Staphylococci (Ch 18) PDF

Read Quiz Comprehensive Overview of Staphylococcal Infections and Virulence Introduction Staphylococci are a genus of Gram-positive bacteria that are known to cause a variety of human infections. This c...

Read Quiz Comprehensive Overview of Staphylococcal Infections and Virulence Introduction Staphylococci are a genus of Gram-positive bacteria that are known to cause a variety of human infections. This content piece synthesizes various perspectives and detailed academic insights into the mechanisms, pathogenesis, virulence factors, and clinical manifestations of Staphylococcal infections, primarily focusing on Staphylococcus aureus. Physiology and Structure of Staphylococcus Staphylococci are facultative anaerobic organisms ubiquitously found on the skin and mucous membranes of humans and other animals. Understanding their physiological structure is crucial for grasping their pathogenic effects: Cell Wall Components Teichoic Acids: Species-specific and make up to 30-50% of dry weight. Poor immunogens, contribute to the rigidity and pathogenicity of the cell wall. Capsule: Composed of polysaccharides. Clinically significant serotypes are 5 and 8. https://www.studocu.com/en-us/notes 12/4/24, 6 59 PM Page 1 of 5 :  Capsule-deficient mutants are more efficiently phagocytosed by neutrophils and show decreased virulence. Protein A (Spa) Functions: Immune evasion by binding the Fc region of IgG, preventing proper binding to neutrophil Fc receptors. Acts as a B-cell superantigen, binding IgM on B-cells, causing apoptosis. Clinical Relevance: A virulence factor in septic arthritis and murine pneumonia. Enzymes Virulence Enzymes: Staphylococcal enzymes like β-lactamase, catalase, coagulase, V8 protease, and staphopain degrade host components, enhancing infection and providing nutrients for bacteria. Biofilms: S. epidermidis and other coagulase-negative staphylococci are less toxigenic but proficient biofilm formers, leading to chronic infections. Virulence Factors Staphylococcal pathogenicity involves multi-factorial mechanisms, wherein timely expression of various virulence factors is essential for causing disease: Toxins Cytotoxins: Alpha-toxin (Hla): Pore-forming, toxic to various cell types. Beta-toxin: Sphingomyelinase C, specific for sphingomyelin. https://www.studocu.com/en-us/notes 12/4/24, 6 59 PM Page 2 of 5 :  Delta-toxin: Membrane-disrupting, nonspecific. Gamma-toxin and Panton-Valentine Leukocidin (PVL): Bi- component toxins, beta-barrel structure. Exfoliative Toxins: ETA and ETB: Serine proteases causing Staphylococcal Scalded Skin Syndrome (SSSS) by degrading desmosomes. Superantigens: Toxic Shock Syndrome Toxin (TSST-1): Hyperstimulates the immune system by binding to MHC II molecules and T cell receptors, causing TSS. Enterotoxins: Causes food poisoning, heat-stable, encoded on various SaPIs. Regulation of Virulence Factors Temporal Expression In vitro studies have identified a characteristic temporal pattern of cell- surface and extracellular virulence factors: During exponential growth: Expression of cell-surface factors is prioritized. Post-exponential phase: Repression of cell-surface genes and activation of extracellular toxin genes. Agr System The accessory gene regulator (agr) system uses quorum sensing to regulate the expression of virulence factors based on cell density: At low cell density: Surface proteins are expressed, and toxins are downregulated. At high cell density: Surface proteins are downregulated, and toxins are expressed. https://www.studocu.com/en-us/notes 12/4/24, 6 59 PM Page 3 of 5 :  Clinical Manifestations of Staphylococcal Infections Skin Infections Impetigo, folliculitis, furuncles, carbuncles, and wound infections are common forms. Invasive Infections Bacteremia and Endocarditis: S. aureus is a common cause, with high mortality, especially in intravenous drug users. Pneumonia and Empyema: Caused by inhalation or hematogenous spread, leading to severe conditions like necrotizing pneumonia. Osteomyelitis and Septic Arthritis: S. aureus is the predominant cause, requiring immediate treatment. Toxin-Mediated Syndromes Staphylococcal Scalded Skin Syndrome (SSSS): Primarily affects neonates and young children, leading to desquamation. Staphylococcal Food Poisoning: Caused by ingestion of enterotoxin- laden foods, leading to gastroenteritis. Toxic Shock Syndrome: Systemic toxemia caused by TSST-1, often linked to tampon use in menstruating women. Conclusion Staphylococcal infections represent a significant challenge in clinical microbiology due to their diverse disease manifestations and evolving antibiotic resistance. Understanding their virulence mechanisms and clinical impact is crucial for developing effective treatments and preventive measures. This in-depth study provides a comprehensive understanding of https://www.studocu.com/en-us/notes 12/4/24, 6 59 PM Page 4 of 5 :  the multifaceted nature of staphylococcal pathogenesis and highlights key areas for ongoing research and clinical focus. For further details, refer to the specific sections on each pathogen's properties, toxins, regulatory systems, and clinical presentations as outlined in the synthesized document sources. https://www.studocu.com/en-us/notes 12/4/24, 6 59 PM Page 5 of 5 :