Control of Microbial Growth Chapter 13

Main goal of controlling microbial growth is

to reduce microbial load and reduce infection or contamination

Sterilization is

removal/killing of ALL microbes

Disinfection/Antisepsis is

inactivation of microbes

Sanitization/Degerming is

decreasing microbial load

CDC, NIH, & WHO established 4 levels

BSL-1-4

UTA micro labs are

BSL-2

BSL-1

very little risk, agents that do not cause infections, sink for hand washing and door to close off lab. (Freshman labs)

BSL-2

moderate risk, restrictive access, PPE, self closing doors, eyewash station, autoclave or sterilization method. Examples of microorganisms present are S. aureus, Salmonella spp. and Viruses like hepatitis, mumps, and measles

BSL-3

Exotic/indigenous pathogens, Potential to cause lethal infections by inhalation. BSL-2 plus respirator, bio safety cabinets, handsfree wash sink, two sets of doors, directional air flow. None at UTA. Examples of microorganisms present are M. tuberculosis, B. anthracis West Nile Virus, HIV.

BSL-4

Most dangerous, likely fatal, BSL-3 plus full biohazard suit, change clothing on entry, shower on exit, decontaminate all material on exit, lab must have own air supply. “Exotic” pathogens; Ebola and Marburg viruses.

Critical

must be sterile; items used inside the body (i.e. sterile tissue or bloodstream) Example: Surgical instruments

Semicritical

do not require high level sterilization; items might contact non-sterile tissue (e.g. gut) but not penetrate tissue. Example: respiratory therapy equipment

Noncritical

do not require sterilization; items contact but do not penetrate intact skin. Example: Stehoscopes

Fomite

Inanimate object

Aseptic technique is used to

prevent sterile environment from becoming contaminated

Forms of sterilizations are

Heat, Pressure , Filtration, and Chemical (sterilant)

Disinfectant

Inactivation/kill of microbes on fomites Example: Include vinegar and bleach

Antiseptic

acts on microbes but not organism/tissue Example: hydrogen peroxide, rubbing alcohol

Some microbes may not be inactivated

disinfection ≠ sterile!

\-cides

kill

\-static

stop growth

Degree of control can be observed with

microbial death curve

Microbial death curve is used to

Measure of percentage of kill

Decimal reduction time (DRT)

how much time it takes to kill 90% (1 log reduction) of population

6 types of physical control

Temperature, Pressure, Desiccation, Radiation, Sonication , and Filtration

Heat Sterilization is the

oldest and most common

Thermal Death Point

lowest temp that will kill in 10 min

Thermal Death Time

length of time to kill at a certain temperature (Bunsen burner)

Moist Heat is

application of high temperature liquid/vapor, better than dry (autoclave)

Dry Heat is

incineration; direct application of high heat (>250C)

Autoclave

raise temperature of water above boiling point (\~121C) by raising pressure to 15 psi

Two types of autoclave sterilization

Gravity and Prevacuum

Gravity

uses steam to push out air (shoots steam)

Prevacuum

vacuums out air first

Pasteurization

semi-sterilizes food but does not ruin food quality, and many methods rely on “flash” heating foods to kill most microbes

Refrigeration & Freezing

Slows metabolism, Ultra low temps (-80C) can be used for preservation, Usually not sterilization method but static

Pascalization is when

high pressure used in food industry to kill microbes

Pascalization is used in combination with

temperature in autoclaves

Desiccation is

drying or dehydration, used to preserve food an example is beef jerky

Lyophilization is

freeze-drying; rapid freezing then placed under vacuum

water activity is

osmosis

Salts or sugars can be used to lower

water activity of foods/materials without physical drying

Ionizing radiation

enters into cells and disrupts molecular structures such as DNA (X-rays and gamma rays)

Ionizing radiation can be

used to sterilize non-autoclavable items, alternative to pasteurization in canned foods

Non-ionizing radiation

does not penetrate glass, plastics, etc. but can damage cells w/ direct exposure

UV irradiation

forms thymine dimers in DNA causing lethal mutations

Sonication is

High frequency sound waves to disrupt cell structure, causes lysis ,and is used in laboratory and clinical settings

Filtration is the

use of a barrier to physically separate microbes

Membrane filtration

removes microbes from liquid samples

Air is commonly filtered through

high-efficiency particulate air (HEPA) filters.

