Chap. 7: Fundamentals of Microbial Growth and Decontamination

Microbial Growth

Cell division that produces new cells and increases the total cell pop.

Cells living in biofilm communities…

Communicate and collaborate to survive

Where does biofilm formation occur when adhering to a surface?

Indwelling surfaces (ex. catheters and heart valves) are possible havens for biofilms

Binary Fission

• Occurs in most prokaryotes

• Asexual process

What happens during binary fission?

2 genetically identical daughter cells are created

What is Budding?

• Asexual reproduction

• Original cell elongates → small outgrowth on one side

• Chromosome is duplicated

• Performed by certain fungi and bacteria

Spore Formation

• Can be sexual or asexual in fungi

• Asexual in bacteria

• Bacterial endospores are thick-walled, non growing structure

Phase One: Lag Phase

Delay occurs while cell adjusts to new environment

Phase Two: Log Phase

Period of rapid exponential growth

Phase Three: Stationary Phase

• Nutrients depleted → waste accumulates

• Pop. growth ↓

Phase Four: Death has

• Waste buildup and decreasing nutrients → cell death

• Small number of cells survive by adapting and feeding off dead cells

Chemostat

• Fresh growth medium is added

• Waste and excess cells are removed

What happens in LOW temperature?

Decreased enzymatic reactions

What happens in INCREASED temperature?

• Speeds up enzymatic reaction

• Increase growth rate

What happens in HIGH temperatures?

Denature cell proteins

Psychrophiles

Cells thrive between -20 C to 10C

Psychrotrophs

• 0-30C

• Associated with food borne illness

Mesophiles

• 10-50C

• Associated with most pathogens

Thermpholes

• 40-75C

• Associated with compost piles and hot springs

Extreme thermophiles

grow around 65-120 C

Barophiles

Can withstand high-pressure environment of the deep sea

Acidophiles

P+ pump exports excess P+ from the cytoplasm to raise pH

Neutralophiles

• Best growth in pH range of 5-8

• Majority of microorganisms

Alkaliphiles

• Growth in basic pH range of 9-11

• Associated with soda lakes

Halophiles

• Thrives in high-salt environments

• Must overcome osmotic stress

  • Keep high concentrations of organic materials and ions in their cytoplasm

Facultative Halophiles

Tolerate higher salt but may not grow well

Plasmolysis

Shrinking of the cytoplasm and plasma membrane due to osmosis

Most pathogens thrive in…

Low-oxygen environments within the host

In cells, some oxygen is converted into…

Reactive oxygen species (ROS)

• Hydrogen peroxide

• ROS can damage proteins and DNA

• Microbes hav evolved ways to detoxify ROS

What does catalase do?

Convert H2O2 → H2O and O

Obligate aerobes

Absolute dependence on O2 for cellular processes

Microaerophiles

Only uses small amounts of O2

Facultative Anaerobes

• Grow with and without O2

• Switch between using O2 and fermentation

Aerotolerant Anaerobes

• Tolerate O2 but doesn’t use it

• Can deactivate ROS

Obligate Anaerobes

Can’t eliminate ROS

90% of a cell’s dry weight is…

Carbon, hydrogen, nongaseous oxygen, and nitrogen

Heterotrophs

Requires external source of organic carbon (Sugars, lipids, and proteins)

Autotrophs

Does not require external source

• Uses carbon fixation: organic → inorganic carbon

Nitrogen Fixation

Cells get their nitrogen from the atmosphere

Phototrophs

Organisms that use light energy

Chemotrophs

Organisms that breakdown chemical compounds for energy

Broth Media

Made by adding various nutrients to purified water

Petri plates are made by…

Adding agar to liquid media

Defined media

Chemically defined or precisely known composition

Complex media

Contains a mixture of organic and inorganic nutrients that are unknown

Differential media

Media formulated to visually distinguish once microbe from another

Selective media

Ingredients foster the growth of certain bacteria and suppress the growth of others

Thioglycate

Converst O2 to water

• Molecular oxygen is removed

Purpose of the Streak Plate Technique

Isolate bacteria

• As cell divides, pop. increased to form a mound of cells called a colony

Manual cell counting

• Microscope

• Specialized counting chamber that has volumetric grid

Coulter counter

Machine that counts the number of cells as they pass through a thin tube

Flow cytometer

• Laser light used to detects cells passing through a narrow channel

  • Cells are fluorescently labeled

Viable plate count

Direct enumeration of bacteria using agar plates

Numerical data for plate counts is represented as…

Colony-forming units per milliliter

Indirect methods rely on…

• Secondary reflections of overall pop. size

• To indirectly measure cell numbers, measure turbidity

  • Spectrophotometer measures transmission or absorbance

Physical analysis

Staining and microscopy to observe morphological features

Biochemical analysis

Involves collection of media that assess metabolic properties

Genetic methods

Help to quickly identify microbes

Decimal reduction time

Times in minutes it takes to kill 90% of a given microbial pop. at a set temperature

Thermal death time

Shortest period of time at a certain temp. needed to kill all microbes in a sample

Thermal death point

Minimum temp. need to kill all microbes within 10 minutes

Autoclave

Machine that applies to steam heat along with pressure to sterilize

• Pressure of 15 pounds per square inch

Why is boiling not an efficient sterilization method?

Endospores can withstand hours of boiling

Pasterurization

Used to eliminate pathogens

• Application of moderate heat (↓ liquid’s BP)

• NOT a sterilizing technique

Ionizing radiation

• Damage nucleic acids

• Passes through packaging

Nonionizing radiation

Causes thymine dimers

What are HEPA filters?

• Randomly arranged rivers that removed 99% of airborne substances

• Doesn't sterilize air

Purpose of pore size 0.1 µm

Filter out bacteria and protists

Purpose of pore size 0.01 µm

Remove viruses

Chemical control of microbial growth involves chemicals called…

Germicides

Germicides that kill microbes are known as…

Microbiocidal

Germicides that only inhibit microbial growth are…

Microbioastatic

Disinfectants

Used to treat inanimate objects

Antiseptics

Applied to living tissue

Alcohols

• Denature proteins and attack lipid membranes

• Used to disinfect small equipment

Detergents

Can damage the lipid envelope of certain viruses and the lipid membrane of certain bacterial cells

Mycobacterium control

• Can can tuberculosis and leprosy

• Contains cell walls rich in waxy mycotic acids

Endospore Control

Most effective way to ensure elimination of endospores is by autoclaving

Viral Control

• Lipids in viral envelope are sensitive to heat, drying, and detergents

• Naked viruses are usually inactivated by chlorine-based agents