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Title: Characterization of staphylococcal small colony variants and their pathogenic role in biomaterial-related infections with special reference to Staphylococcus epidermidis
Author: Matar, Suzan
ISNI:       0000 0001 3621 0446
Awarding Body: University of Nottingham
Current Institution: University of Nottingham
Date of Award: 2004
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There are many surgical implanted devices in current use and all are prone to biomaterial-related infections (BRI) associated with staphylococcal biofilm formation. BRI are usually associated with S. epidermidis or S. Aureus and are characterized by treatment failure and chronicity resulting in reoperation, removal of the implant, and loss of function or death. Staphylococcal small colony variants (SCVs) may be generated by exposure to sublethal concentrations of antibiotics or nutrient limitation which may occur in biofilms. Although the characteristics of S. aureus SCVs have been well studied, little information on SCVs of S. epidermidis and their potential role in BRI is currently available. This study was designed to investigate the biochemical and phenotypic characteristics of S. epidermidis SCVs to further identify characteristics which may contribute to their ability to cause these increasingly important infections. Exposure to two to four times the gentamicin MIC led to the emergence of stable S. epidermidis SCVs, and the ability to produce SCVs was strain dependent. These variants were isogenic by PFGE and less immunogenic by western blotting, and SDS-PAGE analysis of whole cell preparations and cell wall fractions showed altered protein profiles when compared to wild type strains. S epidermidis SCVs were resistant to aminoglycosides such as amikacin and/or netilmicin and they were thiamine and/or menadione auxotrophs. Chemiluminescence assays showed a decreased ATP content reflecting the deficiency in electron transport systems which results in a growth rate – all characteristics similar to those of S. aureus SCVs. Analysis of virulence factor production indicated that S. epidermidis SCVs showed increased lipolytic and proteolytic activity when compared to those of S. aureus. Some S. epidermidis SCVs showed phase variation in exopolysaccharide production which enabled them to be more adherent to uncoated plastic -a property that may also be important for the later stages of development of biofilms. Invasion assays demonstrated that some S. epidermidis and S. aureus SCVs were internalised by HUVECs by a receptor-mediated mechanism which differed from that of the wild type strains. Interaction of staphylococci with HUVECs induced cytokine production but SCVs stimulated production of IL1, IL-6 and IL-8 at lower concentrations than their related wild type parents in the first 6 hours of co-incubation. SCVs were also less damaging to the HUVEC cell line after 24 hours when compared to wild type strains. This study supports the suggestion that a switch to the S. epidermidis SCV phenotype could be a mechanism exploited by the wild type strains to facilitate their survival inside the host. The chronicity and increased antibiotic resistance associated with BRI could in part, be explained by the characteristics of SCVs identified in this study. In particular the ability to survive intracellularly combined with reduced immunogenicity and resulting decreased cytokine production, may contribute to persistence of infection. Although SCVs are resistant to some antibiotics, surviving intracellularly may further protect staphylococci from other drugs which are unable to enter mammalian cells. Resistance may be further enhanced for some strains in biofilms where enhanced polysaccharide production may also limit antibiotic access.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: WC Communicable diseases