Module 4 - Microbe Control

Historical methods of microbial growth

salting, smoking, pickling, drying, exposure to sunlight (UV)

Control of microbes is by:

physical agents, chemical agents, mechanical removal

Sterilization

destorys/removes all microbes, materials subjected called sterile, not used on humans

Common uses of sterilization

surgical instruments, syringes (needles)

Agents & techniques for sterilization

autoclave (high temp and pressure, moisture), sterilants (chem agents)

Disinfection

physical or chemical; disinfectant, can kill vegetative pathogens not endospores, reduces contamination, used on inanimate objects

Common uses of disinfecting

examination table, food prep area, thermometers

Agents & techniques for disinfecting

bleach, iodine, boiling

Decontamination

sanitization, cleansing which mechanically removes microbes and debris, used on inanimate objects, reduces contamination

Common uses for decontamination

cooking utensils, dishes, bottles, cans

Agents & techniques for decontamination

sanitizers (soaps/detergents), commercial dish washers

Antisepsis

degermation: decontamination of living surfaces, scrub skin, immerse skin in chemicals

Sepsis

growth of microbes in blood and other tissues

Asepsis

practice of preventing entry of infectious agents into tissues

Agents & techniques used for antisepsis

alcohol wipes, surgical hand scrub, betadine

Techniques for antisepsis

chemical agents applied to body surfaces and surgical incisions, destroys/inhibits vegetative pathogens, sterile methods

Bactericide

kills vegetative bacteria

Fungicide

kills fungal spores

Virucide

kills viruses

Sporicide

kills bacterial endospores

Germicide/microcide

kills microbes

Endospores

resistant to heating, drying, freezing, radiation, and chemicals, has very strong but simple sturcture making it hard to kill

Formation stimulus of endospores

depletion of nutrients, and/or water

Sporiuation

spore formation

Sporangilum

vegetative cell that has turned into a sporulating cell 6-8 hrs

Germination

spore releases vegetative cell when environment improves, agent begins to breakdown cortex, core rehydrates and takes up nutrients, grows out of endospore coat

First phases of sporulation

sporangium engulfs the forespore after chromosome duplication, then forspore becomes the endospore

Diseases related to persistence and resistance of spores:

Bacillus anthracis: anthrax

Clostridium tetani: tetanus

C. botulism: botulism

How spores cause disease:

enter tissues, germinate, and cause disease

Where spores can be:

can be in cultures media, wounds, food such as cans

Killing endospores

if something kills them then it can kill vegetative cells and microbes below it

Antimicrobial effects on cell wall

damage, blocks synthesis, which leads to fragility and can lyse easily (done by detergents and alcohols)

Antimicrobial effects on cell membrane

surrounds animal viruses, disruption loss of selective permeability, loss of vital molecules and entry of damaging chemicals

Antimicrobial effects on nucleic acid synthesis

no DNA means no replication, no RNA means no transcription/translation and no proteins

Antimicrobial effects on proteins

inhibits ribosomes meaning no protein synthesis

deactivation of proteins leads to denaturation, which can be forced shape change or block active site of enzymes

Physical agents

include heat and radiation

Chemical angents

includes serializing agents and disinfectants

Mechanical methods

include filtration

Heat

moist heat or dry heat, moist kills at lower temps since lower water levels mean more protein stability

Pasturization

disinfection of beverages contaminated during collection and processing, can be juice, milk, beer, wine, retains flavor and food value

Thermal death time

time in min required to kill all microbes at a specified temp

Thermal death point

minimum temp required to kill all microbes in 10 min

Radiation

energy emitted from atomic activities and dispersed at high velocity through matter or space

Irradiation

bombardment (of microbes ) with radiation

Ionizing radiation

double DNA breaks, leading to protein damage, can go through barriers, called cold sterilization

Non ionizing radiation

UV radiation , crosslinks DNA leads to no replication and protein production, not as penetrating (easily blocked), used for air handling

Cold

only decreases microbe activity

Desication

dehydration at room temp

Lophilization

freeze-drying, preserves microbes. kills delicate bacteria

Antimicrobial chemicals

can be liquid, gas, or solid

Aqueous solution

chem dissolved in water

Tinctures

chem dissolved in alcohol or water-alcohol mixtures

Desired qualities of germicide

• rapid long-term action (low concentration)

• solubility and stability

• broad-spectrum and non-toxic to tissue

• efficient penetration

• low cost

Factors that can affect microbicidal activity

• nature of microorganism

• nature of material being treated

• degree of contamination

• time of exposure

• strength and chem action

• targets (cw, DNA, proteins)

Halogens (chlorines)

forms can be liquid or gas, example is bleach

What chlorine does in water:

release of hypochlorus acid (HOCl) and oxidizer which denatures enzymes

Chlorines become less effective when:

exposed to light, high pH, excessive organic matter

Iodine

liquid, penetrates cells and interferes with metabolic functions, and be irritating/toxic

Free Iodine

topical antiseptic, burns, disinfectant for plastic & rubber

Iodophors

complex of iodine and alcohol, doesn’t sterilize, disinfect, prep skin for surgery, burns

Hydrogen peroxide

liquid, produces toxic reactive oxygen, only works at high concentrations

Hydrogen peroxide as antiseptic

skin and wound care

Hydrogen peroxide as disinfectant

contact lenses, implants, plastic equipment

Hydrogen peroxide as sterilization

delicate reusable instruments (vaporized H2O2, industrial items and enclosed spaces)

Aldehydes

organics with a -CHO functional group, disrupts enzymes & DNA, extremely toxic

• glutaraldehyde- rapid action

• formaldehyde/formalin- slower reaction

Ethylene oxide

colorless gas, reacts with funx groups of proteins and DNA

chemoclave: chemical sterilization, plastics and delicate instruments

explosive, causes tissue damage

Phenol

liquid, first major antimicrobial chemical, disrupts cw, membranes, enzymes

Triclosan (phenol)

disinfectant and antiseptic chem added to many products (soaps, plastic, toothpaste/cosmetics, toys), leads to antibiotic resistance

Surfactants

solid or liquid, detergents, soaps, alcohols, guats, inhibited by organic matter, ineffective against spores and many veg, bac.

Form of surfactants

polar molecules with hydrophilic and hydrophobic regions, which can bind to lipid layer and penetrate hydrophobic region creating leaks and lysis

Alcohols

endospores not killed, liquid, ethyl or isopropyl are appropriate, must be high concentration but evaporation limits effectiveness

Soap

weak microbiocide, used for mechanical removal

Pseudomonas

bac. that grows abundantly in soap dishes

Quats (quaternary ammonium compounds)

positive charge with central N atom, break down cell membrane, used to sanitize objects and surfaces

Filtration

removes microbes from air and liquids, filter allows liquid or air to pass but not microbes, used for liquids that can’t withstand heat