How Staphylococcus Aureus in Blood can cause Fatal Infections

Abstract:

The presence of bacteria in the blood is called bacteraemia. Blood is a sterile medium. Therefore there are not any bacteria in the blood under normal circumstances. So, presence of any organism can cause various diseases. Transient bacteraemia ca

The presence of bacteria in the blood is called bacteraemia. Blood is a sterile medium. Therefore there are not any bacteria in the blood under normal circumstances. So, presence of any organism can cause various diseases. Transient bacteraemia can occur in normal individuals after defecation and after brushing teeth. Usually these bacteria are removed from the blood stream by the spleen and liver, but sometimes, some of these bacteria get the chance to stay in organs like the heart, and in the ends of growing bones, and thereby avoid reaching the spleen and liver.

Staphylococcus aureus is one such bacterium that can stay in these organs, and cause serious diseases, which could be fatal if untreated. Infective endocarditis is a potentially fatal disease caused by staphylococcus aureus. It is responsible for 25% - 66.7% of infective endocarditis cases occurring world wide.
Intravenous drug users are at a high risk of developing infective endocarditis, because a lot of Staphylococcus aureus organisms enter the blood when they inject drugs into their body. These bacteria enter the blood stream and establish themselves in the damaged heart valves (especially in prostatic heart valves). They can produce adhesins, dextran and fibronecting binding proteins, which help them to attach to the heart valves.
The organism starts multiplying after attaching to the wall. This leads to attraction of more platelets and deposition of fibrin. So finally the organisms are covered with platelets. These growths are called vegetations and can be of several centimeters in size. Vegetations help organisms to hide from the body’s surveillance system. It takes about five weeks for this process to occur. These vegetations act as foci that continuously introduce bacteria to the blood stream. So these bacteria can spread to various organs and cause diseases in other organs too.

Staphylococcal infective endocarditis could be dangerous in several ways.  The local damage done to the heart valves can give rise to various cardiac problems, which can be life threatening. Sometimes the vegetations can dislodge from their site of origin and travel to different organs in the body. These emboli are septic and can cause serious illnesses throughout the body. There are also immune complexes formations in response to the presence of micro-organisms in the blood. Immune complexes are composed of microorganisms and antibodies and complement proteins. These immune complexes circulate in the blood. They can deposit in organs like kidneys and cause serious problems like kidney failure, which is a life threatening disease.

The patients with infective endocarditis may initially present with pyrexia of unknown origin. Heart murmurs are always detected in patients with this disease. Apart from those main symptoms, the patient may have loss of weight, loss of appetite nausea, vomiting, malaise and night sweats. On examination the doctor may find Osler nodes, splinter haemorrhages in nail beds and petechial lesions in the skin. Earlier this was invariably a fatal disease.  Now with the discovery of antibiotics, staphylococcus aureus infections can be treated successfully if identified earlier.
The disease is diagnosed by doing a blood culture. The condition is treated with antibiotics that are powerful enough to eradicate the organisms from the blood. This may take several weeks. Treating infective endocarditis caused by staphylococcus aureus is very hard, because of the emergence of antibiotics resistance strains, especially when the organism is hospital acquired. Therefore beta lactamase stable penicillin such as cloxacilline is given along with an aminoglycoside, rifampicin or fusidic acid. Vancomycin or teicoplanin is given if the patient is allergic to penicillin. They are also given to treat methicillin resistant staphylococci.