Increased bacterial adherence and biomass in Pseudomonas aeruginosa bacteria exposed to clarithromycin

Long-term low-dose macrolides alter response in patients with chronic sessile Pseudomonas aeruginosa colonization. We examined the effect of clarithromycin on 1) adherence of P. aeruginosa cells and 2) biofilm formation. A suspended-coupon continuous-flow biofilm reactor model was used. Adherent P. aeruginosa bacteria were established for 24 h, immediately followed by a 24-h continuous-flow operation (CFO) phase with serial sampling. In addition, the effect of clarithromycin on adherent biomass was assessed quantitatively using a colorimetric assay. Isolates preexposed to clarithromycin were more adherent to the suspended coupons than nonexposed isolates (P=0.021). After 2 h of CFO, a 1.30+/-0.86 log colony-forming unit (CFU)/cm(2) decrease was observed in controls compared with a 0.08+/-0.55 log CFU/cm(2) decrease in isolates exposed to clarithromycin. Furthermore, a concentration-dependent increase in biofilm biomass was observed with the addition of clarithromycin in a standard mucoid P. aeruginosa strain (1-64 microg/mL, P<0.001) and 44 clinical P. aeruginosa strains (2 or 32 microg/mL, P<0.001). Clarithromycin increased bacterial adherence to the suspended coupons, and increased biomass was observed in isolates treated with clarithromycin.