BETA-LACTAMASE-PRODUCING STRAINS IN THE SPECIES PREVOTELLA-INTERMEDIAAND PREVOTELLA-NIGRESCENS

A total of 96 strains were collected that included laboratory strains and clinical isolates classified Prevotella intermedia sensu lato and the type strains of the species P. intermedia sensu stricto and Prevot ella nigrescens. Susceptibility to amoxicillin and amoxicillin-clavula nic acid was determined by the Etest. PCR-DNA probe assays were used t o speciate each strain as P. intermedia sensu stricto or P. nigrescens . By Etest, 71 strains (74%) were susceptible to both amoxicillin and amoxicillin-clavulanic acid with minimum inhibitory concentrations in the 0.016-0.064 mu g/ml range. In contrast, amoxicillin minimum inhibi tory concentrations of 25 strains (26%) were in the range of 1.5-96 mu g/ml with concomitant amoxicillin-clavulanic acid minimum inhibitory concentrations in the low range 0.016-0.38 mu g/ml, indicating a produ ction of beta-lactamase as confirmed by nitrocefin tests. Of these bet a-lactamase-producing strains, 20% (5/25) were identified as P. interm edia sensu stricto by the PCR-DNA probe assay and 72% (18/25) as P. ni grescens. Our results provide support for the major role of P. nigresc ens in the failure of therapy using beta-lactam antibiotics.