Bacterial Skin Infections
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Questions and Answers

What is a key characteristic of Staphylococci?

  • Can produce catalase as their by-product (correct)
  • Non-catalase producing organisms
  • Gram-negative spherical cells
  • Spore forming and motile

    • Which of the following describes Staphylococci's arrangement?

  • Single cells
  • Chains like Streptococci
  • Clusters arranged similarly to grapes (correct)
  • Cubic formations

    • Which exfoliative toxin is encoded by the eta gene?

  • Exfoliative toxin A (correct)
  • Exfoliative toxin C
  • Exfoliative toxin D
  • Exfoliative toxin B

    • What is the main action of the Toxic Shock Syndrome Toxin-1 (TSST-1)?

    <p>Acts as a superantigen leading to severe inflammatory responses</p> Signup and view all the answers

    Which population is primarily affected by Staphylococcal Scalded Skin Syndrome (SSSS)?

    <p>Newborns and infants</p> Signup and view all the answers

    What type of bacteria are Staphylococci classified as?

    <p>Gram-positive and aerobic or facultative anaerobic</p> Signup and view all the answers

    What role does Panton-Valentine Leukocidin (PVL) play in Staphylococci virulence?

    <p>Contributes to the pathology of bullous impetigo</p> Signup and view all the answers

    Which of the following is NOT a virulence factor of Staphylococci?

    <p>Lipopolysaccharide</p> Signup and view all the answers

    What type of cells does Panton-Valentine Leukocidin primarily target?

    <p>Polymorphonuclear leukocytes</p> Signup and view all the answers

    What is one of the key roles of hyaluronidase?

    <p>To facilitate the spread of bacteria through connective tissues</p> Signup and view all the answers

    Which two proteins form the components of Panton-Valentine Leukocidin?

    <p>LukS-PV and LukF-PV</p> Signup and view all the answers

    What potential effect does Panton-Valentine Leukocidin have on white blood cells?

    <p>Causes pore-formation in their membranes</p> Signup and view all the answers

    What mechanism does beta-lactamase utilize?

    <p>Degrades the ring structure of penicillin</p> Signup and view all the answers

    What is a significant virulence factor in Community-Acquired Methicillin-Resistant Staphylococcus aureus (CA-MRSA)?

    <p>Panton-Valentine Leukocidin</p> Signup and view all the answers

    What is the role of lipase in bacterial infections?

    <p>To degrade lipids on the skin surface</p> Signup and view all the answers

    How does Panton-Valentine Leukocidin affect phagocytosis?

    <p>It suppresses phagocytosis</p> Signup and view all the answers

    What is the effect of the pore-forming activity of PVL on cation permeability?

    <p>Increases cation permeability</p> Signup and view all the answers

    Which of the following is also known as the spreading factor in bacteria?

    <p>Lipase</p> Signup and view all the answers

    What does the minimal inhibitory concentration (MIC) indicate?

    <p>The lowest concentration of a drug that inhibits the growth of bacteria</p> Signup and view all the answers

    What percentage of S.aureus is estimated to produce beta-lactamase?

    <p>Approximately 90%</p> Signup and view all the answers

    Which genes are associated with resistance in mecA or mecC-positive organisms?

    <p>mecA and mecC</p> Signup and view all the answers

    What type of organism is most likely to be resistant to all extended spectrum penicillins, carbapenems, and cephalosporins, except ceftaroline?

    <p>mecA-positive organisms</p> Signup and view all the answers

    What are the two forms of coagulase found in Staphylococcus?

    <p>Bound and free coagulase</p> Signup and view all the answers

    What effect does free coagulase have on blood plasma?

    <p>It clots the blood plasma</p> Signup and view all the answers

    Which of the following statements accurately describes mecA or mecC-positive Staphylococcus species?

    <p>They have a higher chance of causing invasive infections</p> Signup and view all the answers

    In what percentage of S.aureus can one find mecA or mecC gene presence?

    <p>65%</p> Signup and view all the answers

    What is the primary function of beta-lactamase produced by S.aureus?

    <p>To degrade beta-lactam antibiotics</p> Signup and view all the answers

    What is the primary role of coagulase in Staphylococcus species?

