Microbiology - Gram Positive Bacteria
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Questions and Answers

Which Gram-positive bacterium is primarily responsible for causing strep throat and skin infections?

  • Clostridium tetani
  • Bacillus subtilis
  • Streptococcus pyogenes (correct)
  • Streptococcus pneumoniae

    • What unique feature distinguishes Streptococcus pneumoniae from other Gram-positive bacteria?

  • Presence of a polysaccharide capsule (correct)
  • Rod-shaped morphology
  • Non-pathogenic status
  • Ability to form endospores

    • Which of the following diseases is primarily caused by Mycobacterium tuberculosis?

  • Tuberculosis (correct)
  • Whooping cough
  • Meningitis
  • Chickenpox

    • What is a non-characteristic feature of Actinobacteria?

    <p>Primarily pathogenic lifestyle</p> Signup and view all the answers

    In terms of microscopic morphology, how are most Gram-positive bacteria classified?

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

    Which of the following Gram-positive bacteria is known for forming endospores?

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

    What is a common habitat for Streptococcus pneumoniae?

    <p>Respiratory tract of humans</p> Signup and view all the answers

    Which Gram-positive bacterium is classified as an Actinobacterium?

    <p>Mycobacterium leprae</p> Signup and view all the answers

    What disease is associated with Streptococcus pyogenes that can occur following a throat infection?

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

    Which of the following statements about Gram-positive bacteria is incorrect?

    <p>They typically stain pink in the Gram staining process.</p> Signup and view all the answers

    Which characteristic is NOT true about Gram-positive bacteria?

    <p>They are always pathogenic.</p> Signup and view all the answers

    What is a common virulence factor of Chlamydia trachomatis?

    <p>Unusual cell wall that allows growth inside phagocytes.</p> Signup and view all the answers

    Which of the following is true regarding the Actinobacteria phylum?

    <p>Some members are known to produce antibiotics.</p> Signup and view all the answers

    Bacillus anthracis is notable because it is a potential agent of bioterrorism due to its:

    <p>Production of stable endospores.</p> Signup and view all the answers

    Which of the following is an incorrect statement about Streptococcus pneumoniae?

    <p>It typically forms endospores.</p> Signup and view all the answers

    How does the structure of the cell wall of Gram-positive bacteria facilitate their classification?

    <p>Thicker peptidoglycan layer.</p> Signup and view all the answers

    What distinguishes Firmicutes from Actinobacteria?

    <p>Firmicutes have a lower GC content in their DNA.</p> Signup and view all the answers

    Chlamydia can be transmitted to koalas, leading to which of the following conditions?

    <p>Hypertrophy of eyelids.</p> Signup and view all the answers

    What disease is primarily associated with Streptococcus pyogenes, which is known to be contagious and mostly affects young children?

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

    Which of the following characteristics is unique to Streptococcus pneumoniae among the genera mentioned?

    <p>Demonstrates alpha-haemolysis on blood agar</p> Signup and view all the answers

    What makes encapsulated strains of Streptococcus pneumoniae significantly more virulent compared to non-encapsulated strains?

    <p>Ability to overcome phagocytosis</p> Signup and view all the answers

    Which Gram-positive cocci are known to be non-motile and can be both normal flora and pathogenic species?

    <p>Both B and C</p> Signup and view all the answers

    What is a common trait of Staphylococcus aureus that contributes to its ability to survive in harsh environments?

    <p>Resistance to high salt concentrations</p> Signup and view all the answers

    What diagnostic test is highly relevant for Staphylococcus aureus, specifically serving to identify this organism?

    <p>Coagulase test</p> Signup and view all the answers

    Which of the following Gram-positive bacteria is primarily responsible for yogurt and cheese production?

    <p>Lactobacillus thermophilus</p> Signup and view all the answers

    What best describes the arrangement of cocci in Streptococcus species in contrast to Staphylococcus species?

