Transcript Lecture 5
Case Study Streptococcus pyogenes Dr Olga Perovic, Department of Clinical Microbiology & Infectious Diseases, NHLS,WITS, 2007 Dr Olga Perovic 1 Case studies First child present with history: Five years old child complains of severe pain in his throat. He had a fever as well. Dr Olga Perovic 2 Case studies Present history of second child Six years old child presented with low blood pressure, dry skin which started pealing early in the morning. Few days ago presented with impetigo – purulent skin infection. Dr Olga Perovic 3 Case studies Present history of third child 18 years old matric student presented with low grade fever, hart murmur, low grade fever. From past medical history, he had tonsillitis as child, commonly. Dr Olga Perovic 4 What is common amongst these three cases? One organism: Streptococcus pyogenes, Was brought up to attention even in 1840. Dr Olga Perovic 5 When history started? In the 1840s, Dr. Ignaz Semmelweis brought up a lifethreatening pelvic infection of women immediately after childbirth. So “puerperal” means “to bring out a child.” This infection was due to group A streptococci. Dr Olga Perovic 6 Streptococcus pyogenes Streptococcus pyogenes (Group A streptococcus)-GAS is a Gram-positive coccus that occurs in chains or in pairs. The organism requires enriched medium containing blood to grow. Dr Olga Perovic 7 The cell envelope of a Group A streptococcus Dr Olga Perovic 8 Why this organism causes such dramatic and different diseases? Because it can be harmless and innocent (can be colonizer), but suddenly become invasive and dangerously deadly. Can mimic human heart antigen and produce antibodies against it – rheumatic heart disease. Can produce toxins that causes such rapid onset of systemic manifestation –toxic shock syndrome in news “super bug” or “flesh eating bacteria”. Dr Olga Perovic 9 How does it? GAS causes localized infection such as pharyngitis, skin infections. which can be spread in the host while evading phagocytosis and confusing the immune system. GAS penetrates to the tissues causing suppurative infections which can be explained by evading phagocytosis (got an capsule) and confusing immune system. Produces enzymes and toxins – pyrogenic . Non suppurative poststreptococcal sequelae: rheumatic fever: mimic human heart antigen (Mprotein) and trigger production of antibodies against heart tissue (hypersensitivity type 2). Dr Olga Perovic 10 GAS toxin is Super antigen These toxins act as superantigens. As antigens, they do not requiring processing by antigen presenting cells. They stimulate T cells by binding class II MHC molecules directly and nonspecifically. They stimulate massive cytokine release. Dr Olga Perovic 11 Epidemiology Streptococcus pyogenes is one of the most frequent pathogens of humans. 5-15% of normal individuals harbor the organism, usually in the respiratory tract, without signs of disease. As normal flora, S. pyogenes can infect when host defenses are compromised. Streptococcus pyogenes infections, prompting descriptions of "flesh eating bacteria" in the news media. Dr Olga Perovic 12 Diagnosis Diagnosis is based on cultures from clinical specimens. Acute glomerulonephritis and acute rheumatic fever are identified by antistreptococcal antibody titers. In addition, acute rheumatic fever is diagnosed by clinical criteria. Dr Olga Perovic 13 Treatment and prevention Penicillin is still effective in treatment of Group A streptococcal disease. It is important to identify and treat Group A streptococcal infections in order to prevent sequelae. No effective vaccine has been produced, but specific M-protein vaccines are being tested. Dr Olga Perovic 14