    <p>To protect against phagocytosis</p> Signup and view all the answers

    What is the primary purpose of the coagulase test?

    <p>To confirm the presence of S.aureus</p> Signup and view all the answers

    Which of the following is a type of coagulase test?

    <p>Slide coagulase test</p> Signup and view all the answers

    A positive coagulase test result is indicated by what?

    <p>Presence of agglutination after 1-4 hours</p> Signup and view all the answers

    Which source is NOT a chief source of Staphylococcus infection?

    <p>Contaminated food</p> Signup and view all the answers

    What does the tube coagulase test detect?

    <p>Free coagulase</p> Signup and view all the answers

    Which of the following control measures is advised for Staphylococcus in hospitals?

    <p>Strict adherence to infection-control policies</p> Signup and view all the answers

    Which staphylococci are typically resistant to antibiotics?

    <p>Staphylococcus aureus</p> Signup and view all the answers

    Where can antibiotic-resistant staphylococci commonly reside?

    <p>On the skin and in the nose</p> Signup and view all the answers

    What does the term 'agglutination' refer to in the coagulase test?

    <p>The clumping of bacterial cells</p> Signup and view all the answers

    Which component is primarily used in the coagulase test?

    <p>Blood plasma</p> Signup and view all the answers

    What is the primary function of pyrogenic exotoxins produced by group A Streptococci?

    <p>They transform plasminogen into plasmin.</p> Signup and view all the answers

    Which disease is commonly associated with streptococcal toxic shock syndrome?

    <p>Scarlet fever</p> Signup and view all the answers

    How do pyrogenic exotoxins act as superantigens?

    <p>By stimulating T cells through MHC II binding.</p> Signup and view all the answers

    What is a significant consequence of the action of pyrogenic exotoxins in the body?

    <p>Shock and tissue injury.</p> Signup and view all the answers

    Which of the following is NOT a characteristic of pyrogenic exotoxins?

    <p>They are produced by Group B Streptococcus.</p> Signup and view all the answers

    What is the most common form of anthrax in humans?

    <p>Cutaneous Anthrax</p> Signup and view all the answers

    What is the primary change that occurs in a papule as it develops in cutaneous anthrax?

    <p>It rapidly changes into a vesicle.</p> Signup and view all the answers

    Where are the most common infection sites for cutaneous anthrax lesions?

    <p>Face, neck, and upper extremities</p> Signup and view all the answers

    What characteristic feature is commonly associated with a prominent lesion from cutaneous anthrax?

    <p>A central black eschar</p> Signup and view all the answers

    What is the initial appearance of a cutaneous anthrax lesion after spore entry?

    <p>A pruritic papule</p> Signup and view all the answers

    What is the primary effect of Panton-Valentine Leukocidin (PVL) at high concentrations on PMNs?

    <p>It causes PMN lysis.</p> Signup and view all the answers

    Which form of IgG is not affected by the binding of Protein A?

    <p>IgG3</p> Signup and view all the answers

    What is a significant cause of food poisoning linked to staphylococcal infections?

    <p>Enterotoxin B</p> Signup and view all the answers

    What potential consequence can result from the release of reactive oxygen species (ROS) from lysed PMNs?

    <p>Tissue necrosis</p> Signup and view all the answers

    Which statement accurately describes enterotoxins in relation to gut enzymes?

    <p>Enterotoxins are partially resistant to gut enzymes.</p> Signup and view all the answers

    What is the role of superantigens in the immune response?

    <p>Trigger an overreactive immune response.</p> Signup and view all the answers

    What is a significant characteristic of enterotoxin B in staphylococcal infections?

    <p>It is heat-stable.</p> Signup and view all the answers

    What consequence can result from a low concentration of Panton-Valentine Leukocidin (PVL) on PMNs?

    <p>Direct binding to mitochondrial membranes.</p> Signup and view all the answers

    What hemolysis pattern is characterized by the complete lysis of red blood cells?

    <p>Beta-hemolysis</p> Signup and view all the answers

    What is a primary use of mannitol in culturing Staphylococcus aureus?

