Antibiotic tolerance in the absence of PQS production.

Killing curves of log phase grown P. aeruginosa PAO1 cultures treated with 5 µg/ml ciprofloxacin were recorded. Killing was significantly delayed in the pqsA and pqsH mutant compared to the wild-type and the pqsL mutant as determined by OD₆₀₀ determinations (A) and CFU counts after 3 h of exposure (B). Error bars mark the standard deviation of three independent experiments. CFU counts of the PAO1 wild-type and the pqsL mutant were significantly different (p<0.05, as determined by t-test) as compared to the pqsA and pqsH mutants.