Doctoral Degrees (Medical Microbiology)

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Browsing Doctoral Degrees (Medical Microbiology) by browse.metadata.advisor "Hoek, Kim Gilberte Pauline"

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    A phenotypic and genotypic characterisation of strain types, virulence factors and agr groups of colonising Staphylococcus aureus associated with bloodstream infection
    (Stellenbosch : Stellenbosch University, 2015-03) Karayem, Karayem; Hoek, Kim Gilberte Pauline; Whitelaw, Andrew Christopher; Stellenbosch University. Faculty of Medicine and Health Sciences. Dept. of Pathology: Medical Microbiology
    ENGLISH ABSTRACT : Several studies investigating the molecular characteristics of Staphylococcus aureus have been conducted worldwide, however, in South Africa, most of these have focused on Methicillinresistant S. aureus (MRSA). This study investigated the phenotypic and genotypic characteristics of isolates of S. aureus collected from the blood and nasal cavity of patients admitted to Tygerberg Hospital, South Africa. Investigations included determining the association between blood and nasal isolates, describing the molecular epidemiology of the population, determining the prevalence of various virulence factor genes among the different clones and descibing the accessory gene regulator (agr) functionality of S. aureus clones. Pulsed-field gel electrophoresis (PFGE), performed on 208 blood and nasal isolates from 162 patients with S. aureus bacteraemia, showed that 93 (57.4%) of the patients were colonised with the same strain type (p =0.061). MRSA was significantly associated with endogenous bacteraemia (same strain obtained from the blood and the nose) (p = 0.042). Molecular typing of the 208 blood and nasal isolates (43.3% MRSA) revealed that the majority of strains were ST239-t37-agr I (25.5%) which harboured different SCCmec types including SCCmec type III and a potentially novel type presumed to consist of ccrC/Class A mec. ST612-MRSA-IV was the second most predominant clone (10.2%). Other MRSA clones included ST5-t045 with a potentially novel variant of SCCmec type I consisting of ccrA1B1 and a ccrC/Class B mec; and ST461-MRSA-IV, reported for the first time in South Africa. All 18 (8.7%) pvl-positive isolates were MSSA except one isolate (ST612-MRSA-IV). The identification of novel MRSA clones (ST641-MRSA-IV), MSSA STs (ST2122, ST2126), and the potentially novel SCCmec type and type I variant suggest the local emergence of new clones. Twenty-one isolates (representing nine clonal complexes (CCs)) previously characterised by Multi-locus Sequence Typing (MLST) were analysed for the prevalence of 38 virulence factor genes. There was an association between different enterotoxin gene cluster (egc) gene combinations and CC5, CC22, CC30, and CC45. Both CC15 and CC97 were negative for Superantigen (SAg) genes. The intracellular adhesion locus A (icaA) gene was common (90.4%) and detected in all CCs (except CC30) and the enterotoxin I (sei) gene was significantly more widespread in MRSA isolates (77.8% in MRSA; 25.0% MSSA; p = 0.03). Accessory gene regulator dysfunction was significantly higher amongst MRSA than MSSA isolates and was more commonly associated with ST36-MRSA-II, ST239-MRSA-III and ST239-MRSA- ccrC/Class A mec. Shifting of agr in the same host was not common. Key findings in this study relate to the likely emergence of populations at Tygerberg Hospital, as evidenced by novel STs and potentially novel SCCmec types. The identification of a circulating clone within the burns unit both illustrates the potential for organisms to spread within the hospital, as well as reinforcing the value of molecular typing for infection control purposes. The association of different agr types, agr functionality, and virulence factors with typing data has shown results consistent with other studies, as well as some unusual results. However, the clinical relevance of these associations is not yet well understood, and should form the basis of further research.