Microbio Last Exam Chapter 11

Decontamination

physical, chemical and mechanical methods to destroy or reduce undesirable microbes in a given area

ex: asepsis, disinfection, sanitization, degermation

Primary targets are microorganisms capable of causing infection or spoilage

vegetative bacterial cells or endospores

fungal hyphen and spores, yeast

protozoan trophozoites and cysts

worms

viruses

prions

Highest resistant microbes

prions, bacterial endospores

Moderate resistant microbes

Pseudomonas sp.

Mycobacterium tuberculosis

Staphylococcus aureus

Protozoan cysts

Least resistance microbes

most bacterial vegetative cells

fungal spores and hyphae, years

enveloped viruses

protozoan trophozoites

Sterilization

a process that destroys all viable microbes, including viruses and endospores

disinfection

a process to destroy vegetative pathogens, not endospores

inanimate objects

antiseptic

disinfectants applied directly to exposed body surfaces to destroy or inhibit vegativatie pathogens

ex: iodophors, antibacterial soap, chlorhexidine

sanitization

any cleansing technique that mechanically removes microbes from inanimate surfaces

dex: dishwashing, laundering clothes

degermation

removes microorganisms from living tissue through mechanical means

sepsis

the growth of microorganism in the tissues

ex: infected wounds, blood infection

disinfection

destruction of vegetative pathogens on inanimate objects

ex: 5% bleach, boiling water

sterilization

the removal or deconstruction of all viable microbes

ex: autoclave, ionizing radiation (correctly applied)

Microbial death

hard to detect, microbes often reveal no conspicuous vital signs to begin with

permanent loss of reproductive capability, even under optimum growth conditions

Factors that affect death rate

number of microbes

nature of microbes in the population

temperature and pH of environment

concentration or dosage of agent

mode of action of the agent

presence of solvents, organic matter or inhibitors

the cell wall

cell wall becomes fragile and cell lyses

some antimicrobial drugs, detergents, and alcohol

cellular targets of physical and chemical agents

the cell membrane

loses integrity

detergent

cellular targets of physical and chemical agents

protein and nucleic acid synthesis

prevention of replication, transcription, translation, peptide
bond formation, protein synthesis

chloramphenicol, ultraviolet radiation, formaldehyde

cellular targets of physical and chemical agents

proteins

disrupt or denature proteins

alcohols, phenols, acids, heat

cellular targets of physical and chemical agents

Methods of Physical Control

1) Heat- moist and dry

2) Cold temperatures

3) Desiccation

4) Radiation

5) Filration

moist heat action and heat effectiveness

lower temperatures and shorter exposure time

coagulation and denaturation of proteins

dry heat action and heat effectiveness

moderate to high temperatures

dehydration, alters protein structure

incineration

Thermal death time (TDT)

shortest length of time required to kill all test microbes at a specified temperature

Thermal death point (TDP)

lowest temperature required to kill all microbes in a sample in 10 minutes

steam under pressure

sterilization

autoclave

15 psi/ 121 C/ 10-40 min

steam must reach surface of item being sterilized

item must not be heat or moisture sensitive

mode of action- denaturation of proteins, destruction of membranes and DNA

tyndallization

intermittent sterilization for substances that cannot withstand autoclaving

items exposed to free-flowing steam for 30-60 minutes, incubated for 23-24 hours and then subjected to steam again

repeat cycle for 3 days

used for some canned foods and laboratory media

disinfectant

boiling water

boiling at 100 C for 30 minutes to destroy non-spore-forming pathogens

disinfection

Pasteurization

heat is applied to kill potential agents of infection and spoilage without destroying the food flavor or value

63 C - 66 C for 30 minutes (batch method)

71.6 C for 15 seconds (flash method)

not sterilization (kills non-spore-forming pathogens and lowers overall microbe count/ does not kill endospores or many nonpathogenic microbes)

dry heat

using higher temperature than moist heat

• incineration: flame or electric heating coil

  • ignites and reduces microbes and other substances

• dry ovens: 150 C - 180 C coagulate proteins

Cold

microbiostatic

Microbiostatic

slows the growth of microbes

refrigeration 0-15 C and freezing < 0 C

used to preserve food, media, and cultures

Desiccation/ Dehydration

gradual removal of water from cells, leads to metabolic inhibition

not effective microbial control - many cells retain ability to grow when water is reintroduced

