Ch.5 micro+disease

Which concentration of alcohol is the most effective germicide?

75%

The D value is defined as the time it takes to kill

90% of bacteria in a population

Name two products commonly sterilized using ethylene oxide gas.

Any of the following are posssible answers: Pillows, mattresses, electrical equipment, plastic Petri dishes and pipettes, and implantable devices such as pacemakers and artificial hips.

Why do critical instruments need to be sterile, whereas semicritical instruments need only be free of viruses and vegetative bacteria?

Because critical instruments come into direct contact with normally sterile body tissues whereas semicritical instruments do not (they come into contact with mucous membranes).

Why would the term sterilization not encompass prions?

Because prions were only recently discovered and are much more difficult to destroy than microorganisms and viruses.

Why would water treatment facilities be concerned about disinfection by-products?

Because some have been linked to long-term health risks.

Why is it important that the commercial canning process destroys the endospores of Clostridium botulinum?

Because the obligate anaerobe, which produces botulinum toxin (one of the most potent toxins known) can grow in low acid canned foods.

How does ultraviolet light kill microorganisms?

Damages DNA

Explain why it takes longer to kill a population of 109 cells than it does to kill a population of 103 cells.

Death of microbes occurs at a constant rate; it takes more time to kill a large population of bacteria than it does to kill a small population because only a fraction of organisms die during a given time interval.

What is the difference between the mechanism of a depth filter and that of a membrane filter?

Depth filters trap microbes in complex passageways that retain particles; membrane filters have small pores that allow liquid to pass but hold microbes back.

Explain why it is essential to dilute iodophores properly.

Dilution affects the amount of free iodine available, and it is the free iodine that's antimicrobial.

How do high concentrations of sugar and salt preserve foods?

Draws water out of cells, dehydrating them.

Which of the following can most reliably be used as a sterilant?

Ethylene oxide gas

How are heat-sensitive liquids sterilized?

Filtration

Preservation by freezing is sometimes compared to drying. Why would this be so?

Frozen water is unavailable for microbial growth.

Why could sterilization by gamma irradiation be carried out even after packaging?

Gamma rays can penetrate packaging.

How is an iodophore different from a tincture of iodine?

In an iodophore, the iodine is linked to a carrier molecule so that free (unbound) iodine is released slowly; in a tincture, iodine is dissolved in alcohol. An iodophore is less irritating to the skin than a tincture.

When canning, why are low-acid foods processed at higher temperatures than high-acid foods?

In low-acid foods, the endospores of Clostridium botulinum must be destroyed because otherwise those spores can germinate and the vegetative cells grow, producing the toxin that causes botulism. C. botulinum cannot germinate/grow in high acid foods (low pH) so processing methods do not need to destroy their endospores.

How does incineration destroy microbes?

It burns cell components to ashes.

How does microwaving a food product kill bacteria?

Microwaves do not kill bacteria directly but by the heat generated in the object being microwaved

What is the most chemically resistant non-spore-forming bacterial pathogen?

Mycobacterium species; the species that is of greatest concern medically is M. tuberculosis.

Would pasteurization destroy endospores?

No. Endospores can tolerate that degree of heat.

Why would a heavy metal be a more serious pollutant than most organic compounds?

Organic compounds can be broken down, and would therefore loose their toxicity.

How is preservation different from pasteurization?

Preservation inhibits the growth of microorganisms whereas pasteurization significantly decreases the number of spoilage microbes.

How is sterilization different from disinfection?

Sterilization eliminates all microbes; disinfection simply eliminates most or all pathogens.

Would it be safe to say that if all bacterial endospores had been killed, then all other medically important microorganisms had also been killed?

Yes, because endspores are the most resistant form of microorganism.

Which of the following is false? a) A high-level disinfectant cannot be used as a sterilant.

a high-level disinfectant cannot be used as a sterilant.

Which of the following is the most resistant to destruction by chemicals and heat?

bacterial endospores

Ultraviolet light kills bacteria by

damaging DNA

Commercial canning processes are designed to ensure destruction of which of the following?

endospores of Clostridium

All of the following are routinely used to preserve foods except

ethylene oxide

Unlike a disinfectant, an antiseptic

is non toxic enough to be used on human skin

Describe three groups of microorganisms that are resistant to certain chemical treatments.

The text mentions four—endospores, protozoan cysts and oocysts, Mycobacterium species, and Pseudomonas species.

Describe four factors to consider when selecting a germicide.

The textbook lists seven, including toxicity, activity in the presence of organic material, compatibility with material being treated, residue, cost and availability, storage and stability, and environmental risk.

What is the primary reason that wine is pasteurized?

To destroy microorganisms that could spoil the wine.

What is the primary reason that milk is pasteurized?

To destroy pathogens in milk that might otherwise cause disease.

What is the most important function of nitrate in cured meat?

To inhibit the growth of Clostridium botulinum.

Aseptically boxed juices and cream containers are processed using which of the following heating methods?

Ultra-high-temperture