    <p>To screen for nasal carriers of S. aureus</p> Signup and view all the answers

    How long should specimens contaminated with mixed microbiota be incubated to observe colonies of Staphylococcus?

    <p>18 hours</p> Signup and view all the answers

    Which of the following statements is true regarding the hemolysis patterns observed in Staphylococcus?

    <p>Three hemolysis patterns are identified: alpha, beta, and gamma.</p> Signup and view all the answers

    What property of Staphylococcus aureus allows its recovery from respiratory specimens?

    <p>Fermentation of mannitol</p> Signup and view all the answers

    Which feature does NOT describe gamma-hemolysis?

    <p>Results in a clear zone around colonies</p> Signup and view all the answers

    What is the significance of Staphylococcus aureus being grown on mannitol salt agar?

    <p>It allows for the differentiation of pathogenic and non-pathogenic staphylococci</p> Signup and view all the answers

    Which of the following statements accurately describes a characteristic of Staphylococcus species?

    <p>Only S. aureus can utilize mannitol</p> Signup and view all the answers

    What distinguishes Staphylococcus aureus from other Staphylococcus species during the coagulase test?

    <p>The presence of coagulase, an exoenzyme</p> Signup and view all the answers

    What type of coagulase test is used to detect free coagulase?

    <p>Tube coagulase test</p> Signup and view all the answers

    A positive coagulase test result is indicated by what observation?

    <p>Presence of agglutination after 1-4 hours</p> Signup and view all the answers

    Which of the following is NOT a chief source of Staphylococcus infection?

    <p>Contaminated water sources</p> Signup and view all the answers

    Which control measure is recommended to manage Staphylococcus risks in hospitals?

    <p>Strict adherence to infection-control policies</p> Signup and view all the answers

    In the context of Staphylococcus, what does the term 'fomites' refer to?

    <p>Biologically inert objects that can harbor infections</p> Signup and view all the answers

    What is the primary purpose of performing a coagulase test?

    <p>To identify the presence of S.aureus specifically</p> Signup and view all the answers

    Which of the following coagulase tests detects bound coagulase?

    <p>Slide coagulase test</p> Signup and view all the answers

    What appearance do B.anthracis colonies exhibit on Blood Agar Plates?

    <p>Non-hemolytic with a rough texture and ground glass appearance</p> Signup and view all the answers

    What is a significant characteristic of inhalation anthrax?

    <p>Severe substernal pain and mediastinal edema</p> Signup and view all the answers

    What is the incubation period for inhaled anthrax spores?

    <p>Up to 6 weeks</p> Signup and view all the answers

    Which method is NOT used for the definitive identification of Bacillus anthracis?

    <p>Microscopic observation of Gram-negative bacilli</p> Signup and view all the answers

    Which of the following features describe the distinctive morphology of B.anthracis colonies?

    <p>Curled hair or Medusa head appearance</p> Signup and view all the answers

    What feature does the blood agar plate culture demonstrate concerning Bacillus anthracis?

    <p>Sodium bicarbonate's effect on the capsule</p> Signup and view all the answers

    Which of the following statements about inhalation anthrax is true?

    <p>It can lead to high mortality rates if untreated.</p> Signup and view all the answers

    In which specific aspect does B.anthracis colony appear non-hemolytic?

    <p>It does not lyse red blood cells.</p> Signup and view all the answers

    What is the characteristic progression of a cutaneous anthrax lesion after spore entry?

    <p>Develops from a pruritic papule to a central black eschar.</p> Signup and view all the answers

    Which area is least likely to be affected by cutaneous anthrax lesions?

    <p>Lower back</p> Signup and view all the answers

    What is the main initial clinical manifestation of cutaneous anthrax?

    <p>Pruritic papule at the site of spore entry.</p> Signup and view all the answers

    What leads to the formation of necrotic ulcers in cutaneous anthrax infections?

    <p>Coalescence of vesicles.</p> Signup and view all the answers

    Which characteristic is associated with the prominent lesion of cutaneous anthrax?

    <p>Formation of a central black eschar.</p> Signup and view all the answers

    Which condition is characterized by a rapid progression from superficial to deep tissue involvement and often begins at a site of trauma?

