Chapter 13: Control of Microbial Growth (Final)

sepsis

bacterial contamination

asepsis

the absence of significant contamination- aseptic surgery techniques prevent the microbial contamination of wounds

sterilization

removing and destroying all microbial life

commercial sterilization

killing clostridium botulinum endospores in canned goods

antisepsis

destroying harmful microorganisms from living tissue

degerming

the mechanical removal of microbes from a limited area (injection)

sanitization

lowering microbial count on eating utensils to sake levels

biocide (germicide)

treatment that kill microbes

e.g. fungicide

bacteriostasis

inhibiting, not killing, microbes

selection of disinfectant

fast acting in presence of organic materials

effective against all microorganisms w/out. destroying tissue or acting as toxin

easily penetrate material

easy to prepare and stable

inexpensive

not have an unpleasant odor

microbial exponential death rate

for each minute treatment is applied, 90% of remaining population is killed

bacterial population die at constant rate when heated/treated with antimicrobial chemicals

effectiveness of treatment depends on

number of microbes

environment

time of exposure

microbial characteristics

actions of microbial control agents

damage to plasma membrane

- cause leakage of celullar content, interfere with cell growth

damage to proteins (enzymes)

damage to nucleic acids

what does heat do?

denature enzymes

thermal death point (tdp)

lowest temperature at which all cells in a liquid culture are killed in 10min

thermal death time (tdt)

minimal time for all bacterial in a liquid culture to be killed at a particular temperature

decimal reduction time (drt)

minutes to kill 90% of a specific population of a bacteria at a given temperature

moist heat

coagulate/denatures proteins

autoclave

steam under pressure

121C at 15 psi for 15min

kills all organisms (except prions) and endospores

steam must contact the item's surface

preferred method for sterilization in health care environments

use test strip to indicate sterility

autoclave machine

steam to enter the steam chamber and expel air

chamber pressure and temp build to proper levels

after the appropriate period of time, another valve opens to allow steam to escape the chamber

autoclave sterilization times

small containers- 5min or less

large containers- 70min

test tube-15min

E.flask- 15-30min

pasteurization

reduces spoilage organisms and pathogens in milk and juices

high-temperature short-time (htst)

72C for 15 sec

thermoduric

organisms survive, but are unlikely to cause disease or to spoil refrigerated milk

ultra high temperature treatments

will sterilize milk, creamer, and juice which can then be stored without refrigeration

rapidly heated to 140C for 4sec, followed by rapid cooling

dry heat sterilization

kills by oxidation

flaming

incineration

hot-air sterilization

oven 170C, 2hrs

filtration

passage of substance through a screen like material

used for heat-sensitive materials

high-efficiency particulate (hepa) filters

remove microbes >0.3 um in diameter

membrane filters

remove microbes >0.22 um

pores sizes as small as >0.05 um are available which can filter out viruses and large proteins

physical methods of microbial control

refrigeration

deep-freezing

lyophilization (freeze drying)

high pressure

denature proteins, alter carbohydrate structure

desiccation

absence of water prevents metabolism

osmotic pressure

uses high concentrations of salts and sugars to create hypertonic environment, causes plasmolysis

ionizing radiation

x-rays, gamma rays, electron beams

ionizes water to create reactive hydroxyl radicals

damages DNA by causing lethal mutations

gamma rays

penetrate deeply but require hours to sterilize

high-energy electron beams

less penetration, but fast (seconds)

ionizing radiation uses

food industry (spices, certain melas, vegetables)

sterilization of pharmaceuticals, disposable dental and medical supplies

nonionizing radiation

ultraviolet, 260nm

damages dna by creating thymine dimers

effective, but doesn't penetrate, good for surfaces

must avoid contact with eyes and skin

nonionizing radiation uses

uvc "germicidal" lamps used in hospital rooms, nurseries, operating rooms, cafeterias

visible blue light (470nm)

kills a wide range of bacteria due to the formation of a singlet oygen

microwaves

kill by heat, not especially antimicrobial

sonication

high frequency ultrasound waves to disrupt cell structures

rapid changes in pressure within the intracellular liquid

phenol

first used by joseph lister

injure lipids of plasma membranes, causing leakage

remain active in presence of organic matter

phenolics

derivative of phenol

reduced irritation increased effectiveness

e.g. O-phenylphenol, in Lysol

bisphenols

contain two phenol groups connected by a bridge

disrupt plasma membranes

bisphenols examples

hexachlorophene- control skin infections

triclosan- antimicrobial soaps, toothpaste, mouthwash, kitchen plastics, use discontinued

biguanides

effective against gram-positive bacteria, and enveloped viruses

disrupt plasma membranes

biguanides examples

chlorhexidine- surgical hand scrubs

alexidine- works faster than chlorhexidine

essential oils (EOs)

