Antimicrobial Drug Susceptibility Test of Pythium insidiosum by Disc Diffusion Method

Background: Pythiosis is a life-threatening disease caused by the fungus-like organism Pythium insidiosum. It causes disease in both animals and humans. Amphotericin B antifungal is less effective because it lacks ergosterol, a drug target in the cell membrane. Objective: To evaluate antimicrobial susceptibility test of P. insidiosum isolated from human pythiosis by disc diffusion method. Methods: The antimicrobial drug susceptibility test by disc diffusion method was tested against 10 clinical isolated strains of P. insidiosum. Antimicrobial drugs comprise of 8 antibiotics (chloramphenicol, cefotaxime, ciprofloxacin, gentamycin, tetracycline, meropenem, oxacillin, and vancomycin) and 2 antifungal drugs (itraconazole and amphotericin B) which were included in the test. Results: Antimicrobial drugs susceptibility tests were performed on 10 clinically isolated strains of P. insidiosum. Six of them showed susceptibility to antimicrobial drugs. The cutaneous pythiosis strain (SIMI 8569) showed the highest number of susceptibilities to antimicrobial agents (chloramphenicol, ciprofloxacin, gentamycin, tetracycline, vancomycin, and itraconazole). In addition, 4 strains of P. insidiosum (M 29, SIMI 6666, SIMI 7873, and SIMI 2989-42) were not inhibited by all antimicrobial drugs. Conclusions: This result concluded that chloramphenicol, tetracycline, and itraconazole inhibited the mycelial growth of P. insidiosum better than the other drugs. The inhibition effects of these drugs were observed in 40% - 60% of the strains. Further experiments should be carried out to evaluate the tested drugs in various concentrations with other more susceptible methods to get more precise concentrations exposed to P. insidiosum isolates such as broth dilution or dilution assays.