Molecular characterisation of Cryptococcus neoformans and Cryptococcus gattii present in tree hollows, their antifungal susceptibility, and chemical factors influencing their growth on woody debris
| dc.contributor.advisor | Botha, Alfred | en_ZA |
| dc.contributor.advisor | Vismer, Hester | en_ZA |
| dc.contributor.advisor | Boekhout, Teun | en_ZA |
| dc.contributor.author | Vreulink, Jo-Marie | en_ZA |
| dc.contributor.other | Stellenbosch University. Faculty of Science. Dept. of Microbiology. | en_ZA |
| dc.date.accessioned | 2020-02-16T11:45:57Z | |
| dc.date.accessioned | 2020-04-28T15:10:34Z | |
| dc.date.available | 2020-02-16T11:45:57Z | |
| dc.date.available | 2020-04-28T15:10:34Z | |
| dc.date.issued | 2020-03 | |
| dc.description | Thesis (PhD)--Stellenbosch University, 2020. | en_ZA |
| dc.description.abstract | ENGLISH ABSTRACT: Members of the Cryptococcus neoformans/Cryptococcus gattii species complex causes cryptococcosis; a disease that is a major burden among HIV/AIDS patients in South Africa. Infection is likely obtained via inhalation of basidiospores from the environment. Basidiospores are produced during opposite-sex mating that occurs between MATα and MATa strains or through same-sex mating. Although it is well established that the habitats of pathogenic cryptococci can serve as infection sources, little was known about the prevalence of environmental pathogenic cryptococci and their relation to clinical isolates in South Africa. It was suggested that environmental factors could affect mating type occurrence, yet nothing was known about this aspect. Furthermore, it was unestablished if South African environmental isolates presented different antifungal susceptibilities than clinical isolates. To address these facets, pathogenic cryptococci were first isolated from the South African environment. Following molecular characterisation, the epidemiological relationship between the environmental and clinical isolates was investigated. Subsequently, the effect of chemical factors on the growth of strains found to colonise trees differentially was examined. Lastly, the antifungal susceptibility of the environmental isolates was compared to that of clinical isolates. Pathogenic cryptococci were isolated from woody debris samples collected on three sampling dates from trees situated in a public park in Cape Town (PPCT) and on one sampling date from trees located on a privately-owned game farm in the Northern Cape (GFNC), whereafter the isolates were molecularly characterised. Since trees were not permanently colonised by C. gattii sensu stricto MATa, it was estimated whether chemical factors in the wood could have affected the occurrence of C. gattii s.s. MATa. A positive correlation was detected between the numbers of C. gattii s.s. MATa and the ammonium-nitrogen (NH₄-N) concentration. Subsequently, the effect of low and high ammonium chloride (NH₄Cl) concentrations on the growth of C. gattii s.s. MATa and MATα was investigated in woody microcosms. Antifungal susceptibility differences between environmental and clinical isolates were evaluated by determining the amphotericin B (AmB) and fluconazole (FLU) susceptibility of the isolates. The pathogenic cryptococci isolated from the PPCT trees were predominantly C. gattii s.s. ST230 followed by C. neoformans s.s. genotype AFLP1/VNI ST23. Since ST23 was previously isolated from infected patients, the PPCT trees might be an infection source. Growth studies revealed that C. gattii s.s. MATa isolates were able to compete better with MATα isolates in microcosms supplemented with a high NH₄Cl concentration, which provided a possible explanation for the absence of MATa in PPCT trees after the first sampling date. All of the environmental isolates were more susceptible to AmB than clinical isolates. In contrast, environmental C. neoformans s.s. genotype AFLP/VNI and C. gattii s.s. isolates were less susceptible to FLU than corresponding clinical isolates, indicating that FLU resistance can develop among environmental isolates. Furthermore, temporal variation in C. gattii s.s. ST230 isolates’ FLU susceptibility was potentially linked to variations in iron, NH₄-N and sodium concentrations within their original woody habitat. This study indicates that environmental factors can affect the numbers and antifungal susceptibility of pathogenic cryptococci in the South African environment. | en_ZA |
