MICR101A_8_Control of Microbial Growth

STERILIZATION

The removal or destruction of all living microorganisms

Sterilant

ethylene oxide

Disinfection

destruction of vegetative (non-endospore-forming) pathogens

Disinfection

most commonly applied to the use of a chemical to treat an inert surface or substance

antisepsis

If the (disinfection) treatment is directed at living tissue, it is called ______

antisepsis

Destruction of vegetative pathogens on living tissue

Disinfection

Destruction of vegetative pathogens on inanimate objects

Degerming

results in mechanical removal rather than killing most of the microbes in a limited area

Degerming

 e.g. before the animal receive an injection, the skin is swabbed with alcohol

Degerming

Mostly a mechanical removal by soap and water or an alcohol soaked swap

Sanitization

intended to lower microbial counts to safe public health levels and minimize the chances of disease transmission from one user to another

Sanitization

May be done with high-temperature washing or by dipping into a chemical disinfectant

Suffix “-cide”

meaning “kill”

Suffix “-stat” or “-stasis”

Treatments that only inhibit the growth and multiplication of bacteria (don’t kill)

Sepsis

- from the Greek for decay or putrid

- indicates bacterial contamination

Antisepsis

prevent contamination

Aseptic

an object or area is free of pathogens

Asepsis

the absence of significant contamination

Factors that Influence the Effectiveness of Antimicrobial Treatments

1. Number of microbes

2. Environmental influence

3. Time of exposure

4. Microbial characteristics

Heat

May inactivate certain vitamins or antibiotics in a solution

Thermal Death Time (TDT)

the minimal length of time for all bacteria in a particular liquid culture to be killed at a given temperature

Decimal Reduction Time (DRT)

the time, in minutes, in which 90% of a population of bacteria at a given temperature will be killed

Methods of Applying Heat

1. Moist Heat

2. Dry Heat

3. Pasteurization

Boiling or Flowing Steam

Kills vegetative bacterial and fungal pathogens and many viruses within 10 minutes but less effective on endospores

Autoclaving

Very effective method of sterilization

Autoclaving

The preferred method of sterilization in health care environments, unless the material to be sterilized can be damaged by heat or moisture

Autoclaving

The higher the pressure in the autoclave, the higher the temperature

steam

is the one responsible for autoclaving

PASTEURIZATION

Method by Louis Pasteur

PASTEURIZATION

• Heat treatment for milk (72°C for about 15 sec) that kills all pathogens and most nonpathogens.

Direct flaming

Burning contaminants to ashes

Incineration

Burning to ashes

Direct flaming

Used for inoculating loops

Incineration

Used for disposal of contaminated dressings, animal carcasses, and paper.

Hot-air sterilization

Oxidation

Hot-air sterilization

Used for empty glassware

Filtration

The passage of a liquid or gas through a screen-like material with pores small enough to retain microorganisms

Filtration

used to sterilize heat-sensitive materials, such as some culture media, enzymes, vaccines, and antibiotic solution

Refrigeration

Has a bacteriostatic effect

Deep-freezing

An effective method for preserving microbial cultures, food, and drugs

Lyophilization

Most effective method for long-term preservation of microbial cultures, food, and drugs (vaccines)

High Pressure

alters the molecular structures of proteins and carbohydrates, resulting in the rapid inactivation of vegetative bacterial cells

High Pressure

Endospores are relatively resistant to

High Pressure

An advantage is that these treatments preserve the flavors, colors, and nutrient values of the products

Desiccation

In the absence of water, microorganisms cannot grow or reproduce but can remain viable for years.

Osmotic Pressure

use of high concentrations of salts and sugars to preserve food is based on this effect

Ionizing radiation

have shorter wavelength (less than 1 min)

Non-Ionizing radiation

have longer wavelength (greater than 1nm)

DISK-DIFFUSION METHOD

 Used in teaching laboratories to evaluate the efficacy of a chemical agent

PHENOL

are often used in throat lozenges for its local anesthetic effect but has little antimicrobial effect at low concentrations

PHENOL

irritates the skin and has disagreeable odor

PHENOLICS

are derivatives of phenols that has been chemically altered to reduce its irritating qualities or increase its antibacterial activity in combination with a soap or detergent

