In vitro susceptibility of Thai Pythium insidiosum isolates to antibacterial agents

Navaporn Worasilchai, Ariya Chindamporn, Rongpong Plongla, Pattama Torvorapanit, Kasama Manothummetha, Nipat Chuleerarux, Nitipong Permpalung

Research output: Contribution to journalArticlepeer-review

4 Scopus citations


Human pythiosis is a life-threatening human disease caused by Pythium insidiosum. In Thailand, vascular pythiosis is the most common form and carries a mortality rate of 10 to 40%, despite aggressive treatment with radical surgery, antifungal agents, and immunotherapy. Itraconazole and terbinafine have been the mainstay of treatment, until recently, based on case report data showing potential synergistic effects against Brazilian P. insidiosum isolates. However, the synergistic effects of itraconazole and terbinafine against Thai P. insidiosum isolates were not observed. This study tested the in vitro susceptibilities of 27 Thai human P. insidiosum isolates (clade II, n = 17; clade IV, n = 10), 12 Thai environmental P. insidiosum isolates (clade II, n = 4; clade IV, n = 8), and 11 non-Thai animal P. insidiosum isolates (clade I, n = 9; clade II, n = 2) to antibiotics in eight antibacterial classes to evaluate alternative effective treatments. Tetracycline and macrolide antibiotics demonstrated in vitro activity against Thai P. insidiosum isolates, with doxycycline MICs (1 to 16 μg/ml), minocycline MICs (1 to 4 μg/ml), tigecycline MICs (1 to 4 μg/ml), azithromycin MICs (1 to 16 μg/ml), and clarithromycin MICs (0.125 to 8 μg/ml) being the lowest, on average. Synergistic effects of tetracyclines and macrolides were also observed.

Original languageEnglish (US)
Article numbere02099-19
JournalAntimicrobial agents and chemotherapy
Issue number4
StatePublished - 2020


  • Antibacterial agents
  • Pythium insidiosum
  • Susceptibility profile

ASJC Scopus subject areas

  • Pharmacology
  • Pharmacology (medical)
  • Infectious Diseases


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