Susceptibility testing of Propionibacterium acnes comparing agar dilution with E test

Area of Science:

• Ophthalmology
• Microbiology
• Infectious Diseases

Background:

• Propionibacterium acnes (P. acnes) is a significant cause of nosocomial infections, particularly endophthalmitis.
• Limited data exists on the susceptibility of P. acnes to newer beta-lactam antibiotics and fluoroquinolones.
• Emerging evidence suggests quinolones possess activity against P. acnes, warranting further investigation.

Purpose of the Study:

• To evaluate the antibiotic susceptibility of clinical P. acnes isolates.
• To compare agar dilution and E test methods for determining P. acnes susceptibility.
• To identify appropriate antimicrobial agents for treating P. acnes endophthalmitis in a rabbit model.

Main Methods:

• Antibiotic susceptibility testing of 13 clinical P. acnes isolates and 3 ATCC strains.
• Comparison of National Committee for Clinical Laboratory Standards agar dilution method with the E test.
• Testing against 14 different antibiotics, including newer beta-lactams and fluoroquinolones.

Main Results:

• All clinical P. acnes isolates demonstrated susceptibility to piperacillin, piperacillin-tazobactam, ampicillin-sulbactam, ticarcillin-clavulanate, cefotaxime, cefotetan, ceftriaxone, cefoxitin, imipenem, and clindamycin.
• High-level susceptibility was observed for ciprofloxacin, sparfloxacin, and ofloxacin.
• E test and agar dilution methods showed comparable susceptibility patterns, with minor discrepancies for specific antibiotics.

Conclusions:

• Clinical eye isolates of P. acnes are susceptible to newer antimicrobial agents, including fluoroquinolones and broad-spectrum beta-lactams.
• Both agar dilution and E test methods are reliable for assessing P. acnes susceptibility.
• Findings support the use of these agents in managing P. acnes endophthalmitis.