mixtures of hydrocarbons extracted from plants

preserve food

microbial action due to phenolics and terpenes

stronger activity against gram-positive bacteria

tea tree oil and pine oil

broad spectrum of activity that includes gram-positive and gram-negative bacteria and fungi

iodine

impairs protein synthesis and alters membranes

iodine examples

tincture- solution in aqueous alcohol

iodophor- combined with organic molecules, povidone iodine (Betadine)

chlorine

oxidizing agent, shut down cellular enzymes systems

chlorine examples

bleach (HOCl)

chloromine (chlorine + ammonia)

alcohols

denatures proteins and dissolves lipids

no effect on endospores and nonenveloped viruses

best action at 70%

ethanol and isopropanol

require water

alcohol-based hand sanitizers

62% alcohol

effective against most bacteria

not effective against endospore producers and noneveloped viruses (e.g. Clostridium difficile, Norovirus)

oligodynamic action

very small amounts exert antimicrobial activity

denature proteins

silver nitrate

used to prevent ophthalmmia neonatorum (eye drops), wound dressing

mercuric chloride

limited use as disinfectant (toxic)

copper sulfate

an algicide, copper and silver ions used in water disinfection

swimming pools

zinc chloride

found in mouthwash

acid-anionic sanitizers

anions react with plasma membrane

used for cleaning food and processing facilities

quaternary ammonium compounds (quats)

cations (NH4+) are bactericidal, denature proteins, disrupt plasma membrane

broad spectrum, except ineffective against endospores and mycobacteria

sulfur dioxide

prevents wine spoilage

organic acids

inhibit metabolism

sorbic acid, benzoic acid, and calcium propionate prevent molds in some foods

nitrites and nitrates

prevent endospore germination (Clostridium botulinum)

primary used with meat products

nitrites preserve the red color of meat

antibiotics

used exclusively for food preservation, not for treating disease

bacteriocins

proteins produced by one bacterium that inhibits another

e.g. nisin and natamycin

aldehydes

inactivate proteins by cross-linking with functional groups

e.g. formalin and glutaraldehyde

formalin

used for preserving specimens, limited due to cancer risk

glutaraldehyde

used on respiratory therapy equipment

sporicidal in 3-10 hours, can't be autoclaved

gaseous chemosterilants

cross-links nucleic acids and proteins

used for heat sensitive material

e.g. ethylene oxide, chlorine dioxide

ethylene oxide

must be used in a sealed chamber

can sterilize large pieces of equipment and furniture

chlorine dioxide

used in enclosed building areas or water treatment

also used as an aqueous solution for surface disinfection

supercritical fluids

Co2 compressed into a supercritical state, both gaseous and liquid properties

use: food industry, medical implants like bones

peroxygens

oxidixing agents

e.g. hydrogen peroxide and peracetic acid, beonzoyl peroxide, ozone

hydrogen peroxide

not good as an antiseptic for open wounds

good disinfectant (non living surfaces)

aseptic food packaging

bioquell

bioquell

hot gaseous hydrogen peroxide

sterilizing spaces and surfaces such as hospital rooms

peracetic acid (PAA)

effective liquid sterilant

used in disinfection of food poisoning and medical equipment

benzoyl peroxide

topical acne medication

ozone

water disinfection

principles of effective disinfection

concentration of disinfectant

organic matter- often interfere with disinfection

pH

temperature

time

use-dilution tests

current standard for evaluating disinfectants

metal cylinders are dipped in test bacteria and dried

placed in disinfectant for 10min at 20C

transferred to culture media to determine whether the bacteria survived treatment

variations of use-dilution tests

can be used to test the effectiveness of antimicrobial agents against endospores, viruses, fungi, and Mycobacterium tuberculosis

disk-diffusion method

evaluates efficacy of chemical agents/disinfectants

filter paper disks are soaked in a chemical and placed on a culture

look for zone of inhibition

gram-negative bacteria

more resistant to biocides

due to lipopolysaccharide in their outer membrane

pseudomonas and burkholderia are unusually resistant

mycobacteria

exhibit considerable resistance to biocides

TB must undergo special testing

bacterial endospores

very resistant to many biocides

nonenveloped viruses

more resistant than enveloped virues

prions

problem with disinfection or surgical instruments

biosafety levels

ranked by severity of disease and ease of transmission (BSl 1-4)

BSL-1

cause disease in healthy hosts, minimal risks

nonpathogenic strains of E.coli

BSL-2

disease with moderate severity, moderate risk to workers and envi

Staphylococcus aureus

BSL-3

exotic, lethal through respiratory transmission

Mycbacterium tuberculosis

BSL-4

exotic, high risk of aerosol-transmitted infections, fatal

Ebola and Marburg viruses