Antibacterial activity of oral antibiotics against anaerobic bacteria.

The spectrum and the antibacterial susceptibility of anaerobic bacteria to oral antibiotics isolated from clinical specimens was assessed in two different centres, the first receiving specimens from University departments and the second from general practitioners and small hospitals. Susceptibility was studied with a microtiter ready-to-use panel system, using the manufacturer's modified Wilkins-Chalgren's broth as the test medium for the following antibiotics: ampicillin, ampicillin+sulbactam, amoxicillin+clavulanic acid, cephalexin, cefaclor, cefuroxime, cefetamet, clindamycin, doxycycline and erythromycin. Anaerobic bacteria frequently encountered in clinical specimens from the University departments were mainly resistant Bacteroides spp., especially Bacteroides fragilis, Propionibacterium spp. and Peptostreptococcus spp., whereas in the outpatient center, Peptostreptococcus spp, Actinomyces spp. and Veillonella parvula (usually considered as colonizing flora) represented 90% of the cultured bacteria. The study shows that the members of most Bacteroides spp. encountered in a hospital environment are resistant to most of these agents (except clindamycin, amoxicillin+clavulanic acid, and ampicillin+sulbactam), whereas the gram-positive pathogens are widely covered by most of the orally available agents studied including cefetamet.