slals 8 The Suapbylececds bolation and edenticaion 3. Why is the coagulase test
ID: 269986 • Letter: S
Question
slals 8 The Suapbylececds bolation and edenticaion 3. Why is the coagulase test considered to be the definitive test for S aures? 4. What is the role of coagulase in the pathogenesis of S. awreus? 5, what is the role of ?-toxin in the pathogenesis of aamas? 6. What are health-care-acquired infections? 7. Why are the staphylococci among the leading causes of nosocomial infections? 8. Why are staphylococcal infections becoming increasingly difficult to treat? 9. Why might hospital patients be tested for nasal carriage of S, aureus? 10. Describe results from a coagulase, DNase, and novobiocin test that would suggest a mixed culture was used for the tests, as opposed to a pure culture.Explanation / Answer
3) Coagulase is an enzyme, which brings about clotting of human or rabbit plasma. It acts with a coagulase reacting factor(CRF) present in plasma, binding to prothrombin and converting fibrinogen to fibrin. Coagulase is tightly bound to the surface of the bacterium S. aureus and S. aureus is generally coagulase-positive, meaning that a positive coagulase test would indicate the presence of S. aureus. Other species are usually coagulase negative.
4) Coagulase is an enzyme, which brings about clotting of human or rabbit plasma. It acts with a coagulase reacting factor(CRF) present in plasma, binding to prothrombin and converting fibrinogen to fibrin. Coagulase enzyme helps it bind fibrin and form walled off abscesses, a major feature of S. aureus infection. S. aureus will produce coagulase to surround itself with the coat of clotted blood proteins, which protects the bacterium against host defences.
5) Alpha hemolysin or alpha toxin is one of the most important toxins produced by staphylococcus. It lyses erythrocytes, which will release nutrients and growth factors which in turn aid the multiplication of the bacteria in the blood stream. It is also leucocidal, cytotoxic,dermonecrotic, neurotoxic and lethal. It is lethal to macrophages, lysosomes, muscle tissue, renal cortex and circulatory system.
6) Health-care acquired infections are usually called nosocomial infections, which can be acquired from a hospital or healthcare setting. They are caused by viral, bacterial, and fungal pathogens; the most common types are bloodstream infection (BSI), pneumonia (eg, ventilator-associated pneumonia [VAP]), urinary tract infection (UTI), and surgical site infection (SSI).
7) Staphylococcus is an opportunistic pathogen, it is usually present on the skin of many healthy people, but can cause a disease in people in a hospital facility for a long time, having a weakened immune system, having an open cut or sore, burn or trauma patients etc. Hospital acquired infections are usually caused by MRSA or methicillin resistant Staphylococcus aures. They are resistant to many beta lactma antibiotics and other anitmicrobial agents. Hence these strains can cause post-operative wound infections and other hospital cross-infections.
8) As explained in the earlier answer, many staphylococci have now garnered resistance against a number of antibiotics like beta lactams such as penicillin which is routinely used in hospitals, and to some other antimicrobial agents as well. MRSA is a common causative agent, and now the cause of concern is community acquired MRSA strains(CA-MRSA), which was earlier restricted to hospital setting(HA-MRSA)
9) Staph germs are mostly spread by skin-to-skin contact. Up to 50% of a given population could asymptomatically carry Staphylococcus aureus in their nares, thereby serving as a source for contact transmissions and endogenous infections. Staphylococcus aureus causes purulent bacterial infections with a considerable number of life-threatening complications and thus, is a serious cost factor in public health. Hence hospital patients are tested for nasal carriage of S.aureus.
10) Novobiocin test is used to differentiate coagulase-negative staphylococci (CONS) and presumptively identify the isolate as Staphylococcus saprophyticus (novobiocin resistant). In a mixed culture of S. aureus and S. saprophyticus would produce positive results for coagulase and DNase and be resistant to novobiocin,whereas S. epidermidis is novobiocin-sensitive. A pure cultures of S. aureus will be positive for coagulase and DNase but sensitive to novobiocin. A pure culture of S. saprophyticus will be negative for coagulase and DNase but resistant to novobiocin. Staphylococcus epidermidis is sensitive to novobiocin, providing an important test to distinguish it from Staphylococcus saprophyticus, which is coagulase-negative, as well, but novobiocin-resistant.
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