Bacteriology Overview: Gram Positive Organisms
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Questions and Answers

What is the main clinical finding associated with pharyngitis caused by S pyogenes?

  • Tender cervical lymph nodes (correct)
  • Rash and blisters
  • Cough and runny nose
  • Abdominal pain

    • Which toxin produced by S pyogenes is a protease that destroys tissue?

  • Pyrogenic exotoxin A
  • Erythrogenic toxin
  • Toxic shock syndrome toxin
  • Exotoxin B (correct)

    • Which of the following diseases is NOT caused by S pyogenes?

  • Pneumonia (correct)
  • Rheumatic fever
  • Taste dysfunction (correct)
  • Scarlet fever

    • What can occur if the host lacks antitoxin to erythrogenic toxin produced by S pyogenes?

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

    Which condition can be a complication of untreated pharyngitis caused by S pyogenes?

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

    Which disease is characterized by necrotizing fasciitis caused by S pyogenes?

    <p>Streptococcal gangrene</p> Signup and view all the answers

    What happens in the case of puerperal fever related to S pyogenes?

    <p>It can cause endometritis after delivery.</p> Signup and view all the answers

    Which of the following is a symptom of streptococcal toxic shock syndrome?

    <p>High fever and rash</p> Signup and view all the answers

    Which of the following genera are medically important Gram-positive cocci?

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

    What type of infections can Streptococci cause?

    <p>Skin infections and sepsis</p> Signup and view all the answers

    What is one of the important properties of Streptococci?

    <p>They are usually arranged in chains or pairs</p> Signup and view all the answers

    What type of hemolysis is associated with alpha-hemolytic streptococci?

    <p>Incomplete lysis of red blood cells</p> Signup and view all the answers

    Which enzyme is produced by beta-hemolytic streptococci for hemolysis?

    <p>Streptolysin O and Streptolysin S</p> Signup and view all the answers

    What antigen determines the group of beta-hemolytic streptococci?

    <p>C carbohydrate</p> Signup and view all the answers

    What is a characteristic of gamma-hemolytic streptococci?

    <p>They are non-hemolytic</p> Signup and view all the answers

    Which of the following is NOT a disease caused by Streptococci?

    <p>Diabetes mellitus</p> Signup and view all the answers

    Which group of streptococci is known for being the most frequent cause of pharyngitis?

    <p>Group A streptococci</p> Signup and view all the answers

    What is the main virulence factor of beta-hemolytic streptococci?

    <p>M protein</p> Signup and view all the answers

    Which type of streptococci can cause neonatal meningitis and sepsis?

    <p>Group B streptococci</p> Signup and view all the answers

    Which group of streptococci is NOT killed by penicillin G?

    <p>Enterococci (Group D)</p> Signup and view all the answers

    What hemolytic reaction is typical of nonenterococci group D streptococci?

    <p>Variable with most being alpha-hemolytic</p> Signup and view all the answers

    Which type of streptococci produces no hemolysis?

    <p>Gamma-hemolytic streptococci</p> Signup and view all the answers

    Which streptococci group is characterized by being Bacitracin-resistant?

    <p>Group B streptococci</p> Signup and view all the answers

    Which of the following is a principal alpha-hemolytic organism?

    <p>Streptococcus pneumoniae</p> Signup and view all the answers

    What is a distinguishing feature of viridans streptococci compared to S pneumoniae?

    <p>They are not bile-soluble.</p> Signup and view all the answers

    Which species of viridans streptococci is known for synthesizing dextrans found in dental plaque?

    <p>Streptococcus mutans</p> Signup and view all the answers

    What can result from the normal flora of streptococci gaining access to tissues or blood?

    <p>Infective endocarditis.</p> Signup and view all the answers

    Which enzyme produced by Group A streptococci activates plasminogen to form plasmin?

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

    What is the role of hyaluronidase produced by Group A streptococci?

    <p>It aids in the spread of streptococci.</p> Signup and view all the answers

    Which toxin is responsible for the rash associated with scarlet fever?

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

    How does Streptolysin O differentiate from Streptolysin S?

    <p>It is oxygen-labile.</p> Signup and view all the answers

    What is a common condition caused by group A streptococci associated with superficial skin infections?

    <p>Streptococcal pyoderma</p> Signup and view all the answers

    Which serious condition is commonly linked to group B streptococci in newborns?

    <p>Neonatal sepsis</p> Signup and view all the answers

    In which location is Streptococcus agalactiae typically found?

    <p>Female genital tract</p> Signup and view all the answers

    What is the typical onset period for acute glomerulonephritis following a skin infection with certain group A streptococci?

