Evaluation of the E test for antimicrobial susceptibility testing of Porphyromonas gingivalis.

The antimicrobial susceptibilities of 81 recent clinical Porphyromonas gingivalis isolates and two reference strains were determined by the E test, a new method, and were compared with the minimal inhibitory concentrations for these strains obtained by the reference agar dilution method on supplemented Brucella blood agar. The following agreements were obtained: benzylpenicillin 100%, ampicillin 96%, cefaclor 82%, cefuroxime 91%, erythromycin 93%, clindamycin 99%, tetracycline 66%, doxycycline 89%, metronidazole 77% and ciprofloxacin 77%. Very major discrepancies were observed with ciprofloxacin. This study indicates that the E test is an acceptable method to determine the susceptibility of P. gingivalis for most antimicrobials.

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 agar dilution method on supplemented Mueller-Hinton test medium. Eighty-three A.a. strains, 80 recent isolates from 40 periodontally healthy or diseased subjects, and three type strains were included in the study. Serotype a represented 20, serotype b 32, serotype c 17, and serotype e 7 and nontypable 4 of the tested strains. The most effective drugs against all A.a. serotypes in vitro were cefaclor, cefuroxime, tetracycline hydrochloride, doxycycline, trimethoprim-sulfamethoxazole (cotrimoxazole), and ciprofloxacin, which inhibited 100% of the strains at 4.0 micrograms/ml, 4.0 micrograms/ml, 1.0 microgram/ml, 2.0 micrograms/ml, 0.06 microgram/ml, and 0.015 microgram/ml, respectively. Serotypes a and e were more susceptible to cefaclor and cefuroxime than were serotypes b and c; 100% of the first two groups were inhibited at 2.0 micrograms/ml and 1.0 microgram/ml. Ampicillin inhibited 92% of the tested strains at 1.0 microgram/ml. Serotype b was always susceptible to ampicillin. Metronidazole exhibited the best activity against serotype a strains. The lowest minimal inhibitory concentration values 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 antimicrobial susceptibility patterns of different A.a. serotypes, except to metronidazole. Also, the new oral cephalosporins and cotrimoxazole, rare antimicrobial agents in periodontology, showed promising efficacy against all A.a. strains.