Microbial growth micro

what is microbial control ?

Microbial control is all about reducing or eliminating unwanted microbes (decontamination). This can be done through physical, chemical, or mechanical methods.

Main Targets of Microbial Control

What type of organism do we focus on when it comes to microbial control?

We focus on microbes that cause infection or spoilage, including:

• Vegetative bacterial cells (active, growing bacteria)

• Fungal hyphae + spores, yeast

• Protozoan trophozoites + cysts

• Viruses

• Endospores

• Prions (the hardest of all to destroy)

How should you think of resistance?

Least resistant - Yeast, fungal spores/hyphae

Moderate resistance - Pseudomonas

Highest resistance - Endospores

Term                Type of surface          Control mechanism            Example

Antisepsis:     

Disinfectant:

Sanitization :    

Degermation:   

Sterilization:    

Antisepsis:     Living tissue      Kills some organisms         Iodine solutions

Disinfectant: Non-living         Kills some organisms              bleach

Sanitization :    Non-living      Dislodges organisms from surface Dish washing

Degermation:    living                 Dislodges organisms          Hand washing

Sterilization:    Non-living      Kills all cells including endospores Autoclaving, gamma
irradiation

What is Microbial Death?

How is it measured?

Microbes don’t show vital signs, so death is defined as:

Permanent loss of the ability to reproduce, even under perfect conditions.

Measured two ways:

• Qualitative (+/– growth) - test if any antibacterial left 

• Quantitative (plate counts) - # of bacterial / how many molds

Factors That Affect Death Rate , how do these effect death rate ?

• Number of microbes

• Nature of microbes

• Temperature & pH

• Concentration of agent

• Mode of action

• Organic matter present

• Number of microbes → more microbes = takes longer to kill

• Nature of microbes → resistance level, mixed culture vs pure

• Temperature & pH → warm temp = faster killing

• Concentration of agent → higher concentration may kill faster

• Mode of action → what the agent targets

• Organic matter present → blood, mucus, dirt can block the agent

If you start with 1,000,000 organisms and a D=10 minutes how long would it take to achieve a 12D sterilization? 

what is a d value ?

population reduces at a predictable rate
D-value (decimal reduction time)

D-value

Time required to kill 90% of a microbial population under specific conditions.

• High population = takes longer

• Washing/scrubbing reduces the number → so it works faster

12 x 10 = 120 minutes 

Chemical + physical agents kill microbes by damaging these parts how?

Cell wall

Cell membrane

DNA/RNA synthesis

Proteins

Cell wall

→ Becomes fragile → cell lyses (detergents, alcohol)

Cell membrane

→ Loses integrity → leakage (surfactants)

DNA/RNA synthesis

→ Stops replication/translation (UV light, formaldehyde)

Proteins

→ Denatures enzymes → no metabolism (heat, acids, alcohols)

Methods of Physical Control

how do these effect 

Heat (most common)

Cold

Desiccation

Radiation

Filtration

1. Heat (most common)

• Moist heat (faster, lower temp) → denatures proteins

• Dry heat (higher temp, longer time) → dehydration + oxidation

2. Cold

→ Slows growth, doesn’t kill

3. Desiccation

→ Removing water inhibits microbes

4. Radiation

→ UV damages DNA
→ Ionizing radiation → sterilization

5. Filtration

→ Removes microbes from air or liquids (HEPA, membrane filters)

Heat: Mode of Action & Effectiveness

Moist heat: what temperature, time and its effectiveness

dry heat : what temp , time , example 

Moist heat

• Low temp + short time

• Denatures proteins

• Examples: autoclave, boiling

Dry heat

• High temperature

• Longer time

• Examples: oven, incineration

Thermal Death Measurements

Thermal Death Time (TDT)?

Thermal Death Point (TDP)?

Which one is used for items that are not sensitive and items that are sensitive?

Thermal Death Time (TDT)

→ Shortest time to kill everything at a specific temp.

Thermal Death Point (TDP)

→ Lowest temperature that kills everything in 10 min.

Thermal death times (TDT) are used for items that are temperature sensitive, while thermal death points (TDP) are used for items that are temperature insensitive. ________ insensitive

The only moist heat method that guarantees sterilization is?

Autoclaving

What is autoclaving? what does it kill? what are the 2 requirments ? psi? tmep? min?

What is tyndallization? What does it do?  min? how many days?

what is boiling and what does it do ? degrees? min?

Autoclave: 15 psi, 121°C, 10–40 min. Sterilizes everything if it’s not heat/moisture sensitive, Kills proteins, membranes, DNA; Steam must reach surface of item being sterilized ; Item must not be heat or moisture sensitive

Tyndallization: For items that cannot handle autoclave, Cycle: Steam 30–60 min, Incubate 24 hrs, Repeat for 3 days , Disinfection (not sterilization)

Boiling: 100°C for 30 min, Kills most pathogens (not endospores) → Disinfection

What is pasteurization?

what are the three main pasteurization methods?

degree / temp? for each

Kill pathogens without ruining the taste or quality of food. (Disinfection)

Three main pasteurization methods

1. Batch method
   63°C for 30 minutes

2. Flash (HTST – High Temp Short Time)
   72°C for 15 seconds
   (Most commonly used for milk)

3. Ultra (UHT – Ultra High Temperature)
   135°C for 1–2 seconds
   → Can make milk shelf-stable

DRY HEAT

what is it 

What are the 2 types, and how do they work?

temp for first one?

