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).
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.