Beta-lactamase production and antibiotic susceptibility testing of anaerobic Gram-negative bacilli isolated from oral and maxillofacial infections

Abstract number: 1733_1157

Bancescu G., Bancescu A., Dumitriu S., Preoteasa E., Pana M., Andrei M.

Objectives: The aim of the present study was to identify at species level and to test in vitro the susceptibility to antibiotics of the anaerobic Gram-negative bacilli strains isolated from 60 pus samples collected by needle aspiration from Rumanian patients with different oral and maxillofacial infections.

Methods: Microscopy of Gram-stained direct smears and cultures on selective and non-selective media incubated both aerobically and anaerobically, were performed in each pus specimen. The strictly anaerobic bacteria were identified to genus and species level using the conventional methods of diagnosis and the Rapid ID 32 A system (bioMérieux, Marcy-l'Etoile, France). The anaerobic Gram-negative rods isolates were tested for b-lactamase production by nitrocefin disk. The susceptibility of these strains was tested against: metronidazole, penicillin G, ampicillin, amoxicillin/clavulanic acid and clindamycin by disk diffusion method and E-test (Ab Biodisk, Solna, Sweden).

Results: The Gram-negative bacilli isolates represented 73% of the 64 strictly anaerobic bacteria strains and belonged to Fusobacterium nucleatum and different species of Prevotella and Bacteroides. The Prevotella isolates were the most frequently identified anaerobic Gram-negative bacilli (31 strains), with P. melaninogenica predominating. Correlating the direct microscopy with the culture results, Prevotella was found to be the only bacteria involved in the aetiology of two cases of submandibular space abscess. All anaerobic Gram-negative bacilli isolates were susceptible to metronidazole, clindamycin and amoxicillin/clavulanic acid. The b-lactamase production was detected among the Prevotella isolates (13%), while the other Gram-negative bacilli strains were susceptible to all tested b-lactam antibiotics.

Conclusion: The most frequently isolated anaerobic species was P. melaninogenica. As antibiotics are often prescribed empirically in the treatment of acute oral and maxillofacial infections – which are usually mixed infections, involving anaerobic bacteria that may be b-lactamase producers – it is recommended to choose an association of a penicillin with a b-lactamase inhibitor. Clindamycin might be a good alternative, especially in patients allergic to penicillin. Monitoring of local susceptibility patterns of anaerobic bacteria is necessary for antibiotic selection in the initial therapy.

Session Details

Date: 31/03/2007
Time: 00:00-00:00
Session name: European Society of Clinical Microbiology and Infectious Diseases
Location: ICC, Munich, Germany
Presentation type:
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