Evaluation of the E test for antimicrobial susceptibility testing of Actinobacillus actinomycetemcomitans

Actinobacillus actinomycetemcomitans and Haemophilus aphrophilus in systemic and nonoral infections in Finland

The oral cavity is the ecological niche for Actinobacillus actinomycetemcomitans and Haemophilus aphrophilus, but occasionally they cause severe nonoral infections. In this study we present 20 systemic or nonoral infections due to A. actinomycetemcomitans and H. aphrophilus, comprising all isolates of these species forwarded to and stored in Finnish reference laboratories during the years 1988-2000. The time from specimen collection to correct species identification was 9.3 days for A. actinomycetemcomitans and 10.7 days for H. aphrophilus. A. actinomycetemcomitans strains represented serotypes a, b, c, and d. Arbitrarily primed PCR distinguished four A. actinomycetemcomitans and six H. aphrophilus genotypes. Antimicrobial susceptibility testing with benzylpenicillin, amoxicillin, tetracycline, metronidazole, azithromycin, and trovafloxacin showed generally good activities against the present strains, and the susceptibility patterns closely resembled those of oral strains. The prolonged time to recover and identify A. actinomycetemcomitans and H. aphrophilus from systemic and nonoral infections may delay the correct diagnosis of the patient, but the good antimicrobial efficacies of antimicrobial agents against these pathogens give a good prognosis for the patients and advance the treatment of severe infections caused by these fastidious organisms of oral origin.

In vitro antimicrobial susceptibility of oral strains of Actinobacillus actinomycetemcomitans to seven antibiotics

BACKGROUND/AIMS

Periodontal infections with Actinobacillus actinomycetemcomitans seem to be refractory to conventional therapy. The aim of the present study was to test the in vitro susceptibilities of A. actinomycetemcomitans strains to a panel of seven orally administrable antibiotics.

METHODS

A total of 60 isolates of A. actinomycetemcomitans recovered from 43 individuals with gingivitis or periodontitis were tested. In addition, laboratory strains UP-6 and JP2 were analysed. The E-test was employed in order to determine minimal inhibitory concentrations (MIC) of antibiotics ampicillin/sulbactam, roxithromycin, azithromycin, doxycycline, metronidazole, ciprofloxacin, and moxifloxacin.

RESULTS

A. actinomycetemcomitans was highly susceptible to both fluoro-quinolones (MIC90 of 0.006 microgram/mL of ciprofloxacin and 0.032 microgram/mL of moxifloxacin). Good susceptibilities were found for ampicillin/sulbactam and doxycycline (MIC90 of 0.75 microgram/mL and 1 microgram/mL, respectively), and moderate susceptibilities for azithromycin (MIC90 of 3 microgram/mL). Most strains were resistant to metronidazole and roxithromycin. Cluster analysis revealed two larger clusters of A. actinomycetemcomitans strains with the smaller cluster assembling isolates with significantly higher MICs of most antibiotics.

CONCLUSIONS

Due to reported favourable pharmacokinetics, the fluoro-quinolone moxifloxacin appeared to be a promising candidate for adjunctive systemic antibiotic therapy in periodontal infections with A. actinomycetemcomitans.

Clinical and microbiological effects of adjunctive antibiotics in treatment of localized juvenile periodontitis. A controlled clinical trial

The aim of this study was to assess the clinical and microbiologic effects of the combination of amoxicillin and metronidazole therapy as an adjunct to mechanical treatment in the management of localized juvenile periodontitis. Twenty-five localized juvenile periodontitis (LJP) patients from a Brazilian population were randomly allocated into an experimental group receiving mechanical treatment and antibiotics, and a control group receiving mechanical treatment and placebo. Clinical and radiographic assessments, as well as microbiologic sampling for Actinobacillus actinomycetemcomitans, were performed at baseline and one year after the end of the treatment. At the termination of the study A. actinomycetemcomitans could be isolated from the oral cavity of all patients in the control group who harbored the bacterium at baseline and in 4 out of 8 patients in the experimental group. Both treatment modalities resulted in significant benefit on an individual basis. The experimental group, however, displayed better results than did the control group regarding gingival index (GI), probing depth (PD), clinical attachment level (CAL), and radiographic analysis of crestal alveolar bone mass, but not with respect to plaque index (PI). No serious adverse effects of the antibiotic treatment were observed in the present study.

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.