Influence of temperature on mutational resistance to 4-quinolones

Minimum inhibitory concentration (MIC) values of ciprofloxacin (CAS 85721-33-1), ofloxacin (CAS 82419-36-1) or levofloxacin (CAS 100986-85-4) against Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus and Staphylococcus epidermidis were determined at 37, 30 and 25 degrees C on nutrient agar. With E. coli and S. aureus, reducing the incubation temperature from 37 to 30 to 25 degrees C decreased the MIC values for each drug. With P. aeruginosa, temperature reduction also decreased the MIC values for ciprofloxacin but increased the MICs for ofloxacin or levofloxacin. With S. epidermidis, temperature reduction increased the MICs for ciprofloxacin and ofloxacin but with levofloxacin the MICs were identical at 37 or 25 degrees C but higher at 30 degrees C. Mutants of these bacterial species were selected on nutrient agar containing five times their respective MICs of the 4-quinolones at 37, 30 and 25 degrees C. with S. epidermidis, temperature reduction always reduced its mutation frequency to resist 4-quinolones, whereas with the other three species the effect of temperature was more variable, and in some instances even elevated their mutation rates.