Effects of disinfectants and ciprofloxacin on quorum sensing genes and biofilm of clinical Pseudomonas aeruginosa isolates.

BACKGROUND

Pseudomonas aeruginosa is one of the most virulent bacteria and quorum sensing (QS) genes have an importance on virulence factors such as biofilm that provide resistance against disinfectants and antibiotics.

OBJECTIVE

This study aimed to determine the minimum inhibitory concentrations of the disinfectants, to investigate the effects of disinfectants and ciprofloxacin on biofilm production mature biofilm of clinical P. aeruginosa isolates, and it was aimed to investigate the effects of the agents on the expression levels of several QS-related genes in the isolates.

METHODS

Minimum inhibitory concentration (MIC) levels of polyhexamethylene biguanide (PHMB), chlorhexidine (CHX), quaternary ammonium compounds (QAC), glutaraldehyde (GLU) and ciprofloxacin (CIP) against clinical P. aeruginosa isolates were evaluated by microdilution method. Effects of the agents on the biofilm producing capacities of clonally unrelated nine strains were investigated by spectrophotometric method. Alterations in the expression of QS-related genes (lasI, lasR, rhlI and rhlR) were investigated by qPCR in three isolates that were CIP-susceptible and strong biofilm producer.

RESULTS

According to microdilution method results, three isolates were found as resistant, one isolate was found as intermediate susceptible and five isolates were found as susceptible to CIP, and CHX (7.81-31.25 μg/mL) had the lowest MIC against P. aeruginosa. CHX inhibited biofilm production levels of eight of nine isolates, and GLU and CIP inhibited six of nine isolates in the presence of agents at MIC levels. GLU inhibited the mature biofilm levels of three of nine isolates at MIC and MIC/4 levels and four of nine isolates at MIC/2 levels. Expression levels of QS-related genes were reduced or induced in the presence of different disinfectants.

CONCLUSIONS

More efforts are required to decrease the risk of ineffective and low-dose application of disinfectants and antimicrobials against bacteria. Targeting of QS-related genes may be a reasonable strategy for the inhibition of virulence factors in P. aeruginosa.