Chapter 6

Could Louis Pasteur, in the 1800s, have grown rabies viruses in cell culture instead of in living animals?

no, a virus needs a living host

If bacterial cells were given a sulfur source containing radioactive sulfur (35S) in their culture media, in what molecules would the 35S be found in the cells?

sulfur-containing amino acids and vitamins such as thiamine and biotin.

Heat lamps are commonly used to maintain foods at about 50°C for as long as 12 hours in cafeteria serving lines. The following experiment was conducted to determine whether this practice poses a potential health hazard. Beef cubes were surface-inoculated with 500,000 bacterial cells and incubated at 43-53°C to establish temperature limits for bacterial growth. The following results were obtained from heterotrophic plate counts performed on beef cubes at 6 and 12 hours after inoculation:

-holding temp. at 43 degrees -they could have produced spores that were resistant -S. aureus: staphylococcal food poisoning -S. typhimurium: typhoid fever -C. perfringens: Clostridium perfringens gastroenteritis

Why is the prevention of biofilms important in a health care environment?

Microbes in biofilms are probably 1000 times more resistant to microbicides. CDC estimate that 70% of human bacterial infections involve biofilms. They form in medical devices, including mechanical heart valves and catheters.

If the Space Station in Earth orbit suddenly ruptured, the humans on board would die instantly from cold and the vacuum of space. Would all the bacteria in the capsule also be killed?

No, instead, they would loose their water content and be lyophilized.

Is a colony formed as a result of streaking a plate always derived from a single bacterium? Why or why not?

No, there are other organisms that could contaminate it -Ex: staph forms clumps, so how can you be sure that there aren't other strains in that clump

How would one determine whether a microbe is a strict anaerobe?

Only grows in the presence of NO oxygen. At the bottom of a tube.

Why is it difficult to define psychrophile, mesophile, and thermophile?

Their temperatures for possible growth somewhat overlap each other and are not rigidly defined. It is possible for a psychrophile to grow in temperatures considered mesophile.

Assume that after washing your hands, you leave ten bacterial cells on a new bar of soap. You then decide to do a plate count of the soap after it was left in the soap dish for 24 hours. You dilute 1 g of the soap 1:106 and plate it on heterotrophic plate count agar. After 24 hours of incubation, there are 168 colonies. How many bacteria were on the soap? How did they get there?

There were 168 x 10^6 bacteria on that 1g of soap

Could a pure culture of bacteria be obtained by the streak plate method if there were only one desired microbe in a bacterial suspension of billions?

When a microbe to be isolated is present in small numbers, its number must be greatly increased by selective enrichment before it can be isolated with the streak plate method

Could humans exist on chemically defined media, at least under laboratory conditions?

Yes because chemoheterotrophs can survive on a chemically defined media and humans are chemoherterotrophs

Are bacteria capable of growing at a high osmotic pressure likely to be capable of growing in the mucus found in nostrils?

Yes because staphylococcus aureus found in the nasal passage have high tolerance to sodium chloride.

Given a shallow pan and a deep pot with the same volume, which would cool faster? Why?

a shallow pot would cool faster due to surface area providing less opportunity for bacteria to grow

In what way is budding different from binary fission?

binary fission is splitting into two smaller daughter cells which then becomes larger on their own budding forms a small initial outgrowth which then enlarges and splits when it approaches the size of the parent cell

What is the technical name for bacteria that require a higher-than-atmospheric-concentration of CO2 for growth?

capnophiles

Why is sugar added to fruit to make jams and jellies?

forms the gel structure in jams. Acts as a preservative to preserve colour and inhibit mould growth.

Can you think of any reason why a colony does not grow to an infinite size, or at least fill the confines of the Petri plate?

inhibitors accumulate both within the colony and in the medium

Of what value are hemolysins to pathogens?

leaves a clear zone around the bacterial growth

Oxygen is so pervasive in the environment that it would be very difficult for a microbe to always avoid physical contact with it. What, therefore, is the most obvious way for a microbe to avoid damage?

produce enzymes to neutralize them against toxicity

If a single bacterium reproduced every 30 minutes, how many would there be in 2 hours?

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