    <p>2-3 weeks after infection</p> Signup and view all the answers

    Why are microbiologic smears considered useless in diagnosing pharyngitis caused by streptococci?

    <p>S.pyogenes and viridans streptococci cannot be visually distinguished.</p> Signup and view all the answers

    Which autoimmune condition may develop after a group A streptococcal infection and is characterized by carditis?

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

    What indicates that streptococci cultured from the pharynx may be group A streptococci?

    <p>Inhibition by Bacitracin disk.</p> Signup and view all the answers

    What type of bacteria is Streptococcus pneumoniae primarily associated with?

    <p>Upper respiratory tract infections.</p> Signup and view all the answers

    What is the preventive measure against acute glomerulonephritis following skin infections caused by nephritogenic streptococci?

    <p>Early eradication of streptococci from colonization sites</p> Signup and view all the answers

    What is the main factor that influences the recurrence of rheumatic fever?

    <p>Recurrence of streptococcal infections</p> Signup and view all the answers

    What shape do pneumococci typically have under microscopic examination?

    <p>Lancet-shaped cocci.</p> Signup and view all the answers

    What laboratory findings are typically elevated in patients with rheumatic fever?

    <p>ASO titers and ESR</p> Signup and view all the answers

    How can the type of streptococcus pneumoniae be identified using its capsules?

    <p>Using type-specific antiserum and observing swelling.</p> Signup and view all the answers

    What is the role of viridans streptococci in infectious endocarditis?

    <p>Entering the bloodstream from the oropharynx</p> Signup and view all the answers

    What is the primary treatment for group A streptococci infections?

    <p>Penicillin G.</p> Signup and view all the answers

    What preventative measure can help avoid recurrence of rheumatic fever?

    <p>Monthly injections of benzathine penicillin.</p> Signup and view all the answers

    What distinguishes pneumococci as virulent?

    <p>The presence of a polysaccharide capsule.</p> Signup and view all the answers

    Study Notes

    Bacteriology Overview

    • The course covers Gram positive organisms, Gram negative organisms, and Viruses.

    Gram Positive Organisms

    • Gram Positive organisms are further subdivided into Gram positive cocci and Gram positive rods.

    Gram Positive Cocci

    • Two medically important genera are Staphylococcus and Streptococcus.
    • These are non-motile and do not form spores.

    Streptococci

    • These are spherical cocci usually arranged in chains or pairs.
    • All streptococci are catalase-negative.

    Streptococci Properties

    • An important identification criterion is the type of hemolysis.

    Alpha-hemolytic

    • Incomplete lysis of red blood cells.
    • Results in a green zone around colonies.

    Beta-hemolytic

    • Complete lysis of red blood cells.
    • Results in a clear zone around colonies.
    • Caused by hemolysins like streptolysin O and streptolysin S.

    Gamma-hemolytic

    • No lysis of red blood cells.
    • Some streptococci are non-hemolytic.

    Streptococci Classification

    • Based on hemolysis on blood agar:

    • Alpha-hemolytic: Partial hemolysis (e.g., non-groupable streptococci, S. pneumoniae and S. viridans)

    • Beta-hemolytic: Complete hemolysis (e.g., Group A & B, S. pyogenes and S. agalactiae)

    • Gamma-hemolytic: No lysis (e.g., Group D, Enterococcus spp)

    • Based on antigenic differences in C carbohydrate

    • Group A, B, C, D, other groups(E-U)

    Human Streptococcal Pathogens

    • S. pyogenes
    • S. agalactiae (Group B)
    • Viridans streptococci
    • S. pneumoniae
    • Enterococcus faecalis

    Group A Streptococci (S. pyogenes)

    • Among the most important human pathogens.
    • Common cause of pharyngitis (sore throat).
    • Characteristics: Inflammation, exudate, fever, leukocytosis, and tender cervical lymph nodes. Usually resolves spontaneously in 10 days.

    Group B Streptococci (S. agalactiae)

    • Colonize the genital tract of some women.
    • Can cause neonatal meningitis and sepsis.
    • Usually Bacitracin-resistant.

    Group D Streptococci

    • Includes Enterococci (e.g. Enterococcus faecalis) and non-enterococci (e.g., Streptococcus bovis).
    • Enterococci: Grow in 6.5% NaCl; not killed by penicillin G; part of normal gut flora.
    • Non-enterococci: Are inhibited by 6.5% NaCl and killed by penicillin G.
    • Hemolytic reaction is variable; some are beta-hemolytic; most are alpha-hemolytic or non-hemolytic.

