Predominance of Cryptococcus neoformans Var. grubii in Ahvaz, Molecular Identification and Evaluation of Virulence Factors

Abstract

Background: Cryptococcus neoformans is an encapsulated yeast pathogen with worldwide distribution, and the highest incidence of cryptococcosis was attributed to C. neoformans (var. grubii. The pathogenicity of Cryptococcus species is associated with several factors, including capsule and melanin production, growth at 37 ºC, and secretion of extracellular enzymes. Objectives: The present study aimed to isolate and identify Cryptococcus species from pigeon guano in Ahvaz, Iran and investigate important virulence factors in the isolates. Methods: Seventy-three isolates of C. neoformans var. grubii were identified based on classical and molecular microbiology methods. Capsule size was measured by the grow yeasts in the presence of 5% CO2. Specific media demonstrated the activity of extracellular enzymes (phospholipase, hemolysin, proteinase, esterase, urease, catalase, and gelatinase). Besides, melanin production was evaluated by the niger seed agar medium. Results: Two hundred and seventeen samples were examined for the presence of Cryptococcus over 165 days in Ahvaz. All tested isolates were contained capsules with variable sizes under 5% CO2 concentration. Moreover, 100% of isolates were produced extracellular enzymes (urease, hemolysin, and catalase), whereas no proteinase and gelatinase activities were observed among isolates. Furthermore, most isolates had phospholipase (93.1%) and esterase activities (86.3%). Also, melanin was produced by all of the isolates. Conclusions: Although two methods were used for recovery of Cryptococcus, only Cryptococcus was isolated from pigeon guano, and swabs from the cage walls were negative. Cryptococcus neoformans var. grubii was the only species from pigeon droppings from Ahvaz with more pathogenic factors. Owing to the high pathogenicity of the isolates, the frequency of the disease is expected to be higher.