Effect of macrolides and anti-pseudomonas aeruginosa antibiotics on eradicating pseudomonas aeruginosa biofilms

Objective To investigate the effect of macrolides and anti-pseudomonas aeruginosa antibiotics on eradicating pseudomonas aeruginosa biofilms.Methods P.aeruginosa biofilms were prepared with silicone tile incubated with P.aeruginosa for 24 hours.The biofilms were treated with different antibiotics for certain period of time.The viable bacterial counts on biofilms were performed by serially diluted method.Results The viable bacterial counts on biofilms incubated with azithromycin,erythromycin 2 mg/L(1/16 MIC) or midecamycin 32 mg/L(1/16 MIC) for 5 hours showed no significant difference from those of the controls untreated with any antibiotics.3 MIC amikacin(3 mg/L) and meropenem(12 mg/L) reduced the adhesion of bacteria to 9.12%,13.34% respectively.The combination of azithromycin with amikacin and meropenem decreased the number of adherent bacteria to 0.03% and 0.49%;while the combination of midecamycin showed no significant decrease in the viable bacterial counts of biofilms.Conclusion Azithromycin and erythromycin,which have no antibacterial activity against P.aeruginosa,can promote the biofilm eradicating effect of anti-pseudomonas aeruginosa antibiotics by enhancing the permeability of bactericidal antibiotics into biofilm.Midecamycin does not have the same efficacy.