Actinomyces spp.: a disregarded pathogen?

Abstract number: 1134_02_368

Palombarani S., Almuzara M., Bombicino K., Rodriguez H., Bertona E., Famiglietti A., Vay C.

We present 45 Actinomyces spp isolations, their identification to a species level and their clinical sources. In addition, we perform susceptibility testing of 23 of those strains to 13 drugs. The identification of Actinomyces spp was done taking into account their cultural features, growth’s atmosphere and biochemical and enzimatical tests, according to schemes proposed by Sarkonen N., Funke G., Moncla B.,Hillier S., and Bernard K. We studied too, the clinical sources of Actinomyces spp, if they were isolated lonely or in association with mucosa's normal flora. The susceptibility testing was performed by the agar dilution method, with Mueller Hinton agar supplemented with 5% sheep blood. The reading of minimum inhibitory concentration (MICs) were done after 48 hours incubation at 37°C in at atmosphere enriched with CO₂. All strains were grown at 37°C on sheep blood agar plates with CO₂ added. A. radingae, A. europaeus, and A. odontolyticus were the most frequent isolated species ( 7 each one) followed by A. israelii, A. graevenitzii, A. turicensis and A. viscosus. In 27 isolations, Actinomyces spp were recovered as sole microorganism, and in the 18 remainder, in association with mucosa's normal flora. There were not relations between Actinomyces species and the clinical sources of the samples. MICs for penicilin, ampicilin and cefotaxime were from <0.016 to 0.25 mg/ml. There was a bimodal behaviour with macrolides : erythromycin, azithromycin and clarithromycin (MICs from 0.032 to 128 mg/ml) and the same was observed with quinolones: levofloxacin, ciprofloxacin and moxifloxacin (MICs from 0.032 to 8 mg/ml). All isolations presented MICs for vancomycin <0.125 mg/ml. The identification of the Actinomyces genus presents diagnostic difficulties due to its growth requirements. Some species are not so infrequent, and the sources from which they are recovered suggest that they may be of clinical relevance, for they are often isolated as sole pathogen.