    <p>Necrotizing Fasciitis</p> Signup and view all the answers

    Which combination regimen includes Daptomycin and Piperacillin-tazobactam for treating recurrent cellulitis?

    <p>Daptomycin + Piperacillin-tazobactam</p> Signup and view all the answers

    What is the characteristic feature of Non-Bullous Impetigo in terms of its contagiousness compared to Bullous Impetigo?

    <p>More contagious than Bullous Impetigo</p> Signup and view all the answers

    Which patient population is most likely to experience recurrent cellulitis due to predisposed conditions?

    <p>Patients with lymphedema and obesity</p> Signup and view all the answers

    What severe outcome can occur as a result of Necrotizing Fasciitis if not treated promptly?

    <p>Bacteremia with secondary tissue damage</p> Signup and view all the answers

    What is a characteristic feature of the spores produced by Clostridium perfringens?

    <p>Spores can be centrally, subterminally, or terminally located.</p> Signup and view all the answers

    Which toxin produced by Clostridium perfringens is associated with lethal necrotizing effects?

    <p>Alpha toxin</p> Signup and view all the answers

    Which of the following statements about Clostridium perfringens is FALSE?

    <p>It produces spores that are typically smaller than the rods.</p> Signup and view all the answers

    What type of flagella do Clostridium species possess?

    <p>Peritrichous</p> Signup and view all the answers

    What is the primary ecological niche of Clostridium perfringens?

    <p>Soil and marine sediments</p> Signup and view all the answers

    What is a significant risk associated with cutaneous anthrax if left untreated?

    <p>Progression to hemodynamic instability</p> Signup and view all the answers

    Which of the following symptoms is NOT typically associated with gastrointestinal anthrax?

    <p>Fever and chills</p> Signup and view all the answers

    What is the primary reason gastrointestinal anthrax can be difficult to diagnose?

    <p>It mimics other gastrointestinal diseases</p> Signup and view all the answers

    How long does it typically take for an eschar to fully develop in cutaneous anthrax?

    <p>7-10 days</p> Signup and view all the answers

    Which method is NOT commonly used for diagnosing anthrax?

    <p>Urine sample testing</p> Signup and view all the answers

    What is the primary outcome of antibiotic therapy in cutaneous anthrax?

    <p>Prevention of further dissemination</p> Signup and view all the answers

    Ingestion of infected meat is associated with which form of anthrax?

    <p>Gastrointestinal anthrax</p> Signup and view all the answers

    What is a key feature of injection anthrax as compared to cutaneous anthrax?

    <p>Presence of localized edema without eschar</p> Signup and view all the answers

    What is the role of Streptokinase in bacterial infections?

    <p>To liquidate pus and promote spread</p> Signup and view all the answers

    Which of the following describes the function of Deoxyribonucleases (DNases) in bacterial virulence?

    <p>Degrading DNA to enhance tissue spread</p> Signup and view all the answers

    How is the virulence factor M protein significant to streptococcal infections?

    <p>It binds to antibodies, evading the immune response</p> Signup and view all the answers

    Which of these factors is NOT typically considered a virulence factor in Streptococcus pneumoniae?

    <p>Lipopolysaccharides</p> Signup and view all the answers

    In biochemical testing of Streptococcus species, which reaction is specifically tested?

    <p>Sugar fermentation reactions</p> Signup and view all the answers

    What is the primary mechanism of action for Hyaluronidase in bacterial infections?

    <p>To liquefy body tissues and enhance spread</p> Signup and view all the answers

    What type of hemolysis is associated with the complete disruption of erythrocytes?

    <p>Beta hemolysis</p> Signup and view all the answers

    Which of the following virulence factors is responsible for the formation of pus during infection?

