Systematic Bacteriology: Staphylococcus to Lactobacillus
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Systematic Bacteriology: Staphylococcus to Lactobacillus

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Questions and Answers

What do Streptococcus milleri produce from dietary sucrose, contributing to the development of dental caries?

  • Streptococcal pyrogenic exotoxins
  • M protein
  • Hyaluronidase
  • Fructan and/or glucan (correct)

    • What is the most serious infection occurring in patients with abnormal heart valves?

  • Tonsillitis
  • Dental caries
  • Subacute bacterial endocarditis (correct)
  • Pharyngitis

    • What is the characteristic arrangement of Streptococcus pyogenes cells?

  • Gram-positive rods
  • Gram-positive cocci in chains (correct)
  • Gram-negative rods
  • Gram-negative cocci

    • What is the most important virulence factor of Streptococcus pyogenes?

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

    What is the commonest infection caused by Streptococcus pyogenes?

    <p>Pharyngitis and/or tonsillitis</p> Signup and view all the answers

    What is the alternative antibiotic given to penicillin-allergic patients?

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

    What is the term for the complete hemolysis caused by Streptococcus pyogenes on blood agar?

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

    What is the purpose of giving a single large dose of ampicillin or amoxicillin before dental procedures?

    <p>To prevent subacute bacterial endocarditis</p> Signup and view all the answers

    What is the arrangement of Staphylococcus bacteria?

    <p>In grape-like clusters</p> Signup and view all the answers

    What is the primary difference between coagulase-positive and coagulase-negative Staphylococcus?

    <p>The ability to produce staphylocoagulase</p> Signup and view all the answers

    Which of the following is NOT a characteristic of Staphylococcus aureus?

    <p>Catalase-negative</p> Signup and view all the answers

    What is the primary habitat of Staphylococcus aureus?

    <p>Anterior nares</p> Signup and view all the answers

    What is the function of staphylocoagulase in Staphylococcus aureus?

    <p>Converts plasma fibrinogen to fibrin</p> Signup and view all the answers

    What type of haemolysis is produced by Staphylococcus aureus on blood agar?

    <p>Complete haemolysis</p> Signup and view all the answers

    Which of the following is a virulence factor of Staphylococcus aureus?

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

    What is the primary difference between Staphylococcus aureus and Staphylococcus epidermidis?

    <p>Pathogenic potential</p> Signup and view all the answers

    What is the primary mode of transmission of pharyngitis?

    <p>Respiratory droplets</p> Signup and view all the answers

    What is the characteristic tonsillar exudate in cases of tonsillitis?

    <p>Grayish white exudate</p> Signup and view all the answers

    What is the possible complication of streptococcal pharyngitis after 2-4 weeks?

    <p>Rheumatic heart disease</p> Signup and view all the answers

    What is the characteristic feature of scarlet fever?

    <p>All of the above</p> Signup and view all the answers

    What is the effective treatment for S.pyogenes diseases?

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

    What is the characteristic arrangement of Enterococcus species?

    <p>In short chains</p> Signup and view all the answers

    What is the ability of Enterococci to grow in broth containing?

    <p>6.5% NaCl</p> Signup and view all the answers

    Why can Enterococci survive in the root canal?

    <p>All of the above</p> Signup and view all the answers

    What is the function of a biofilm in microorganisms?

    <p>To make them more resistant to destruction and antimicrobials</p> Signup and view all the answers

    Which species is most commonly isolated from infections involving biofilm-producing microorganisms?

    <p>Enterococcus faecalis</p> Signup and view all the answers

    What is the characteristic shape of Neisseria genus members?

    <p>Kidney-shaped</p> Signup and view all the answers

    Which Neisseria species is a commensal inhabitant of the oro- and nasopharynx of healthy individuals?

    <p>Neisseria lactamica</p> Signup and view all the answers

    What is the primary function of pili in Neisseria gonorrhoeae?

    <p>To mediate attachment to epithelial cells</p> Signup and view all the answers

    What is the selective medium used to isolate Neisseria gonorrhoeae from specimens contaminated by other microbes?

    <p>Modified Thayer-Martin medium</p> Signup and view all the answers

    What is the primary symptom of gonorrhoea in males?

    <p>Acute urethritis with dysuria and purulent discharge</p> Signup and view all the answers

    What is the primary mode of transmission of Neisseria gonorrhoeae causing oral gonorrhoea?

    <p>Orogenital exposure</p> Signup and view all the answers

    What is the primary mode of transmission of diphtheriae?

    <p>By droplets or direct contact</p> Signup and view all the answers

    What is the composition of the local pseudomembrane in diphtheria?

    <p>Mucosal cell debris, infection products and fibrinous exudates</p> Signup and view all the answers

    What is the primary mechanism of toxin production in diphtheria?

    <p>The diphtheria bacilli produce toxins that are absorbed and disseminated through blood</p> Signup and view all the answers

    What is the typical duration of the incubation period of diphtheria?

