In vitro activity of antifungals in combination with essential oils against the oomycete Pythium insidiosum.

AIMS: The aim of this study was to investigate the in vitro susceptibility of Pythium insidiosum to combinations of the antifungal drugs terbinafine or itraconazole with Melaleuca alternifolia, Mentha piperita and Origanum vulgare essential oils (EOs). METHODS AND RESULTS: In vitro combinations of antifungal drugs with EOs were evaluated by checkerboard microdilution method against 20 Brazilian isolates of P. insidiosum. The tests were performed according to protocol M38-A2, and the interpretation of each combination result was based on the values of the fractional inhibitory concentration index. The combinations of itraconazole with EOs presented prominent synergistic effects against P. insidiosum isolates, and no antagonism was observed with these combinations. However, the combinations of terbinafine with EOs resulted in indifferent or antagonistic effects. CONCLUSIONS: The combination of plant-derived bioactive compounds with antifungal drugs may be an alternative therapy for the control of infections caused by P. insidiosum. Studies of new therapeutic protocols involving these proposed combinations are needed. SIGNIFICANCE AND IMPACT OF THE STUDY: The antimicrobial combinations using EOs with terbinafine or itraconazole can be an attractive therapeutic option for controlling P. insidiosum infections.

In vitro susceptibility of Brazilian Pythium insidiosum isolates to essential oils of some Lamiaceae family species.

The present study aimed to evaluate the in vitro antimicrobial action of Origanum vulgare, Origanum majorana, Mentha piperita and Rosmarinus officinalis on Pythium insidiosum oomycete zoospores. The antimicrobial activity evaluation was performed by the broth microdilution method according to CSLI M38-A2 documentation adapted to phytopharmaceuticals. Twenty-two P. insidiosum isolates were evaluated, and the minimum inhibitory concentration was determined at 100% growth inhibition. All P. insidiosum isolates evaluated showed a minimum inhibitory concentration ranging from 0.05 to 1.75 mg/mL when O. vulgare oil was used and from 0.11 to 3.5 mg/mL for O. majorana, M. piperita and R. officinalis oils. The results obtained indicate that the essential oils tested showed antimicrobial activity on P. insidiosum, with O. vulgare essential oil showing the best performance. These findings emphasize the potential use of plant essential oils as control agents in P. insidiosum infections; further research, however, is needed so as the in vivo activity of these oils can also be evaluated.

In vitro susceptibility of zoospores and hyphae of Pythium insidiosum to antifungals.

OBJECTIVES: The purpose of this study was to compare the in vitro susceptibilities of 22 Brazilian isolates of Pythium insidiosum to antifungals using a standardized inoculum of zoospores and a proposed novel inoculum prepared from cultured mycelia (hyphae) of P. insidiosum. METHODS: A zoospore suspension of P. insidiosum was obtained by the zoosporogenesis technique. The hyphal inoculum was prepared from a suspension of P. insidiosum mycelium. Susceptibility to each drug was evaluated using the CLSI M38-A2 method. RESULTS: Of the 88 MIC comparisons performed, 36 (41%) showed the same MIC value for the two inocula. The agreement (differences not greater than one dilution) between MICs obtained with both types of inocula was 39.8% (35/88). In other MIC comparisons analysed, 17 (19.3%) showed differences of two or three dilutions. CONCLUSIONS: We conclude that the use of hyphal inocula of P. insidiosum for in vitro susceptibility tests could be a suitable method for evaluating antimicrobial susceptibility, particularly when it is not possible to obtain a standardized zoospore inoculum.