    <p>Chains versus clusters</p> Signup and view all the answers

    Identifying which organism involves observing Gram-positive cocci in pairs and short chains during a sputum analysis?

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

    What type of infections can Staphylococcus aureus primarily cause?

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

    Study Notes

    • This material has been reproduced by the University of Sydney.
    • Copyright Act 1968 applies.
    • Further reproduction is subject to copyright protection.

    Learning Outcomes - Gram Positives

    • Discuss the importance of bacteria in medicine and human disease, with examples.
    • Name 6 medically-relevant Gram-positive bacteria (and 1 G-ve) and give details of:
      • phylogeny
      • microscopic morphology
      • normal habitat
      • human diseases caused
      • distinctive/unique features

    Relevant Unit of Study Learning Outcomes

    • LO1: Understand the microbial world and its relationships with other life forms and the environment.
    • LO2: Describe and understand organism structures, functions, and bio-relationships of major microbial groups (bacteria, fungi, viruses, protozoa) in humans and the environment
    • LO3: Describe pathological processes of infection in humans for each microbial group.

    Phylogenetic Tree of Bacteria

    • The tree is based on the alignment of 16S rRNA sequences.
    • Bacterial names shown represent phylum-level groups.
    • The tree is adapted from Brock.
    • Diverse groups of bacteria are showcased.

    Gram-Positive and Gram-Negative Bacteria: Medical Importance

    • Both Gram-positive and Gram-negative bacteria are medically important.
    • Gram-positive examples: Firmicutes (Bacillus, Clostridium, Lactobacillus, Staphylococcus, Streptococcus), Actinobacteria (Mycobacterium).
    • Gram-negative example: Chlamydiae (Chlamydia).

    Chlamydia

    • Aerobic, heterotrophic, G-ve cocci
    • Obligate intracellular parasites of humans and animals.
    • Cause sexually transmitted disease and eye infections.
    • Cannot be grown on agar; small genome (~1 Mb)
    • Dependent on host cells for ATP and metabolites.
    • Causes urethritis (STD) and trachoma(eye infection)
    • A serious pathogen for koalas.
    • Unusual cell wall allows growth inside phagocytes.
    • No peptidoglycan → intrinsic resistance to all antibiotics targeting peptidoglycan.

    Gram-Positive Bacteria: Phylum Firmicutes, Phylum Actinobacteria

    • Distinguished from Gram-negatives by thicker peptidoglycan and lack of outer membrane.
    • Divided into Firmicutes (low GC) and Actinobacteria (high GC) groups. GC means %GC content of DNA.
    • Firmicutes: facultative anaerobic rods or cocci, some form endospores.
    • Actinobacteria: aerobic rods or filaments, some form exospores (e.g., Streptomyces).

    Firmicutes: Gram-Positive Rods

    • May be facultatively anaerobic or strictly anaerobic.
    • Contain both normal flora and pathogenic species.
      • Lactobacillus (normal flora)
      • Bacillus (primarily soil organisms, some are pathogens)
      • Clostridium (primarily soil organisms, some are pathogens).

    Bacillus

    • Facultative anaerobic, heterotrophic, G+ve rods.
    • Ubiquitous in the environment, especially soil.
    • Transient flora on skin.
    • Older/starving/stressed cells make endospores.
    • B. anthracis causes anthrax: highly infectious and deadly disease, usually zoonotic (transmitted from animals).
    • A possible bioterrorism agent due to stable endospores.
    • Anthrax exotoxin consists of 3 secreted proteins that work together to kill cells.
    • Anthrax has cutaneous, gastrointestinal, and pulmonary presentations with varied mortalities.

    Clostridium

    • Anaerobic, heterotrophic, G+ve rods with endospores.
    • Habitat: soil, human and animal gut.
    • Some species are normal flora; some are pathogens.
    • Pathogenic clostridia produce potent exotoxins.
      • C. tetani → tetanus
      • C. botulinum → botulism.

