A Retrospective Analysis of Anaerobic Bacteria Isolated in 236 Cases of Pleural Empyema and their Prevalance of Antimicrobial Resistance in Turkey.

Background: Parapneumonic effusions usually occur secondary to an infection and produce pus (empyema) that accumulates in the pleural space. We aimed to evaluate the prevalence of anerobes in patients with empyema and to assess their resistance patterns for seven antimicrobials.

Methods: Pleural fluid specimens from 236 patients were inoculated on Schaedler agar. Anaerobic bacteria were identified via API 20 A. Susceptibility testing for penicillin, ampicillin + sulbactam, amoxicillin + clavulanate, cefoxitin, clindamycin, metronidazole, and imipenem were performed with the E-test.

Results: There were 118 anaerobic bacterial strains detected in 66 (27.9%) of the 236 specimens. Gram-positive anaerobic cocci were detected in 54.23% and the predominant cocci were 41 Peptostreptococcus spp, (34.75%) followed by 17 P. acnes (14.41%) and 6 C. tertium (5.08%). The Gram-negative anaerobes were B. fragilis (28, 23.73%), P. melaninogenica (8, 6.78%), P. intermedia (4, 3.39%), F. nucleatum (6, 5.08%), F. mortiferum (5, 4.24%), and P. asaccharolytica (3, 2.54%). All anaerobic strains were susceptible to ampicillin + sulbactam, amoxicillin + clavulanate, and imipenem. The highest MIC was found to be > 256 µg/mL for penicillin in B. fragilis strains, 128 µg/mL for cefoxitin in P. melaninogenica strains, 32 µg/mL for clindamycin and 64 µg/mL for metronidazole in P. acnes strains. Clindamycin resistance was detected in 46.6% B. fragilis, and 17.6% for P. acnes. Thirty-eight (32.2%) strains produced beta-lactamase.

Conclusions: The use of antimicrobial agents for thoracic empyema should be based on the isolated pathogens and their resistance profiles. Clinicians should be aware of the wide diversity of anaerobic genera and species in cases of pleural empyema.