Lyophilization

freeze drying

preservation

Ionizing radiation

deep penetrating power that has sufficient energy to cause breaks in DNA

• gamma rays, X-rays, cathode rays

• used to sterilize medical supplies and food products

• ex: preserving food with ionizing radiation

non-ionizing radiation

little penetrating power so it must be directly exposed

• UV light creates pyrimidine dimer, which interfere with replication

• ex: sterilizing air, water or surfaces

filtration

physical removal of microbes by passing a gas or liquid through a filter

used to sterilize heat sensitive liquids and air in hospital isolation units and industrial clean rooms

chemical agents in microbial control

disinfectants, antiseptics, sterilants, degermers, and preservatives

High-level germicides

kill endospores, may be sterilants

• devices that are not heat sterilizable and intended to be used in sterile environments (body tissue)

Intermediate level germicides

kill fungal spores (not endospores), tubercle bacillus, and viruses

• used to disinfect devices that will come in contact with mucous membranes but are not invasive

low-level germicides

eliminate only vegetative bacteria, vegetative fungal cells, and some viruses

• clean surfaces that touch skin but not mucous membranes

Factors that affect germicidal activity of chemicals

nature of the material being treated

degree of contamination

time of exposure

strength and chemical action of the germicide

germicidal categories

1) Halogens

2) Phenolics

3) Chlorhexidine

4) Alcohols

5) Hydrogen peroxide

6) Aldehydes

7) Gases

8) Detergents and soaps

9) Heavy metals

10) Dyes

11) Acids and Alkalis

Chlorine (Cl2), hypochlorites (chlorine bleach), chloramines

halogen

• denaturate proteins by disrupting disulfide bonds

• intermediate level

• unstable in sunlight, inactivated by organic matter

• water, sewage, wastewater, inanimate objects

Iodine (I2), iodophors (betadine)

halogen

• interferes with disulfide bonds of proteins

• intermediate level

• milder medical and dental degerming agents, disinfectants, ointments

Phenolics

disrupt cell walls and membranes and precipitate proteins

low to intermediate level (bactericidal, fungicidal, virucidal, no sporicidal)

• lysol

• triclosan

triclosan

antibacterial additive to soaps

Chlorhexidine

a surfactant and protein denaturant with broad microbicidal properties

low to intermediate level

Hibiclens, Hibitane

used as skin determine agents for preoperative scrubs, skin cleaning, and burns

Alcohols

ethyl, isopropyl in solutions of 50-95%

act as surfactants dissolving membrane lipids and coagulating proteins of vegetative bacterial cells and fungi

intermediate level

Hydrogen Peroxide

produce highly reactive hydroxyl-free radicals that damage protein and DNA while also decomposing to O2 gas - toxic to anaerobes

antiseptic at low concentrations

strong solutions are sporicidal

Aldehydes

kill by alkylating protein and DNA

Glutaraldehyde

Formaldehyde

Glutaraldehyde

in 2% solutions (Cidex) used as sterilant for heat sensitive instruments

• high level

Formaldehyde

disinfectant, preservative, toxicity limits use

• formalin - 37% aqueous solution

• intermediate to high level

Gases and Aerosols

ethylene oxide, propylene oxide

strong alkylating agents

high level

sterilize and disinfect plastics and pre-packaged devices, foods

Detergents and Soaps

Quaternary ammonia compounds (quats)

very low level

Quaternary ammonia compounds (quats)

act as surfactants that alter membrane permeability of some bacteria and fungi

detergents and Soaps

mechanically remove soil and grease containing microbes

Heavy Metals

solutions of silver and mercury kill vegetative cells in low concentrations by inactivating proteins

low level

silver nitrate, silver

Dyes as antimicrobial agents

aniline dyes are very active against gram-positive species of bacteria and various fungi

sometimes used for antisepsis and wound treatment

low level, narrow spectrum of activity

Acids and Alkalis

low level of activity

• organic acids prevent spore germination and bacterial and fungal growth

• acetic acid inhibits bacterial growth

• benzoic and sorbic acid inhibit yeast