BIGUANIDES

especially effective against gram-positive bacteria and also gram-negative bacteria except of most pseudomonas

IODINE

one of the oldest and most effective antiseptics

IODINE

active against all kinds of bacteria (many endospores, various fungi, some viruses)

Ethanol

Effectively kills bacteria and fungi but not endospores and non-enveloped viruses

Ethanol MOA

Denatures proteins, disrupts membranes, dissolves lipids including lipid components of enveloped viruses

Ethanol (antiseptic)

Unsatisfactory antiseptic when applied to wounds

Ethanol (concentration)

70% ethanol is the recommended optimum concentration

Pure ethanol (100%)

Less effective than aqueous solutions because denaturation requires water

Isopropanol

Often sold as rubbing alcohol; slightly superior to ethanol as an antiseptic and disinfectant

Isopropanol (advantages)

Less volatile, less expensive, more easily obtained than ethanol

Heavy Metals and Compounds

Examples include silver, mercury, copper; can be biocidal or antiseptic

Oligodynamic action

Ability of small amounts of heavy metals to exert antimicrobial activity

Heavy Metals (MOA)

Metal ions combine with sulfhydryl groups on proteins, causing denaturation

Silver (antiseptic)

Used as an antiseptic in a 1% silver nitrate solution

Silver (dressings)

Impregnated dressings that release silver ions help fight antibiotic-resistant bacteria

Silver-sulfadiazine

Topical cream for burns

Mercuric chloride

Bacteriostatic, broad-spectrum but limited due to toxicity and ineffectiveness in organic matter

Copper sulfate

Used primarily to destroy green algae

Surface-Active Agents

Decrease surface tension among molecules of a liquid

Soap and detergent

Have little antiseptic value but are important in mechanical removal of microbes through scrubbing

Soap (mechanism)

Breaks oily film into droplets (emulsification), lifts microbes off when lather is washed off

Soap (degerming)

Effective as a degerming agent; washing hands with soap and water is an effective sanitation method

Quaternary Ammonium Compounds (Quats)

Most widely used cationic detergents

Quats (MOA)

Cleansing ability related to positively charged portion of the molecule

Quats (bactericidal)

Strongly bactericidal against gram-positive, less active against gram-negative

Quats (fungicidal)

Fungicidal, amebicidal, virucidal against enveloped viruses; ineffective against endospores and mycobacteria

Quats examples

Benzalkonium chloride, cetylpyridinium chloride

Chemical Food Preservatives

Prevent spoilage by microorganisms

Sulfur dioxide

Used in winemaking

Sodium benzoate

Prevents mold growth in cheese and soft drinks

Sodium nitrate/nitrite

Added to meat products like ham, bacon, hotdogs, and sausage

Nitrite functions

Preserves red color of meat, prevents botulism endospore growth

Antibiotics in food

Nisin and natamycin used for food preservation

Nisin

Inhibits endospore-forming spoilage bacteria in cheese

Natamycin (pimaricin)

Antifungal antibiotic used in cheese

Aldehydes

Among the most effective antimicrobials

Formaldehyde

Used to preserve biological specimens and inactivate bacteria and viruses in vaccines

Formalin

37% aqueous solution of formaldehyde

Glutaraldehyde

Less irritating and more effective than formaldehyde; used to disinfect hospital instruments

Glutaraldehyde (action)

2% solution is bactericidal, tuberculocidal, virucidal in 10 minutes, sporicidal in 3-10 hours

Chemical Sterilization

Uses gaseous chemosterilants as substitutes for physical sterilization

Ethylene oxide

Kills all microbes and endospores but requires several hours of exposure; toxic and explosive

Chlorine dioxide

Short-lived gas used to fumigate buildings contaminated with anthrax spores

Plasma Sterilization

Sterilizes long, hollow tubes using gas excited by electromagnetic fields

Plasma Sterilization (process)

Uses a vacuum, electromagnetic field, and chemicals like hydrogen peroxide or peracetic acid

Peroxygens and Oxygen Forms

Include hydrogen peroxide and peracetic acid

Hydrogen peroxide

Not a good antiseptic for wounds but disinfects inanimate objects; sporicidal at high concentrations

Heated hydrogen peroxide

Used as a sterilant for atmosphere and surfaces