Microbiology Chapter 7

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

90% of the microbes die each minute and 90% of the million bacteria will always be bigger than the half million.

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?

A practical exception to this definition could be endospores and those that have prions.

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.

Is Betadine® an antiseptic or a disinfectant when it is used on skin?

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

Compare the effectiveness of moist heat (boiling, autoclaving, pasteurization) and dry heat.

Boiling kills vegetative forms of bacterial pathogens, many viruses, and fungi but is not always a reliable sterilization process. Autoclave provides temperatures higher than boiling water. It is the preferred method of sterilization unless the material can be damaged by heat or moisture. It is most effective when the organisms either are contacted by the steam directly or are contained in a small volume of aqueous (primarily water) liquid. Pasteurization- kill organisms that cause spoilage of food and drink. Microbes that survive pasteurization are unlikely to cause disease or early spoilage. Dry Heat- kills by oxidation. It effectively sterilizes laboratory equipment during flaming.

Explain how the type of microbe affects the control of microbial growth.

Controls of microbial growth usually target a characteristic and if that microbe lacks it, then it will not be affected.

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.

How is microbial growth in canned foods prevented?

Drying is often used to preserve foods (e.g. fruits, grains, etc.). Methods involve removal of water from commercial sterilization: product by heat, evaporation, freeze-drying, and addition of salt or sugar.

Describe how filtration, low temperatures, high pressure, desiccation, and osmotic pressure suppress microbial growth.

Filtration- allows passage of a liquid or gas but has small enough pores that can retain microorganisms. Low Temperature- prevents most microbes from being able to reproduce because of their suppressed metabolic rate. Slow freezing is best. High Pressure- alters the molecular structure of proteins and carbohydrates which results in the rapid inactivation of vegetative bacterial cells. Desiccation- microorganisms cannot grow or reproduce in the absence of water, they can remain viable for years however. Osmotic Pressure- high concentrations of salts and sugar create a hypertonic environment that causes water to leave the microbial cell.

Differentiate halogens used as antiseptics from halogens used as disinfectants.

Halogens like Iodine are used as antiseptics, it kills bacteria, many endospores, various fungi, and some viruses. It impairs protein synthesis and alters cell membranes. Halogens like chlorine are used as a disinfectant. It uses oxidation to prevent much of the cellluar enzyme system from functioning.

Explain how radiation kills cells.

Ionizing radiation- has a short wavelength about 1nm. It ionizes water which forms highly reactive hydroxyl radicals the kill organisms by reacting with their organic cellular components and damaging them. This is especially true in DNA. Nonionizing Radiation- has a longer wavelength greater then 1nm. It can damage the DNA of exposed cells by causing bonds to form between adjacent pyrimidine bases. Organisms must be directly exposed because it can not penetrate far. Microwaves- can kill most vegetative pathogens when heating up food.

List the advantages of glutaraldehyde over other chemical disinfectants.

It is less irritating. It is a sterilizing agent.

Why is alcohol effective against some viruses and not others?

It targets the lipid membrane of enveloped viruses. Spores are resistant.

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?

It would depend on what the situation dictates. Use of Biguanides would be useful on the sneeze because of chlorhexidine.

Describe the effects of microbial control agents on cellular structures.

Many microbial control agents target plasma membranes in order to leak the cellular contents of the cell that interfere with the cell growth. If nucleic acids are damaged, then the cell can no longer replicate and carry on any synthesis.

Identify the methods of action and preferred uses of chemical disinfectants.

Phenolics are suitable agents for disinfecting pus, saliva, and feces. Biphenols- used to control infections in nurseries, and is an ingredient in soaps, toothpastes, and mouthwashes. Biguanides- affect bacterial cell membranes. common in microbial control on skin and mucous membranes and is used in surgical hand scrubs. Essential oils- similar to phenolics. can be used to disinfect hard surfaces like countertops and can be used on skin. Alcohols- kill bacteria and fungi but not endospores and nonenveloped viruses. It denatures proteins usually, but can also disrupt membranes. Heavy Metals- can be biocidal or antiseptic

What chemicals are used to sterilize?

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

What chemical disinfectants can be considered sporicides?

Sporicides: Phenols Glutaraldehyde B-Propiolactone Ethylene oxide Peroxyl acids

Define the following key terms related to microbial control: sterilization, disinfection, antisepsis, degerming, sanitization, biocide, germicide, bacteriostasis, and asepsis.

Sterilization- is the removal or destruction of all living microorganisms. Disinfection- control directed at destroying harmful microorganisms. Antisepsis- disinfection directed at living tissue. Degerming- mechanical removal of most of the microbes in a limited area. Sanitization- intended to lower microbial counts to safe public health levels and minimize the changes of disease transmission from one user to another. Biocide/Germicide- kill microorganisms Bacteriostasis- inhibit the growth and multiplication of bacteria. Asepsis- the absence of significant contamination

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

The distribution of liquid. The more liquid in an area, the easier to it is to sterilize it.

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.

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

Yes because humans have a plasma membrane. The microbial control agent needs to attack something humans do not have.

List the factors related to effective disinfection.

concentration of disinfectant organic matter pH time

The presence or absence of endospores has an obvious effect on microbial control, but why are gram-negative bacteria more resistant to chemical biocides than gram-positive bacteria?

gram negative bacteria have a waxy lipid membrane and thick cells as well as endospores.

Describe the patterns of microbial death caused by treatments with microbial control agents.

if the death curve is plotted logarithmically, the death rate is constant; factors that influence the effectiveness:number of microbes, the more microbes there are, the longer it'll take.environmental influences: the presence of organic matter often inhibits the action of chemical antimicrobials.time of exposure: often require extended exposure to affect more-resistant microbes or endospores microbial characteristics: affect the choice of chemical and physical control methods

Interpret the results of use-dilution tests and the disk-diffusion method.

metal rings dipped in test bacteria are dried, dried cultures are placed in disinfectant for 10 min at 20 degree C; rings are transferred to culture media to determine whether bacteria survived treatment a clear zone will appear around the disk if it works well.

Identify chemical sterilizers.

plasma- free radicals destroy microbes, use on tubular instrumentssupercritical fluids- CO2 with gaseous and liquid properties, use on medical implantsperoxygens- oxidizing agents, use on contaminated surfaces

Identify the appropriate uses for surface-active agents.

soap- degerming acid-anionic detergents- sanitizing quaternary ammonium compounds- bactericidal, denature proteins, disrupt plasma membrane