Microbiology Chapter 7

Dry Heat Sterilization

* sterilizing oven * heated by gas or electricity - thermostatically controlled * less effective in killing microorganisms than steam - requires higher temps and longer exposure time * used in spacecraft sterilization * examples: fixed oils, glycerin, petrolatum products, glassware, instruments

Factors related to effective disinfection

1. Appropriate for microbial group targeted 2. Appropriate concentration 3. Material being disinfected (pH, organic matter present?) 4. Length of exposure

Why is alcohol effective against some viruses and not others?

1. I'd expect the alcohol to dissolve away the lipid envelopes of some viruses. 2. For viruses that don't have envelopes, there's a possibility that the alcohol will interact with the proteins of the capsid more strongly than they interact with each other, thus dissociating the virus. 3. For viruses that don't fit in categories 1 and 2, the protein capsid is put together in a way that they won't interact with alcohol much. So your virus remains intact.

Peroxygen

1. active against gram pos and neg bacteria 2. no virucidal activity

Autoclave sterilization time

121 degrees C, 15 minutes

Ultra high temperature, short time

140 degrees C for <1 second

Hot air sterilization time

170 degrees C, 2 hours

High temperature, short time

72 degrees C for 15 seconds

Membrane filtration can remove microbes of what size?

>0.22 µm

HEPA can remove microbes of what size?

>0.3 µm

Why are gram negative bacteria more resistant to chemical biocides than gram positive bacteria?

A biocide is a chemical compound that can inhibit growth or even kill organisms. A good example are antibiotics, chemicals that are anti-microbial, directed against bacteria. Gram-positive and Gram-negative bacteria differ in their cell walls. Gram-positive bacteria have 1 membrane and a relative thick peptidoglycan layer, while Gram-negative bacteria have an inner membrane, a thin peptidoglycan layer, and a outer membrane. That outer membrane protects the Gram-negatives against many antibiotics that could otherwise damage the peptidoglycan layer or the inner cell.

Would a chemical microbial control agent that affects plasma membranes affect humans?

A microbial agent that targets the plasma membrane of the microorganism would not be advised because humans also have a plasma membrane. For this reason, it is important to develop a microbial agent that targets components of the microorganism that are not present in the host cell. For example, penicillin is an antibiotic that targets the cell well. Since the cell wall is not present in human cells, penicillin causes no damage to the host cell. When controlling microorganims, chemical agents that inhibit certain metabolic pathways are also useful, providing that such a metabolic pathway does not exist in humans. For example, some antibiotics target folic acid metabolism in bacteria. Because this metabolic pathway does not exist in humans, such a chemical agent would not cause damage to the human host.

What is a prion?

A non-living protein particle that has misfolded proteins. Prions invade living space and kill living tissue. Mad cow disease.

Asepsis

Absence of significant contamination. Aseptic surgical techniques prevent microbial contamination of wounds.

What characteristics make surface-active agents attractive to the dairy industry?

Acid-Anionic Sanitizers: important in cleaning dairy utensils and equipment; Non-toxic; non-corrosive; and fast acting.

Describe the effects of microbial agents on cellular structures.

Alteration of the membrane permeability, damage to proteins, damage to nucleic acids.

Is Betadine and antiseptic or a disinfectant when it is used on the skin?

An antiseptic. Anything that is applied to the skin will be an antiseptic and anything applied to objects is considered a disinfectant.

If you wanted to disinfect a surface contaminated by vomit and a surface contaminated by a sneeze, why would your choice of disinfectant make a difference?

Because there are different microbes that live in the gut compared to the nasopharynx. Viruses, bacteria,etc. Here's an example: Gram negative bacteria live in gut, not in nose, so you'd want to ensure the disinfectant was effective against them as well as vs. gram positive bacteria. So you'd want to pick a more verstatile and stronger disinfectant to clean up the vomit.

How is microbial growth in canned foods prevented?

By heating, it denatures the proteins in the food which render the bacteria harmless.

How does Osmotic Pressure control microbial growth?

Causes plasmolysis

Sepsis

Microbial contamination

Antibiotics in Food

Nisin and Natamycin prevent spoilage of cheese

The effectiveness of treating microbial disease depends on:

Number of microbes, Environment (organic matter, temp, biofilms), Time of exposure, Microbial characteristics

Chemical Food Preservatives include:

Organic acids, Nitrites, Antibiotics

What chemical disinfectants can be considered sporicides?

Phenols; Glutaraldehyde; B-Propiolactone; Ethylene oxide ;Peroxy acids.

Nitrites

Preservatives used by the meat industry as a curing agent to prevent bacterial growth. They can pose a chemical hazard if meat is burned or overbrowned. Prevents endospore formation.

The usual definition of sterilization is the removal or destruction of all forms of microbial life. How could there be practical exceptions to this simple definition?

Prions have a high resistance to all forms of sterilization; sterilization implies to the absence of prions.

How is it possible that a solution containing a million bacteria would take longer to sterilize than one containing a half-million bacteria?

Rate of microbial death: The number of microbes. The more microbes to begin with, the longer it takes to eliminate the entire population. other factors: environment influences; time of exposure; microbial characteristics.

Types of Low Temperature methods of microbial control?

Refrigeration, Deep Freezing, Lyophilization

Sterilization

Removing all microbial life

Degerming

Removing microbes from a limited area

Disinfection

Removing pathogens

Antisepsis

Removing pathogens on living tissue

Gaseous Sterilant

STERILANT - Commonly used on objects that cannot be sterilized by heat or liquid, used on electronic equipment

endospore

The DNA and other essential parts of a bacterium coated with several hard layers. Dormant.

