Population diversity and virulence characteristics of Cryptococcus neoformans/C. gattii species complexes isolated during the pre-HIV-pandemic era

Abstract

Cryptococcosis has become a major global health problem since the advent of the HIV pandemic in 1980s. Although its molecular epidemiology is well-defined, using isolates recovered since then, no pre-HIV-pandemic era epidemiological data exist. We conducted a molecular epidemiological study using 228 isolates of the C. neoformans/C. gattii species complexes isolated before 1975. Genotypes were determined by URA5 restriction fragment length polymorphism analysis and multi-locus sequence typing. Population genetics were defined by nucleotide diversity measurements, neutrality tests, and recombination analysis. Growth at 37˚C, melanin synthesis, capsule production, and urease activity as virulence factors were quantified. The pre-HIV-pandemic isolates consisted of 186 (81.5%) clinical, 35 (15.4%) environmental, and 7 (3.1%) veterinary isolates. Of those, 204 (89.5%) belonged to C. neoformans VNI (64.0%), VNII (14.9%) and VNIV (10.5%) while 24 (10.5%) belonged to C. gattii VGIII (7.5%), VGI (2.6%) and VGII (0.5%). Among the 47 sequence types (STs) identified, one of VNII and 8 of VNIV were novel. ST5/VNI (23.0%) in C. neoformans and ST75/VGIII (25.0%) in C. gattii were the most common STs in both species complexes. Among C. neoformans, VNIV had the highest genetic diversity (Hd = 0.926) and the minimum recombination events (Rm = 10), and clinical isolates had less genetic diversity (Hd = 0.866) than environmental (Hd = 0.889) and veterinary isolates (Hd = 0.900). Among C. gattii, VGI had a higher nucleotide diversity (π = 0.01436) than in VGIII (π = 0.00328). The high-virulence genotypes (ST5/VNI and VGIIIa/serotype B) did not produce higher virulence factors levels than other genotypes. Overall, high genetic variability and recombination rates were found for the pre-HIV-pandemic era among strains of the C. neoformans/C. gattii species complexes. Whole genome analysis and in vivo virulence studies would clarify the evolution of the genetic diversity and/or virulence of isolates of the C. neoformans/C. gattii species complexes during the pre-and post-HIV-pandemic eras.

Cryptococcus gattii Species Complex as an Opportunistic Pathogen: Underlying Medical Conditions Associated with the Infection

“…The predominance of VGIV among the HIV-associated C. gattii cases was expected since nearly 90% of the HIV-associated C. gattii isolates we have collected were from South Africa and Botswana, where VGIV is the predominant molecular type found in AIDS patients (10,15,33). A strong association of VGIV with AIDS patients is supported by the fact that we found no VGIV isolates in our stock cultures from the pre-HIV era (38). The VGIV isolates are serotype C and are found mostly in tropical and subtropical regions, such as India, Sub-Saharan Africa, Mexico, and Columbia, but infrequently in temperate zones (10).…”

Multilocus sequence typing of strains from the Cryptococcus gattii species complex from different continents

“…This genotype is poorly represented in our sampling. This VGIII strain came from the USA, in which this genotype was commonly reported 2,11,40 . VGIII is found predominantly in clinical and environmental sources in Mexico, Colombia and the USA 11,41 .…”

Associations between Cryptococcus Genotypes, Phenotypes, and Clinical Parameters of Human Disease: A Review

“…C. neoformans VNI ST5 strains can cause infections in both HIV-infected and HIV-negative patients and are found in China, Vietnam, South America, Thailand, Korea, Laos, and USA [ 106 , 115 , 116 , 117 , 118 , 119 , 120 , 121 , 122 , 123 , 124 , 125 , 126 , 127 , 128 , 129 , 130 , 131 , 132 , 133 , 134 ]. In China and Vietnam, cryptococcosis is predominately caused by ST5 strains [ 116 , 119 , 121 , 123 , 124 , 133 ].…”

“…Though these clinical outcome ST5 data are limited and more information is required, one might hypothesize that individuals of Chinese or Vietnamese descent may be more susceptible to ST5 strains and may be more prone to poor clinical outcomes compared to individuals of African descent. In regards to ST specific cryptococcal phenotypes, ST5 cryptococcal cells have significantly increased variability in cell sizes and capsule sizes but no difference in urease activity, melanin formation, or population doubling time [ 22 , 127 , 131 ]. A GWAS comparing genetic sequences of ST5 to non-ST5 strains have identified genes that are associated with ST5 (more virulent phenotypes) and non-ST5 (less virulent phenotypes) [ 119 ].…”