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 (C)</p> Signup and view all the answers

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

<p>Cocci (C), Bacilli (D)</p> Signup and view all the answers

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

<p>Clostridium (A)</p> Signup and view all the answers

What is a common habitat for Streptococcus pneumoniae?

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

Which Gram-positive bacterium is classified as an Actinobacterium?

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

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

<p>Scarlet fever (B)</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. (B)</p> Signup and view all the answers

Which characteristic is NOT true about Gram-positive bacteria?

<p>They are always pathogenic. (A)</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. (C)</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. (C)</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. (A)</p> Signup and view all the answers

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

<p>It typically forms endospores. (C)</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. (A)</p> Signup and view all the answers

What distinguishes Firmicutes from Actinobacteria?

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

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

<p>Hypertrophy of eyelids. (B)</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 (A)</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 (C)</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 (A)</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 (A)</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 (D)</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 (A)</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 (C)</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 (A)</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 (D)</p> Signup and view all the answers

What type of infections can Staphylococcus aureus primarily cause?

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

Flashcards

Acidophilus bacteria

Facultative anaerobic, heterotrophic, Gram-positive, non-spore-forming rods. Found in the mouth, gut, and vagina. Usually non-pathogenic but may have a probiotic effect.

Lactobacillus bacteria

Gram-positive bacteria, used as probiotics to compete with pathogens in the gut; also used in the production of cheese and yogurt.

Staphylococcus bacteria

Gram-positive, facultative anaerobic, heterotrophic cocci. Form clusters and can be normal flora (on skin, nose) or pathogens (wound infections).

Staphylococcus aureus

A type of Staphylococcus, often an opportunistic pathogen that causes wound infections, boils, impetigo, and toxic shock syndrome.

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Streptococcus bacteria

Gram-positive, facultative anaerobic, heterotrophic cocci. Form chains and are found in the mouth and gut. Some types are beneficial, others cause infections.

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Streptococcus pyogenes

A harmful Streptococcus species that leads to scarlet fever, often affecting young children.

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Streptococcus pneumoniae

A harmful Streptococcus species associated with pneumonia and meningitis.

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Coagulase test

A diagnostic test used to identify Staphylococcus aureus, based on its ability to clot plasma.

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Impetigo

A skin infection caused by Staphylococcus aureus and/or Streptococcus pyogenes.

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Nosocomial infection

An infection acquired in a healthcare setting.

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Chlamydia trachomatis

A bacterium that causes urethritis (a sexually transmitted disease) and trachoma (an eye infection).

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Virulence factor of Chlamydia

Unique cell wall structure allowing growth within phagocytes (immune cells).

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Gram-positive bacteria

Bacteria with a thick peptidoglycan layer in their cell wall, lacking an outer membrane.

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Peptidoglycan

A polymer essential for the structure of the cell wall in some bacteria.

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Firmicutes

A phylum of Gram-positive bacteria, often facultative anaerobic rods or cocci (some form endospores).

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Actinobacteria

A phylum of Gram-positive bacteria, typically aerobic rods or filaments (some form exospores).

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Bacillus

A genus of facultatively anaerobic, rod-shaped bacteria, often found in soil.

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Endospores

Highly resistant structures formed by some bacteria, including Bacillus, for survival during harsh conditions.

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Bacillus anthracis

A species of Bacillus that causes anthrax, a highly infectious disease.

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Zoonotic Disease

A disease that can be transmitted from animals to humans.

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Gram-positive bacteria

Bacteria that retain the crystal violet stain in a Gram stain procedure, typically have a thick peptidoglycan cell wall.

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Gram-negative bacteria

Bacteria that do not retain the crystal violet stain in a Gram stain, characterized by a thin peptidoglycan layer and an outer membrane.

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Medically-important bacteria

Bacteria that can cause disease in humans, important in medical practice.

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Firmicutes

A phylum of Gram-positive bacteria, medically relevant and containing several common pathogenic species.

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Actinobacteria

A phylum of Gram-positive bacteria with diverse roles in the environment and some medically-important species.

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Chlamydia

A genus of Gram-negative bacteria that are obligate intracellular parasites.

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Bacillus

A genus of Gram-positive, rod-shaped bacteria. Some species produce endospores.

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Clostridium

A genus of Gram-positive, rod-shaped bacteria that often produce endospores.

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Lactobacillus

A genus of Gram-positive, rod-shaped bacteria usually involved in fermentation.

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Staphylococcus

A genus of Gram-positive bacteria that often form clusters.

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Streptococcus

A genus of Gram-positive bacteria that often form chains.

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Mycobacterium

A genus of Gram-positive bacteria known for a thick waxy cell wall.

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Phylogenetic tree

A branching diagram showing the evolutionary relationships among organisms, often based on genetic analysis.

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16S rRNA

A ribosomal RNA molecule used in phylogenetic analysis to determine evolutionary relationships.

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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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