Chapter 11 Physical and Chemical Agents - (NSU - BIOL 251) - Microbiology by Talaro

Contaminant

Unwanted microbes present in a given time, place or amounts; microbes which are present in wrong place or in wrong amounts

Methods for Decontamination

physical, chemical, mechanical

Highest resistance

Bacterial endospores & Prions (not alive)

Moderate resistance

protozoan cycts, Pseudomonas sp., Staphylococcus aureus, Mycobacterium tuberculosis

Least resistance

vegetative(dividing) bacterial cells, fungal spores, hyphae, molds, enveloped viruses, yeasts, protozoan trophozoites

Decontamination

destruction, removal or reduction in number of undesirable microbes in a given area

Sterilization

any process that destroys or inactivates all viable microorganisms, including viruses and endospores

Sterile

condition of a material after is has been sterilized. Complete absence of living microbes or microbes capable of life.

Disinfection

A process to destroy vegetative pathogens, not endospores, on inanimate objects. Too toxic for use on living organisms. (bleach, boiling water)

Antisepsis

Disinfectants applied directly to exposed body surfaces; Use of chemical agents to destroy/inhibit vegetative pathogens on body surfaces (iodine, hydrogen peroxide, germicidal hand soap); does not rid of endospores

Sepsis

growth of microorganisms or presence of toxins in blood or tissues

Asepsis

practice which prevents entry/infection

Sanitation

Any cleansing technique that mechanically removes microbes; cleansing, removal of debris, microbes, and toxins from inanimate surfaces to reduce potential for infection/spoilage

Determination

dramatically reduce numbers of microbes on living tissue (skin) typically combined with use of antisepsis

-static

means to stand still (refrigeration)

-cidal

to kill (bleach)

Conditions influencing the killing of microbes

time of exposure, type/resistance to spores, microbial load, action of the agent/action of agent

Targets of antimicrobial agents

Cell wall

cell membrane

protein synthesis

protein function

Mode of Action of Antimicrobial Agents

Cellular targets, such as the cell wall, cell membrane, and protein and nucleic acid synthesis, protein function

Cell wall target (mode of action)

block cell wall synthesis, digest the exposed cell wall, disrupt cell wall; cell wall becomes fragile and cell lyses (Some antimicrobial drugs, such as penicillin, detergents and alcohol)

Cell membrane target (mode of action)

chemicals which are ampiphatic will intercalate into lipid bilayer-> disturb the regular arrangement of bilayer lipids-> membrane no longer effective barrier (detergents and surfactants)

Protein synthesis and nucleic acid synthesis (mode of action)

block DNA replication, translation, transcription, peptide bond formation, protein synthesis, alter DNA sequence; cells will not be able to multiply, and will eventually die. e.g chloramphenicol, UV radiation, formaldehyde

Protein function target (mode of action)

unfolded, mis-foldes or denatured proteins cannot function as enzymes, disrupt protiens (Examples: alcohols, metalic ions, phenolic compounds, heat)

Physical methods of microbial control

heat, cold, radiation, filtration, desiccation

Moist heat

Requires lower temperature and shorter exposure time as compared to dry heat; steam autoclave; gets into cells and denatures proteins more rapidly; causes proteins to aggregate/precipitate

Autoclave

steam under pressure, 15 PSI, 121C; 10-40 min; kills vegetative cells and endospores. Sterilizes, and is good for decontamination of liquids, heat tolerant solids

Autoclave mode of action

denaturation of proteins, destruction of membranes and DNA

Boiling

100C for 30 min; disinfection and destruction of non-spore forming pathogens

Pasteurization

Heat applied to kill potential agents of infection without destroying the food flavor or value; disinfection, not sterilization

Batch method pasteurization

63°C-66°C for 30 minutes

Flash method pasteurization

71.6C for 15 seconds

Dry heat

Uses moderate to high temperatures (as compared to moist heat); hot air (low moisture content; dehydration, alters protein structure; incineration (flame or heating coil) or dry ovens

Dry ovens

150 to 180 degrees Celsius, coagulate proteins

Microbiostatic

Slows the growth of microorganisms

Cold methods

bacteriostatic-> retards or suspends growth; used to preserve food, media, and cultures, does not kill the majority of microbes

Dessication (dehydration)

Gradual removal of water from cells, leads to metabolic inhibition; not effective microbial control - cells retain ability to grow when water is reintroduced

Lyophilization

freeze drying; preservation

Ionizing radiation

gamma rays, x-rays, cathode rays; DNA breaks or major changes are lethal, so cell dies. (food irradiation, mail, med instruments); change at the subatomic/atomic level - electrons leave orbit

Non-ionizing radiation

UV light, direct exposure; crosslinking of nucleotide bases in DNA, pyrimidine dimers, problems for DNA replication and cell division; changes energy states

Filtration

Physical removal of microbes by passing a liquid or gas through a filter; especially for liquids that are sensitive to heating and air in hospital isolation units/industrial clean rooms; used for vaccine production or blood products.

High-level germicides

Kill endospores, may be sterilants, and used on critical items that are not heat sterilizable

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

kill vegetative bacteria, fungi, protozoa, and some viruses; used on 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

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

Alcohols

membrane disruption, protein denaturation. Not sporicidal. 50-95% ethanol, Isopropanol (toxic) good for enveloped viruses; intermediate level

Iodine

One of the oldest and most effective antiseptics; works against all bacteria and many endospores, fungi, and viruses; alters plasma membrane

Tincture

Iodine combined with alcohol

Iodophor

iodine combined with an organic carrier molecule, example is Betadine

Hydrogen peroxide

High reactive; forms -OH free radicals; damages proteins and DNA while recomposing oxygen gas; toxic to anaerobes; Kills spores at high concentration; antiseptic at low concentrations

Disinfectants

surface tension action, membrane disruption, protein precipitation. Quaternary ammonium compounds; very low level decontamination

Quats

Quaternary ammonium compounds; acts as surfactants that alter membrane permeability of some bacteria and fungi

Soaps (and detergents)

mechanically remove soil and grease containing microbes