microbiology ch.5

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.

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 tem¬peratures 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.

This graph shows the time it takes to kill populations of the same microorganism under different conditions. What conditions would explain the differences in lines a, b, and c?

Population "b" was killed more quickly than population "a". Because the two populations started with the same number of organisms and they are the same kind of organism, population "b" must have been subjected to more destructive or toxic conditions than population "a". These could have been a higher temperature, greater concentration of germicide, or greater intensity of destructive radiation. Populations "a" and "c" are dying at the same rate so they are under equally toxic conditions. The difference is that population "c" started with a smaller number of organisms and was reduced to a zero cell number in a shorter time period.

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.

Which of the following is false? a) A high-level disinfectant cannot be used as a sterilant. b) Critical items must be sterilized before use. c) Low numbers of endospores may remain on semicritical items. d) Standard sterilization procedures do not destroy prions. e) Quaternary ammonium compounds can be used to disinfect food preparation surfaces.

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

Which of the following is the most resistant to destruction by chemicals and heat? a) Bacterial endospores b) Fungal spores c) Mycobacterium tuberculosis d) E. coli e) HIV

a) Bacterial endospores

Which concentration of alcohol is the most effective germicide? a) 100% b) 75% c) 50% d) 25% e) 5%

b) 75%

Ultraviolet light kills bacteria by a) generating heat. b) damaging DNA. c) inhibiting protein synthesis. d) damaging cell walls. e) damaging cytoplasmic membranes.

b) damaging DNA.

Commercial canning processes are designed to ensure destruction of which of the following? a) All vegetative bacteria b) All viruses c) Endospores of Clostridium botulinum d) E. coli e) Mycobacterium tuberculosis

c) Endospores of Clostridium botulinum

Which of the following can most reliably be used as a sterilant? a) Alcohol b) Phenolic compounds c) Ethylene oxide gas d) Iodine

c) Ethylene oxide gas

The D value is defined as the time it takes to kill a) all bacteria in a population. b) all pathogens in a population. c) 99.9% of bacteria in a population. d) 90% of bacteria in a population. e) 10% of bacteria in a population.

d) 90% of bacteria in a population.

Aseptically boxed juices and cream containers are processed using which of the following heating methods? a) Canning b) High-temperature-short-time (HTST) method c) Low-temperature-long-time (LTLT) method d) Ultra-high-temperature (UHT) method

d) Ultra-high-temperature (UHT) method

All of the following are routinely used to preserve foods except a) high concentrations of sugar. b) high concentrations of salt. c) benzoic acid. d) freezing. e) ethylene oxide.

e) ethylene oxide.

Unlike a disinfectant, an antiseptic a) sanitizes objects rather than sterilizes them. b) destroys all microorganisms. c) is non-toxic enough to be used on human skin. d) requires heat to be effective. e) can be used in food products.

is non-toxic enough to be used on human skin.

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.

This diagram shows the filter paper method used to evaluate the inhibitory effect of chemical agents, heavy metals, and antibiot¬ics on bacterial growth. A culture of a test bacterium is spread uniformly over the surface of an agar plate. Small filter paper discs containing the material to be tested are then placed on the surface of the medium. A disc that has been soaked in sterile distilled water is sometimes added as a control. After incubation, a lawn (film of growth) will cover the plate, but a clear zone will surround those discs that contain an inhibitory compound. The size of the zone reflects several factors, one of which is the effectiveness of the inhibitory agent. What are two other factors that might affect the size of the zone of inhibition? What is the purpose of the control disc? If a clear area were apparent around the control disc, how would you interpret the observation?

The concentration and the molecular weight of the inhibitory compound affect the size of the zone of inhibition (compounds with a low molecular weight will diffuse farther from the disc more rapidly). The purpose of the control is to check for the effects of any variables other than those being tested. The researcher needs to show that there were no unknown materials in the filter paper that affected bacterial growth because these would otherwise give misleading information about the effectiveness of the substances being tested. If a clear area of inhibition is observed, then some unknown material is affecting bacterial growth and the results of the experiment are therefore not reliable.

An agriculture extension agent is preparing pamphlets on prevent¬ing the spread of disease. In the pamphlet, he must explain the appropriate situations for using disinfectants around the house. What situations should the agent discuss?

The kitchen is the most appropriate area for carrying out disinfection. Food is the major source of infectious microorganisms in the household. Kitchen surfaces can harbor microbes from contaminated foods, food residues, skin and respiratory fluids. A buildup of these organisms can be transmitted to prepared food. Other situations for disinfection do arise. The bedding and toiletries of people with infectious conditions should be disinfected.

As a microbiologist representing a food corporation, you have been asked to serve on a health food panel to debate the need for chemical preservatives in foods. Your role is to prepare a statement that compares the benefits of chemical preservatives and the risks. What points must you bring up that indicate the benefits of chemi¬cal preservatives?

The strongest argument is that without preservatives, the incidence of food harboring and transmitting dangerous disease increases dramatically. It should be discussed that the illnesses associated with foodborne disease carry more consequences than the health effects of even nitrate and nitrite preservatives.

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.