Staphylococcus aureus - Pathogenicity

Pathogenicity 

Staphylococcus aureus produces- Infections & Intoxications

Infections- Cocci gain access to damaged skin, mucosal or tissue site -Colonize by adhering to cells or extracellular matrix -Evade the host defense mechanisms and multiply - Liberating toxins, – Stimulate inflammation - Cause tissue damage

Intoxications-The diseases are caused by bacterial toxins – produced either in the host or preformed in vitro

1.    STAPHYLOCOCCAL INFECTIONS

§  Most common of bacterial infections- range from trivial to fatal

§  Characterised by localized pyrogenic lesions (not spreading like streptococcal lesions)

§  Common Staphylococcal infections are:

a)  Skin and soft tissue infection

 Folliculitis – Furuncle (boil) – Abscess (breast abscess)- Carbuncle – Impetigo – Paronychia- less often, cellulitis- Wound infection

·         Folliculitis - It is inflammation of the hair follicles; A small red bump or pimple develops at infection sites of hair follicle

·         Sty: A sty is folliculitis affecting one or more hair follicles on the edge of the upper or lower eyelid.

·         Furuncle/boils: If infection extends from follicle to neighbour tissue, Furuncle. Thus it is deep seated infection, originating from folliculitis; Causes redness, swelling, severe pain- Commonly found on the neck, armpit and groin regions- common name- "boils"

·         Carbuncle: Carbuncle is an aggregation of infected furuncles; Carbuncles may form large abscesses; It is a large area of redness, swelling and pain, with pus.

·         Impetigo:  superficial skin infection, usually produces blisters or sores on the face, neck, hands, and diaper area - initially watery, then pus containing and finally honey coloured crust

b) Musculoskeletal infection

·         Osteomyelitis – inflammation of bone

·         Septic arthritis – knee, shoulder, hip

·         Pyomyositis – skeletal muscle infection

·         Bursitis (bursa- fluid filled sacs in the joints)

c) Respiratory

·         Tonsilitis

·         Pharyngitis

·         Sinusitis

·         Otitis – ear infection

·         Bronchopneumonia

·         Lung abscess

·         Empyema – pus in pleural cavity (lungs)

d) Central nervous system

·         Abscess

·         Meningitis

·         Intracranial thrombophlebitis – blood clot in cerebral vein

e) Endovascular

·         Bacteremia – bacteria in blood

·         Septicemia – blood stream infection

·         Pyemia – pus forming bacteria in blood stream (from an abscess)

·         Endocarditis – inflammation of heart valve

f) Urinary

·         Urinary tract infection – routine infections, also in association with local instrumentation, implants or diabetes

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