to generate E1 strain, then cultured in antibiotic-free environment for 10 days to obtain E2 strain. Changes in MIC values, susceptibility profile and virulence (protease, elastin, biofilm formation, motility) of these strains were evaluated compared to the original P. aeruginosa ATCC 9027. After antibiotic exposure, P. aeruginosa strains developed resistance to the ciprofloxacin with the MIC values increased by 32 times, and the exposed strains only developed resistance to ciprofloxacin and other fluoroquinolones but not to unrelated antibiotics. The resistant phenotype did not revert fully after 10 days in antibiotic-free environment. In addition, there was noticeable changes in the pathogen’s virulence factors during antibiotic exposure. In summary, sub-MICs exposure of P. aeruginosa provided positive selection for antibiotic resistant phenotype, which did not revert after 10 days in antibiotic- free environment. Exposure to sub-MIC level of antibiotics caused significant changes in virulence and antibiotic susceptibility of the pathogen.