The antifungal activity of local anesthetics (LA) upon Aspergillus was already previously described (1). However, the mechanisms behind this activity still remain unclear. Our objectives were to study the fungicidal activity of LA, lidocaine (Lid) and Bupivacaine (Bup), against pathogenic species of Aspergillus in two different developmental states (resting versus germinated conidia). Clinical isolates of A. fumigatus (6 strains), A. flavus (5 strains) and A. niger (5 strains) were grown in Sabouraud agar slants (Difco) at 25ºC, for 5 days. A final concentration of 106 conidia.ml-1 was incubated either in RPMI 1640 medium with MOPS or in PBS, with serial dilutions of Lid (Sigma) (between 1.25 and 10 mg.ml-1) and Bup (Sigma) (between 0.06 and 5 mg.ml-1). Following 7 and 10 hours of incubation at 37ºC, conidia were washed and suspended in PBS with 2% of glucose and stained with 1 μg.ml-1 of propidium iodide (PI). Flow cytometry (Beckman Coulter XL-MCL flow-cytometer, Hialeah, USA) was used for detection and quantification of PI stained conidia. PI could not stain conidia in presence of concentrations lower than 5 mg.ml-1 of Lid and 2.5 mg.ml-1 of Bup. At highest concentrations of both LA (10 mg.ml-1 of Lid and 5 mg.ml-1 of Bup in PBS), PI stained all Aspergillus species after 10 hours, being A. fumigatus the most resistant - 20% of stained conidia versus 37% and 88% of A. flavus and A. niger, respectively. A. niger was the most susceptible species, already showing a significant percentage of stained conidia following 7 hours of incubation in RPMI 1640 medium. Suspended in PBS, conidia did not germinate and show hyphal growth as in RPMI 1640 medium. LA showed a higher fungicidal activity upon resting conidia comparing with germinated conidia. Both LA presented fungicidal activity at higher concentrations. This activity may change accordingly the developmental state resting conidia versus germinated conidia, the second showing promoted resistance. 1. Rodrigues AG, Araujo R, Pina-Vaz C. Inhibitory effect of local anesthetics on germination and mycelium formation by Aspergillus. Clin Microbiol Infect 9 (Suppl.1): 223, 2003.
Full conference title:
15th Annual Focus on Fungal Infections
- FFI 15th (2005)