Bacterial Growth and Metabolism

Bacterial Metabolism encompasses all the biochemical reactions and requirements for a bacterium's survival, growth, and reproduction.
Bacterial Growth primarily occurs through binary fission, a process of cell division resulting in two identical daughter cells.

Carbon and Nitrogen are key elements for bacteria, providing building blocks for essential molecules.
Growth factors are essential metabolites that bacteria cannot synthesize themselves and must obtain from their environment, examples include amino acids, vitamins, and minerals like sodium, potassium, magnesium, and calcium.

Oxygen is a crucial factor for bacterial growth, bacteria are categorized based on their oxygen needs:
- Obligatory aerobes: require oxygen for survival, examples include Mycobacterium tuberculosis and Pseudomonas.
- Facultative anaerobes: can grow with or without oxygen, examples include Staphylococcus and Escherichia coli.
- Obligatory anaerobes: cannot tolerate oxygen and die in its presence, examples include Clostridium.
- Microaerophilic: thrive in low oxygen environments, examples include Campylobacter.
Carbon Dioxide is generally present in the atmosphere at 0.04% and is sufficient for most bacteria. Some bacteria, like Neisseria, however, require higher concentrations (5-10%).
Moisture is essential for bacterial growth. Drying can be detrimental, though some bacteria, like Mycobacterium tuberculosis, can survive in dry conditions for weeks.

Most pathogenic bacteria prefer a neutral pH around 7.5.
Acidophiles: flourish in acidic environments, examples include Lactobacilli.
Alkalophiles: thrive in alkaline environments, examples include Vibrio cholerae.

Microorganisms are categorized based on their optimal temperature range:
- Psychrophiles: thrive in cold temperatures.
- Mesophiles: grow best at moderate temperatures, the majority of human microbiota and pathogens are mesophiles, with an optimal temperature around 37°C.
- Thermophiles: prefer hot temperatures.
- Hyperthermophiles: thrive in extremely hot environments.

Bacterial respiration is an energy-yielding metabolic process where organic compounds like glucose are broken down to produce ATP.
Aerobic respiration occurs in the presence of oxygen.
Anaerobic respiration occurs without oxygen.
Electron transport phosphorylation: The process of generating ATP by transferring electrons through a chain of proteins.

Fermentation is a metabolic process that occurs in the absence of oxygen and does not involve electron transport chains.
ATP is generated through substrate-level phosphorylation during fermentation.
Facultative anaerobes can switch between aerobic and fermentative metabolism depending on oxygen availability.
Obligate anaerobes lack the ability for respiration and rely solely on fermentation.

| Feature | Anaerobic Respiration | Fermentation |*
|---|---|---|*
| Definition | Energy production without oxygen using ETC | Conversion of sugars to energy without oxygen, yielding less energy |*
| Organisms | Certain bacteria and eukaryotes like muscle cells | Yeasts, bacteria, and some muscle cells |*
| Final electron acceptor | Nitrate, sulfate, CO2 | Organic molecules like pyruvate |*
| End products | H2S, NH3, ethanol | Lactic acid, ethanol, CO2 |*
| Process complexity | More complex, multiple steps and pathways | Simpler, mainly glycolysis followed by conversion |*
| Energy | More efficient than fermentation | Less efficient, rapid energy production but less ATP |*
| ATP yield | Higher, generally more than fermentation | Lower, typically 2 ATP per glucose molecule |*
| Use of glycolysis | Yes, followed by | Yes, followed by fermentation pathways |*

Enzymes are biological catalysts that accelerate chemical reactions without being changed.
Substrate is the substance acted upon by an enzyme.
Functions of bacterial enzymes:
- Nutritional: help bacteria digest nutrients in their environment.
- Virulence: contribute to the spread of disease, examples include fibrinolysin, hyaluronidase, and hemolysin.
- Antibiotic resistance: breakdown antibiotics, for example, β-lactamase destroys the penicillin molecule.
- Laboratory diagnosis: used to identify bacteria causing diseases, for example, coagulase is used to diagnose Staphylococcus aureus.

Pigments can aid in the identification of bacteria.
Types:
- Endopigments: remain bound to the bacterial cell, examples include the golden yellow pigment of Staphylococcus aureus.
- Exopigments: diffuse into the surrounding media, examples include Pseudomonas aeruginosa producing pyocyanin and pyoverdin, which turn the media greenish.

Toxins are highly poisonous substances produced by certain bacteria and can cause tissue damage.
Endotoxins: non-diffusible, remain bound to the bacterial cell and are released only when the cell dies.
Exotoxins: diffusible, released by living bacteria into the surrounding environment.

Preparation of antitoxins: passive immunization, provides immediate protection.
Preparation of toxoids: active immunization, stimulates the body's own immune response.

Four major phases observed in the bacterial growth cycle:
- Lag phase: initial phase where cells prepare for multiplication and adapt to the new medium.
- Logarithmic (Exponential) phase: rapid multiplication and growth, typically where antibiotics are most effective.
- Stationary phase: growth slows down due to limited nutrients and accumulation of waste products.
- Decline (Death) phase: number of living cells decreases as resources are exhausted.

Dental plaque is a biofilm of microorganisms that grows on surfaces within the mouth.
Stages of dental plaque biofilm growth:
- Stage I: attachment (lag phase).
- Stage II: growth (logarithmic phase).
- Stage III: maturity (stationary phase).
- Stage IV: dispersal (death phase).