Abstract
The role of clarithromycin (CAM) in biofilm formation has recently been reported. Inhibition of the production or promotion of the dissolution of the glycocalyx, a major component of biofilm, has been implicated in its mechanism of action. However, the details remain unclear. We used an experimental model of complicated urinary bladder infection and automated simulation of the variations in urinary antimicrobial concentration to study the efficacy of CMA in inhibiting biofilm formation and obtained the following results.
1) Priro to biofilm formation, Pseudomonas aeruginosa (P. aeruginosa) was exposed to ciprofloxacin (CPFX, MIC: 8μg/ml), which was active against the organism, at a dose of 200 mg t. i. d. for 7 days. The bacteria were apparently eradicated from the culture medium in the experimental model of bladder infection (model bladder) after 32 hours. However, when the medium was changed to eliminate the antimicrobial agent on Day 7, bacterial regrowth was initiated after 4 hours. Scanning electron microscopy demonstrated sequential biofilm formation on the surface of glass beads in the model bladder diverticulumn, suggesting inside the biofilm were a source of regrowth.
2) Prior to biofilm formation, P. aeruginosa was also exposed to CAM alone, which has no antimicrobial activity against the organism (MIC:> 128μg/ml) at a dose of 200 mg t. i. d. for 7 days. In this situation, CAM was not active against P. aeruginosa and the bactericidal concentration in the model bladder did not decrease markedly, reaching the initial level (107 CFU/ml) within 48 hours. However, although numerous bacteria were attached to the glass beads in the diverticulum, no biofilm was formed.
3) Exposure to a combination of CPFX and CAM (each at 200 mg t. i. d. for 7 days) resulted in the eradication of bacteria from the model bladder at 32 hours, and no bacterial regrowth was demonstrated after the medium was exchanged on Day 7. In addition, no biofilm was formed and the bacteria did not become attached to the glass beads.
4) The content of alginate, a major component of P. aeruginosa biofilm, was measured per 5 glass beads on Day 3, 5, and 7 after starting drug administration. The alginate content increased with time when CPFX was given alone at a dose of 200 mg t. i. d. In contrast, the alginate content increased slightly on Day 3, but decreased to below the detection limit on Days 5 and 7 when CAM was given alone at a dose of 200 mg t. i. d. In addition, the alginate level was also below the detection limit on Day 7 when a combination of CPFX and CAM was given (each at 200 mg t. i. d.).
5) Therefore, the inhibition of glycocalyx production may be implicated in the mechanism by which CAM prevents biofilm formation.
