MICR J210 1st Edition Lecture 13Outline of Last Lecture I. An overview of Medical MycologyII. Systemic Mycoses Caused by Pathogenic FungiIII. Superficial, Cutaneous, and Subcutaneous MycosesIV. Fungal Intoxications and AllergiesV. Classification of parasitesOutline of Current 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 saprophyticusStaphylococciThese 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. Morphology: Clustered cocci, from Greek Staphyle= grapes Gram positive Generally found as commensals on skin and upper respiratory tract Swab around the nares for a sample Most species are harmless There are about 40 species of Staphylococci Most are not associated with humans (mostly harmless) 3 are of interest clinically as opportunists Staphylococcus aureus-the most pathogenic Distinguish between staph aureus and non staph aureus Staphylococcus epidermidis Staphylococcus saprophyticusGeneral Characteristics of Staph Gram-positive Catalase positive Catalase is an enzyme that breaks down peroxide to get rid of the oxide radicals that can potentially kill pathogens Facultative anaerobes-they can ferment Ability to grow in high-salt conditions Tolerant to dessication (drying out) Tolerant to irradiation (UV from sun) And tolerant to heat Tolerant to heat (up to 60oC for up to 60 mins)Pathogenicity of Staph Staph. sp are opportunistic pathogensSurvive on the skin as commensals and become opportunistic when there is a breachin the skin or mucosa Infections result when barriers (skin or mucosa) are breached, allowing entry. Production of disease depends on the 3 virulence factors (some factor that allows the pathogen to cause disease)Physical evasion of phagocytosisProduction of enzymes to protect against phagocytosisProduction of toxinsEvade the immune system and other that are simply just toxicStaphylococcus Aureus Defenses against phagocytosisProtein A-Virulence factorPresent on surface of S. aureus, Protein A binds to the Fc region of Ig molecules, thereby preventing opsonization. Since Ig molecules are opsonins, binding to their Fc region renders opsonization impossible for that Ig molecule. The bacteriabinds to the other end of the Ig moleculeBound coagulase-VirulenceEnzyme bound to S. aureus bacteria which activates clotting of the serum clottingfactors.This forms a protective fibrin clot around the bacteria, protecting them from phagocytes. Walls them off from the immune system. Neutrophils and macrophages can’t access the pathogenGlycocalyx-Capsule (Virulence)Both S. aureus and S. epidermis can synthesis slime layers forming a biofilm to protect themselves from phagocytes.The slime also allows attachment to artificial surfaces such as catheters, artificial heart valves or artificial joints.Catalase-Virulence Enzyme which neutralizes hydrogen peroxide generated by lysosomes in phagocytes (allows bacteria to grow in the environment)This protects against killing of staph sp. once inside the phagocytesThe bacteria can survive in the pathogen once it has been engulfed bc it neutralizes the hydrogen peroxide produced by the phagocyte PyogenicProduces pusInflammatory response attracts PMNs to the site of infectionArea fills with dead PMNS, dead tissue debris and fluid, bacteriaPuss-filled area has low O2 and low pHNot well vascularizedPhagocytes do not work well in the pus microenvironmentBacterial populations can resurge. Other enzymes produced by S. aureus.Cell-free coagulase, Secreted form which causes clottingHyaluronidaseBreaks down intracellular matrix in body, allowing bacterial invasionBreaks down connective tissue (hyaluronic acid)StaphylokinaseDissolves blood clots, allowing Staph to fee itself from clotted blood.Secrete staphlokinase to reverse clotting process and spread to other areasLipasesDissoves lipids in sebaceous secretions, allowing the bacteria to live on the skin.Beta-lactamase (and other antibiotic resistance factors)Staph strains are known for development of antibiotic resistance.Drug resistance Toxins released by Staph aureasCytolytic toxins (exotoxins)Produced by SAand breaks open host cells. (allowing bacteria to penetrate deeper)Leukocidin, lyses white blood cells, protecting against phagocytosis.Hemolysin, lyses red blood cells (most SA strains). Steal Iron from Hemoglobin for their own useExfoliative toxinsDissolves desmosomes, causing outer layers of skin to peel offStaphylococcal scalded skin syndrome (SSSS)EnterotoxinsCause food poisoning and vomitingToxic Shock Syndrome toxinSkin Infections caused by Staph Aureus ImpetigoContagious skin infection which produces blisters and sores on mostly the face, and sometime the hands.Associated with lower socioeconomic groupsCommon skin infection among children with poor hygiene.Diffuse infection: spreads on the inside (doesn’t go very deep)Both Staph and Strep can cause impetigo Folliculitis (boil, skin abcess)Pus-filled lumps that are tender, warm, and/or painfulLocallized infection of hair follicleBoil should be drained under aseptic conditionsFolliculitis of an eyelash is a sty (usually not drained)Do not drain or lance a boil on the eye (the area is too sensitive so let it heal on its own) Feruncle / CarbuncleAbcess larger than a boil, usually found on the back of the neckCommon in adolescent teenage boysRequires surgical drainingA furuncle is an acute, round, firm, tender, circumscribed, perifollicular staphylococcal infection that usually presents as central pus areaA carbuncle is two or more confluent furuncles with separate heads.  Caused by two exotoxins produced by some strains of SA. Usually found in infantsIt’s thought that bacteria may gain entry at the umbilical stump. Umbilicus gets infected with staphToxin enters into blood stream and dissolves skin desmosomes Involves large areas of the skin, causing large blisters that rupture, causing exfoliation of the skin. Often resembles third degree