beta-lactamase production in Prevotella intermedia, Prevotella nigrescens,and Prevotella pallens genotypes and in vitro susceptibilities to selectedantimicrobial agents

The present study investigated the beta-lactamase production of 73 Prevotel la intermedia, 84 Prevotella nigrescens, and 14 Prevotella pallens isolates and their in vitro susceptibilities to six antimicrobial agents. The P. in termedia and P. nigrescens isolates were recovered from oral and estraoral samples obtained from subjects in two geographic locations from 1985 to 199 5, The clonality of the beta-lactamase-positive and beta-lactamase-negative isolates and the clustering of the genotypes were studied by arbitrarily p rimed-PCR fingerprinting. beta-Lactamase production was detected in 29% of P. intermedia isolates, 29% of P. nigrescens isolates, and 57% of P, pallen s isolates. No difference in the frequencies of beta-lactamase production b y P. intermedia and P. nigrescens between isolates from oral and extraoral sites, between isolates obtained at different time periods, or between P. i ntermedia isolates from different geographic locations was observed. Howeve r, the P. nigrescens isolates from the United States were significantly mor e frequently (P = 0.015) beta-lactamase positive than those from Finland. N o association between the genotypes and beta-lactamase production or betwee n the genotypes and the sources of the isolates was found. The penicillin G MICs at which 90% of the isolates were inhibited were 8 mu g/ml for P. irt ermedia, 8 mu g/ml for P. nigrescens, and 16 mu g/ml for P. pallens. For th e beta-lactamase-negative isolates, the corresponding values were 0.031, 0. 031, and 0.125 mu g/ml, and for the beta-lactamase-positive isolates, the c orresponding values were 16, 8, and 32 mu g/ml. All isolates were susceptib le to amoxicillin-clavulanate, cefoxitin, metronidazole, azithromycin, and trovafloxacin. The MICs of amoxicillin-clavulanate and cefoxitin were relat ively higher for the beta-lactamase-positive population than for the beta-l actamase-negative population.