    Non-Beta Hemolytic Group streptococci

    • Viridans streptococci (e.g. Streptococcus mitis, S. sanguis, and S. mutans)
    • Not bile-soluble
    • Not inhibited by optochin.
    • Part of normal human pharynx flora.
    • Can reach bloodstream to cause infective endocarditis.
    • S. mutans synthesizes polysaccharides (dextrans) leading to dental caries.

    Transmission

    • Most streptococci are part of a normal flora in throat, skin and intestines.
    • Produce disease when they gain access to tissues or blood.

    Pathogenesis of Group A Streptococci:

    • Produce eight important toxins/enzymes:
    • Streptokinase: Activates plasminogen to form plasmin, dissolving blood clots.
    • Dnase: Depolymerizes DNA in exudates or necrotic tissue.
    • Hyaluronidase: Hydrolyzes ground substance of connective tissue, aiding streptococci spread.

    B. Toxins and Hemolysins

    • Erythrogenic toxin: Causes scarlet fever rash.
    • Streptolysin O: Hemolysin that is oxygen-labile (inactivated by oxidation).
    • Streptolysin S: Oxygen-stable hemolysin. Not antigenic.
    • Pyrogenic exotoxin A: Similar to staphylococcal toxic shock syndrome toxin (TSST).
    • Exotoxin B: Protease rapidly destroying tissue, associated with necrotizing fasciitis.

    Clinical Findings

    • S. pyogenes causes three types of disease
      1. Pyogenic diseases: Pharyngitis, Cellulitis
      2. Toxigenic diseases: Scarlet fever, toxic shock syndrome
      3. Immunologic diseases: Rheumatic fever, acute glomerulonephritis.
    • Pharyngitis: characterized by inflammation, exudate, fever, leukocytosis, and tender cervical lymph nodes.
    • S. pyogenes can enter skin defects to produce: cellulitis, necrotizing fasciitis (gangrene), lymphangitis, or bacteremia.
    • S. pyogenes can enter the uterus after delivery to produce endometritis and sepsis.
    • Streptococcal pyoderma (impetigo): superficial skin infection.
    • Glomerulonephritis: May occur following skin infections (more frequent); develops 2-3 weeks after skin infection due to certain group A streptococcal types in children.
    • Group B streptococci cause neonatal sepsis and meningitis. Especially in pre-term infants.
    • Infective endocarditis is caused by viridans streptococci that intermittently enter the bloodstream from the oropharynx.

    Streptococcus Pneumoniae

    • Causes pneumonia, bacteremia, meningitis, and infections of the upper respiratory tract (otitis, sinusitis).
    • Important physical properties include being lancet-shaped diplococci or short chains and producing alpha-hemolysis on blood agar.
    • Possess polysaccharide capsules of more than 85 antigenically distinct types.
    • Capsules are virulence factors interfering with phagocytosis.
    • Produces IgA protease, which may enhance colonization of the upper respiratory tract.

    Laboratory Diagnosis (General for all streptococcus types)

    • Microbiological smears are mostly useless for pharyngitis because viridans streptococci are present in normal flora and indistinguishable from pathogenic types. Useful for skin lesions.
    • Cultures on blood agar plates show small, translucent beta-hemolytic colonies within 18-48 hours.
    • Inhibited by Bacitracin disk, likely group A streptococci.
    • ASO titers are high soon after group A streptococcal infections.

    Treatment (General for all streptococcus types)

    • All group A streptococci susceptible to penicillin G.
    • Neither rheumatic fever nor AGN benefit from penicillin treatment after onset.
    • Endocarditis caused by most viridans streptococci is curable by prolonged penicillin treatment.

    Prevention (General for all streptococcus types)

    • Rheumatic fever prevention: Prompt treatment of group A strep pharyngitis with penicillin.
    • Prevention of recurrent streptococcal infections (e.g., with benzathine penicillin): Important in persons with previous rheumatic fever.

    Laboratory Differentiation (Beta vs Alpha hemolytic streptococci)

    • Gram-positive cocci are differentiated based on hemolysis, sensitivity to bacitracin, and CAMP test results.
    • Gram-positive cocci are differentiated based on hemolysis, sensitivity to optochin, bile solubility, and Inulin fermentation tests.

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    Description

    This quiz provides an overview of gram-positive organisms, focusing on the properties and classification of streptococci. Learn about the different types of hemolysis and the importance of genera such as Staphylococcus and Streptococcus in microbiology. Test your understanding of these key concepts in bacteriology.

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