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Susceptibility testing of Propionibacterium acnes comparing agar dilution with E test
M A Smith1, P Alperstein, K France
1Department of Medicine, Long Island Jewish Medical Center, New Hyde Park, New York 11042, USA.
Abstract:
Propionibacterium acnes has been identified as a significant agent of nosocomial infections, including endophthalmitis. Data concerning susceptibility of P. acnes to newer beta-lactam antibiotics and fluoroquinolones are limited. Recent reports suggest that quinolones have activity against these organisms sufficient to warrant further study. We undertook a study to select appropriate antimicrobial agents for use in a rabbit model of P. acnes endophthalmitis. We compared the antibiotic susceptibilities of P. acnes by using the National Committee for Clinical Laboratory Standards method of agar dilution with the E test. Thirteen clinical isolates obtained from eye specimens and three American Type Culture Collection control strains were tested against 14 antibiotics. All the clinical isolates were susceptible by both methods to piperacillin, piperacillin-tazobactam, ampicillin-sulbactam, ticarcillin-clavulanate, cefotaxime, cefotetan, ceftriaxone, cefoxitin, and imipenem in addition to clindamycin but were resistant to metronidazole. The clinical P. acnes isolates also displayed high-level susceptibility to ciprofloxacin, sparfloxacin, and ofloxacin. Almost all the P. acnes strains demonstrated E-test MICs within 2 dilutions of the MICs observed by the agar dilution method. Those few strains for which discrepancies were noted exhibited E-test susceptibilities three- to fivefold dilutions lower than the agar dilution method susceptibilities but only with ampicillin-sulbactam, ticarcillin-clavulanate, and/or clindamycin. On the basis of our study, all of clinical eye isolates were susceptible to these newer antimicrobial agents and the two methods demonstrated similar susceptibility patterns.
Insights
Propionibacterium acnes, a cause of eye infections, remains susceptible to newer antibiotics like fluoroquinolones and beta-lactams. This study confirms susceptibility in clinical isolates, guiding treatment for P. acnes endophthalmitis.
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.