Sub-inhibitory concentrations of ceftazidime and tobramycin reduce the quorum sensing signals of Pseudomonas aeruginosa

Aim: Concentrations of antimicrobials below minimum inhibitory concentration (subMIC) may reduce the production by Pseudomonas aeruginosa of virulence factors such as elastase. We sought to determine whether the reduction in elastase production may be mediated by a reduction in acyl-homoserine lactones. Methods: Pseudomonas aeruginosa in broth was exposed to three conditions for ceftazidime and tobramycin: control, 6% MIC and 25% MIC. Elastase was assayed using elastin congo red. N-(3-Oxododecanoyl)-homoserine lactone (C12-HSL) and N-butyryl-homoserine lactone (C4-HSL) were assayed using biosensor Escherichia coli. Results: Elastase was unchanged with ceftazidime. Elastase was reduced by 16% at 6% MIC tobramycin and reduced by 70% at 25% MIC tobramycin (P