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A Contrast of Three Inoculation Techniques used to Determine the Race of Unknown Fusarium oxysporum f.sp. niveum Isolates
Published on: October 28, 2021
Fusarium spp. causing invasive disease in humans: A case series from north India
Sudesh Gourav1, Himanshu Mishra1, Immaculata Xess1
1Department of Microbiology, All India Institute of Medical Sciences, New Delhi, India.
Abstract:
Owing to their inherent resistance to different classes of antifungals, early identification of Fusarium spp. is crucial. In this study, 10 clinical isolates were included from patients with invasive fusariosis involving lungs, sinuses, or both. Clinico-radiological data were collected. Samples were processed by standard laboratory procedures. Three gene regions (ITS, TEF1, and RPB2) were amplified by PCR for multilocus sequencing. Fusarium MLST, FUSARIUM-ID, and FUSARIOID-ID databases were used for final identification. Antifungal susceptibility testing was performed by broth microdilution following CLSI M38-A3 and Sensititre™ YeastOne™ YO9 plate. Pulmonary involvement was seen in all patients, and sino-nasal involvement was present in six. Radiologically, consolidations and cavitations were present in eight and six cases, respectively. Halo sign was present in six; reverse halo sign was also found in three of them. Direct microscopy showed septate hyphae that were morphologically different from those found in aspergillosis. Results of the molecular identification were as follows: two Fusarium irregulare, one Fusarium pernambucanum, one Fusarium incarnatum, one Fusarium sp. FIESC 30, two Fusarium keratoplasticum, one Fusarium falciforme, one Fusarium pseudonygamai, and one Fusarium delphinoides. For both Fusarium solani (FSSC) and Fusarium incarnatum-equiseti (FIESC) species complexes, amphotericin B had the lowest minimum inhibitory concentrations (MICs). Importantly, for terbinafine, all FIESC isolates had low MICs, while FSSC isolates had high MICs. In some cases, early identification of Fusarium spp. is possible by means of morphology of hyphae on direct microscopy and findings on radiology. Molecular identification, at least to the species complex level, is crucial for the choice of antifungals.
Insights
Early identification of Fusarium species is vital due to antifungal resistance. Molecular identification is crucial for selecting appropriate antifungals, guiding treatment for invasive fusariosis.
Area of Science:
- Medical Mycology
- Clinical Microbiology
- Infectious Diseases
Background:
- Invasive fusariosis poses a significant threat due to inherent antifungal resistance in Fusarium species.
- Accurate and timely identification of Fusarium species is critical for effective treatment strategies.
Purpose of the Study:
- To evaluate the clinical and radiological features of invasive fusariosis.
- To identify Fusarium species using multilocus sequencing and assess their antifungal susceptibility.
- To correlate molecular identification with treatment implications.
Main Methods:
- Collected 10 clinical isolates from patients with invasive fusariosis.
- Performed multilocus sequencing using ITS, TEF1, and RPB2 gene regions.
- Conducted antifungal susceptibility testing via broth microdilution (CLSI M38-A3 and Sensititre™ YeastOne™ YO9).
Main Results:
- Identified various Fusarium species including F. irregulare, F. pernambucanum, F. incarnatum, F. sp. FIESC 30, F. keratoplasticum, F. falciforme, F. pseudonygamai, and F. delphinoides.
- Pulmonary and sino-nasal involvement were common, with characteristic radiological findings like consolidations, cavitations, and halo signs.
- Amphotericin B showed low MICs for both Fusarium solani (FSSC) and Fusarium incarnatum-equiseti (FIESC) species complexes. Terbinafine susceptibility varied, with low MICs for FIESC and high MICs for FSSC.
Conclusions:
- Morphological and radiological findings can suggest Fusarium species early.
- Molecular identification to the species complex level is essential for guiding antifungal therapy.
- Accurate species identification impacts the choice of antifungals, especially concerning terbinafine resistance in certain Fusarium species.
