Dr.Qurat-Ul-Ain Senior Demonstrator Microbiology, KEMU, Lahore Staphylococci Dr.Qurat-Ul-Ain Senior Demonstrator Microbiology, KEMU, Lahore

A) Exogenous: patients or carriers PATHOGENICITY: Source of infection: A) Exogenous: patients or carriers B) Endogenous: From colonized site Mode of transmission: A) Contact: direct or indirect( through fomites) B) Inhalation of air borne droplets

Disease: Diseases produced by Staphylococcus aureus are studied under 2 groups: A) Infections B) Intoxications

A) INFECTIONS: Mechanism of pathogenesis: 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 Cause tissue damage

B) INTOXICATIOINS: The disease is caused by the bacterial exotoxins, which are produced either in the infected host or preformed in vitro. There are 3 types- Food poisoning Toxic shock syndrome Staphylococcal scalded skin syndrome

Pemphigus neonatorum Ritter’s disease Toxic epidermal necrolysis Bullous impetigo

Types of SSSS: In new born Ritter’s disease Pemphigus neonatorum Severe form Milder form In new born Ritter’s disease Pemphigus neonatorum In older patients Toxic epidermal Bullous necrolysis impetigo

Superantigens (SAgs) cause non-specific activation of T-cells resulting in polyclonal T cell activation  and massive cytokine release. The most important of which is Interferon gamma which activates the macrophages. The activated macrophages over-produce proinflammatory cytokines such as IL-1, IL-6 and TNF-alpha. In normal circumstances TNF- alpha is released locally in low levels and helps the immune system defeat pathogens. However, when it is systemically released in the blood and in high levels (due to mass T-cell activation resulting from the SAg binding), it can cause severe and life-threatening symptoms, including shock and multiple organ failure.  

2 types of TSSS known: i) Menstrual TSSS: Here colonization of S.aureus occurs in the vagina of menstruating woman who uses highly absorbent vaginal tampons. ii) Non menstrual TSSS: Here colonization of S.aureus occurs in other sites like surgical wound.

1) Food poisoning: Enterotoxin is responsible for manifestations of staphylococcal food poisoning. Eight types of enterotoxin are currently known, named A, B, C1-3, D, E, and H. It usually occurs when preformed toxin is ingested with contaminated food. The toxin acts directly on the autonomic nervous system to cause the illness, rather than gut mucosa.

The common food items responsible are - milk and milk products, meat, fish and ice cream. Source of infection- food handler who is a carrier. Incubation period- 2 to 6 hours. Clinical symptoms- nausea, vomiting and diarrhoea. The illness is usually self limiting, with recovery in a day or so.

Mechanism Of Action: The action of enterotoxins leads to increased chloride ion permeability of the apical membrane of intestinal mucosal cells. These membrane pores are activated either by increased cAMP or by increased calcium ion concentration intracellularly. The pore formation has a direct effect on the osmolarity of the luminal contents of the intestines. Increased chloride permeability leads to leakage into the lumen followed by sodium and water movement. This leads to a secretory diarrhea within a few hours of ingesting enterotoxin.

Staphylococcus saprophiticus It causes urinary tract infection in young female. Coagulase Negative Staphylococci (it is novobiocin resistant) The commonest coagulase negative is: Staph. epidermidis Pathogenesis: They produce very small amounts of toxins. Pathogenesis is mainly due to production of (slime) which consists of: a. Polysaccharide b. Techoic acid enhanced by presence of fibrinogen. This makes them sticky on biomaterial like catheters. Sticky material called is Biofilm.

1. Endocarditis in artificial valves “shunts”. They Cause: 1. Endocarditis in artificial valves “shunts”. 2. Infections of spitz holter valves connecting brain ventricle with jugular vein 3. Infection of cannulae 4. Infection of Intravenous catheters 5. Infections of prosthesis e.g. Artificial valves (heart) Orthopaedic fixing nails 6. Infection in premature babies (Bacteriaemia) 7. Infection in Oncology patients 8. Staphylococcus saprophyticus causes urinary infection in young females

Treatment of Coagulase Negative Staphylococci “Staphylococcus epidermidis” and others : Depends on testing antibiotics sensitivity on the isolates But Vancomycin is the drug of choice for severe serious infection