Control of Microbial Growth

The ways we use to control microorganisms are either physical or chemical

Physical

• heat

• Irradiation

• filtering

• washing

Chemical

• Antimicrobial Chemicals like or disinfectants

Control of Microbial Growth

Removing or killing all microorganisms is called Sterilization and a Steril item is one completely free of microbes

• Destruction of microorganisms means they cannot be "revived to multiply even when transferred from the sterilized product to an ideal growth medium

• other terms are used if you get rid of most microorganisms

Approaches to Control

Disinfection

• method that eliminates most or all pathogens

• use of Chemicals or disinfectants

Disinfectants are biocides

• something that is toxic to all of life

Tend to use biocides that are more toxic to microbes than uS

• Germicides more to toxic bacteria

• Bactericides kill bacteria

• Antiseptics are skin disinfectants

Decontamination

• reducing the number of pathogens to a level that is considered safe

• method depends on the contamination and the level of Safety

• Good Washing, heat, Chemicals possible

Degerming

• used to decrease the number of microbes in an area-skin

• Antiseptics are classified as degerming agents

Sanitized

• Drastically decrease the number of microbes to a level that meets accepted health standards

• Implies clean in appearance

• Does not indicate a specific level of Safety or control

Pasteurization

• Brief heat regimen used to treat foods to reduce the number of pathogens to what is considered a safe level

Preservation

• The process of treating perishables to delay spoilage

• special storage conditions or growth inhibitors

• Alternatively, Chemical preservatives can be added to a product.

  • Bacteriostatic-inhibit the growth of bacteria but does not kill them

Situational Conditions

The level of control needed to ensure Suftey and health can vary based on the contaminants and the situation

Daily Life

• soap, water, refrigeration, cleaning surfaces, cooking food

Food Production

• Physically remove and Chemically inhibit

• Heat treat, irradiate certain foods,

• certain additives FDA-Safe

• Clean Surfaces in the facility

Water Treatment

• water free of pathogenic bacteria, protozoa and viruses

• chorine used, does not kill parasite oocytes Cryptosporiaun partem

Hospitals

• nosocomial - hospital-acquired infections

  • pathogens are more likely to break the Skin

• Hospitals need to be extremely careful

• Prions are not usually considered when talking about sterilization but hospitals must be cautious when handling patients infected with them

Laboratories

• contamination can occur in the stock

  • experiments or technitian

• Instruments must be sterile

  • environment disinfected

• Aseptic technique used when handling

• waste must be treated

Selection of an Antimicrobial procedure

Type of Microorganism

Bacterial endospores

• Bacillus and Costrindium

  • most resistant

• 30 minutes to kill bacteria =10 hours to kill endospores

• extreme heat or chemical treatment needed

Protozoan Cysts and oocytes

• Intestinal pathogens

• readily killed by boiling

• fecal-oral, can infect animals

  • Cause diarrhea

Mycobacterium

• resistant to lots of chemicals because of waxy cell walls

• stronger, more toxic disinfectants used

  • Tuberculosis

Pseudomonas

• found in the environment, can grow on many disinfectants

  • problem in hospitals

Naked Virus

• virus without a lipid envelope. Resistant to many disinfectants

  • poliovirus

• conversely, enveloped viruses tend to be very sensitive to these chemicals

Numbers of Microorganisms present

Affects the time it takes to kill a population

only a portion of organisms die at a given interval

The percent that dies are the same for each interval, creating a logarithmic killing scenario

Decimal reduction time (D-time)

• Time it takes to kill 90% of a population of bacteria under specific Conditions

• used in canning

Selection of an Antimicrobial procedure

Environmental Conditions

• Temperature, pH, and organic debris, affect how well a method works

  • ex: bleach kills Mt 150s at 50° C

Composition of the Item

• the method of microbial control can't destroy what you are trying to sterilize or the container that holds it

• some plastics and metals can't be heated

• moisture Sensitive things live robber and metal can't be treated with liquid chemical disinfectants

Potential Risk of Infection

• Medical Safety procedures for medical items depend on risks of transmitting infectious agents

critical instruments

• Things in direct contact with body tissues

• Sterilized

semicritical instruments

• come into contact with Mucus membranes but not tissue

• Need to be free of viruses and bacteria but a few endospores are acceptable

Non-Critical instruments

• don’t come into contact with broken skin

• low risk

Physical Methods to Destroy Microorganisms

heat

• moist

• Dry

filtration

Radiation

High Pressure

Heat

Safe, fast, reliable, inexpensive

• non-toxic

Can decrease number of microbes

can be moist or dry

Moist Heat

Destroys microorganisms by permanently denaturing and coagulating their proteins

Boiling

• 100 degrees C (Sea level)

• can be used to make water safe to drink but not sterilized due to endospores

Pasteurization

Brief application of high heat to greatly reduce the number of heat-sensitive microorganisms usually in food

• Milk, juice, wine, vinegar

slow spoilage, increase shelf life, and preventing disease while preserving food quality

