MICR J210 1st Edition Lecture 14Outline of Last Lecture I. StaphylococciII. General characteristics of StaphIII. Pathogenicity of StaphIV. Staphylococcus AureusV. Skin Infections caused by Staphylococcus Aureus VI. Staph Food PoisoningVII. Systemic Staphylococcus InfectionsVIII. General Immunity to StaphIX. Treatment of StaphX. Nosocomial and Iatrogenic InfectionsXI. Staph EpidermisXII. Reducing Nosocomial InfectionsXIII. Laboratory Tests for StaphXIV. Staphylococcus saprophyticusXV. Streptococcus pneumoniaXVI. Streptococcus FaecalisOutline of Current Lecture I. StreptococciThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.II. Streptococcus pyogenesIII. Streptococcus agalactiaeIV. Viridans streptococcusV. Streptococcus pneumoniaeVI. ComplianceCurrent LectureStreptococci Gram-positive cocci,  Facultative anaerobesThey can grow both in the presence and absence of oxygen More than 30 species Arranged in pairs or chains Often categorized based on Lancefield classificationDivided into serotypes based on bacteria’s surface antigensLancefield groups A and B include the significant human pathogens Also classified by patterns of hemolysis on blood agarα (alpha) – incomplete hemolysisIncomplete digestion of hemoglobin creates a “shadow” on the agar plateβ (beta) – complete hemolysisCompletely digestion of hemoglobin creates halo around the colonies in the plane of the mediumMost cases of staphγ (gamma) – no hemolysisColonies sit on top of the agar and they are not involved with hemoglobinStreptococcus pyogenes Group A Strep (Lancefield classification)Gram positiveCatalase negativeβ-hemolyticPathogenic strains often form capsulesBacitracin-sensitive Virulence determinants for Group A StrepCapsule Composed of hyaluronic acid Similar to host connective tissue component (“camouflages” bacteria) Helps resist phagocytosis by PMNM protein Fimbrial antigen – most important virulence factor Mediates attachment (Adhesin) Attachment to the pharynx (back of the throat) Inactivates C3b (prevents opsonization) More than 90 variants exist of the M protein Therefore, this is not a good candidate for a vaccineProtein F of cell wall Implicated in attachment to throat mucosaStreptokinase Enzyme which breaks down blood clots (allowing bact. to escape) (Purified, this enzyme is used as a “clotbuster” for treating heart attack and stroke) Virulence determinants for Group A Strep (continued)C5a Peptidase Inactivates C5a (prevents recruitment of PMN & macrophages)Hyaluronidase Released at certain points in cell cycle, it aids invasion of connective tissues. Causes fasciitis. DNAse Helps organism spread within infected tissue Enzyme breaks down DNA Neutrophils release their DNA when they die in a sticky solution to trap bacteria…DNAse breaks this sticky solution down in order to escape Streptococcal pyrogenic exotoxin A (Spe A) Superantigen which activates T cells non-specifically Induces massive release of cytokines Family of toxins produced by species which cause scarlet fever or necrotizing fasciitis.Streptolysins Two types released, O and S (lysis = breaking open the cell wall) Lyse blood cells (including phagocytes) Enzyme responsible for beta-hemolytic classification Pathogenesis, Group A StrepOpportunistic pathogenSpread by respiratory droplets Especially in crowded areas such as classrooms, day care, etcRisk factors for infection Depleted commensal microbiota If you take antibiotics and deplete normal flora, strep pygenes will take over Impaired immunity Large innoculum (if you are in an area with a high concentration of this bacteria you are at a greater risk of contracting this bacteria)Due to sensitivity to antimicrobial drugs, mortality (death rate) due to this pathogen has declined over the years, but Group A Strep still causes significant disease and must be identified and treated quickly.Do not mutate as rigorously as strep Pharyngitis (Strep Throat)Infection of the throat with Group A Strep accompanied with inflammation of the pharynx Pharynx appears red with swollen lymph nodes Purulent (pus-containing) abcesses cover the tonsils Often mis-diagnosed (instead of viral pharyngitis) Need bacteriological test to confirm Strep. Can lead to Rheumatic Fever. Signs and symptoms of Strep ThroatThroat pain, difficulty swallowing, red and swollen tonsils, sometimes with white patches or streaks of pus, swollen, tender lymph nodes in the neck, fever, headache, rash, stomachache, often accompanied by vomiting in younger children Unfortunately, many of these symptoms are similar to those of a sore throat caused by viral tonsillitis (i.e. common cold). However, one big difference is that strep throat is not usually associated with a cough. A throat swab or rapid antigen test can determine whether or not the tonsillitis is strep throat. If so, antibiotic treatment must get started right away. Skin infections Impetigo (Diffuse infection) Highly communicable diffuse skin infection Similar to symptoms caused by Staphylococcus aureus Staphylococcus aureus – disease is self-limiting (immune system will eventually kick in and take over) Streptococcus pyogenes – possible complications (commonly goesdeeper in the skin) Progression of Group A Strep skin infectionsInfections can start from the superficial epidermis (impetigo), and can go deeper intothe dermis (erysipelas) and subdermal area (cellulitis), all the way into the fascia (necrotizingfasciitis) and the muscle (myositis).  ErysipelasSkin inflammation of involving lymph nodes (usually spread from impetigo)Most common in faces of children and the elderlyNot common in other ages because of the strengthened immune system in young adults Necrotizing faciitisAlso known as “flesh-eating bacteria”Happens with group A strep and with staphStreptococci enter body through breaks in the skinBacteria secrete toxins and enzymes, destroying tissuesBacteria spread along connective tissues or fascia.Use HyaluronidaseDisease also involves toxemia, or release of toxins by bacteriaToxic Shock Syndrome can shut down the organs of the patientMortality is around 50% by organ failure Scarlet FeverRash and accompanying sore throat caused by Streptococcus