Microbial Control

Most methods of microbial control target cells in which stage

log phase rather than stationary phase when microbes are resistant/survival stage

Why control microbial growth

• Microbes are naturally a part of our existence.

• They have a role in the Earth’s ecosystem helping to maintain balance.

• Humans have a normal resident microflora which are antagonistic toward harmful pathogens.

• Prevention of the overgrowth of potentially harmful pathogens is necessary.

Targets of microbial control –

infectious microbes and those that cause spoilage

targeting microbial cell walls and membranes

Damage to membrane proteins or lipids, disruption of bilayer, weakening that leads to leakage or lysis

targeting microbial nucleic acid and proteins

– Cellular metabolism will cease if proteins are inhibited or denatured

– Cellular reproduction will cease if there are mutations; proteins that are produced from these nucleic acid sequences will also be affected

Factors affection the efficacy of microbial control methods

• Material to be treated

– Materials covered in organic matter

– Environmental conditions (temperature, pH)

• Susceptibility of microorganisms

– Size of population

– Composition of population

• Control agent

– Concentration, duration of exposure

Most resistant to least resistant microbes

• Prions: infectious naked proteins

• bacterial endospores: resistant, dormant form that protects against environmental influence

• mycobacterium: contains waxy mycolic acids in cell wall to protect from heat, desiccation, and chemicals

• small non-envelope viruses: naked viruses; proteins are heartier and harder to destroy; smaller and harder to target

• Gram negative microbes: outer membrane

• fungi- have hearty shells/ thick cell walls

• large non-enveloped virus: tiny but bigger and easier to target

• Gram positive bacteria

• Lipid envelope virus

Biosafety levels

• Safety levels for dealing with pathogens – designed to protect workers in facilities that handle them.

• Currently, the levels are BSL 1 through BSL 4

High temp as a physical agent of control

Pathogens are usually mesophiles so heating to tempertures beyond maximum stops/inhibits maybe kills them

Temperature affects

cells directly by unravelling their molecules

radiation primarily affects

DNA

dry heat

air with a low moisture content that has been heated by a flame or electric heating coil.

-Microbicidal

– Dehydrates (pulls water out) the cell – removing necessary water & alters protein structure; oxidizes cells burning them into ashes

Moist Heat

high moisture content, can penetrate cells e.g. hot water, boiling water, steam (vaporized water).

microbicidal

results in combustion

– Kills microbes by coagulating proteins (denaturing) and lysing cell membranes. – Boiling – kills vegetative cells and most viruses in minutes; endospores, cysts and some viruses will survive

autoclave

-use of high temperature pressurized steam to sterilize equipment, materials and biological waste.

-meant to get rid of endospores

-usually 120 degrees C

Generally endospores require

121 degreesC for 15 mins of moist heat destroys most heat-resistant species

Pasteurization:

heat is applied to liquids to kill potential agents of infection & spoilage, while retaining liquid’s flavor and food

High temp short time (HTST) –

type of pasteurization; materials exposed to 72degrees C for 15 secs] is the most commonly used method

Low temp Long time (LTLT) –

pasteurization type; materials are held at 63 degree C for 30 mins.

Ultra High temp (UHT)–

pasteurization type; heat liquid 134°C for 1 - 2 seconds Mini flash pasteurizer

Louis Pasteur

a trained chemist who invented the process called pasteurization – the heating of thermolabile liquids to prevent microbial growth. He also determined the role of microbes in food spoilage and recognized their role in the process of fermentation.

Low Temperature

Microbistatic; slows everything down; gradual cooling will only kill sensitive microbes;Temps of -70C to -135 C is regularly used to preserve bacteria, viruses, fungi.

thermodurics

mesophiles that survive pasteurization

lyphilized

dried microbes; combination of freezing and drying for long term preservation

filtration as microbial control

mechanical control; movement through a filter stops/filters microbes good for heat sensitive liquid (drugs); uses a membrane filter and vacuum to sterilize liquid- key is to use a filter small enough to filter microbes

irridation

short wavelengths of high energy waves; When cells are irradiated, molecules absorb some of the energy. Ions can form because orbital electrons are ejected from an atom. Molecule most affected by radiation in a cell is DNA; results in denaturation and broad scale mutations.

X-ray and gamma rays are

ionizing radiations that produce enough energy to eject electrons from atoms and create ions.

UV rays are

non-ionizing radiation, and excites atoms, raising them to higher energy and the formation of abnormal bonds.

ionizing radiation

sterilizing radiations; ions form that impact cells; usually irriversible; breaks bonds of DNA

non-ionizing radiation

disinfecting- abnormal bonds firm and cannot penetrate barriersl can be repaired; Some secondary lethal effects include chemical changes in organelles and the production of toxic substances

Sterilization

is the process by which all living cells, spores, and viruses on an object are destroyed.

Disinfection is

the killing, or removal, of disease-producing organisms from inanimate surfaces; it does not necessarily result in sterilization.

antisepsis

degermination; like disinfection but applies to removing pathogens from surfaces of living tissues

sanitation

reducing the microbial population to safe levels and usually involves cleaning and disinfection

-icide/-icidal

suffix meaning destruction of a type of microbe

degerming

removing of microbes by mechanical means

-stasis/-static

suffix meaning inhibition but not complete destruction of microbial type

aseptic

refers to an environment or procedure free of pathogenic contaminants

microbial death rates

• The permanent loss of reproductive capability, even under optimum growth conditions.
• Death is not instantaneous – begins when a certain threshold of the microbicidal agent (time and
concentration) is met.
• As time increases, death continues in an exponential manner.

Decimal reduction time

the amount it takes to kill 90% of a microbial population and helps measure the efficacy of the treatment

older cells are generally

harder to kill