SYSTEMIC BACTERIOLOGY
Staphylococci
General Characteristics:
• Ubiquitous organisms, medically the most important group and cause major
problems in hospitals in compromised patients with debilitating diseases,
extensive surgery, immunosuppression, etc.,
• May be part of the normal flora of carriers in the anterior nares, perineum, GIT,
skin, etc.
Physiology and structure:
• Gram-positive cocci arranged in grape-like clusters, non-motile, non-sporing,
app Jim diameter.
• Colonies are sharply defined, round, and convex, and grow readily on ordinary
media.
• Aerobe and facultative anaerobe
• On mar conkeys agar – very small and pink colonies due to lactose
fermentation
• Catalase positive, oxidase negative, ferment glucose and mannitol, producing
add but no gas.
• Coagulase (‘clumping factor) positive
• Protein A (useful for identification)
• Capsule
• Species-specific teichoic acid.
Epidemiology
• Normal flora on human skin and mucosal surfaces.
• Person-to-person spread through direct contact or exposure to contaminated
fomites.
• Risk factors include the presence of a foreign body, previous surgical
procedures, and the use of antibiotics that suppress the normal microbial
flora.
• Patients at risk for specific diseases include menstruating women (TSS),
infants (scalded skin syndrome), and children with poor oral hygiene
(impetigo) and intravascular catheters (bacteremia).
Clinical manifestations
• Local or contiguous infections:
o Skin – Folliculitis, boils, carbuncle, impetigo, furuncle
o Eye – styes, conjunctivitis
