IN-VITRO ANTIMICROBIAL SUSCEPTIBILITY OF DIFFERENT SEROTYPES OF ACTINOBACILLUS-ACTINOMYCETEMCOMITANS

In vitro susceptibility of Actinobacillus actinomycetemcomitans (A.a.) serotypes to selected antimicrobial agents was investigated by the ag ar dilution method on supplemented Mueller-Hinton test medium. Eighty- three A.a. strains, 80 recent isolates from 40 periodontally healthy o r diseased subjects, and three type strains were included in the study . Serotype a represented 20, serotype b 32, serotype c 17, and serotyp e e 7 and nontypable 4 of the tested strains. The most effective drugs against all A.a. serotypes in vitro were cefaclor, cefuroxime, tetrac ycline hydrochloride, doxycycline, trimethoprim-sulfamethoxazole (cotr imoxazole), and ciprofloxacin, which inhibited 100% of the strains at 4.0 mug/ml, 4.0 mug/ml, 1.0 mug/ml, 2.0 mug/ml, 0.06 mug/ml, and 0.015 mug/ml, respectively. Serotypes a and e were more susceptible to cafa clor and cefuroxime than were serotypes b and c; 100% of the first two groups were inhibited at 2.0 mug/ml and 1.0 mug/ml. Ampicillin inhibi ted 92% of the tested strains at 1.0 mug/ml. Serotype b was always sus ceptible to ampicillin. Metronidazole exhibited the best activity agai nst serotype a strains. The lowest minimal inhibitory concentration va lues for benzylpenicillin, ampicillin, erythromycin, doxycycline, and metronidazole were encountered among serotype b isolates. The results of the present study indicate minor differences in the in vitro antimi crobial susceptibility patterns of different A.a. serotypes, except to metronidazole. Also, the new oral cephalosporins and cotrimoxazole, r are antimicrobial agents in periodontology, showed promising efficacy against all A.a. strains.