Microbial Control (MICRO. Exam 3)

Ch. 11

Physical agents

1. Heat— dry & moist

2. Radiation— ionizing & non-ionizing

SHORT ANSWER— clinical/lab/household items/food

• do you need to achieve sterilization (not pasteurization)

• do you need to reuse the item? (burn it)

• can the item withstand the agents?

• is it practical & safe

• will agent penetrate (UV light)

• is the method cost worth it (expensive)

What does DRY heat use?

• Incineration

• Dry oven

Denaturation

Cannot renature back to its original state once unraveled

• “-cidal” = kills

How does DRY heat work?

Uses moderate to high temperatures:

• Causes dehydration (ex. dried food)

• Changes protein’s structure

• Slower because it requires such high temperatures

Incineration (sterilization)

800-1000C: Flame, furnaces, & incinerators 

• Reduces number of microbes

• Common practice in labs

Hot Air Oven (sterilization)

150-180C for 2-4 hours: Circulation of hot air

• Coagulation of proteins

What does MOIST heat use?

• Autoclave (steam)

• Boiling water

How does MOIST heat work?

Uses lower temperature + shorter duration (+ H2O)

• Causes coagulation & denaturation = slows down metabolism 

• Faster at achieving sterilization = MORE effective 

Pressurized Steam (sterilization)

Autoclave (121 °C for 10- 40 minutes): increased pressure = more steam

• kills endospores

• causes denaturation of DNA

Non-pressurized Steam (sterilization)

Tyndallization: intermittent sterilization for substances that cannot withstand autoclaving

• Cycle of free-flowing steaming & incubation for 3 days

• Allows endospores to germinate

Boiling Water (disinfection)

100 C water for 30 minutes

• destroys non-endospore-forming pathogens

Pasteurization (disinfection)

Flash method: 71.6 C for 15 seconds

• Destroys non-endospore-forming pathogens (DOES NOT kill endospores)

• Only prevents food spoilage w/o ruining flavor

Ionizing (sterilization)

X-rays, gamma rays

• Penetrates through cell walls = breaks in DNA double bonds

• Allows toxic radicals to oxidize/destroy structures within the cell

Non-ionizing (disinfection)

UV light rays

• Causes adjacent T bases to link together

• Distorts the DNA

Mechanical agents

Filtration— air & liquids

Chemical agents

1. Gases

2. Liquids— animate or inanimate

Decontamination

To destroy or reduce undesirable microbes in a given area

Examples of Decontamination

Asepsis, disinfection, sanitization, degermation, or sterilization

Sepsis

Growth of microorganisms in living tissue

Examples of Sepsis

Presence of infected wounds or blood infection

Asepsis

Techniques that prevent the entry of microorganisms into sterile tissues

Aseptic techniques in Lab vs Clinical setting

• Lab: heating loop

• Clinical: sterile drapes, sterile gloves, & antiseptic skin cleansers

Examples of Asepsis

Cleansing the skin with iodine prior to surgery & using sterile needles

Antiseptic

Chemicals used on living tissue (animate) = decrease microorganisms in minor wounds/scrapes

• destroy/inhibit vegetative pathogens

Examples of Antiseptic

iodophors, antibacterial soap, or chlorhexidine

Disinfection

Chemicals used on inanimate objects = decrease microorganisms on their surface

• destroys vegetative pathogens, NOT bacterial endospores

Examples of Disinfection

5% bleach or boiling water

Sterilization

Complete destruction of all viable microorganisms

Examples of Sterilization

Autoclaving or ionizing radiation

Sanitization

Cleansing technique that removes microorganisms + debris from inanimate surfaces

Examples of Sanitization

Dishwashing & laundering clothes

Degermation

Cleansing technique that removes microorganisms + debris from living tissue (animate)

Examples of Degermation

Surgical hand scrub & alcohol wipes

• mechanical movement of washing hands under water

Microbistasis

Antimicrobial agent that temporarily prevents microbes from multiplying

• heat

Microbicidal agents (germicides)

Destroys a certain group of microorganisms (disinfection & antisepsis)

• bactericide, fungicide, virucide, sporicidal

Highest resistance of Infectious agents

Bacterial endospores

• Prions

Moderate resistance of Infectious agents

Resistant vegetative Bacteria (w/ cell walls)

• M. tuberculosis, Staphylococcus, Pseudomonas

• Naked viruses

• Protozoan oocysts

Lowest resistance of Infectious agents

All other bacteria (vegetative cells)

• Yeast/fungi/mold

• Reproductive spores

• Enveloped viruses

• Protozoan trophozoites

Microbial death

Permanent loss of their ability to reproduce/multiply 

• hard to detect (little signs)

What factors influence rate of microbial death?

• Number/population size

• Endospore vs. Vegetative?

