Bacterial Growth Lecture 4

Study Notes

Lecture presented by Dr. Rasha Mokhtar Elnagar, specializing in Medical Microbiology and Immunology.

Major elements:
- Carbon: Autotrophs obtain carbon from inorganic substances (like CO2), while heterotrophs get it from organic compounds (sugars, lipids, proteins)
- Nitrogen: Autotrophs use inorganic forms like nitrogen gas (N2) and ammonia (NH3); heterotrophs obtain nitrogen from organic compounds.
Minor elements: Essential trace elements include Na, Ca, phosphorus, K, Mg, iron, and sulfur.

pH:
- Most pathogenic bacteria thrive in neutral pH (6.8-7.4).
- Acidophilic bacteria survive in acidic pH (3-5) (e.g., Helicobacter pylori, lactobacillus).
- Alkaliphilic bacteria prefer alkaline conditions (up to 10.5) (e.g., Vibrio cholerae).
Temperature:
- Normal flora and many pathogens grow at or near 37°C (human body temperature).
- Bacteria are classified by their temperature preference:
  - Psychrophilic: 0°C-20°C
  - Mesophilic: 20°C-44°C (most disease-causing bacteria)
  - Thermophilic: 50°C-80°C
Osmotic pressure:
- Most bacteria grow in isotonic (0.9% NaCl) and hypotonic solutions.
- Hypertonic solutions dehydrate most bacteria, but some halophilic bacteria can tolerate high salt concentrations.
Gaseous requirements:
- Oxygen:
  - Strict aerobes require oxygen to grow (e.g., Mycobacterium, Pseudomonas)
  - Strict anaerobes cannot tolerate oxygen (e.g. Clostridium)
  - Facultative anaerobes can grow with or without oxygen (e.g., Escherichia coli)
  - Microaerophiles need low levels of oxygen (e.g., Helicobacter, campylobacter)
  - Aerotolerant anaerobes are not harmed by oxygen, but they don't need it to grow (e.g., Enterococcus faecalis)
- Carbon Dioxide (CO2):
  - Most bacteria require low CO2 levels (0.03%).
  - Capnophilic bacteria need higher levels (5-10%) (e.g., Streptococcus pneumoniae, Neisseria, Brucella abortus).
- Moisture: Water is essential for bacterial growth and metabolic reactions.

Bacterial growth is the division of a bacterium into two daughter cells.
The growth curve shows the relationship between microbial quantity and incubation time.
Phases of growth:
- Lag phase: No increase in number of living bacterial cells.
- Exponential (log) phase: Exponential increase in the number of living bacterial cells.
- Stationary phase: Plateau in the number of living bacterial cells; rate of cell division and death are roughly equal.
- Decline phase: Exponential decrease in the number of living bacterial cells.

Aerobic respiration: Biochemical pathway that uses oxygen to produce energy (38 ATP).
- Glycolysis produces pyruvic acid and a small amount of ATP
Anaerobic respiration: Biochemical pathway that doesn't use oxygen, with different electron acceptors like nitrate or sulfate to generate energy.
- Produces less ATP than aerobic respiration
Fermentation: Biochemical pathway that doesn't use oxygen. Used by some bacteria and muscle cells to produce energy.
- Produces a small amount of ATP from glucose.

A patient with a leg wound, showing thin dark fluid draining and Gram-positive, obligate anaerobic, spore-forming bacilli in the wound swab, most likely has an infection caused by Clostridium tetani.