Antibiotic sensitivity of comedonal Propionibacterium acnes

Area of Science:

• Dermatology
• Microbiology
• Pharmacology

Background:

• Propionibacterium acnes (P. acnes) and P. granulosum are implicated in acne vulgaris.
• In vitro antibiotic sensitivity studies often show P. acnes and P. granulosum are sensitive to therapeutic levels.
• Clinical response to antibiotic therapy for acne vulgaris is slower than expected from in vitro data.

Purpose of the Study:

• To investigate the antibiotic minimum inhibitory concentration (MIC) levels of P. acnes and P. granulosum isolated from comedonal material.
• To determine the required sensitivity for an assay to detect antibiotic concentrations in comedonal material.

Main Methods:

• Minimum Inhibitory Concentration (MIC) studies were performed on P. acnes and P. granulosum.
• Organisms were isolated from comedonal material.
• Antibiotic concentrations tested ranged from 0.05 to 25 microgram/ml.

Main Results:

• The assay would need to detect antibiotic concentrations of 0.05 microgram/ml or less in comedonal material.
• Two bacterial isolates exhibited resistance to one or more antibiotics at the 25 microgram/ml level.
• One isolate demonstrated a MIC level of 12.5 microgram/ml for tetracycline.

Conclusions:

• Some P. acnes and P. granulosum strains isolated from comedonal material show resistance to antibiotics at clinically relevant concentrations.
• Antibiotic resistance in these bacteria may contribute to the delayed clinical response observed in acne vulgaris treatment.
• Further investigation into antibiotic concentrations within comedonal material is warranted.