Characterisation of coagulase-negative staphylococci associated with endocarditis
The aim of this thesis was to investigate whether there are specific genotypes and/or phenotypes of coagulase-negative staphylococci with a propensity to cause infective endocarditis and to investigate any identified virulence factors as markers of infection. In this study, strains of endocarditis-related coagulase-negative staphylococci were genotyped by determining their macrorestriction genomic profile using pulsed-field gel electrophoresis. The strains were also investigated for phenotypic characteristics that predisposed the microorganisms to infect heart valves. By comparing coagulase-negative staphylococcal strains recovered from endocarditis patients with isolates from other significant infections (prosthetic device-related osteomyelitis and catheter-associated sepsis), no specific genotype or phenotype with a predilection to cause endocarditis was identified. However, the majority of the endocarditis-associated and other infection strains expressed the potential virulence factors lipase and esterase. Another approach to the investigation of virulence determinants used patient's serum to screen a Staphylococcus epidermidis NCTC 11047 genomic DNA library for cellular and secreted staphylococcal products that were expressed in vivo. The characterisation of two clones, which reacted with serum collected from a S. epidermidis-related endocarditis patient identified a staphylococcal pyruvate dehydrogenase complex E2 subunit and a novel secreted protein with homology to a Staphylococcus aureus staphyloxanthin biosynthesis protein and a secreted protein of unknown function described in Staphylococcus carnosus. Investigation of the secreted protein previously undetected in S. epidermidis, termed staphylococcal secretory antigen (SsaA), identified a potential marker of S. epidermidis-related endocarditis.