Bacteriology 250 Chapter 9


Removal or destruction of all microbes, including viruses and bacterial endospores, in or on an object (not prions)


misfolded proteins, also can misfold other proteins, contagious


an environment or procedure that is free of contamination by pathogens


use of physical or chemical agents to inhibit or destroy microorganisms, especially pathogens, only refers to inanimate objects, endospores and some viruses not affected


spongiform, holes in the brain, mad cow disease, chronic wasting disease (deer), scrapie (sheep), NV-CJD (Creutzfeldt-Jakob disease, humans)


Use of a chemical (an antiseptic) on the skin or other tissue


Removal of microbes from a surface by scrubbing (i.e. washing hands)


disinfecting places and utensils, used by public, meet accepted health standards (gov. regulations), disinfect at home, sanitize in public


the use of heat to kill pathogens and reduce the number of spoilage microbes in food and beverages


indicate that a chemical or physical agent inhibits microbial metabolism and growth but does not necessarily kill microbes; bacteriostatic, virustatic, fungistatic etc.


refers to agents that destroy or permanently inactivate a particular type of microbe; virucide, bactericide, fungicide etc.

Microbial death

the permanent loss of reproductive ability under ideal environmental conditions

Microbial death rate

a way to evaluate efficacy of an antimicrobial agent, usually found to be constant over time for any particular microbe under specific conditions

Two steps of Action of Antimicrobial Agents

1.Alteration of cells walls and membranes
2.Damage to proteins and nucleic acids

Ideally agents should be....

inexpensive, fast-acting, stable during storage, and capable of controlling microbial growth while being harmless to humans, animals and objects (we don't have cell walls while microbial growth does)

High level germicides

Kill all pathogens, including endospores

Intermediate-level germicides

Kill fungal spores, protozoan cysts, viruses and pathogenic bacteria

Low-level germicides

Kill vegetative bacteria, fungi, protozoa, and some viruses

Four Biosafety Levels

-Biosafety level 1(BSL-1) Doesn't cause disease in healthy humans
-Biosafety level 2 (BSL-2) Handling moderately hazardous agents
-Biosafety level 3 (BSL-3) Handling all microbes in safety cabiniets
-Biosafety level 4 (BSL-4) Handling microbes that cause

Microbial control with Heat

-denatures proteins
-interfere with integrity of cytoplasmic membrane and cell wall
-Disrupt structure and function of nucleic acids

Thermal Death Point

Lowest temperature that kills all cells in broth in 10 minutes (set time, variable temp)

Thermal Death Time

Time to sterilize volume of liquid (variable time, set temp)

Moist heat

disinfects, sanitizes, sterilizes and pasteurizes, denatures proteins and destroys cytoplasmic membranes, more effective than dry heat. Methods: boiling, autoclaving, pasteurization, and ultra high temperature sterilization

Dry Heat

not as efficient as moist, for materials that can't be sterilized with moist heat (like paper), denatures proteins and oxidizes metabolic and structural chemicals, higher temp and longer times than moist heat


ultimate means of sterilization

Refrigeration and Freezing

Decrease in metabolism, growth and reproductions, more bacteriostatic, halts pathogen growth

Slow Freezing

more effective in killing due to formation of ice crystals, damaging cells and cell walls

Quick Freezing

prevents cell damage

Yersinia pestis

bubonic plague

2 most dangerous microbes in refrigerated foods

Listeria and Yersinia


drying, inhibits growth due to the removal of water, (think raisins)


freeze-drying, used for long term preservation of microbial cultures

Osmotic Pressure to control microbes

high concentrations of salt or sugar in foods to inhibit growth, cells in hypertonic solution of salt or sugar lose water

Fungi's ability over bacteria a

have a greater ability to survive hypertonic environments than bacteria


Ionizing radiation which affects DNA by penetration (used for food), creates ions that denature molecules, electron beams used (but don't penetrate well), gamma rays and xrays also used (but require lots of time)

Non-ionizing radiation

good for sterilizing surfaces, affects 3D structure of proteins and nucleic acids

UV Light Controlling Microbes

doesn't penetrate well, is good for disinfecting air, transparent fluids, and surfaces of objects

Phenol and Phenolics

Denature proteins, disrupt cell membranes, effective in presence of organic matter, active for a long time, disagreeable odor, used in health care settings, labs and homes


used in trash bags


used to be a common disinfectant for children, caused brain damage


Intermediate-level disinfectants, denature proteins and disrupt membranes, more effective as soap for removing bacteria, but not as effective as soap is at removing viruses, works better when diluted


Intermediate-level antimicrobial chemicals, damage enzymes (iodine tablets (hiking, disinfect water, doesn't kill endospores), iodophores, chlorine, bleach, chloramines, and bromine disinfection)

Oxidizing Agents

Peroxides, ozone, and peracetic acid, kill by oxidation of enzymes, high-level disinfectants and antiseptics

Hydrogen Peroxide

can disinfect and sterilize serfaces, works best for deep puncture wounds w/o oxygen due to catalase activity

Ozone and Chlorine

used for treatment of drinking water (ozone in Europe and chlorine in the US)


Surface active chemicals, soaps and detergents, quats

Soaps and detergents

Soaps: hydrophilic (grabs water) and hydrophobic (breaks up oils) ends
Detergents: positively charged organic surfactants


low level disinfectants, disrupt cellular membranes, ideal for medical and industrial applications, NH4+, not killing, wash things away

Heavy Metals

denature proteins, bacteriostatic and fungistatic agents, silver nitrate (prevents blindness in babies, not used anymore) thimerosal (preserves vaccines, still used in a few), copper (controls algal growth)


compounds with terminal -CHO groups, denature proteins and inactivate nucleic acids, Glutaraldehyde (disinfects and sterilizes), Formalin (embalming and disinfection of rooms and instruments)

Gaseous Agents controlling microbes

used in closed chambers to sterilize items, denature by cross-linking functional groups, used in hospitals and dental offices
Can be hazardous to people, highly explosive, poisonous, and carcinogenic


antimicrobial, act against microorganisms, human tears contain lysozyme (also in saliva) that can digest peptidoglycan cell walls of bacteria, also lysozyme can reduce bacteria in cheese, prionzyme removes prions from medical instruments


naturally made antibiotics and semisynthetic and synthetic chemicals, typically used for disease treatment, some used to control microbes outside the body

Phenol Coefficient

Evaluates efficacy of disinfectants and antiseptics, compares agent's ability to control microbes to phenol, has been replaced by newer methods

Use-dilution test

metal cylinders dipped into bacterial broth cultures, cylinder then immersed into dilution of disinfectant, cylinders removed, washed and placed into tube of medium. The most effective agents entirely prevent growth at highest dilution, current standard U

Kelsey-Sykes capacity test

Alternative assessment (Europe), Bacterial suspensions added to the chemical being tested, samples removed at certain times and then incubated, lack of bacterial reproduction reveals minimum time required for disinfectant to be effective

In-Use test

Swabs taken from objects before and after application of disinfectant or antiseptic, swabs inoculated into growth medium and incubated, medium monitored for growth