Chapter 8: Staphylococci: Diseases & Key Features

Distinguished from other groups by their production of catalase, these bacteria are characterized by their grape-like clusters and their ability to thrive as both commensal microbiota and aggressive agents of disease. The primary focus is on Staphylococcus aureus, the most virulent member, which employs a diverse array of virulence factors such as Protein A to evade the immune system, coagulase to facilitate localized clotting, and a suite of exotoxins and superantigens. The clinical impact of S. aureus is broad, encompassing invasive infections like deep-tissue abscesses, necrotizing pneumonia, and potentially fatal septicemia, as well as pure toxinoses including rapid-onset food poisoning, toxic shock syndrome, and scalded skin syndrome. The chapter highlights the critical challenge of antibiotic resistance, specifically the emergence of methicillin-resistant S. aureus (MRSA) driven by the acquisition of the PBP-2a gene. It draws important distinctions between hospital-acquired and community-acquired MRSA, with the latter often exhibiting increased virulence through toxins like Panton-Valentine leukocidin. Laboratory identification techniques are detailed, including the use of mannitol fermentation and gold-pigmented colony observation. Additionally, the text covers coagulase-negative species, specifically Staphylococcus epidermidis, which is notorious for forming protective biofilms on prosthetic implants, and Staphylococcus saprophyticus, a leading cause of urinary tract infections in specific populations. The chapter also notes the discovery of Staphylococcus argenteus, a non-pigmented relative of S. aureus, underscoring the necessity for precise diagnostic differentiation and aggressive treatment strategies to manage these hardy and adaptable microorganisms.