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Questions and Answers
Which virulence factor contributes to P.aeruginosa's innate antibiotic resistance?
Which virulence factor contributes to P.aeruginosa's innate antibiotic resistance?
What is the primary pathogenic species of Neisseria responsible for gonorrhoea?
What is the primary pathogenic species of Neisseria responsible for gonorrhoea?
What role do fimbriae play in the virulence of Neisseria?
What role do fimbriae play in the virulence of Neisseria?
Which of the following is NOT a virulence factor of P.aeruginosa?
Which of the following is NOT a virulence factor of P.aeruginosa?
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How does P.aeruginosa typically colonize different environments?
How does P.aeruginosa typically colonize different environments?
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What is a common characteristic of Escherichia coli?
What is a common characteristic of Escherichia coli?
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Which type of flagella arrangement does Salmonella exhibit?
Which type of flagella arrangement does Salmonella exhibit?
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What is a major virulence factor of Vibrio cholerae?
What is a major virulence factor of Vibrio cholerae?
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What disease is predominantly caused by the pathogenic strains of Escherichia coli?
What disease is predominantly caused by the pathogenic strains of Escherichia coli?
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Which factor contributes to the pathogenicity of Salmonella enterica?
Which factor contributes to the pathogenicity of Salmonella enterica?
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What characteristic is true of Rickettsia?
What characteristic is true of Rickettsia?
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How does Vibrio cholerae primarily spread among populations?
How does Vibrio cholerae primarily spread among populations?
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What role do Bacteroides play in the human body?
What role do Bacteroides play in the human body?
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What is the significance of the virulence factor, endotoxin, found in Gram-negative bacteria like Escherichia coli?
What is the significance of the virulence factor, endotoxin, found in Gram-negative bacteria like Escherichia coli?
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What type of environment does Pseudomonas aeruginosa thrive in?
What type of environment does Pseudomonas aeruginosa thrive in?
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Which of the following is considered a zoonotic disease associated with Gram-negative bacteria?
Which of the following is considered a zoonotic disease associated with Gram-negative bacteria?
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What is a primary disease caused by Treponema?
What is a primary disease caused by Treponema?
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Which of the following best describes a common virulence factor of bacteria?
Which of the following best describes a common virulence factor of bacteria?
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Which property differentiates Escherichia from other bacteria in the Enterobacteriaceae family?
Which property differentiates Escherichia from other bacteria in the Enterobacteriaceae family?
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What is the significance of classifying bacteria based on phylogeny and phenotypes?
What is the significance of classifying bacteria based on phylogeny and phenotypes?
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Which bacteria are noted for being diverse Gram-negative pathogens?
Which bacteria are noted for being diverse Gram-negative pathogens?
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Study Notes
Medically-Important Gram-Negative Bacteria
- This material is reproduced by the University of Sydney under the Australian Copyright Act.
- Specific learning outcomes involve discussing bacteria's role in medicine and human disease, naming relevant Gram-negative bacteria, describing their phylogeny, microscopic morphology, normal habitat, human diseases caused, and unique characteristics.
Classification of Bacteria
- Bacteria are categorized using both a phenetic (based on observable characteristics) and phylogenetic (based on genetic relatedness) approach.
- Phenetic characteristics include Gram reaction, morphology, carbon/energy sources, and electron acceptors (aerobic/anaerobic).
- Phylogenetic characteristics include ribosomal RNA sequence and other DNA, RNA, and protein sequences.
- In some cases, the classification based on genetics matches observed characteristics (e.g., endospore formers are Gram-positive). Other cases reveal differences between classification methods.
- Both methods are useful for different classification purposes.
Diversity of Gram-Negative Bacteria
- Several medically relevant Gram-negative bacteria are discussed, including:
- Escherichia coli
- Salmonella
- Vibrio cholerae
- Pseudomonas aeruginosa
- Neisseria
- Rickettsia
- Bacteroides
- Treponema pallidum
Specific Bacterial Species (Examples)
-
Escherichia coli (E. coli):
- Facultative anaerobe, heterotrophic, Gram-negative rods
- Found in the gut; some strains cause infections (e.g., 0157, 0111), most are normal flora and beneficial.
- Examples of virulence factors are endotoxins, enterotoxins
- Used as a model organism in microbiology.
-
Salmonella:
- Facultative anaerobe, heterotrophic, Gram-negative rods
- Found in animal guts; some strains are pathogenic to humans (e.g., foodborne infections, typhoid).
- Includes S. enterica and S. typhi.
- Virulence factors include endotoxin, enterotoxin, and cytotoxin.
-
Vibrio cholerae:
- Facultative anaerobic, heterotrophic, Gram-negative curved rods
- Mostly found in marine environments; causes cholera (severe diarrhea)
- A key virulence factor is cholera toxin.
-
Pseudomonas aeruginosa:
- Aerobic, heterotrophic, Gram-negative rods
- Primarily opportunistic infections, common in nosocomial settings (e.g. burn injuries).
- Innate antibiotic resistance, haemolysin, and proteases are key virulence factors.
-
Neisseria species:
- Aerobic, heterotrophic, Gram-negative diplococci
- Exists as a carrier in the human throat and nose
- Pathogenic species include N. gonorrhoeae (causes gonorrhea) and N. meningitidis (causes meningitis).
- Virulence factors include capsule for immune evasion and fimbriae for tissue adhesion.
-
Rickettsia species:
- Aerobic, heterotrophic, Gram-negative coccobacilli
- Obligate intracellular parasites of arthropods.
- Cannot be cultured in vitro.
- Vectors are arthropods (e.g., fleas, lice, ticks).
- An example is R. prowazekii, responsible for epidemic typhus.
-
Bacteroides species:
- Obligate anaerobe, heterotrophic, Gram-negative rods
- Significant component of human normal flora.
- Plays a crucial role in digestion.
- Opportunistic pathogens; example includes B. fragilis which cause infection in the gut (e.g., abscesses).
-
Treponema pallidum:
- Anaerobic, heterotrophic, Gram-negative spirochetes.
- Obligate parasite; causes syphilis.
- Classified by its morphology and motility.
Additional Bacterial Aspects
- Phylogenetic trees based on 16S rRNA alignments are important for classifying bacterias.
- Identifying specific bacteria using selective and differential microbiological media (e.g. XLD) is introduced.
- Pathogenesis, clinical outcomes and relevant public health are also discussed.
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Description
Explore the role of gram-negative bacteria in medicine and human disease with this quiz. Discuss their classification, phylogeny, morphology, and associated diseases. Understand how phenetic and phylogenetic characteristics categorize these important microorganisms.
