title: Penetration of erythromycin through Staphylococcus epidermidis biofilm.
abstract: BACKGROUND
  The catheter related infection caused by Staphylococcus epidermidis biofilm is increasing and difficult to treat by antimicrobial chemotherapy. The properties of biofilms that give rise to antibiotic resistance are only partially understood. This study aimed to elucidate the penetration of erythromycin through Staphylococcus epidermidis biofilm.
  
  
  METHODS
  The penetration ratio of erythromycin through Staphylococcus epidermidis biofilms of 1457, 1457-msrA, and wild isolate S68 was detected by biofilm penetration model at different time points according to the standard regression curve. The RNA/DNA ratio and the cell density within the biofilms were observed by confocal laser microscope and transmission electromicroscope, respectively.
  
  
  RESULTS
  The penetration ratios of erythromycin through the biofilms of 1457, 1457-msrA, and S68 after cultivation for 36 hours were 0.93, 0.55 and 0.4, respectively. The erythromycin penetration ratio through 1457 biofilm (0.58 after 8 hours) was higher than that through the other two (0.499 and 0.31 after 24 hours). Lower growth rate of the cells in biofilm was shown, with reduction of RNA/DNA proportion observed by confocal laser microscope through acridine orange stain. Compared with the control group observed by transmission electrmicroscope, the cell density of biofilm air face was lower than that of agar face, with more cell debris.
  
  
  CONCLUSIONS
  Erythromycin could penetrate to the Staphylococcus epidermidis biofilm, but could not kill the cells thoroughly. The lower growth rate of the cells within biofilm could help decreasing the erythromycin susceptibility.
authors.affiliation: Department of Urology, First Affiliated Hospital of People's Liberation Army General Hospital, Beijing, China.
authors.forename: Mao-hu
authors.initials: MH
authors.lastname: Lin
authors.forename: Lei
authors.initials: L
authors.lastname: He
authors.forename: Jie
authors.initials: J
authors.lastname: Gao
authors.forename: Yun-xi
authors.initials: YX
authors.lastname: Liu
authors.forename: Ji-jiang
authors.initials: JJ
authors.lastname: Suo
authors.forename: Yu-bin
authors.initials: YB
authors.lastname: Xing
authors.forename: Ning
authors.initials: N
authors.lastname: Jia
mesh_terms: D000165:Acridine Orange; D000900:Anti-Bacterial Agents / Q000493:pharmacokinetics*; D018441:Biofilms; D004269:DNA, Bacterial / Q000032:analysis; D004917:Erythromycin / Q000493:pharmacokinetics* / Q000494:pharmacology; D046529:Microscopy, Electron, Transmission; D012329:RNA, Bacterial / Q000032:analysis; D013212:Staphylococcus epidermidis / Q000187:drug effects / Q000378:metabolism*
chemical_list: D000900:Anti-Bacterial Agents; D004269:DNA, Bacterial; D012329:RNA, Bacterial; D004917:Erythromycin; D000165:Acridine Orange