The oral cavity constitutes one of the principal ecological niches for obligate anaerobic bacteria (33). These microor- ganisms play an important role in the pathogenesis of oral infections (3) and focal infections of oral origin (4). In Spain, the antibiotics most widely used therapeutically in the dental setting include particularly amoxicillin (AMX), amoxicillin–clavulanic acid (AMX-CLA), metronidazole (MTZ), clindamycin (CM) and azithromycin (AZM) (3). In accord- ance with the latest guidelines for the prevention of focal infections of oral origin (mainly bacterial endocarditis and pros- thetic joint infection) drawn up by Expert Committees, AMX continues to be the antibiotic of choice for patients ‘at risk’ Oral Microbiology Immunology 2007: 22: 298–303 Printed in Singapore. All rights reserved Ó 2007 The Authors. Journal compilation Ó 2007 Blackwell Munksgaard Susceptibility of oral obligate anaerobes to telithromycin, moxifloxacin and a number of commonly used antibacterials Toma ´s I, Toma ´ s M, A ´ lvarez M, Velasco D, Potel C, Limeres J, Diz P. Susceptibility of oral obligate anaerobes to telithromycin, moxifloxacin and a number of commonly used antibacterials. Oral Microbiol Immunol 2007: 22: 298–303. Ó 2007 The Authors. Journal compilation Ó 2007 Blackwell Munksgaard. Introduction: Obligate anaerobes are closely involved in the pathogenesis of oral and focal infections. The objective of this study was to evaluate the susceptibility profiles of obligate anaerobes of oral origin to telithromycin (TLM), moxifloxacin (MXF), and other antibiotics that are commonly used in dentistry. Methods: The study sample comprised 172 obligate anaerobes isolated from the saliva of 43 adult volunteers. The minimum inhibitory concentrations (MICs) were determined by the agar dilution technique in Brucella agar medium supplemented with vitamin K, haemin and 5% (volume/volume) laked sheep blood, and incubated under anaerobic conditions. The Clinical and Laboratory Standards Institute methodology was followed and its criteria were used for the qualitative interpretation of the results. The antibiotics evaluated were: amoxicillin (AMX), amoxicillin-clavulanic acid (AMX-CLA), clinda- mycin (CM), metronidazole (MTZ), azithromycin (AZM), TLM and MXF. Results: Resistance to AMX (MIC 90 P 16 mg/l) was observed in 45.3% of the obligate anaerobes and resistance to CM (MIC 90 P 16 mg/l) was found in 18.6%. All the isolates were sensitive to MTZ (MIC 90 ¼ 1 mg/l) and 98.8% were sensitive to AMX-CLA (MIC 90 ¼ 2 mg/l). The MIC 90 values for AZM, TLM and MXF were P16, P8 and P2 mg/l, respectively. Conclusion: Pathogenic, opportunistic and non-pathogenic obligate anaerobes showed high percentages of resistance to AMX and CM, and high MIC values for AZM in the absence of recently administered antibiotics. MXF showed a higher activity than TLM, similar to that detected for AMX-CLA and MTZ. In consequence, MXF could represent a possible alternative antimicrobial against obligate anaerobes of oral origin, particularly in those patients with allergy, intolerance or lack of response to AMX-CLA or MTZ. I. Toma ´s 1 , M. Toma ´s 2 , M. A ´ lvarez 3 , D. Velasco 2 , C. Potel 3 , J. Limeres 1 , P. Diz 1 1 Faculty of Medicine and Dentistry, Santiago de Compostela University, Santiago de Com- postela, Spain, 2 Research Laboratory and Microbiology Department, Juan Canalejo Hos- pital, La Corun ˜a, Spain, 3 Research Laboratory and Microbiology Department, Xeral-Cı ´es Hospital, Vigo, Spain Key words: moxifloxacin; obligate anaer- obes; oral flora; telithromycin Inmaculada Toma ´ s Carmona, Unidad de Pacientes Especiales, Facultad de Medicina y Odontologı ´a, Universidad de Santiago de Compostela, C./Entrerrios s/n, 15782 Santiago de Compostela, Spain Tel.: +34 981 563100 (ext. 12344); fax: +34 981 562226; e-mail: pdiz@usc.es Accepted for publication November 13, 2006