Control of Microbial Growth

Disinfectants

Chemical agents that eliminate most pathogens on surfaces. (99.9%)

Antiseptics

destroying harmful microorganisms from living tissue

Sterilants

Agents that destroy all forms of microbial life, including spores.

Sepsis

bacterial contamination

Asepsis

The absence of pathogenic microorganisms, used in surgery to prevent infection of wounds

Biocides Method

Substances that kill a wide range of organisms. but not necessarily endospore

Bacteriostatic Methods

Techniques that inhibit microbial growth without killing.

D-value

Time required to reduce microbial population by 90%. (or 10 fold)

D-value calculation

same at generation time, exponetional

Biological Safety Levels determination factors

infectivity, work w/agent in the lab, ease of transmission, and potential disease severity

BSL-1

low-risk, No diseases in healthy orgamisms, basic precautions, basic sterile technique

BSL-2

indigenous, varying severity of infection, moderate risk

BSL-3

indigenous or exotic, can cause lethal diseases in respiratory transmission

BLS-4

exotic microbes, high risk of aerosol-transmitted infection and usually fatal without treatment, few labs done w/ these

Physical microbial control

Heat

-dry

-moist

filtration

high pressure

desiccation

osmotic pressure

Chemical microbial control

Disinfectants

-phenol

-alcohol

-halogens

-antibiotics

Dry heat

Kills by oxidation

-flaming, incineration, hot-air sterilization

Moist heat

Denatures enzymes and proteins

-Autoclave and Pasteurization

Autoclave

applies steam under pressure

-kills all organisms and endospores.

Pasteurization

reduces spoilage, organisms, and pathogens in milk and juices

-Treatments:

• High-temperature short-time (HTST): 72o C for 15 sec

• Ultra-high-temperature (UHT): 140o C for 4 sec

-milk and juices not kept refrigerated were treated with UHT

Filtration

Passage of liquids and air through screen-like material

Used for heat-sensitive materials

Removed microbes, not killed, not truly sterol

Phenol

break plasma membrane and denature proteins

rare, used to compare chemical agents

Phenolics

break plasma membrane and denature proteins

used on surfaces, skin, mucous membrane, and instruments

Bisphenols

disrupt plasma membrane

used in soaps and lotions

trisclosal is a common ingredient

Halogens

iodine, chlorine and fluorine

iodine

oxidize sulfer amino acids, nucleotides, and fatty acid's

antiseptic

chlorine

oxidizes hypochlorous acid altering cellular components

disinfects water, dairy equipment, utensils, house items

Heavy Metals and microbes

kill microbes by binding to proteins, thus inhibiting enzymatic activity

Heavy metals and humans

bioaccumulate and excessive concentrations can have toxic effects on humans

-mercury causes neurological damage

-silver causes argyria

Antimicrobial Activity Conditions

Population size

Composition

-microbs x sensitivity to antimicrobial

Concentration

-higher kills more

Duration of exposure

-more exposure=more killed

Temp

- higher kills more

Local environment (pH, organic matter concentration, and biofilms)

Disk-Diffusion

Filter paper disks are soaked in a chemical and placed on the spread plate; After incubation, measure the zone of inhibition

Surfactant

-group of chemical compounds that lower the surface tension of the water

-in soaps and detergents

-interact with oils and grease to create emulsions in water lifting away dirt

-degermining since no microbes are killed, only carried away