B1-Staphylococcus.pdf

Staphylococcus  General characteristics Gram positive spherical cells arranged in grape-like clusters normally grow on skin and mucous membrane non-motile non spore-forming  General characteristics ▪facultative anaerobes ▪active fermenters ▪produce pigment hence colonies appear...

Staphylococcus  General characteristics Gram positive spherical cells arranged in grape-like clusters normally grow on skin and mucous membrane non-motile non spore-forming  General characteristics ▪facultative anaerobes ▪active fermenters ▪produce pigment hence colonies appears white to deep yellow Easily acquire antibiotic resistance Catalase producers (Streptococci are catalase negative)  Virulence Factors Cell wall Protein A – antiphagocytic Fibronectin-binding protein (PnBP) – promote binding Cytolytic exotoxins – hemolysin Superantigen exotoxins – enhances T lymphocyte response Enterotoxins Toxic shock syndrome toxin Exfoliative toxin – causes scalded skin syndrome  Virulence factors Coagulase - Clots plasma Catalase - Converts hydrogen peroxide into water and oxygen; vs. catalase negative Streptococci Others: hyaluronidase or spreading factor, staphylokinase (fibrinolysis), lipases, nucleases Types of skin lesions Macules – flat lesions characterized by change in color of the affected area Papules – raised lesion, solid in consistency, less than 5 mm diameter Plaques – flat with elevated surface, more than 5 mm diameter Nodules – rounded raised lesions, more than 5 mm diameter Urticaria (wheals and hives) – annular or ring-like papules or plaques with pinkish color Vesicles – circumscribed fluid-filled lesions, less than 5 mm diameter Macule Papule Nodule Plaque Urticaria Vesicle Types of skin lesions Bullae - circumscribed fluid-filled lesions, more than 5 mm diameter Pustules – circumscribed, exudate-filled lesions Purpura – skin lesions due to bleeding into the skin – Petechiae – less than 3 mm diameter – Ecchymosis - more than 3 mm diameter Ulcer – crater-like lesion that may involve the deeper layers of the epidermis and dermis Eschar – necrotic ulcer covered with a blackened scab or crust Bullae Pustule Eschar Ulcer Purpura Staphylococcus aureus Pathology 1. Localized skin infections ▪ Small, superficial abscess involving hair follicles, sweat or sebaceous gland – STY ▪ Subcutaneous abscess around foreign body, splinters – FURUNCLES, BOILS ▪ Deep, multiloculated skin infection that can lead to bacteremia and require debridement – CARBUNCLE ▪ Localized, superficial, spreading crusty skin lesion - IMPETIGO ▪ Staphylococcal scalded skin syndrome/ Ritter’s disease - in newborns and children - Starts with perioral erythema all over the body for 2 days - Nikolsky sign – displacement of the skin even with slight pressure - Blister formation then desquamation (due to exfoliative toxin) Sty Boils Impetigo  Pathology – Localized skin infections can metastasize due to trauma and can lead to Osteomyelitis Arthritis Acute endocarditis – usually associated with contaminated needles Septicemia Pneumonia – can lead to empyema (lung abscess)  Pathology 2. Toxic shock syndrome Common in menstruating women with tampons – 1970s S/S: Fever, vomiting, diarrhea, hypotension, rash, multiple organ system involvement 3. Staphylococcal gastroenteritis S/S: nausea, vomiting, diarrhea, no fever Short incubation period – 30 mins to 8 hrs COAGULASE NEGATIVE STAPHYLOCOCCUS Staphylococcus epidermidis ocauses infection on prosthetic devices Staphylococcus saprophyticus ocauses urinary tract infections  Epidemiology Ubiquitous Mode of transmission: droplets, lesion drainage Control:cleanliness, hygiene and aseptic management of lesions ▪ aerosols ▪ ultraviolet irradiation ▪ antiseptics