Filters usually have pore size of

0\.2 µm

Filtration is useful when

media cannot be autoclaved

Phenols are

Carbon molecule with benzene ring and –OH group

Carbolic acid

first used by Joseph Lister for surgical wounds

Lysol

original formulations

Triclosan

commonly used in hand soaps; banned by FDA in 2017

Mercury

treated syphilis but banned b/c of neural toxicity effects

Silver

used today to treat burn wounds, pediatric ophthalmia neonatorum, and in antibiotics

Copper sulfate

used as algicide to treat pools

Zinc

mouthwashes, calamine lotion, baby powder

Iodine

oxidizes cellular components; commonly used as a iodophor

Chlorine

used to treat water, bleach, and swimming pool smell

Fluorine

Deposits in tooth enamel and provides disruption in microbial fermentation and processes, dental products

Alcohols is used

as disinfectants and antiseptics, can be combined with iodine

Surfactants

Chemicals that lower surface tension of water, soaps and detregent’s

Soaps are

fatty acid salts

Detergents are

synthetic polar & non-polar molecules

Quaternary ammonium salts are

cationic detergents (LYSOL)

Chlorhexidine is a

common surgical scrub and longer lasting than iodophors

Alexidine is a

faster acting surgical scrub “up and coming”

Formaldehyde

fixes specimens by cross-linking proteins

Glutaraldehyde acts faster than

formaldehyde; common disinfectant of surgical equipment

Ethylene oxide is a

gaseous sterilizer that has high penetrating ability

β-propionolactone

clear liquid or vapor with strong odor; wide variety of sterilization; medical, tissue, milk, etc.

Hydrogen peroxide

common & cheap disinfectant

Peracetic acid

more effective than H2O2 ; immune to inactivation by catalases and peroxidases

Benzoyl Peroxide

present in acne medications; very effective against Propionibacterium acnes

Ozone gas

used to clean air and water supply

Carbamide peroxide

agent in toothpaste that combats biofilms

Sorbic acid

inhibits various cellular enzymes ADDED Good at low pH

Benzoic acid

decreases intracellular pH, interferes with oxidative phosphorylation and AA uptake NATURAL Good at low pH

Propionic acid

inhibit enzymes and decrease intracellular pH (CHEESE) effective at high PH

Sulfur Dioxide

MOA unclear (inhibit protein formation or reduce intracellular pH?)

Nitrites

Nitric Oxide reacts with iron sulfur groups (disrupts ETC)

Nisin

disrupts G+ cell wall production, produced by Lactococcus lactis

Natamycin

antifungal macrolide antibiotic (prevents bacterial synthesis in cheese)

Supercritical Fluids

super pressurized carbon dioxide to the point where it is not a solid liquid or gas.

Phenol Coefficient

– how strong an agent is relative to phenol

Disk diffusion is

measuring degree of inhibition using sterile filter paper disks with chemicals

Use-dilution test

determines agent’s effectiveness on an inanimate surface

In-use test

determine whether disinfectant is contaminated

Sanitization

recue microbial load on fomite

Degerming

re duce microbial load on living tissue

UHT

Super hot at 130C for 2 seconds and last 90 days

HTST

Hot at 72C for 15 seconds and then refrigerated

Phenols MOA

Denature proteins and membranes

Heavy metals MOA

Binds and inhibits proteins

Halogens MOA

oxidization

Alcohol MOA

disrupts membranes and denatures cytoplasmic proteins leads to lysis

Anatomic

negative anion on chain