microbiology unit 6: control of microbial growth

what can bacteria cause

food spoilage

disease

contamination in home, industry, lab, hospitals

what are the 2 broad categories for controlling microbial growth

physical methods

chemical methods

sterilization

the removal or destruction of all living microorganisms including endospores

commercial sterilization

limited heat treatment intended to kill endospores in canned foods

disinfection

control directed at destroying vegetative pathogens on inert surfaces and objects

disinfectant

an agent that disinfects

antiseptic

a disinfectant for living tissue

degerming

the mechanical removal of microbes from small area of living tissue

sanitization

a treatment that lowers microbial counts to safe public health levels and minimizes transmission

aseptic

techniques to maintain sterility

preservation

mechanisms of preventing or delaying spoilage of perishable items

biocide

a treatment that can kill microorganisms

bacteriocide

treatment that can kill bacteria

bacteriostatic

treatment that can only inhibit the growth or multiplication of bacteria

AMA

antimicrobial agent

sterility level of critical items

sterile

sterility level of semi-critical items

high level of disinfection

sterility level of non-critical items

light disinfection/sanitization

critical item examples

surgical instruments and IV fluids

semi critical examples

dental mirror, respiratory equipment

non critical examples

crutches, bed linen, eating utensils

standard way of expressing the efficiency of an AMA is:

D value

D value:

time taken for AMA to kill 90% of bacteria

a minimum of __ minutes is required to kill ___ of bacteria

3, 99.9%

what can alter the effectiveness of AMA?

1. # of microbes

2. time of exposure

3. environmental influences (temp/organic matter)

4. microbial characteristics (bacteria, viruses)

what bacteria are biocides more effective against ?

gram positive

why is it more effective to gram positive instead of negative?

due to the protective outer LPS membrane

what 2 ways can we kill microbes

1. alteration of cell membranes and cell walls

2. disruption of cellular metabolism and reproduction

how will microbes die during the alteration of cell membrane/wall?

change in membrane permeability causes cellular contents to leak out leading to death (lysis)

how will microbes die during disruption of cellular metabolism/reproduction

protein damage

dna/rna damage

physical methods of microbial control

1. heat

2. cold

3. dessication

4. pressure

5. filtration

6. radiation

23types of heat

moist, dry, pasteurization

types of moist heat

boiling

autoclave

what is boiling effective against

kills bacteria, fungi, and most viruses

what is autoclave and what is it effective against

use of steam under pressure

anything that can withstand high temperatures and pressure (media, agar, syringes)

two types of dry heat

direct flaming

hot air sterilization

what is direct flaming

burns contaminants to ashes

hot air sterilization

requires higher temperatures and longer than moist heat

what is pasteurization

mild heating which will reduce pathogen load without changing the taste of food

2 methods of cold:

refrigeration

slow freezing

refrigeration

slows down bacterial growth

slow freezing

lead to growth ice crystals which damage proteins and cell structure to rupture cells

desiccation method

lyophilization

lyophilization

rapid removal of water which usually stops bacteria from reproducing (therefore used for preservation)

what is desiccation not effective on

viruses

do dried body fluids contain infectious microbes

yes

method of pressure

osmotic pressure - use of high sugar or salt concentrations to treat foods

what survives in osmotic pressuring

fungi

filtration

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

examples of filtration

1. HEPA filters for air

2. filter-sterile solutions that cannot be heated

2 methods of radiation

1. ionizing radiation (gamma rays, x rays)

2. non-ionizing radiation (UV rays)

ionizing radiation

-high energy radiation reacts w water making toxic compounds that can destroy DNA

-used for latex gloves, tubing, transplanted tissues

non-ionizing radiation

-UV rays damage DNA

-surface only

-used for water purification, cafeterias, surfaces in surgical suite

3 types of chemical methods

1. antiseptics

2. disinfectants

3. antibiotics

8 major categories of chemical antiseptics and disinfectants

1. phenols

2. heavy metals

3. halogens

4. alcohols

5. surfactants

6. alkylating agents

7. gaseous alkylating agents

8. oxidizing agents

what do phenols disrupt

lipids in the plasma membrane and denatures enzymes

derivatives of phenol

phenolics and bisphenols developed to reduce irritation and increase antimicrobial action

what are phenols effective against

bacteria (mostly positive) and yeasts

what can phenol be used as + examples

disinfectant - lysol

antiseptic - triclosan in anti-bacterial soap and toothpaste

3 types of heavy metals

silver

copper

zinc

what are heavy metals

high molecular weighted metals that denature proteins

silver

-disinfectant (water)

-antiseptic (1% silver nitrate eyedrops, silver-impregnated products)

copper

copper sulphate used to destroy algae in reservoirs, swimming pools, and fungi in paint

zinc

common antiseptic ingredient in mouthwashes and anti-dandruff shampoos

halogens

oxidize proteins and cell membranes

2 examples of halogens

iodophors

chlorine

composition of iodophors

combination of iodine with an organic mc

what are iodophors effective against

bacteria, endospores, fungi, virus

what are iodophors used as

antiseptic (betadine) or for water treatments

what is chlorine effective against

most microorganisms except protozoa and Giardia

widely used as a : + examples

disinfectant

1. bleach

2. treats drinking water + sewage

3. cleaning surfaces, hospital, machines

two forms of alcohols

1. isopropanol (rubbing)

2. ethanol (drinking)

what do alcohols work by

protein denaturation and membrane disrupt

what concentrations of alcohol work best in

70-90%

what is alcohol used as

a disinfectant and antiseptic

what is alcohol effective against

bacteria, fungi, enveloped viruses

what can alcohol induce

endospore formation

types of surfactants

soaps and detergents

main action of surfactants

decrease surface tension of water, allowing emulsification of fats into small droplets

soaps don’t kill microbes, but what instead?

aid in mechanical removal of microbes (degerming)

what are detergents made up of

quaternary ammonium compounds (QUATS)

what are quats

canonic detergents for example cetylpyridinium chloride

what do QUATS disrupt

plasma membranes

what are QUATS effective against

gram positive bacteria, fungi, protozoa, enveloped viruses

what thrives in QUATS

gram - pseudomonas

where can you find QUATS

very common, non-toxic, tasteless disinfectants and antiseptics such as lysol products, mouthwashes, and cleaning wipes

alkylating agents

denature proteins and damage DNA

what are alkylating agents good against

bacteria and viruses

2 types of alkylating agents

1. glutaraldehyde

2. formaldehyde

what is glutaraldehyde used for

a 2% solution to disinfect hospital instruments therefore a sterilant

best form of sterilization?

autoclave

what is formaldehyde used for

a 37% solution that inactivates bacteria and viruses in vaccines and preserves biological specimens

why are alkylating agents not antiseptics

because they are carcinogenic and irritants

2 types of gaseous alkylating agents

1. ethylene oxide

2. propylene oxide

what do these kill

all microbes and endospores

what are they used for

to disinfect/sterilize equipment at room temperature especially for heat sensitive items like Petri dishes

oxidizing agents

highly reactive forms of oxygen that kill microbes by oxidizing their proteins and cell membranes

2 types of oxidizing agents

1. hydrogen peroxide

2. ozone

use of hydrogen peroxide

disinfectants for surfaces and hospitals and gaseous hydrogen peroxide in hospital rooms

why is hydrogen peroxide not ideal for wounds?

because of how it reacts with catalase