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Isolation and in vitro susceptibility of Acanthamoeba from a patient with keratitis
1School of Medical Technology, College of Medicine, National Taiwan University, Taipei, R. O. C.
Abstract:
The acanthamoebae are facultative parasites of man, and may infect the brain, skin, bone, respiratory passages and eyes. Over the past several years, Acanthamoeba keratitis has become a growing problem. This is the first case isolating Acanthamoeba polyphaga from a corneal biopsy of an ophthalmic patient in Taiwan. Direct impression smear by trichrome stain gave positive result. To provide effective clinical treatment, chemotherapeutic agents available for ophthalmic use were tested for its susceptibility with a microtiter plate method. Reading at 24- and 48-hour intervals, only amphotericin B, clotrimazole and neomycin-polymyxin B had an MIC (minimal inhibition concentration) lower than 1,000 micrograms/ml. If reading interval was prolonged to one week, neomycin, 5-flucytosine and gentamicin also showed appreciable activity. Amoebicidal concentrations (AC) and cysticidal concentrations (CC) were much higher than MIC. Only neomycin-polymyxin B, neomycin, and amphotericin B of high concentration were proved to be cysticidal.
Insights
Acanthamoeba keratitis is a growing concern. This study identified Acanthamoeba polyphaga in a Taiwanese patient and tested ophthalmic drugs, finding amphotericin B, clotrimazole, and neomycin-polymyxin B effective against the parasite.
Area of Science:
- Ophthalmology
- Infectious Diseases
- Microbiology
Background:
- Acanthamoebae are opportunistic parasites capable of infecting various human tissues, including the eyes.
- Acanthamoeba keratitis (AK) represents an increasing challenge in ophthalmic patient care.
- This study reports the first isolation of Acanthamoeba polyphaga from a corneal biopsy in Taiwan.
Purpose of the Study:
- To identify the causative agent of keratitis in an ophthalmic patient in Taiwan.
- To evaluate the in vitro susceptibility of the isolated Acanthamoeba strain to various ophthalmic chemotherapeutic agents.
Main Methods:
- Acanthamoeba polyphaga was isolated from a corneal biopsy specimen.
- Direct impression smear with trichrome stain was used for initial identification.
- Microtiter plate method was employed to determine the minimal inhibition concentration (MIC) of chemotherapeutic agents.
Main Results:
- Initial screening showed that amphotericin B, clotrimazole, and neomycin-polymyxin B had MIC values below 1,000 µg/ml at 24- and 48-hour intervals.
- Prolonged incubation (one week) revealed additional activity for neomycin, 5-flucytosine, and gentamicin.
- High concentrations of neomycin-polymyxin B, neomycin, and amphotericin B demonstrated cysticidal activity, while amoebicidal concentrations were significantly higher than MIC.
Conclusions:
- This case highlights the importance of Acanthamoeba polyphaga as a cause of keratitis in Taiwan.
- Specific antimicrobial agents, including amphotericin B, clotrimazole, and neomycin-polymyxin B, show potential for treating Acanthamoeba infections.
- Further investigation into effective cysticidal concentrations is crucial for comprehensive treatment strategies against Acanthamoeba keratitis.