• Tuberculosis, Salmolen Typhoid fever

Temperatures and times vary according to the material and the microorganisms present

High temperature short time (H TST) method

• 72° for 155

Ultra-high-temperature.(U+HT) method

• Designed to kill everything at normal storage conditions

  • not pasteurization

• 140-145° C rapidly for several

seconds, rapidly cooled, aseptically packaged

cloth and robber can be pasteurized with a modified protocol

• 85° C 15 min

Pressurized Steam

water under pressure can reach temperature above boiling to sterilize

• autoclave

• At 1S psi, 121° C for 15 min can kill endospores

Items sterilized must be moister and heat tolerant

• media, surgical instruments, glassware, ect

Flash autoclaving possible

• 135° C for 3 min

• 132° for 4.5 hours to destroy prions

Steam must penetrate item

• more volume, more time, long thin containers on sides, never seal bottles or bags

Indicators that the autoclave is working

• Autoclave tape

• Biologial indicator

  • Gesbacillius sterathermsphiles

Commercial Canning

uses an industrial-sized autoclave called retort

Designed to destroy Clostridium botulinum endospores

can reduce 10¹² endospores to only one

Critical because otherwise endospores can germinate in canned foods

• cells grow in low-acid anaerobic conditions and produce botulinum toxin

canned food commercially sterile

Endospores of some thermophiles May survive

usually not a concern

• only grow at temperatures well above normal storage

Dry Heat

not as efficient as moist heat, needing higher temps and longer times

• 200° C for 90 min = 121° C for 15 moist

Oxidized to ashes, irreversibly denatures proteins

Benchtop incinerators and flaming

medical waste and contaminated animals also incinerated

Hot air ovens

• sterilize glassware, powders, oils anhydrous material

Filtration

Physically removes microorganisms from liquids and air using a membrane

filtration of Fluids

• liquids containing microorganisms passed through a membrane that does not allow the microbes to pass through

• Membranes Made out of inert materials that have a low Aborbancy

  • Size Can Vary

  • 0.2 micrometers is usually used to remove bacteria

• vacuum or pressure used to force liquid through

• Don't use a pore size smaller than necessary

Depth filters

• thick filtration material with long passages.

• longer than microorganisms

• Trapping is aided by electrical charges

Filtration of Air

• HEPA (high-efficiency particulate air) filter remove anything larger than 0.3 micrometers

• filters are used in hospitals, bio Safety cabinets, laminar flow hoods

radiation

• X-rays

• Gamma rays

• Radio waves

• Microwaves

• visible light rays

• Ultra Violet rays

Electromagnetic radiation can either be ionizing or non-ionizing

Both can be used to destroy microbes

Ionizing Radiation

• Gamma rays, X-rays, Electron accelerators

• Strips electrons off atoms

• Harms cells by destroying DNA and damages cytoplasmic membranes as well as creating free radicals

• Bacterial endospores are resistant to ionizing radiation while Gram Neg, bacteria are sensitive

• used to sterilize heat-sensitive material medical equipment, disposable surgical supplies and drugs

• can usually treat with radiation after packaging

• can be used for food to reduce microorganisms and kill pathogens without affecting taste

  • spices, herbs, fruits, veggies, grains, poultry, beef, lamb, pork

• Not everything FDA Approved to be irradiated

  • people have concerns that the resulting food is harmful

  • no evidence food is unsafe

Ultraviolet Radiation

• C 20-300 nanometers) kills Microbes by damaging DNA

• UV light does not penetrate well

  • good for close range and exposed Organisms

  • Drinking water, water reservoirs in lab, Surffaces

• can damage skin and eyes

microwaves

• kill via heat produced

• not reliable due to uneven heating

high Pressure

Destroys without heat

130 K psi thought to denature proteins

and alter the permeability of the cells

Products retain color and flavor

chemical methods

a viable alternative to heat

Germicidal Chemicals react with vital parts of a cell to cause permanent damage

• Precise mechanisms not always known

can be used to disinfect and sterilize

• less reliable et-han physical methods

nontoxic - can be used as antiseptics

bacteriostatic action prevents the growth of bacteria and can be used as a preservative

• Don't kill bacteria

Germicide Potency

Germicides have to be registered by the FDA and EPA so they can perform as Advertised

Efficiency depends on dilution, temp., time, etc. as dictated by the instructions

surface must be cleaned before it is sterilized or disinfected

Sterilants

• can destroy all microorganisms

  • complete destruction may require 6-10 hours

  • Includes endospores and Viruses

  • Good for heat sensitive instruments

High level disinfectants

• kill all Vegetative Microorganisms and viruses - not endospores

• 30 minute treatment

• Good for semi-critical instruments

Intermediate-level . disinfectants

• Destroy all Vegative bacteria, fungi and most viruses

  • not endospores

• used for noncritical instruments

Low-level disinfectants

• Vegetative bacteria except Mycobacteria, fungi, and enveloped viruses -no endospores or naked viruses

