SUSCEPTIBILITY TESTING OF PROPIONIBACTERIUM-ACNES COMPARING AGAR DILUTION WITH E-TEST

Propionibacterium acnes has been identified as a significant agent of nosocomial infections, including endophthalmitis. Data concerning susc eptibility of P. acnes to newer beta-lactam antibiotics and fluoroquin olones are limited. Recent reports suggest that quinolones have activi ty against these organisms sufficient to warrant further study. We und ertook 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 Clini cal Laboratory Standards method of agar dilution with the E test, Thir teen clinical isolates obtained from eye specimens and three American Type Culture Collection control strains were tested against 14 antibio tics, All the clinical isolates were susceptible by both methods to pi peracillin, piperacillin-tazobactam, ampicillin-sulbactam, ticarcillin -clavulanate, cefotaxime, cefotetan, ceftriaxone, cefoxitin, and imipe nem in addition to clindamycin but were resistant to metronidazole. Th e 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 obser ved by the agar dilution method, Those few strains for which discrepan cies were noted exhibited E-test susceptibilities three- to fivefold d ilutions lower than the agar dilution method susceptibilities but only with ampicillin-sulbactam, ticarcillin-clavulanate, and/or clindamyci n. On the basis of our study, all of our clinical eye isolates were su sceptible to these newer antimicrobial agents and the two methods demo nstrated similar susceptibility patterns.