Dry heat requires higher temperatures because it lacks moisture to transfer heat quickly.

Two types:

1. Dry ovens

• 150–180°C

• Kills by oxidizing and coagulating proteins

• CAN sterilize

• Cheaper than autoclaves

• Used for: glassware, metal instruments, powders, oils

2. Incineration

• Direct flame → complete burning

• Absolute destruction of biological materials

• Used for: inoculating loops, biohazard waste

• NOT used for reusable items

COLD

What is it?

What is it used for?

temperatures to slow down or kill?

Cold is microbiostatic, not microbicidal.
→ It slows growth but does not kill.

Used for: foods, vaccines, lab cultures.

Temperatures

• Refrigeration: 1–15°C → slows bacterial growth

• Freezing: < 0°C → stops growth completely

DESICCATION

What is it? 

Does this kill the microbe?

What is lyophilization?

Removes water → microbes go dormant → metabolism stops

This does NOT reliably kill microbes. Many regain activity when water returns.

Lyophilization (freeze-drying) method of DESICCATION

• Freezing + vacuum drying

• Long-term preservation of microbes, foods, vaccines

• Used to preserve as much of the original product properties from before processing resulting in a dried product

RADIATION

Ionizing Radiation? what type of penitration? example? what isit used for?

Ionizing Radiation (deep penetrating)

→ High energy → Knocks electrons out of atoms → breaks DNA

Examples: gamma rays, X-rays, electron beams

Used for:
✔ Sterilizing medical supplies
✔ Sterilizing food
✔ “Cold” sterilization (no heat involved)

Nonionizing Radiation: What type of penetration? What type of exposure? What is it used for? 

Nonionizing Radiation (shallow penetration)

→ UV light
→ Creates thymine dimers in DNA → blocks replication

Requires direct exposure.

Used for:
✔ Disinfecting air
✔ Water
✔ Lab surfaces

Not for deep surfaces or thick materials.

FILTRATION

What is it used for? What is the difference between membrane and deep filters ?

WHat are HEPA filters?

Used when a substance is heat-sensitive.

Fluids

1. Membrane filters

   • Very thin

   • Small pore size (0.2 μm)

   • Physically remove bacteria

2. Depth filters

   • Thick layers of fibers (cellulose)

   • Larger pores

   • Trap organisms by charge or entanglement

HEPA filters remove most microbes from air.

Used in:

• Biosafety hoods

• Hospital rooms

• Airplanes

An ideal chemical agent is:

what is the highes level of germicides ?

Fast; Stable; Cheap; Non-toxic; Works under real-world conditions

High-level germicides are often sporicidal 

Category	Examples	Key Properties / Uses
1. Halogens
2. Phenolics
3. Alcohols
4. Oxidizing Agents
5. Surfactants
6. Heavy Metals
7. Aldehydes
8. Gases
9. Aniline Dyes

Category	Examples	Key Properties / Uses
1. Halogens	Chlorine, Iodine	Disinfect water & surfaces; iodine = antiseptic for skin
2. Phenolics	Lysol, Triclosan	Moderate strength; can irritate skin
3. Alcohols	Ethanol, Isopropanol	Fast-acting; good for degerming skin; leaves no residue
4. Oxidizing Agents	Hydrogen peroxide	High concentrations are sporicidal
5. Surfactants	Soaps (anionic), Quats (cationic), Chlorhexidine	Soaps = degerming; Quats = bactericidal; Chlorhexidine = surgical scrub
6. Heavy Metals	Silver, Mercury	Low toxicity; used in burn creams & newborn eye drops
7. Aldehydes	Formaldehyde, Glutaraldehyde	High-level disinfectants; very toxic; can sterilize
8. Gases	Ethylene oxide (ETO)	Sterilizes heat-sensitive materials; used for medical devices
9. Aniline Dyes	Gentian violet	Low-level disinfectant; mainly antifungal

CHEMICAL PRESERVATIVES

Organic acids

• what does it inhibit 2 things

• what does it prevent?

• what does it lower?

Nitrates/nitrites

• Where is it used 

• what does it prevent?

• what can it form?

CHEMICAL PRESERVATIVES

Organic acids

• Acetic → inhibits bacteria

• Propionic → prevents mold

• Benzoic, sorbic → inhibit yeast

• lower PH

• low level control agen 

Nitrates/nitrites

• Used in meats

• Prevent endospore germination

• Can form carcinogenic nitrosamines

REDUCING WATER AVAILABILITY

What is it used for?

What are some examples?

How is it achieved?

REDUCING WATER AVAILABILITY (Aw)

Used for food preservation.

• Salt → draws water out of bacteria (plasmolysis)

• Sugar → same effect

• Drying + salting is more effective

Still microbiostatic
→ Stops growth but doesn’t kill.

Reducing available water (Aw) is achieved by desiccation ___ or by adding an ____ osmotic ___ agent

What is the difference between bacteriostatic and bacteriocidal?

Bacteriostatic: These agents stop bacteria from growing or reproducing but do not kill them outright. They let the immune system finish clearing the infection.

Bactericidal: These agents kill bacteria directly, reducing the number of living cells. They cause a rapid drop in the bacterial population.