• General Purpos disinfectants

  • intermediate and low-level

Selecting the Appropriat Chemical

Toxicity

• most are toxic to humans

• weigh risks and benefits

Activity in the presence of organic Matter

• some chemicals are inactivated by Organic Materials

compatibility with treated material

• corrosive germicides (hypochlorite) can harm robber and metal

• Electrical equipment can't tolerate liquids and so gaseous alternatives used

Residue

• some may be toxic and need to be rinsed with water

cost and availability

• hypochlorite cheap and aailable (bleach)

• ethylene oxide gas expensive and requires special equipment

Storage and Stability

• some are concentrated

• some are shelf stable

• some need to be mixed-shelf life

Environmental risk

• some germicides are still active even after used to kill desirous microbes

• in waste treatment

  • must be neutralized

Classes of Germicidal Chemicals

Alchols

• 60-80% ethyl or isopropyl alcohol kill vegetative bacteria and fungi-

  • NO ENDOSPORES Or NAKED VIRUSES

• non-toxic, Cheap, no residue. contact time limited. can damage rubber/plastics

• damages lipid membranes and esagulating protiens

• Alcohol and water is more effective

• Anti-Microbial agents can be dissolved

• Antiseptic, hand Sanitizers, disinfect instrumets and surfaces

• Air Dry

Aldehydes

• Glutaraldehyde, orthophthaladehyde and formaldehyde

• Inactivate proteins and nucleic Acids destroy viruses and microorganisms

• 2% glutaraldehyde commonly used for heat-sensitive items

  • must be rinsed

  • TOXIC

• OPA is new - has a shorter processing time, is less irritating

• formaldehyde-gas or aqueous solution called formalin 2740)

  • kills most microbial life

  • suspected carcinogen

Biguanides

• Good antiseptic

• kills vegetative bacteria, fungi, some enveloped viruses

• low toxicity

• sticks to micas membranes and skin

• chlorhexidine-effective

• used in creams, disinfectants, and mouthwashes

• Allergic reactions are rare

Ethylene oxide

• Gaseous Sterilizing agent

• kills everything

• reacts with proteins

• Good for heat or liquid-sensitive material

• penetrates well from fabrics to implantable devices

• uses special Chamber

• Takes 3-12 hours for sterilization, then 8-12 hours heated forced air to remove toxic gas

• mutagenic and can increase risk of Malignancies

Halogens

• oxidizes essencial cell components

  • protien

Chlorine

• Destroys Microorganisms and viruses

• to irritating to be antiseptic

• Cheap, reading available, many uses

• corrosive and toxic

  • can be diluted to 500ppm to be effective against most pathogenic microorganisms, endospores, and Viruses

    • less dilutions with organic materials

• Diluted bleach deteriorates over time - stable forms used in hospitals

• used to Clean drinking water, pool water, Instruments, waster liquids, surfaces

• chlorine dioxide

• strongly oxidizing

  • does not react with organics

• exposive, decomposes rapidly

Iodine

• more expansion

  • Does not kill endospores

• Disinfectant

• Tincture - Iodine in Alcohol

• Idophore

  • not as irritating

  • Dilution is critical

  • Iodine is released slowly

• May contain Psedomona

  • forms biofilms

  • cause nonsocomial infections

metal compounds

• kills Microorganisms by bing important - SH groups (protins with enzymes) rendering them unavailable for their normal function

• toxic

• copper, tin, arsenic, mercury no user used

• Silver is still used

ozone (03)

• unstable, oxidizing

• Decomposes quicly

• Alernative for chorine

Peroxygens

• oxidizing agents that can be sterilants

• Less toxic than ethylene and Aldenyes

• biodegradable

Hydrogen peroxide

• 1202, used as diluted Solution

• Disinfectant, no residue, does not damage rubber, Stainless steel, plastic, or glees

• irritating

• not as effective on living tissue

• Hot solutions used to commercially sterilize containers

• vapor is more effective

Peracetic Acid

• more effective than hydrogen peroxide

• Can be used in living tissue

• used with H₂O₂

• sterilize in an hour

• irritating

Phenolic Compounds

earliest disinfectants

irritates skin, cost-effective, leaves antimicrobial residue

less irritating in diluted Solution

Destroys cytoplasmic membranes and denatures protiens

Kill most vegetative bacteria -not reliable with viruses

• in personal care products

Quaternary Ammonium compounds: Quats

cationic detergents, non-toxic to disinfect food prep areas

• reacts with Negatively charged microbes cell membranes

cost-effective, destroys or removes most

vegetative bacteria and enveloped viruses

• not endospores, Mycobacteria, naked viruses, or Pseasmonas

In personal care Items

Perservation of Perishable Products

Preservatives

• Chemical preservatives used for nonfood products

• food products contain non-toxic chemicals

  • weak organic Acids

  • nitrates and nitrides inhibit the germination of endospores

• Low temp. Storage

• Stops/reduces critical energy function

• Stops all microbic growth

Reducing Available Water

• Adding Salt

• Drying

• lyophilization (freeze drying)