Principles of effective disinfection

concentration of disinfectant; organic matter; pH; time

Alcohols

denature proteins and disrupt membranes

Bisphenols

disrupt plasma membranes, Hexacholorphene, triclosan

Biguanides Chlorhexidine

dissolves cell membrane, skin disinfectant/ surgical scrubs, G+/ G- bactericidal

HEPA filter

filter used in air for patients in controlled environments, sterile rooms for surgery, biological safety cabinets, both liquid and air can be filtered and sterilized.

Why would a can of pork take longer to sterilize at a given temperature than a can of soup that also contains pieces of pork?

heat dispersion is faster through liquid..here soup....than more solid pork. It also may be due to the fact that soup will produce more steam than solid pork..which (i.e steam) will help more in sterilizing. It has nothing to do with microbial content.

Filter sterilization

involves passage of liquids/air through a filter with pores, traps particles/cells/viruses, collected in sterile collection vessel. does not work for viruses.

Microwaves

kill by heat, not especially antimicrobial

Thermoduric organisms

mesophiles that can survive brief periods at higher temperatures

Filtration Sterilization

method of removing microbes from air or liquids that are unable to withstand heat ex: serum, blood products, vaccines, drugs, IV fluids, enzymes, media, milk, beer.

Ionizing Radiation

radiation w/enough energy to free electrons from atoms forming ions, may cause cancer (ex. gamma, X-rays, UV). Ionizes water to release OH. Damages DNA.

Types of surfactants

soap- degerming detergents- sanitizing quat ammonnium- batericidal, denature proteins, disrupt plasma membrane

Use-Dilution Test

test method used to determine the useful dilution of an antimicrobial agent by exposing specific bacteria to various dilutions of the agent. Metal rings placed in disinfectant for 10 min at 20 degrees C. Rings are transferred to culture media to determine whether bacteria survived treatment.

Deep Freezing

used for long-term storage; maintaining temperatures between -50 degrees celcius and -95 degrees celcius

Moist Heat Sterilization

used for sterilization culture media, instruments, dressings, intravenous equipment, applicators, solutions, syringes, etc steam must contact all surfaces. Kills microorganisms by denaturing proteins. Steam must contact item's surface.

Phenol and Phenolics

work by injuring plasma membranes, inactivating enzymes, and denaturing proteins; remain active in the presence of organic matter and are good for cleaning up pus, saliva, and feces; examples are the active ingredient in Lysol and hexachlorophene

Surfactant

any substance that interferes with the hydrogen bonding between water molecules and thereby reduces surface tension.

Refrigeration

artificial cooling that drastically reduces microbial growth of certain bacteria

Mesophile

bacteria that prefer moderate temperature and develop best at temperatures between 25C and 40C

What is DRT?

Decimal Reduction Time. Minutes to kill 90% of a population at a given temperature.

What do heavy metals do to microbes?

Denature Proteins of Microbes.

Equivalent treatments

Different methods that have the same effect on controlling microbial growth.

Which is more likely to be used in a medical clinic laboratory, a use-dilution test or a disk-diffusion test?

Disk-diffusion test. Because this is what is used to measure the effectiveness of specific antibiotics on certain microbes. -A use-dilution test would be more appropriate in industrial uses because it measures what is the lowest amount of chemical needed in a solution to effectively kill microbes.

What chemicals are used to sterilize?

Ethylene Oxide is the gas most frequently used for sterilization.

Nonionizing Radiation

Forms of radiant energy such as radio waves, microwaves, infrared light, and ordinary light that do not have enough energy to cause ionization of atoms in living tissue.

Plasma

Free radicals destroy microbes. Used on tubular instruments.

Heavy Metals used for microbial control

Hg Mercury Ag Silver Cu Copper

Organic Acids in foods

Inhibit metabolism Sorbic Acid, Benzoic Acid, Calium Propiant-Controls mold and bacteria in foods and cosmetics

Bacteriostasis

Inhibiting, not killing, microbes

Halogens

Iodine and Chlorine

Commercial sterilization

Killing C. botulinum endosores

Biocide/Germicide

Killing microbes

How does dry heat sterilization work?

Kills by Oxidation

Sanitization

Lowering microbial counts on eating utensils

What is the lowest temperature at which cells in a culture are killed in 10 minutes?

Thermal Death Point (TDP)

What is the time during which all cells in a culture are killed?

Thermal Death Time (TDT)

What is the connection between the killing effect of radiation and hydroxyl radical forms of oxygen?

These radicals are produced from ionizing radiation that take electrons from other molecules.

How does an autoclave work?

Uses temp above boiling water High pressure steam Higher pressure, higher temp Need direct contact with steam 15 psi at 121 C for 15 mins

Lyophilization

a combination of freezing and drying; used to preserve microorganisms and other cells in a viable state for many years. Uses liquid nitrogen.

Pasteurization

a form of sterilization using high temperatures for short periods of time. Reduces spoilage organisms and pathogens.

Iodine Tincture

a halogen; a mixture of iodine and alcohol; used as an antiseptic

Disk-Dilution Test

a test for antibiotic sensitivity in bacteria; agar plates are inoculated with a standardized suspension of a microorganism. Antibiotic-containing disks are applied to the agar surface. Following overnight incubation, the diameters of the zones of inhibition are interpreted as sensitive (susceptible), indeterminate (intermediate), or resistant.