[Inhibitory activity of azithromycin on biofilm synthesis and synergism between azithromycin and fleroxacin on Pseudomonas aeruginosa in biofilms].
OBJECTIVE
The influence of azithromycin (AZT) on the production of glycocalyx (GLX) from P. aeruginosa biofilms and synergism of antibacterial activities between AZT and fleroxacin (FLX) on P. aeruginosa were investigated.


METHODS
GLX production was measured by using a L-tryptophan method and viable counts in biofilms was determined by using a methylthiazolyldiphenyltetrazolium(MTT) method.


RESULTS
GLX production was reduced significantly from 28.0 +/- 8.1 micrograms/ml at 0MIC to 21.8 +/- 8.2 micrograms/ml at 1/16MIC and 16.7 +/- 7.9 micrograms/ml at 1/4MIC respectively (P = 0.0002). 1/16MIC and 1/4MIC AZT showed no bactericidal activities to P. Aeruginosa in biofilms. Viable counts in biofilms were 6.2 +/- 0.61 Lg/cm2 at 0MIC, 6.1 +/- 0.4 Lg/cm2 at 1/16MIC and 6.2 +/- 0.4 Lg CFU/cm2 at 1/4 MIC respectively (P = 0.63). However, AZT could enhance bactericidal activity of FLX on P. aeruginosa in biofilms. When 1/4MIC FLX was combined with 1/16MIC and 1/4 MIC AZT, viable counts were reduced significantly from 6.1 +/- 0.5 Lg CFU/cm2 to 5.9 +/- 0.3 Lg CFU/cm2 and 5.8 +/- 0.4 Lg CFU/cm2 respectively (P = 0.02). When 1/2MIC FLX was combined with 1/16MIC and 1/4MICAZT, viable counts were reduced significantly from 6.3 +/- 0.7 Lg CFU/cm2 to 5.8 +/- 0.5 LgCFU/cm2 and 5.7 +/- 0.6 Lg CFU/cm2 respectively (P = 0.03).


CONCLUSIONS
Because AZT did not have direct bactericidal activities on P. aeruginosa in biofilms but could inhibit GLX production, We considered that AZT could enhance antibacterial activities of FLX by enhancing permeability of FLX into biofilms.
Fang
X
X
Department of Pulmonary Disease, Chinese PLA General Hospital, Beijing 100853.
Liu
Y
Y
Chen
Q
Q
Wangrui
D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D000890:Anti-Infective Agents / Q000494:pharmacology*; D017963:Azithromycin / Q000494:pharmacology*; D018441:Biofilms / Q000254:growth & development*; D004357:Drug Synergism; D016576:Fleroxacin / Q000494:pharmacology*; D019276:Glycocalyx / Q000187:drug effects; D011550:Pseudomonas aeruginosa / Q000502:physiology
D000900:Anti-Bacterial Agents; D000890:Anti-Infective Agents; D017963:Azithromycin; D016576:Fleroxacin