| dc.description.abstract | AFRIKAANSE OPSOMMING: Lede van die Cryptococcus neoformans/Cryptococcus gattii spesieskompleks veroorsaak cryptococcosis; 'n siekte wat 'n groot las onder MIV/VIGS-pasiënte in Suid-Afrika is. Infeksie word waarskynlik verkry deur inaseming van basidiospore uit die omgewing. Basidiospore word geproduseer tydens teenoorgestelde geslags paring wat plaasvind tussen MATα en MATa stamme of deur paring van dieselfde geslag. Alhoewel dit goed vasgestel is dat die habitatte van patogeniese kryptokokki as infeksiebronne kan dien, was daar min bekend oor die voorkoms van patogeniese kryptokokki in die omgewing en hul verband met kliniese isolate in Suid-Afrika. Daar is voorgestel dat omgewingsfaktore die teenwoordigheid van die paringstipes kan beïnvloed, maar daar is niks oor hierdie aspek bekend nie. Verder is dit nog nie bepaal of Suid-Afrikaanse omgewingsisolate verskillende antifungale vatbaarheid het as kliniese isolate nie. Om hierdie fasette aan te spreek, is patogeniese kriptokokki eerstens vanuit die Suid-Afrikaanse omgewing geïsoleer. Na molekulêre karakterisering is die epidemiologiese verband tussen die omgewings- en kliniese isolate ondersoek. Vervolgens is die effek van chemiese faktore op die groei van die stamme wat bome verskillend gekoloniseer het, ondersoek. Laastens is die antifungale vatbaarheid van die omgewingsisolate vergelyk met dié van kliniese isolate. Patogeniese kriptokokki is geïsoleer vanuit houtagtige detritus monsters wat op drie monsternemings datums versamel is vanaf bome geleё in 'n openbare park in Kaapstad (PPCT) en op een monsternemings datum vanaf bome wat op 'n privaat wildplaas in die Noord-Kaap (GFNC) geleë is, waarna die isolate molekulêr gekarakteriseer was. Aangesien bome nie permanent deur C. gattii sensu stricto MATa gekoloniseer was nie, is dit bepaal of chemiese faktore in die hout die teenwoordigheid van C. gattii s.s. MATa kon beïnvloed het. 'n Positiewe korrelasie was tussen die getalle van C. gattii s.s. MATa en die ammonium-stikstof (NH₄-N) konsentrasie gevind. Daarna was die effek van lae en hoë ammoniumchloried (NH₄Cl) konsentrasies op die groei van C. gattii s.s. MATa en MATα in houtagtige mikrokosms ondersoek. Antifungale vatbaarheidsverskille tussen omgewings- en kliniese isolate was geëvalueer deur die isolate se vatbaarheid tot amfoterisien B (AmB) en flukonasool (FLU) te bepaal. Die patogeniese kriptokokki wat vanuit die PPCT-bome geïsoleer was, was oorwegend C. gattii s.s. ST230 gevolg deur C. neoformans s.s. genotipe AFLP1/VNI ST23. Aangesien ST23 voorheen geïsoleer was vanaf geïnfekteerde pasiënte, is die PPCT-bome moontlik 'n infeksiebron. Groeistudies het aan die lig gebring dat C. gattii s.s. MATa-isolate beter kon meeding met MATα-isolate in mikrokosms wat aangevul is met 'n hoë NH₄Cl-konsentrasie, wat 'n moontlike verklaring bied vir die afwesigheid van MATa in PPCT-bome na die eerste monsternemings datum. Al die omgewingsisolate was meer vatbaar vir AmB as kliniese isolate. In teenstelling daarmee was omgewings C. neoformans s.s. genotipe AFLP1/VNI en C. gattii s.s. isolate minder vatbaar vir FLU as ooreenstemmende kliniese isolate, wat daarop dui dat FLU-weerstandigheid onder omgewingsisolate kan ontwikkel. Verder is temporale variasie in C. gattii s.s. ST230 isolate se FLU-vatbaarheid moontlik gekoppel aan variasies in yster-, NH₄-N- en natriumkonsentrasies binne hul oorspronklike houtagtige habitat. Hierdie studie dui aan dat omgewingsfaktore die getalle en die antifungale vatbaarheid van patogeniese kriptokokki in die Suid- Afrikaanse omgewing kan beïnvloed. | af_ZA |
| dc.description.version | Doctorate | en_ZA |
| dc.embargo.terms | 2022-12-15 | |
| dc.format.extent | xvi, 165 pages : illustrations | en_ZA |
| dc.identifier.uri | http://hdl.handle.net/10019.1/108349 | |
| dc.language.iso | en_ZA | en_ZA |
| dc.publisher | Stellenbosch : Stellenbosch University | en_ZA |
| dc.rights.holder | Stellenbosch University | en_ZA |
| dc.subject.lcsh | Cryptococcus neoformans -- Genetics | en_ZA |
| dc.subject.lcsh | Cryptococcus | en_ZA |
| dc.subject.lcsh | Pathogenic fungi | en_ZA |
| dc.subject.lcsh | Genetic recombination | en_ZA |
| dc.subject.lcsh | Cryptococcus -- Effect of environment on | en_ZA |
| dc.subject.lcsh | Antifungal susceptibility | en_ZA |
| dc.subject.lcsh | Pathogenic fungi -- Molecular aspects | en_ZA |
| dc.subject.name | UCTD | en_ZA |
| dc.title | Molecular characterisation of Cryptococcus neoformans and Cryptococcus gattii present in tree hollows, their antifungal susceptibility, and chemical factors influencing their growth on woody debris | en_ZA |
| dc.type | Thesis | en_ZA |