Antifungal Susceptibility and Virulence of Aspergillus fumigatus Environmental Strains from a Public Tertiary Hospital in Metro Manila, Philippines

Ferrisa B. Ablola, Alice Alma C. Bungay


Background and Objectives: The increase in the number of invasive Aspergillusinfections has been observed among immunocompromised and hospitalized patients. In the Philippines to date, there is no published data that focused on the prevalence of Aspergillusspecies or any other thermotolerant fungal species in a hospital environment. This research served as a primary study to characterize the antifungal susceptibility of environmental strains of Aspergillus fumigatus from a hospital facility against three antifungal agents and to determine the virulence of these isolates on BALB/c mice using an animal survival assay.

Methodology: Ten environmental strains of A. fumigatus were isolated from three air conditioned wards in a medical facility using Andersen Air Sampler. The antifungal susceptibility profile of the isolates were determined against voriconazole, amphotericin B and caspofungin. The virulence of these isolates were also tested on BALB/c mice using an animal survival assay. Moreover, the lung tissues of infected BALB/c mice were subjected to histopathological analyses using Gomori Methenamine Silver stain (GMS) and Hematoxylin & Eosin (H&E) stains.

Results: Etest result for antifungal susceptibility testing showed that two of the ten isolates were resistant to amphotericin B (AF2-A and AF-3A); one isolate resistant to voriconazole (AF2-A) and an isolate that manifested nonsusceptibility to caspofungin m(AF2-A). Epidemiological cut-off values were determined for each antifungal following the M38-A2 CLSI guidelines. BALB/c mice median survival analysis revealed that the isolate with the highest Minimum Inhibitory Concentration (MIC= 4.89 μg/ml) for voriconazole resulted to the most number of mortality with the least number of observation days. GMS AND H&E histopathology slides showed fungal elements embedded on left lung lobe of mice.

Conclusion: This study showed that there were strains of Aspergillus fumigatus from a hospital indoor air which were considered as resistant strains to voriconazole, amphotericin B and caspofungin (AF2-A and AF3- A). Lung tissues of infected mice showed characteristics of bronchopneumonia.


Antifungal susceptibility; survival analysis; environmental isolates; Etest; Gomori Methenamine Silver Stain

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