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?

Fructan and/or glucan

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

Subacute bacterial endocarditis

What is the characteristic arrangement of Streptococcus pyogenes cells?

Gram-positive cocci in chains

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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