In -Vitro selection of ciprofloxacin and levofloxacin - resistant Pseudomonas aeruginosa for investigating flouroquinolone resistance mechanisms

Abstract

Flouroquinolone (FQ) resistance mechanism was investigated in laboratory-derived

resistant Pseudomonas aeruginosa strains. In order to do that, pure strain of Pseudomonas aeruginosa ATCC 9027 was continuously exposed to two FQs (Ciprofloxacin-CIP and Levofloxacin-LEV) separately, with daily adjusted concentrations lower than minimal inhibitory concentration (MIC). After 10 days of serial exposures, the CIP- MIC increased 64 times, from 0.03125 mg/L to 2 mg/L while LEV-MIC increased 32 times from 0.25 to-8 mg/L. When these obtained FQ-resistant strains were cultured in continuously antibiotic-free media for 10 days, interestingly the MIC of FQs still remained high indicating that in vitro FQ-resistance development was irreversible (CIP-MIC: 2 mg/L and LEV-MIC: 8mg/L). Furthermore, these two in vitro- produced FQ-resistant strains also showed cross-resistance to other antibiotics supporting the fact that resistance mechanisms to different antibiotic groups are partly in common. Additionally, we found that, the CIP- exposed P. aeruginosa strain was less resistant to other antibiotics than the LEV-exposed one. It suggested that the resistance mechanism of CIP-exposed strain would have some difference to that of LEV-exposed one even though these two antibiotics, LEV and CIP are chemically closely related. In the near future, further investigation will be performed to analyze the mechanisms of this in vitro- produced FQ-resistance.

Key words: Fluoroquinolones, minimal inhibitory concentration (MIC), antibiotic resistance mechanisms, serial exposure, Pseudomonas aeruginosa