Pathogenic Bacteria

Gram-positive cocci
Two pathogenic bacteria are G+ve B: Staphylococci and Streptococci.
1. Staphylococci:
I- General features:
1. Staphylococci are G+ve cocci (spherical or grapes shape).
2. Are non motile, non capsulated, non spore forming.
3. Staphylococci are oxidase negative & catalase positive which one feature that distinguishes from Streptococci.
4. Staphylococci are part of normal flora of human skin, nose, respiratory and gastrointestinal tracts. Are also fond in air, dust and other in human environments.
5. Staphylococcus has at least 30 spp., three spp of clinical importance are Staphylococcus aureus (S. pyogenes), S. epidermidis (S. albus), S. saprophyticus (S. citrus).
II- Transmission:
S. aureus is major pathogenic spp for human. Transmission of bacteria from human to human by inhalation of respiratory secretion or consumption of contaminated food.
III- Pathogencity & clinical features:
A: Pathogenesis
Pathogenic virulence factors are enable an organism to produce disease. The clinical outcome of an infection depends on the virulence of the pathogen and the opposing effectiveness of the host defense mechanisms.
Pathogenesis of S. aureus depends on the combined actions of several virulence factors, so it is difficult to determine precisely the role of any given factor. S. aureus expresses many potential virulence factors:
? Cell wall virulence factors (Protein A and protein F).
? Cytolytic exotoxins or hemolysins (?, ?, ?, ? toxin).
? Superantigen exotoxins: {Enterotoxins (six major antigenic types: A, B, C, D, E, and G) and Toxic shock syndrome toxin (TSST-1)}