In-vitro activity of spiramycin and metronidazole alone or in combination against clinical isolates from odontogenic abscesses.

One hundred and forty-eight isolates of bacteria from 20 intraoral odontogenic abscesses were tested for their susceptibility to spiramycin and metronidazole alone or in combination. All isolates, except Rothia spp. (one), Enterococcus avium (three), Haemophilus parainfluenzae (one) and Staphylococcus aureus (one) were sensitive to spiramycin and/or metronidazole. Among the anaerobes, spiramycin as well as metronidazole showed good antimicrobial activity against species of Prevotella, Eubacterium, Peptostreptococcus, Bacteroides and Porphyromonas. All the aerobes were resistant to metronidazole. A potential synergic effect was found in 17% of the clinical isolates tested, as the MICs of spiramycin and metronidazole for 25 isolates (21 isolates of Eubacterium, two of lactobacilli, one strain of Peptostreptococcus sp. and one Clostridium clostridiiforme) were significantly reduced by the addition of the other antibiotic.