    <p>Deoxyribonucleases</p> Signup and view all the answers

    Study Notes

    Staphylococci

    General Characteristics

    • Gram-positive, spherical cells arranged in grape-like clusters
    • Can be aerobic or facultative anaerobes
    • Non-motile and non-spore forming
    • Produce catalase, a key identifying characteristic
    • Normal flora of skin and mucous membranes; major reservoir is human nares

    Virulence Factors

    • Toxic Shock Syndrome Toxin-1 (TSST-1): Superantigen causing severe immune response
    • Exfoliative Toxins:
      • Exfoliative Toxin A: Heat-stable, encoded by eta gene
      • Exfoliative Toxin B: Heat-labile, plasmid-mediated
      • Leads to Staphylococcal Scalded Skin Syndrome (SSSS), primarily in newborns
    • Hemolysins: Disrupt red and white blood cells contributing to tissue damage
    • Panton-Valentine Leukocidin (PVL):
      • Lethal enzyme affecting neutrophils, primarily linked to community-acquired MRSA
      • Causes pore formation in cell membranes, increasing inflammatory mediator release
    • Hyaluronidase: Spreading factor that allows bacteria to invade connective tissues
    • Lipase: Degrades skin lipids, facilitating bacterial entry into epidermis
    • Beta-lactamase: Enzyme leading to penicillin resistance, found in ~90% of S. aureus strains

    Coagulase

    • An exoenzyme that clots blood plasma; present in S. aureus
    • Two forms:
      • Free coagulase: Secreted extracellularly
      • Bound coagulase: Attached to the cell wall
    • Coagulase tests differentiate S. aureus from other staphylococci; positive results show agglutination

    Epidemiology and Control of Staphylococci

    Epidemiology

    • Chief sources of infection include:
      • Shedding from human lesions
      • Fomites (contaminated objects)
      • Human respiratory tract
      • Skin
    • Antibiotic-resistant strains may persist in nasal passages or on skin

    Control Measures

    • Emphasize proper hygiene
    • Strict adherence to infection control policies in hospitals
    • Exclusion of infected individuals or personnel to prevent spread

    Pyrogenic Exotoxins

    • Produced by group A, β-hemolytic Streptococci, similar to exfoliative toxins
    • Transform plasminogen into plasmin to escape blood clots
    • Associated with streptococcal toxic shock syndrome and scarlet fever
    • Act as superantigens, binding to MHC II complex and inducing cytokine release, leading to shock and tissue injury

    Streptococcal Pyrogenic Exotoxins (Spe)

    • Three antigenically distinct proteins (SpeA, etc.) produced by Group A Streptococcus.

    MSCRAMMs and PVL

    • Staphylococcus aureus synthesizes MSCRAMMs that assist in pore formation on PMN membranes through γ-hemolysin.
    • PVL (Panton-Valentine Leukocidin) can have different effects on PMNs: high concentrations lead to lysis, while low concentrations induce apoptosis by binding to mitochondrial membranes.
    • Reactive oxygen species (ROS) released from lysed PMNs can cause tissue necrosis.
    • Granule content release from PMNs may trigger an inflammatory response, contributing to necrosis.

    Enterotoxins

    • Staphylococcal enterotoxins A, B, and D are significant sources of food poisoning.
    • Enterotoxin B specifically causes vomiting and diarrhea and is associated with staphylococcal pseudomembranous enterocolitis.
    • Enterotoxins are heat-stable exotoxins classified as superantigens; they interact with multiple T cells, provoking an exaggerated immune response.

    Staphylococcus Identification

    • S. aureus can be differentiated from other Staphylococcus species using coagulase tests, identifying the presence of the coagulase enzyme.
    • Agglutination after 1-4 hours indicates a positive coagulase test result.
    • Hemolysis patterns help classify staphylococci: alpha, beta, and gamma hemolysis.

    Sources of Staphylococcal Infection

    • Chief sources include shedding from human lesions, fomites, respiratory tract, and skin.
    • Antibiotic-resistant strains can be carried on the skin or in the nasal passages.

    Infection Control Measures

    • Effective control measures in hospitals emphasize proper hygiene, strict infection-control policies, and exclusion of infected personnel to reduce S. aureus infections.

    Anthrax Overview

    • Bacillus anthracis forms spores that germinate at the entry site when in the body, leading to growth in tissues.
    • The immune response results in gelatinous edema and congestion, facilitating vegetative cell proliferation.

    Cutaneous Anthrax

    • Represents approximately 95% of anthrax cases; lesions typically appear on upper extremities, face, and neck.
    • Initial presentation is a pruritic papule that evolves into vesicles, which may coalesce to form a necrotic ulcer, with a prominent central black eschar present.