    C. tetani

    • Causes muscle rigidity and death due to respiratory failure.
    • Virulence factor: tetanospasmin (an exotoxin).
    • Requires deep wounds to multiply (anaerobic).
    • Common-source disease, not contagious.
    • Source: soil or manure; inoculated into puncture wounds.
    • Blocks transmission of relaxation signals to muscles, causing body rigidity.

    C. botulinum

    • Causes botulism, a dangerous type of food poisoning (common-source disease).
    • Lives in soil, spores enter food chain, persist in processing, germinate in food (anaerobic, neutral pH).
    • Virulence factor: botulinum toxin (BOTOX) – most deadly poison known. Lethal dose ~1 microgram.
    • Causes flaccid paralysis, opposite effect of tetanus.
    • BOTOX used in cosmetic medicine, despite extreme toxicity.

    Lactobacillus

    • Facultative anaerobic, heterotrophic, G+ve non-sporing rods.
    • Normal flora of mouth, gut, vagina.
    • Non-pathogenic.
    • Probiotic effect (gut competition with pathogens).
    • Cheese and yoghurt production: lactic acid fermentation.

    Gram-Positive Cocci

    • All are non-motile, and are either aerobic or facultative.
    • Contain both normal flora and pathogenic species
      • Staphylococcus
      • Streptococcus

    Staphylococcus

    • Facultative anaerobic, heterotrophic, G+ cocci (clumps).
    • Habitat: human-associated (skin, nose) either normal flora or pathogen (e.g., wound infection).
    • Tough cell wall makes them resistant to physical stress (e.g., desiccation) → long survival in environment.
    • Resistant to salt; trait needed to survive on skin & nose.

    Staphylococcus aureus ("Golden Staph")

    • Opportunistic pathogen.
    • Infections: wound infections, boils, impetigo, toxic shock.
    • Nosocomial spread (hospital strains antibiotic resistant).
    • Morphology arrangement: Staph vs Strep (Staph: clusters).
    • Virulence factors: coagulase, exotoxins.
    • Coagulase is also a diagnostic test.

    Streptococcus

    • Facultative anaerobic, heterotrophic, G+ve cocci (chains)
    • Habitat: mouth and gut of animals and humans.
    • Beneficial streptococci
      • S. thermophilus (yogurt/cheese production)
    • Harmful streptococci
      • S. pyogenes (scarlet fever)
      • S. pneumoniae (pneumonia and meningitis).
    • Virulence factors: capsule, haemolysin; encapsulated strains are 100,000x more virulent.

    Actinobacteria: Streptomyces, Mycobacterium

    • Aerobic.
    • Gram positive filaments or rods
      • Streptomyces (Makes antibiotics)
      • Mycobacterium (causes tuberculosis) Mycobacterium
    • Aerobic, heterotrophic, G+ve rods.
    • Mycolic acids in cell wall → waxy layer → acid-fast stain.
    • Wax protects against stresses, incl. immune system.
    • M. tuberculosis: Tuberculosis (TB)
    • M. leprae: Leprosy
    • M. Tuberculosis: Obligate pathogen of humans, Chronic lung infection.
    • Virulence factors: waxy cell wall (resistance to many stresses, including antibiotics and macrophages).

    General Bacterial Characteristics

    • Classified by phenotype.
    • Diverse habitats and metabolisms.
    • Lack true organelles and multicellularity.
    • Diverse structures, differentiation, life cycles.
    • Pathogens can be closely related to normal flora, including species making antibiotics.
    • Includes medically-significant flora (pathogens and antibiotic-producers).

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    Description

    This quiz focuses on the importance of Gram-positive bacteria in medicine and their relationship with human diseases. You will explore the phylogeny, morphology, habitats, and distinctive features of at least six Gram-positive and one Gram-negative bacteria. Test your understanding of their role in health and disease.

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