Unit 5.1: Bacterial Growth

What does microbial growth refer to?

Microbial growth refers to the increase in the number of cells, not the size

What are the physical requirements for bacteria to grow?

Physical requirements:

• Temperature

• pH

• Osmotic pressure

What are the chemical requirements for bacteria to grow?

Chemical requirements:

• Carbon

• Oxygen

What are Psychrophiles?

Psychrophiles are bacteria that can grow between 0°C and 30°C

• Psychrophiles are responsible for low-temperature food spoilage

What are Mesophiles?

Mesophiles are bacteria that can grow between 15°C and 45°C

• Mesophiles are responsible for pathogens

What are Thermophiles?

Thermophiles are bacteria that can grow between 45°C and 80°C

• Thermophiles are responsible for endospores

What are Acidophiles? Provide an example

Acidophiles are bacteria that can survive pH 0.1 to 5.4

• e.g., Lactobacillus

What are Neutrophiles? Provide an example

Neutrophiles are bacteria that can survive pH 5.4 to 8.0

• e.g., Vibrio cholerae

What are Alkaliphiles? Provide an example

Alkaliphiles are bacteria that can survive pH 5.4 to 8.0

• e.g., Escherichia coli

What is osmotic pressure?

Osmotic pressure is the right water balance between a cell and its environment for normal functioning

What happens when a cell is in a Hypotonic solution?

If a cell is in a hypotonic solution, there is no change and the cell wall remains intact

What happens when a cell is in a Hypertonic solution?

When the cell is in a hypertonic solution, water leaves the cell which leads to plasmolysis

What are examples of reactive oxygen species (ROS)

ROS:

• Superoxide anion

• Hydrogen peroxide

Which enzyme detoxify Superoxide anion?

• Superoxide dismutase detoxifies superoxide anion

Which enzymes detoxify Hydrogen Peroxide?

• Catalase and peroxidase detoxifies hydrogen peroxide

What does catalase positive look like and its conclusion?

Catalase positive looks like bubbling, concluding that the bacteria can use oxygen

What does catalase negative look like and its conclusion?

Catalase negative looks like no change, concluding that the bacteria cannot use oxygen

What are biofilms?

Biofilms are bacterial communities that live on surfaces

Describe the steps of how a Biofilm forms

1. Microbe attaches to a surface

2. Microbe starts secreting extracellular polymeric substance (EPS)

3. Microbes reproduce

4. EPS attracts more microbes, resulting in a bacterial community

5. Bacteria slough off and migrate to colonize new surfaces

What are the advantages of biofilms?

• DNA exchange

• Protection

• Works as a community to carry out complex tasks

Why are biofilms not good for us?

• They are difficult to remove and much more resistant to antimicrobial agents

• Biofilms can form on medical devices, migrating into the body causing infection