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Review of Chapter 10 and 11 from Determinitive 1st and 2nd Editions

Overview of Determinative Bacteriology

  • 1st Edition: Based on phenotypic characteristics and biochemical tests.
  • 2nd Edition: Focuses on the systematics of bacteria based on genetic and evolutionary relationships using differences in rRNA (ribosomal RNA) sequences.

Serology in Infectious Disease

  • Definition of Serology: A branch of immunology that involves the detection and measurement of antibodies and antigens related to infectious diseases.
  • Advantages of Serological Testing:
      - Highly specific for identifying pathogens.
      - Provides a quicker diagnosis compared to traditional methods.
  • Examples of Serological Tests:
      - Slide agglutination test: Detects the presence of specific antibodies.
      - ELISA (Enzyme-Linked Immunosorbent Assay): Used for quantifying antibodies or antigens.
      - Western Blot: Used for confirming the presence of specific proteins.

Phage Typing

  • Definition: A method used to identify bacterial strains by exposing them to a known bacteriophage.
  • Purpose of Phage Typing: Mainly used to trace bacterial outbreaks.

Understanding Bacteria and Cytometry

  • Cytometry in Bacteriology: A technique used to analyze bacteria in a fluid without culturing them.
      - The sample is passed through a laser beam; the machine measures how light is scattered to compare unique patterns from different bacteria.

Domains of Life

  • The Three Domains:
      1. Archaea
      2. Bacteria
      3. Eukaryotes
  • Archaea vs. Bacteria: Only Archaea and Bacteria are found in all three domains.
  • General Features of Archaea:
      - Lack peptidoglycan in cell walls.
      - Not known to cause disease.
      - Often live in extreme environments (Thermophiles, Halophiles, Methanogens).

Taxonomic Hierarchy

  • The order from the highest to the lowest: Domain → Kingdom → Phylum → Class → Order → Family → Genus → Species.

Chapter 11: Proteobacteria Classification

Proteobacteria Overview

  • Classes of Proteobacteria:
      1. Alpha
      2. Beta
      3. Gamma
      4. Delta
      5. Epsilon
      6. Zeta
      - All classes are Gram-negative.

Alpha Proteobacteria

  • Characteristics: Nitrogen fixers.
  • Symbiotic Relationships:
      - Azospirillum with tropical grasses, including sugar cane.
      - Rhizobium with legumes.
  • Nitrogen Fixation Process:
      - Converts N₂ (nitrogen gas) to NH₃ (Ammonia) and further to NH₄⁺ (Ammonium).
  • Nitrification: Two-step process:
      1. Nitrosomonas oxidizes NH₃ → NO₂⁻ (Nitrite).
      2. Nitrobacter oxidizes NO₂⁻ → NO₃⁻ (Nitrate).
Pathogenic Alpha Proteobacteria
  • Agrobacterium: Causes galls in plants.
  • Bartonella: Causes Cat Scratch Fever.
  • Rickettsia: Part of the spotted fever group, transmitted by tick parasites.
  • Brucella: Causes Brucellosis in ungulates.

Beta Proteobacteria

  • Features: Thrive in low-nutrient environments.
  • Pathogenic Representatives:
      - Bordetella pertussis: Causes whooping cough.
      - Neisseria:
        - N. gonorrhoeae: Causes gonorrhea (Leukorrhea).
        - N. meningitidis: Causes bacterial meningitis.

Gamma Proteobacteria

  • Subgroups:
      1. Purple sulfur bacteria: Obligate anaerobes that produce sulfur granules through hydrogen sulfate oxidation.
      2. Intracellular Pathogens:
        - Legionella pneumophila: Causes Legionnaires' disease.
        - Coxiella: Causes Q fever.
      3. Methane Oxidizers: Use methane as a carbon source.
      4. Facultative Anaerobes: Include the following families:
        - Enterobacteriaceae (Enterics): Found in intestinal tracts, ferment glucose, and produce toxins.
        - Escherichia coli:
          - Strain O157:H7 linked to Hemolytic Uremic Syndrome.
        - Salmonella:
          - Contains only 2 species, but many serovars; carriers are reptiles and birds (especially chickens).
          - Salmonella typhimurium: Associated with typhoid fever; asymptomatic carriers may have bacteria in the gallbladder.
        - Shigella: Causes dysentery (watery diarrhea); outbreaks common in childcare facilities.
Pathogenic Species Under Enterobacteriaceae
  • Yersinia:
      - Y. enterocolitica: Transmitted through undercooked pork.
      - Y. pestis: Causes the Bubonic plague (Black Death); rodent reservoir and flea vector.
  • Cronobacter: Responsible for the infant formula recall (2021-2022); associated with nosocomial infections.
  • Other Enterobacteriaceae:
      - E. aerogenes: UTIs, endocarditis, respiratory infections.
      - Serratia marcescens: Contaminant in medical equipment; occurs in saline or sterile solutions.
      - Proteus (P. mirabilis & P. vulgaris): Common in hospital settings, but not the most common cause of infections.

