Microbiology Exam: Module 5

Essential nutrients

• Cell cannot make them on their own, they are elements that need to be acquired by something else

• Cells need them to grow and reproduce (survive)

• Elements

Macronutrients

• Required in a cell in abundance

• Carbon, hydrogen, oxygen, phosphate, nitrogen, sulfur

• Used for structures in cell (make up ATP, proteins, etc.)

Micronutrients

• Required in a cell in small abundance (trace elements)

• Involved for functions

Organic nutrient

Have carbon and hydrogen bonds

Inorganic nutrients

Lack carbon and hydrogen bonds

Carbon source, energy source, source of electrons or hydrogen atoms

All cells need these three things for growth and reproduction

Microbes

Because of their evolutions/diversity they can be autotrophs, heterotrophs, phototrophs, chemotrophs, organotrophs, lithotrophs

Autotrophs

Get carbon from carbon dioxide/inorganic sources

Heterotrophs

Get their carbon from organic sources (ex. eating plants)

Phototrophs

Use sunlight to get energy

Chemotrophs

Get their energy from chemicals in organic molecules

Lithotrophs

Get energy from inorganic sources (eat rocks)

Organotrophs

Get energy from organic sources 

Human cells 

Heterotrophic, chemotrophic and organotrophic 

Plant cells

Autotrophs, phototrophs and organotrophs

Pathogens

• Are heterotrophic, chemotropic and organotrophic

• Need organic material to survive because they need the same materials that we need so disease results from pathogens trying to get sources from us and our bodies fight them off 

Environmental conditions affecting growth

• Temperature 

• pH

• Presence or absence of oxygen

• Level of saltiness

• Amount of pressure

• Amount of radiation (sometimes radiation is beneficial)

Temperature

Can slow down or denature enzymes

pH

If this is changed, the charge of the amino acids changes which changes their function

Microbial static 

Inhibits new growth instead of killing them 

Maximum temperature

Kills microbes, protein denaturation

Obligate

Can only grow in one condition

Facultative

Can grow in both aerobic and anaerobic conditions but grows better in aerobic environments

Heat killing types 

Dry heat and moist heat

Dry heat

• Oxidizes molecules (disrupts bonds in proteins)

• Penetrates more slowly than moist heat

• Can be used for oils and powders and other fragile substances 

• Incineration 

Moist heat

• Boiling, faster, penetrates better

• Destroys membranes and denatures proteins 

• Penetrates more deeply than dry heat

Boiling

• Does not kill endospores

• Good at killing most organisms but not as good as sterilization

Autoclave

• Gets rid of all organisms (sterilization)

• Temperature is at 120 degrees celsius

• Kills endospores

• Sterilization

Positive effects of oxygen

• Best way to make energy in a biological system

• Can be used to do work

• Best final electron acceptor to make energy

Negative effects of oxygen

• Reactive oxygen species 

• ROS include O2- (superoxide radical), H202 (hydrogen peroxide), and OH (hydroxyl radical)

• To counter these ROS, organisms contain enzymes that detoxify these species 

  • Catalase, peroxidase, superoxide dismutase

Obligate anaerobe

• Does not require O2 for energy

• Does not have the ROS-detoxifying enzymes 

• Can only grow in an environment where oxygen is absent 

Facultative anaerobe

• Has ROS-detoxifying enzymes 

• Does not require O2 for growth/energy

• Prefers an environment were oxygen is present but also grows in an anaerobic environment  

Microaerophiles

• Has some ROS-detoxifying enzymes

• Requires O2 for energy

Aerotolerant anaerobes

• Has ROS-detoxifying enzymes 

• Does not require O2 for energy

Obligate aerobe

• Has ROS-detoxifying enzymes 

• Requires O2 for energy

Neutrophiles 

• Survive in neutral conditions 

• Common in humans

• Almost all pathogens

Acidophiles

Survive in acidic conditons

Alkaliphiles

Survive in basic conditions

Halophiles

“salt”

Halophilic

Require high levels of salt

Halotolerant 

Tolerate salt but prefer not 

• Human sweat is salty so they are able to live on the skin 

Physical methods of microbial control

• Refrigeration and freezing (inhibits growth)

• Desiccation and lyophilization

• Osmotic pressure

• Radiation

• Filtration

Biofilms

Give an organism and advantage, harder to eliminate microbes

Microbial growth

Increase in the number of microbes and not the size

Binary fission

• Splitting into two

• Replication of chromosomes 

• Cell division occurs 

• Identical 

Doubling time 

• How long it takes to go from one cell to two cells

• Varies depending on the organism

Lag phase

No nutrients, surviving and waiting for the next meal, working hard to try and prepare to replicate 

Exponential phase

• Growing at a fast rate

• Number of new cells is greater than dead cells

• Most effective place for antibiotics to kill microbes because they target synthesis 

Stationary phase

• Running out of nutrients 

• Number of new cells equal to number of dead cells 

• Endospores start to form at the beginning of this phase, some shut down and some continue on

• Not all the cells are alive when doing a viable plate count 

Death/decline phase

Not replicating exponentially and occurs when nutrients run out

Microscopy

Putting a sample on a dish and counting

Direct method

Microscopic counts

Turbidity 

Total cells 

Indirect method

• Turbidity (spectrophotometer), genetic probing on nucleic acid, measuring metabolic activity (gas and acid production)

Viable plate counts 

Shows the viable cells, shows growth