Bacterial Growth Lecture 4

Study Notes

Lecture on bacterial growth, covering chemical and physical requirements, growth curve, and metabolism

Major elements: Carbon and nitrogen
- Autotrophs: Obtain carbon and nitrogen from inorganic substances, like CO2 and nitrogen gas (N2) or ammonia (NH3)
- Heterotrophs: Obtain carbon and nitrogen from organic compounds like sugars, lipids, and proteins
Minor elements: Na, Ca, phosphorus, potassium, magnesium, iron, and sulfur

pH:
- Most pathogenic bacteria grow best at neutral pH (6.8-7.4)
- Acidophilic bacteria (e.g., Helicobacter pylori, lactobacillus) thrive in acidic pH (3-5)
- Alkaliphilic bacteria (e.g., Vibrio cholerae) prefer alkaline conditions (up to 10.5)
Temperature:
- Normal flora and most pathogens thrive near the human body temperature (37°C)
- Psychrophiles: Grow 0°C - 20°C
- Mesophiles: Grow 20°C – 44°C (bacteria that cause disease fall into this category)
- Thermophiles: Grow 50°C–80°C
Osmotic Pressure:
- Most bacteria can grow in isotonic (0.9% NaCl) and hypotonic solutions
- Hypertonic solutions cause shrinkage and death to bacteria.
- Halophilic bacteria resist high salt concentrations
Gaseous Requirements (O2 & CO2):
- Obligate aerobes: Require oxygen to grow (e.g., Mycobacterium, Pseudomonas)
- Obligate anaerobes: Die in the presence of oxygen (e.g., Clostridium)
- Facultative anaerobes: Can grow with or without oxygen (e.g., Escherichia coli)
- Microaerophiles: Grow best in low oxygen concentrations (e.g., Helicobacter)
- Aerotolerant anaerobes: Do not use oxygen but can grow in its presence without being harmed (e.g., Enterococcus faecalis)
- CO2 Requirements:
- Carbon dioxide (CO2) required for some bacteria, while capnophilic bacteria need higher concentration (5-10%, e.g., Streptococcus pneumonia, Neisseria, Brucella abortus)
Moisture: Water is essential for bacterial growth and metabolic reactions.

Bacterial growth: Division of one bacterium into two daughter cells by simple binary fission. The growth curve represents the relationship between microbial cells and time of incubation
Phases:
Lag phase: No increase in the number of living bacterial cells (fixed, not increasing)
Log (exponential) phase: Exponentialincrease in number of living bacterial cells (dividing rapidly)
Stationary phase: Plateau in the number of living bacterial cells; rate of bacterial division is roughly equal to the rate of death
Decline (death) phase: Exponential decrease in the number of living bacterial cells (dying rapidly),

Bacteria use different metabolic pathways to generate energy:
- Aerobic respiration: Requires oxygen (38 ATP)
- Anaerobic respiration: Does not require oxygen (38 ATP)
- Fermentation: Does not require oxygen (2 ATP)
Specific examples like glycolysis, Krebs cycle, electron transport chain are associated to each of these pathways.

A 28-year-old man with a leg injury developed a wound infection. Evidence of anaerobic, spore-forming gram-positive bacilli was found, suggesting Clostridium tetani as the most likely cause of the infection.