Atividade dos óleos essenciais de Litsea cubeba e Cymbopogon martini sobre isolados do complexo Cryptococcus neoformans
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2015-04-13
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Universidade Federal de Goiás
Resumo
Cryptococcosis is a fungal infection caused by species of the complex
Cryptococcus neoformans (C. neoformans and C. gattii) with high incidence in
patients with acquired immunodeficiency syndrome (AIDS). Antifungal drugs
used in therapy of this infection are scarce and, in addition, have evident toxicity
and low effectiveness, which motivates the search for new candidates to
antifungals. Essential oils (EOs) extracted from the fruit of Litsea cubeba (Litsea
cubeba (Lour.) Pers.) and leaves of Palmarosa (Cymbopogon martini (Roxb.)
Will. Watson) and its major constituents, citral and geraniol, were investigated as
antifungal sources. The aims of this work were to determine the isolated or
associated antifungal activity of EOs and major constituents with amphotericin B
(AMB) or fluconazole (FLU) on 15 isolates and two standard strains of C.
neoformans complex, evaluate the time-kill curve, the action on the biosynthesis
of ergosterol and on cell membrane, in addition to verify the cytotoxicity of EOs
and major constituents on human erythrocytes. By in vitro susceptibility testing
and minimum fungicidal concentration (MFC), the best activities were to L.
cubeba and citral. The EOs and major constituents exhibited minimum inhibitory
concentration (MIC) between 16 and 512 μg/mL and 64 and 2048 μg/mL, with a
MIC90 of 128 μg/mL for L. cubeba and citral, and 512 μg/mL for C. martini and
geraniol. To evaluate the association of EOs and major constituents with
antifungal agents was performed the Chequerboard method, that showed
indifference in the association of AMB and L. cubeba (94.1%) or citral (70.6%). In
association with FLU, L. cubeba was antagonistic (76.5%) and indifferent (94%)
for citral. C. martini and geraniol showed synergism associated with AMB,
respectively, in 52.9 and 70.6% of isolates, and showed indifference when
associated with the FLU in 64.7% and 88.2%. C. gattii 24065 time-kill curve
under the action of EOs and major constituents showed a rapid fungicidal
activity, which occurred after one hour incubation for L. cubeba, C. martini and
geraniol, and after two hours for citral. The amount of ergosterol was quantified
after contact with the EOs and major constituents and showed that L. cubeba
and citral inhibited 100% of sterol biosynthesis in MIC and 64% for C. martini.
This is the probably mechanism of action of these agents, except for geraniol,
which reduced only 12% in MIC. The major compounds of EOs showed no ability
to injure the plasma membrane of C. gattii, since an average of 2.7% propidium
iodide labeled cells were detected by flow cytometry. The in vitro cytotoxicity
assay by hemolysis showed that EOs and major constituents were not toxic in
the MIC and MFCs. Taken together, our results showed that the EOs of L.
cubeba and C. martini and their major constituents, citral e geraniol are
promising as candidates for new antifungal agents.
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TREMÉA, C. M. Atividade dos óleos essenciais de Litsea cubeba e Cymbopogon martini sobre isolados do complexo Cryptococcus neoformans. 2015. 97 f. Dissertação (Mestrado em Biologia da Relação Parasito-Hospedeiro) - Universidade Federal de Goiás, Goiânia, 2015.