This study examined how pH affects the growth and enzyme production of three cutaneous Propionibacterium species (P. acnes, P. avidum, and P. granulosum) using chemostat cultures. All three species showed maximum specific growth rates at pH 6.0, but differed in optimal pH for biomass production: P. acnes and P. avidum peaked at pH 6.0, while P. granulosum peaked at pH 7.0-7.5. Each species produced different combinations of extracellular enzymes including lipase, hyaluronate lyase, phosphatase, and proteinase. Enzyme production varied with pH, with highest activity generally occurring between pH 5.0-6.0. Importantly, enzyme denaturation at extreme pH values reduced detectable activity despite continued production. The authors suggest pH may help explain why P. acnes dominates on normal skin (which is acidic at pH 4.0-6.8) and why P. granulosum appears more frequently in acne lesions (potentially higher pH environments). These findings indicate pH is a major environmental factor influencing propionibacterial ecology on human skin.

Key findings

• All three Propionibacterium species achieved maximum specific growth rates at pH 6.0, with growth ranges of pH 4.5-7.5 for P. acnes and pH 5.0-8.0 for P. avidum and P. granulosum
• Optimal biomass production occurred at pH 6.0 for P. acnes and P. avidum, but at pH 7.0-7.5 for P. granulosum, suggesting differential pH preferences
• Each species produced distinct enzyme profiles: P. acnes produced lipase, hyaluronate lyase, phosphatase, and proteinase; P. avidum produced lipase and proteinase; P. granulosum produced lipase and hyaluronate lyase
• Extracellular enzyme activity peaked between pH 5.0-6.0 for most enzymes, with significant enzyme denaturation occurring at extreme pH values reducing detectable activity
• The acidic pH of normal human skin (4.0-6.8) may favor P. acnes dominance, while potentially neutral pH in acne lesions may favor P. granulosum colonization