gram positive cocci

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gram positive cocci

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Slide 1

    Streptococcus pyogenes
    Streptococcus pyogenes is a gram positive cocci that causes group A streptococcal infections. Strep pyogenes typically produces large zones of beta-hemolysis and can be distinguished from other streptococcal organisms because it is catalase negative and bacitracin sensitive.  It can cause a variety of disease including pyogenic infections of the pharynx and skin.  In the pharynx, it is the classic cause of bacterial strep throat.   In the skin, it can cause impetigo and cellulitis.  This bacteria also causes several diseases mediated by toxins including scarlet fever and toxic shock like syndrome.  Two of the major complications of group A strep infections are mediated immunologic mechanisms, including rheumatic fever caused by the development of antibodies to M protein and acute glomerulonephritis.

Slide 2

    Streptococcus pneumoniae is a Gram positive “lancet-shaped” diplococci that is a major cause of pneumonia, meningitis, and otitis media. Characteristically, this bacteria is alpha hemolytic, which causes dark green colonies on blood agar. It is catalase dark green colonies on blood agar, which allows it to be distinguished from catalase positive Staph aureus. Strep pneumonia can be differentiated from streptococcus viridans using an optochin test. Strep pneumoniae is optochin sensitive while Strep viridans is optochin negative. The bacterium can also be differentiated from Strep viridans because Streptococcus pneumoniae is bile soluble while Strep viridans is not. This organism is encapsulated with a positive quellung reaction. The capsule acts as a virulence factor for the organism. 
    Streptococcus pneumoniae features

Slide 3

    Streptococcus pneumoniae, , is a gram-positive diplococci bacteria. Classically, patients can complain of coughing up rusty sputum if they have pneumonia, , which can help with clinical diagnosis. Patients who have had splenectomies are at risk forsepsis,. Those who have sickle cell anemia, especially children, are also at risk for sepsis, . Other manifestations of strep pneumo can be remembered by the mnemonic MOPS, This bacteria is also one of the most common causes of bacterial meningitis in adults, , and is the most common bacterial pathogen to cause otitis media,  in the ear. Strep pneumonia is a very common cause of pneumonia, , and can also cause acute bacterial sinusitis, 
    Streptococcus pneumoniae

Slide 4

    Staphylococcus epidermidis
    Staphylococcus epidermidis is a Gram positive cocci that is part of the human skin flora. This organism is usually not pathogenic but can cause infection in patients with compromised immune systems. Staphylococcus epidermidis is also a large concern with patients with catheters or other prosthetic devices because it is known to cause adherent biofilms that grow on the devices. Characteristically, it is a catalase positive, coagulase negative bacterium. Staphylococcus epidermidis can be differentiated from staphylococcus saprophyticus, which is also catalase positive, coagulase negative, but sensitivity to novobiocin. Because this organism is a component of normal skin flora, it is a common contaminate of blood cultures. 

Slide 5

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