    <p>2-5 days</p> Signup and view all the answers

    What is the most common complication of diphtheria?

    <p>Myocarditis and neuritis</p> Signup and view all the answers

    What is the primary purpose of laboratory diagnosis in diphtheria?

    <p>To confirm the clinical diagnosis</p> Signup and view all the answers

    What is the primary method of identification of C. diphtheriae?

    <p>Colony morphology and microscopic examination</p> Signup and view all the answers

    What is the primary specimen used for microbiological diagnosis of diphtheria?

    <p>Throat swabs</p> Signup and view all the answers

    Study Notes

    Staphylococcus

    • Staphylococcus species are Gram-positive, spherical bacteria arranged in grape-like clusters, and are facultative anaerobes and catalase-positive.
    • The catalase test is important in distinguishing streptococci (catalase-negative) from staphylococci.
    • The ability to produce staphylocoagulase divides the genus into two groups: "coagulase-positive" and "coagulase-negative".
    • Staphylococcus aureus is coagulase-positive, has the greatest pathogenic potential, and is the most medically important member of the genus.
    • Anterior nares and the skin are the main habitats for S. aureus and S. epidermidis, respectively.
    • S. aureus grows on:
      • Nutrient agar, forming golden yellow pigmented colonies
      • Blood agar, producing colonies surrounded with a zone of ß-haemolysis (complete haemolysis)
    • Important virulence factors of S. aureus include:
      • Staphylocoagulase: converts plasma fibrinogen to fibrin, leading to the formation of a fibrin barrier, protecting bacteria from phagocytes and immune defences, and localizing infection.

    Streptococcus pyogenes

    • Streptococcus pyogenes are Gram-positive cocci arranged in chains, and produce beta-haemolysis (complete haemolysis) on blood agar.
    • Important virulence factors of S. pyogenes include:
      • M protein: enables the bacteria to colonize the skin and inhibits phagocytosis.
      • Streptococcal pyrogenic exotoxins (SPE-A, B, and C): pyrogenic exotoxin A is referred to as erythrogenic toxin or scarlet fever toxin.
      • Enzymes (e.g., streptokinase and hyaluronidase): contribute to the spreading nature of streptococcal infections.
    • Important diseases caused by S. pyogenes include:
      • Pharyngitis (sore throat) and/or tonsillitis
      • Scarlet fever: characterized by the development of scarlet red rash, strawberry tongue, and a whitish coating on the back of the throat.
      • Skin and soft tissue infections (e.g., cellulitis)

    Enterococcus

    • Enterococcus species are Gram-positive cocci arranged in short chains, are catalase-negative, and are found normally in the oral cavity, human intestine, and female genital tract.
    • The commonest two species are Enterococcus faecalis and Enterococcus faecium.
    • Enterococci are:
      • Facultative anaerobes
      • Able to grow at 45°C
      • Able to grow in broth containing 6.5% NaCl
      • Able to grow on mitis salivarius agar, producing dark, blue-black colonies
      • Able to grow on bile esculin agar, giving black colonies
    • Enterococci are responsible for oral conditions, including:
      • Periodontitis (chronic infection of the gingival and periodontal ligaments)
      • Failed root canal treatment
    • Enterococcus faecalis is the species most commonly isolated from these infections.

    Neisseria

    • Neisseria species are Gram-negative cocci arranged in pairs with adjacent sides flattened to give a characteristic kidney-shape, and are aerobic and oxidase-positive.
    • The genus includes:
      • Neisseria gonorrhoeae (gonococci): causes the sexually transmitted disease gonorrhoea.
      • Neisseria meningitidis (meningococci): causes meningitis.
      • Commensal Neisseria species: inhabitants of oro- and nasopharynx of healthy individuals (e.g., N. lactamica and N. sicca).
    • Neisseria gonorrhoeae:
      • Is a fastidious species which grows on:
        • Chocolate agar (enriched medium)
        • Modified Thayer-Martin medium (MTM): a selective medium containing antibiotics, allowing easier isolation of the organism from specimens contaminated by other microbes.
      • Important virulence factors include:
        • Pili that mediate attachment to epithelial cells
        • Outer membrane proteins that contribute to invasion
        • IgA1 protease that may have a role in colonization
      • Important diseases caused by N. gonorrhoeae include:
        • Gonorrhoea: a sexually transmitted infection affecting males and females, causing acute urethritis with dysuria and purulent discharge in males, and cervicitis with a purulent cervical discharge in females.
        • Oral infection (oral gonorrhoea): usually occurs after orogenital exposure.

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    Description

    This quiz covers the morphology, culture characteristics, virulence factors, diseases, and laboratory diagnosis of bacteria including Staphylococcus, Streptococcus, Enterococcus, Neisseria, Corynebacterium, and Lactobacillus.

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