Chapter 11 Part 2: Microbiology

Microbiostatic

slows the growth of microbes

Examples of microbiostatic

refrigeration between 0-15C, freezing below 0C

Purpose of microbiostatic

to preserve foods, media, and cultures

Desiccation

• gradual removal / loss of water from cells

• fancy word for dehydration

Effectiveness of desiccation

not effective - cells can regrow if water is reintroduced

Lyophilization

freeze drying

Ionizing radiation

deep penetrating power with sufficient energy to disrupt electrons; break DNA

Examples of ionizing radiation

gamma rays, x-rays, cathode rays

Application of ionizing radiation

used to sterilize food and medical products

Nonionizing radiation

little penetrating power so it must be directly exposed

Example of nonionizing radiation

UV light

Application of nonionizing radiation

sterilizing water, air, or surfaces

Filtration

physical removal of microbes with the use of a filter; gas or liquid through filter

Purpose of filtration

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

Levels of Chemical Decontamination

• high level germicides

• intermediate level

• low level

High-level germicides

kill endospores; may be sterilants

Intermediate-level germicides

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

low-level germicides

kill vegetative cells, bacteria, and some viruses

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

Function of alcohols

dissolves membrane lipids and coagulating proteins of vegetative bacterial cells and fungi

Classification of alcohol on chemical decontamination

intermediate level

Iodine is classified as

an antiseptic

Effectiveness of iodine

works against all bacteria and many endospores, fungi, and viruses

Function of iodine

alters the plasma membrane of cells

Tincture

iodine mixed with alcohol

Iodophor

iodine mixed with an organic carrier molecule

Function of hydrogen peroxide

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

Hydrogen peroxide is classified as

an antiseptic (at low concentrations)

Hydrogen peroxide is classified as a ____ at high concentrations

sporicidal

Function of quats

surfactants that alter membrane permeability of some bacteria and fungi

Quats are classified as

a low level disinfectant

Function of soaps

mechanically remove soil and grease containing microbes