Inhibition of Lipase Activity in Antibiotic-Resistant Propionibacterium acnes Strains

Background and Objective: Erythromycin-sensitive and/or clindamycin-sensitive strains of Propionibacterium acnes show a reduced lipase production at levels below the minimal growth-inhibitory concentration (MIC). The objective of this study was to determine whether erythromycin and clindamycin concentrations far below the MIC inhibit lipase production in P. acnes strains resistant to these antibiotics. Methods: Of 42 P. acnes strains, 10 showed an MIC >256 µg/ml for erythromycin. Two strains showed MICs of 0.19 and 0.25 µg/ml, while the MIC of the remaining strains was ≤0.016 µg/ml. Lipase activity was determined up to a concentration of 192 µg/ml by cultivation on spirit blue agar + lipase reagent. The 10 strains whose erythromycin MIC was >256 µg/ml were also tested for lipase inhibition by clindamycin. While this method fails to differentiate between inhibition of lipase production and inhibition of lipase activity, the absence of inhibition of lipase activity rules out inhibition of lipase production. Results: Inhibition of lipolysis by sub-MIC concentrations was demonstrated only for clindamycin in 3 P. acnes strains. However, lipase inhibition was seen only at the dilution level immediately below the MIC. Conclusions: Resistant P. acnes strains with high erythromycin and/or clindamycin MICs can be ruled out to show in vitro inhibition of lipase production at antibiotic concentrations far below the MIC.