Farias, L.M.*, Carvalho, M.A.R.; Houw, H.; Oliveira, A.A.P.; Rodrigues, P.H.; Farias, F.F.; Nicoli, J.R.; Costa, J.E.
Laboratório de Microbiologia Oral e Anaeróbios, Departamento de Microbiologia/ICB/UFMG - Belo Horizonte, Minas Gerais, Brasil.

The Fusobacterium genus is constituted by anaerobic Gram-negative rods that grow well under strict anaerobiosis or weakly under low oxygen tensions. The aim of this study was to evaluate the oxygen sensitivity of Fusobacterium strains exposed to atmospheric oxygen. Sixty four strains were studied; 40 recently isolated - Group I, 22 from our collection, maintained in liquid nitrogen - Group II and 2 reference strains (F. nucleatum ATCC 10953 and F. necrophorum ATCC 25286). The strains were inoculated onto Tryptic Soy Agar supplemented with 0.01 mg/mL L-cystine, 0.5% yeast extract and 5% human blood with Steers' replicator after exposure to atmospheric oxygen hourly for up to 20 hours. The plates were incubated under anaerobic conditions (anaerobic chamber: 85% N2, 5% C02, 10%H2) at 37 C for 48 hours. The sensitivity to oxygen was evaluated by the observation of the intensity of growth in each spot, which was classified as full, weak or scattered, or absent. The Group I showed a higher sensitivity to atmospheric oxygen: full growth was not observed after 4 hours of exposure and no growth was detected after 7 hours of exposure of some strains. In regard to the Group II full growth of all strains was observed up to 7 hours and all of them remained viable after 12 hours of exposure After 19 hours of exposure no strain from Group I and only one from Group II grew and there was a complete inhibition of growth after 20 hours. In conclusion, our results showed that the genus is heterogeneous in regard to oxygen sensitivity, specially when comparing recently isolated strains to those stored for 18 months.

Supported by FAPEMIG, CNPq, CAPES and PRPq/UFMG