This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: mycology, Subject name: Microbiology
An elderly diabetic has left sided orbital cellulitis, CT scan of paranasal sinuses shows evidence of left maxillary sinusitis. A Gram-stained smear of the orbital exudates shows irregularly branching septate hyphae. The following is the most likely aetiological agent 
Select and explain. 
A. Aspergillus, B. Rhizopus, C. Mucor, D. Candida
A: Aspergillus
Answer: A: Aspergillus 
Explanation: Infection caused by inhalation of the Aspergillus conidia or mycelial fragments resulting in respiratory diseases, disseminated aspergillosis in brain, kidney and hea.and superficial infection like sinusitis, mycotic keratitis and otomycosis. Sinusitis is caused by A.flavus and A.fumigatus On microscopy, it shows non pigmented septate hyphae with characteristic dichotomous branching at an angle of approximately 45 degrees. Ref: Textbook of Microbiology, Ananthanarayan and Paniker; 9th edition .