Vibrionaceae and Others

  • Vibrionaceae: Found in untreated or brackish water.
      - V. cholerae: Causes cholera, characterized by "rice water stool" and can lead to rapid dehydration and hypovolemic shock.
  • Pasteurellaceae and their impacts:
      - Causes sepsis in cattle and respiratory issues in chickens.
      - Haemophilus influenzae: Causes earaches, bronchitis, and pneumonia in children.

Pseudomonadales

  • Characteristics: Capable of breaking down many organic compounds.
  • Pseudomonas aeruginosa: Associated with infections in burn wounds and nosocomial infections; leading cause of morbidity and mortality in cystic fibrosis patients.
      - Exhibits resistance to antibiotics and may grow in antiseptics.

Delta and Epsilon Proteobacteria

  • Delta Proteobacteria: Important in the sulfur cycle.
  • **Epsilon Proteobacteria:
      - *Campylobacter:* Causes spontaneous abortions in domestic animals.
      - Helicobacter pylori: Known as the cause of peptic ulcers.

Non-Proteobacteria (Gram +)

Cyanobacteria
  • Large oxygen output; are bacteria, not algae; and fix nitrogen through photosynthesis.
Firmicutes
  • Two Groups:
      1. Low G+C ratio.
      2. High G+C ratio (Actinobacteria).
  • Characteristics of Firmicutes:
      - Many produce endospores.
  • Examples:
      - Clostridium: Obligate anaerobes that produce toxins.
        - C. tetani: Causes tetanus (lockjaw).
        - C. botulinum: Causes botulism; linked to home canning.
        - C. perfringens: Causes gas gangrene.
        - C. difficile: Nosocomial infection, often after antibiotic treatment.
      - Bacillus: Endospore-forming, facultative anaerobes.
        - B. anthracis: Causes Anthrax.
        - B. cereus: Associated with cereal grains and rice.
      - Lactobacillus: Produces sour foods (yogurt, pickles).
        - L. acidophilus: Used as a probiotic.
Staphylococcus
  • Characteristics:
      - Cocci that tolerate high osmotic pressure; are normal flora of the skin and nasal passages.
      - Staphylococcus aureus: Opportunistic pathogen (MRSA).
Streptococcus
  • Group Characteristics: Produces hemolysins and causes various diseases:
      - S. pyogenes: Causes pharyngitis, tonsillitis, strep throat, scarlet fever, necrotizing fasciitis, and bacteremia.
      - S. agalactiae: Major cause of neonatal infections, pneumonia, and endocarditis.
      - Enterococcus: Previously classified under Group D Streptococcus; associated with nosocomial infections, UTIs, and wound infections.
      - Listeria monocytogenes: Causes listeriosis, particularly serious for pregnant women; can survive in refrigerated deli meats and cheeses.
Mycoplasma
  • Characteristics: Lack cell walls.
      - Mycoplasma pneumoniae: Leads to walking pneumonia.
Actinobacteria (High G+C)
  • Examples:
      - Streptomyces: A common source of antibiotics.
      - Mycobacterium:
        - Waxy cell walls; acid-fast.
        - M. tuberculosis: Causes tuberculosis.
        - M. leprae: Causes Hansen's disease (leprosy).
Miscellaneous Bacteria
  • Chlamydia: An obligate intracellular parasite.
      - C. trachomatis: Causes chlamydia.
  • Spirochetes:
      - Borrelia:
        - B. burgdorferi: Causes Lyme disease (characteristic bull's-eye rash).
      - Treponema:
        - T. pallidum: Causes syphilis.