    Inhalation Anthrax

    • Known as "Woolsorter's Disease," it leads to severe necrosis and edema in the mediastinum.
    • Symptoms include substernal pain; spore incubation can last up to 6 weeks.
    • Chest X-rays may show notable mediastinal widening, indicating high mortality rates associated with this form.

    Laboratory Diagnosis of Anthrax

    • Blood agar culture reveals non-hemolytic, gray to white colonies with a rough texture and appearance reminiscent of "Medusa head."
    • Definitive identification may include cell lysis using anthrax gamma-bacteriophage, capsule detection via fluorescent antibodies, and toxin gene identification through PCR.

    Streptococcus Overview

    • Streptococcus pneumoniae and Streptococcus mutans are notable species in the Streptococcus genus.
    • Beta-hemolytic: Refers to complete disruption of erythrocytes, resulting in a clear zone around bacterial colonies.
    • Lancefield Classification: Classifies beta-hemolytic streptococci based on group-specific carbohydrates (A, B, C, F, G).

    Biochemical Reactions

    • Essential for identifying species that do not respond to common antibody preparations.
    • Involves a series of biochemical tests:
      • Sugar fermentation reactions.
      • Enzyme presence tests.
      • Susceptibility tests to specific chemicals.

    Virulence Factors of Streptococcus

    • M protein: Essential for virulence; contributes to resistance against phagocytosis.
    • Streptokinase: Enzyme that dissolves blood clots; helps bacteria spread through tissues.
    • Deoxyribonucleases (DNases): Degrade DNA, facilitating streptococci spread by liquefying pus.
    • Hyaluronidase: Breaks down hyaluronic acid in tissues, enhancing spread.
    • Pyrogenic Exotoxins (Erythrogenic Toxin): Cause fever and rash in infections like scarlet fever.
    • Hemolysins: Lyses red blood cells, contributing to the bacteria's virulence.

    Infections Associated with S. pyogenes

    • Recurrent Cellulitis: Common in patients with lymphedema, obesity, venous stasis, or untreated tinea pedis.
    • Necrotizing Fasciitis: Severe infection beginning at trauma sites; rapidly progresses and can lead to bacteremia.

    Impetigo Types

    • Non-Bullous Impetigo: Highly contagious purulent skin infection, often affecting face and extremities; starts as vesicles that coalesce.
    • Bullous Impetigo: Less contagious than non-bullous, characterized by large fluid-filled blisters.

    Anthrax Overview

    • Bacillus anthracis: The causative agent of anthrax diseases; spores germinate upon entry through wounds.

    Cutaneous Anthrax

    • Represents about 95% of anthrax cases; starts as a pruritic papule, developing into vesicles and eventually a necrotic ulcer.
    • Prominent feature includes a central black eschar, sizing 1-3 cm in diameter.

    Types of Anthrax Infections

    • Inhalation Anthrax: Rare but severe; primarily via inhalation; can spread to gastrointestinal tract causing bowel ulcers.
    • Gastrointestinal Anthrax: Results from ingesting infected meat; symptoms may mimic other digestive disorders, includes abdominal pain and bloody diarrhea.
    • Injection Anthrax: Occurs from contaminated drug injections; severe edema with no eschar formation; can lead to sepsis.

    Diagnostics for Bacillus anthracis

    • Testing includes specimens from pus, blood, pleural fluid, and cerebrospinal fluid (CSF).

    Clostridium Characteristics

    • Clostridium perfringens: Large, gram-positive rods, motile with peritrichous flagella; found in soil and animal GIT.
    • Spores: Larger than cell diameter; located centrally, subterminally, or terminally.

    Clostridium Virulence Factors

    • Alpha Toxin: Lecithinase that causes lethal necrotizing damage, linked to type A strains.
    • Beta Toxin: Another necrotizing toxin produced by type B strains, contributing to gas gangrene.

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    Description

    This quiz covers the general characteristics and virulence factors of Staphylococci. Learn about key identifying features, toxins, and their roles in infections, including Toxic Shock Syndrome and Staphylococcal Scalded Skin Syndrome. Understand their impact on human health and disease mechanisms.

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