STM 311-BACTERIOLOGY OSUNTECHCOLLEGE 2021/2022 FIRST SEMESTER EXAMINATION

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ANWSER

 

Question 1:
a. The basic ranks of classification system in bacterial taxonomy include:

  1. Domain – The highest rank, categorizing organisms into Bacteria, Archaea, or Eukarya.
  2. Kingdom – Subdivision of domain. Bacteria fall under the Kingdom Monera.
  3. Phylum – Groups organisms based on major structural features.
  4. Class – A more specific group within a phylum.
  5. Order – Groups bacteria sharing a set of similar nature.
  6. Family – A group of related genera.
  7. Genus – A group of closely related species.
  8. Species – The most specific rank; a group of organisms with similar characteristics and capable of interbreeding.

b. Characteristics used in taxonomy classification:
i. Classical – Based on observable traits like staining properties (e.g., Gram staining), shape, motility, and metabolic capabilities.
ii. Morphological – Based on cell shape, arrangement (cocci, bacilli, spirilla), spore formation, presence of flagella or capsules.
iii. Ecological – Based on the natural habitat, nutrient requirements, temperature, pH preference, and interaction with other organisms.

Question 2:
a. Main species of Staphylococcus of medical importance include:

  • Staphylococcus aureus
  • Staphylococcus epidermidis
  • Staphylococcus saprophyticus

b. Three genera of Gram-positive spore-forming rods:

  1. Bacillus – Aerobic, catalase-positive, soil-dwelling; e.g., Bacillus anthracis.
  2. Clostridium – Anaerobic, catalase-negative, produces toxins; e.g., Clostridium tetani.
  3. Sporosarcina – Unique among cocci to form spores, found in soil and feces.

c. General characteristics of a named Gram-positive cocci bacterium (Staphylococcus aureus):

  • Gram-positive cocci in clusters
  • Catalase positive
  • Coagulase positive
  • Produces golden-yellow colonies
  • Causes infections such as boils, abscesses, and food poisoning

Question 3:
a. (Diagram needed) A well-labeled diagram of a typical bacterial cell should include:

  • Cell wall
  • Plasma membrane
  • Cytoplasm
  • Ribosomes
  • Nucleoid (DNA)
  • Plasmid
  • Flagella
  • Pili
  • Capsule

b. Similarity and dissimilarity between fimbriae and pili:

  • Similarity: Both are hair-like appendages used for attachment.
  • Dissimilarity: Fimbriae are shorter and more numerous; pili are longer and fewer, often used in conjugation.

Question 4:
a. (Graphical diagram needed) Bacterial growth curve phases:

  1. Lag phase – No growth, bacteria adapt to environment.
  2. Log (exponential) phase – Rapid growth and division.
  3. Stationary phase – Growth slows due to nutrient depletion.
  4. Death phase – Decline in population due to waste accumulation.

b. Classification of culture media based on composition:

  1. Synthetic (defined) media – Exact chemical composition known.
  2. Complex (undefined) media – Contains extracts; composition not exactly known (e.g., nutrient broth).
  3. Enriched media – Contains nutrients for fastidious organisms (e.g., blood agar).
  4. Minimal media – Contains only essential nutrients for growth.

c. Four properties of agar:

  • Not digested by most bacteria
  • Melts at high temperature (~100°C)
  • Solidifies at ~40°C
  • Provides a stable surface for bacterial growth

Question 5:
a. Six factors influencing bacterial growth under lab conditions:

  1. Temperature
  2. pH
  3. Oxygen concentration
  4. Moisture
  5. Nutrient availability
  6. Light (for photosynthetic bacteria)

b. Three common methods of separating mixed culture:

  1. Streak plate method – For isolating pure colonies.
  2. Spread plate method – For counting or isolating colonies.
  3. Pour plate method – Useful for enumerating bacteria in samples.

Question 6:
Five classes of bacterial culture media based on purpose/function:

  1. Selective media – Allows growth of specific bacteria only.
    • Examples: MacConkey agar, Mannitol salt agar
  2. Differential media – Distinguishes between bacteria based on metabolic activity.
    • Examples: Eosin methylene blue (EMB) agar, MacConkey agar
  3. Enriched media – Contains extra nutrients for fastidious organisms.
    • Examples: Blood agar, Chocolate agar
  4. Transport media – Maintains viability during transport.
    • Examples: Stuart’s medium, Amies medium
  5. General purpose media – Supports growth of a broad range of bacteria.
    • Examples: Nutrient agar, Tryptic soy agar

Question 7:
a. Three importance of bacterial taxonomy:

  1. Facilitates identification and classification
  2. Helps in understanding evolutionary relationships
  3. Assists in diagnosis and treatment of infections

b. Basic ranks of taxonomy classification:

  1. Domain
  2. Kingdom
  3. Phylum
  4. Class
  5. Order
  6. Family
  7. Genus
  8. Species

c. Four methods of maintaining pure culture:

  1. Refrigeration
  2. Subculturing periodically
  3. Storage in paraffin oil
  4. Lyophilization (freeze-drying)

 

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