• Environmental conditions (pH, temperature)

• Concentration of the agent

What factors influence the effectiveness of an antimicrobial agent?

• Contact time

• Population size of microbes 

• Concentration

• Temperature

Why do control agents target the Cell Wall?

It becomes fragile → Cell lysis 

• Antimicrobial drugs, detergents, & alcohol

• all other vegetative bacteria (lowest)

Why do control agents target the Cell Membrane?

It loses integrity

• Surfactants— lipids

• Protozoal trophozoites

Why do control agents target Proteins + NA Synthesis?

It prevents the entire process (replication, transcription, translation)

• Formaldehyde

• Ultraviolet

Why do control agents target Protein Function?

It causes denaturation

• Heat, alcohols, acids, phenols

Thermal death Point

The lowest temperature required to kill all microbes completely in 10 minutes

• ex. Comparing different bacteria to see if any are heat-resistant (endospores)

Thermal death Time

The shortest time required to kill all microbes at a certain temperature

• Ex. Canning foods

How can cold temperatures help control microbes?

• Decreases metabolic rate

• Bacteriostatic (inhibits growth) 

Desiccation

Reducing water (dries out) → prevents growth/reproduction (allows for food preservation) 

Filtration

Physical removal of microbes by passing a gas or liquid through filter

High-level Germicides

Kill endospores (may be sterilant)

When would you use High-level Germicides?

Devices intended to be used in sterile environments (body tissue)

• NOT heat-sterilizable

Intermediate-level Germicides

Kill fungal spores (NOT endospores), tubercle bacillus, & viruses

When would you use Intermediate-level Germicides?

Devices that will come in contact w/ skin (not invasive tho)

• disinfection

Low-level Germicides

Kill ONLY vegetative bacteria, vegetative fungal cells, & some viruses

When would you use Low-level Germicides?

To clean surfaces that touch skin (not mucous membrane)

Chlorine

Targets Sporicidal (intermediate)

• Gas is HIGHLY toxic → irritates skin

• Unstable in sunlight

What is Chlorine used for?

Large-scale disinfection of drinking water, sewage, & wastewater

What is Hypochlorite used for?

• Swimming pools, spas, drinking water, & fresh food

• Would antisepsis

• Stain removals

What is Chlorhexidine (hibiclens) used for?

• Hand scrubbing, preparing skin sites for incisions/injections (alternative)

• Neonatal wash, eye solution

Silver + Mercury metals

Inactivates proteins → kills vegetative cells (in low concentrations)

What are some drawbacks to using heavy metals?

• Toxic to humans

• Usually causes allergic reactions

• Biological fluids neutralize their actions

• Microbial resistance development

Iodine

Targets Sporicidal (intermediate)

• Toxic IF ingested → can irritate tissue

What is Iodine (iodophors) used for?

Antiseptic prep for surgery/injection, burns, disinfect surfaces

Organic Acids

Prevents spore germination + bacterial/fungal growth

Acetic acid

Inhibits bacterial growth

Propionic acid

Slows mold growth

Lactic acid

Prevents anaerobic bacterial growth

What affects the effectiveness of Chemical agents?

• Nature of the material being treated

• Degree of contamination

• Time of exposure required

• Concentration of the chemical agent

Alcohols

Targets bacteria, viruses, & fungi (intermediate)

• mild irritant → dries out skin

Detergents (surfactant)

Quaternary ammonium compounds:

• Alters membrane permeability of bacteria & fungi (very low)

Soaps

Alkaline compounds:

• Mechanically removes soil/grease containing microbes (sensitive forms)

What would you use Quats for?

• Equipment surfaces, floors, restrooms

• Restaurant utensils

• Clothing, cosmetics

What would you use Soap for?

• Medical instruments, degerming patients’ skin, hand scrubbing

• Hand washing

Hydrogen Peroxide

Targets Sporicials (high)

• Produces oxygen radicals to kill anaerobes

• toxic to eyes & if ingested

What is Hydrogen Peroxide used for?

• Antiseptic for skin/wound cleansing, mouthwash

• Disinfectant for contact lenses, bedding, plastics

What accomplishes microbiocidal effects?

NOT sterilization:

• boiling

• pasteurization

• incineration

Radiation

Energy emitted from atomic activities & dispersed at high velocity through matter/space

Ionizing vs. Non-ionizing radiation

Ionizing: deep penetrating power

Non-ionizing: little penetrating power

Glutaraldehyde

Targets Sporicidal (high)

• toxic if absorbed → can irritate skin

What is Glutaraldehyde used for?

Sterilant for materials usually damaged by heat:

• respiratory therapy equipment, dental instruments, poultry carcasses

Ethylene oxide gas

Target Sporicidal (high)

• CARCINGENGIC

• very dangerous to eyes & lungs

What is Ethylene Oxide used for?

Sterilant for heat-sensitive plastics & delicate hospital instruments