Ch 4

Agar replaced gelatin as the gelling (solidifying) agent for media because

Much fewer bacteria can break down agar than gelatin AND agar is solid at body temperature

The simplest technique for isolating bacteria in growth media is referred to as the

Streak plate method

You are a microbiologist working for a pharmaceutical company and discover a new secreted metabolite that can serve as a medication. Your company asks you to oversee the production of the metabolite. Which of the following is something that is NOT important to consider id you need to grow 5,000 liter cultures of bacteria for the purpose of harvesting the metabolite they secrete?

The death rate of the bacteria after stationary phase is complete

A microbe is discovered growing near a deep sea thermal vent. When researchers bring a sample up to the surface and try to grow it in a lab at room temperature in a normal incubator, they are unsuccessful. Why?

The pressure isn't the same at sea-level as it is on the ocean floor

Prokaryotes are the only organisms able to use atmospheric nitrogen as a nitrogen source

True

Secondary metabolites may be antibiotics

True

A single bacterial cell may multiple to form a visible colony

True through binary fission

It is assumed the every colony observed on a streak plate arose from a single bacterium

Trus

You are in charge of water quality for your city's water treatment plant. of the methods at your disposal, which will be the most efficient and cheapest method of determining the number of viable bacteria in the water coming out of your plant?

Using membrane filtration followed by placing the membrane in a growth medium for a colony counts after incubation

High concentrations of salt and sugar in foods

are useful in preserving the food AND tend to draw water out of a cell

Peptone

refers to a hydrolysate of proteins used in growth media

Organisms that are indifferent to the presence of oxygen and do not use it are

Aerotolerant anaerobes

The solidifying agent used most successfully in bacterial nutrient media is

Agar

The speed of enzymatic reactions approximately doubles for each

10C rise in Temperature

A pure culture in exponential growth phase has a bacterial concentration of 6.4 x 10^8 cells/ml. If the bacterium has a generation time of 1 h, how long ago was the cell concentration 8.0 x 10^7 cells/ml

3 h

A urine sample with more than 100,000 organisms is considered indicative of infection. A urine sample containing 5,000 bacteria, with a generation time of 30 minutes, sits for 3 hours before finally being assayed. How many bacteria will then be present within the sample?

320,000

The optimal temperature for most human pathogens might be expected to range from

35-40C

A hot tub (approx. 104 deg. F or 40 deg. C) would most likely contain

Mesophiles

The lag phase of the bacterial growth curve is marked by

Metabolically active cells

Which of the following is/are obligate aerobes?

Micrococcus luteus

An organism called Bacillus fastidiosus

Might be expected to be very strict as to its growth requirements, would probably be grown on a chemically defined media AND might be expected to have a rod shape

Mycobacterium leprae is typically found infecting the ears, toes, and fingers of its host due to its

Need for cooler temperatures

Organisms that require gaseous oxygen for metabolism are referred to as

Obligate aerobes

In nature, bacteria

Often grow in close association with many other kinds of organisms. May remain in a prolonged exponential phase. Frequently synthesize structure such as slime layers. May adhere to surfaces by means of pili and slime layers. All of the choices are correct.

Shake tubes are used to determine the

Oxygen requirements for bacterial growth

You are working in a clinical laboratory in a hospital setting. You're handed a throat swab from a patient. You are told specifically that the physician is only interested in what Gram positive cells are present. What might you do first to go about working towards this goal? Identification isn't the main goal here-just a first step to work towards determining what Gram positive cells might be there

Perform a Gram stain

Candle jars are usually used to

Provide an atmosphere with CO2

All the bacterial cells that result from the replication of a single original bacterial organism are said to be a

Pure culture

Generally the proteins of thermophiles

Resist denaturation

The scientist that contributed most to the development of pure culture techniques was

Robert Koch

a Physician sends a stool sample to your lab, and wants to know if there are lactose fermenting microbes in the sample. How might you determine if these microbes are present or not from this mixed-microbe specimen?

Streak the sample for isolation on a MacConkey agar plate (which contains lactose and a pH indicator that turns pink when acid byproducts are present)

Organisms may derive energy from

Sunlight AND metabolizing chemical compounds

The enzymes that deal with toxic oxygen-containing molecules is/are

Superoxide dismutase AND catalase

Bacteria on fish caught in the Arctic Ocean would

be psychrophiles AND continue to grow while the fish is in the refrigerator

Agar

has chemical and physical properties that make it almost ideal for solidifying media

Trace elements

include Zinc, copper, and manganese AND may be needed for enzyme function

Late log phase of the bacterial growth curve

is marked by the production of secondary metabolites

The prefix photo- indicates that an organism will make use of ___________ for energy purposes

light

In a rapidly multiplying bacterial population, cell numbers increase

logarithmically

Bacteria may be stored

on a slant in the refrigerator, frozen in glycerol solution AND lyophilized

The optimum pH for growth of most species of bacteria is

pH 7

A medium that inhibits the growth of organisms other than the one being sought is termed a(n)

selective medium

Chemoheterotrophs

use pre-formed organic molecules as a carbon source AND as an energy source

During which phase of the bacterial growth curve does the total number of viable cells decline

Death

Biofilms

Are a polysaccharide-encased community of microorganisms, may enhance bioremediation efforts AND may protect organisms against harmful chemicals

In the cultivation of microaerophilic and anaerobic bacteria

Atmospheric oxygen in a(n) candle/anaerobe jar is converted to water

Organisms that use CO2 as their source of carbon are called

Autotrophs A in Auto A in Atmosphere, CO2 in atmosphere

Prokaryotic cells divide by a process known as

Binary fission

Products which limit pH changes are often incorporated into media and are referred to as

Buffers

During which phase of growth are bacteria most susceptible to antibiotics?

Exponential (log)

In the growth curve of a bacteria population, the bacteria are rapidly increasing in number in the

Exponential (log) phase

Differential media only allows certain bacteria to grow

False

Freezing is an effective means of destroying bacteria

False

In microbiology, growth usually refers to an increase in size of the bacteria

False

One would expect most strict anaerobic organisms to have superoxide dismutase

False

There are 5 stages of growth in an open system of culture

False

Medically important bacteria are often

Grown on agar containing blood AND grown at 37C

Small organic molecules that must be provided to bacteria in order for them to grow are called

Growth factors

Organisms that use organic molecules as their source of carbon are called

Heterotrophs Hetero = orgnaic molecules from Carbon

When doing experiments with bacteria

It is best to use bacteria from the same stage of growth

During which phase of the bacterial growth curve does a bacterial population become much more resistant to harmful conditions?

Late log phase

Carbon, hydrogen, oxygen, nitrogen, phosphorus, and sulfur may be considered

Major elements

You take absorbance readings on a spectrophotometer across a 6 hour culture of E. Coli cells growing in tryptic soy broth (TSB). Your absorbance readings clearly indicate a lag phase, a log phase, and a stationary phase. You come back in and take readings at 8, 10, 12, 14, and 16 hours, but the absorbance number remains the same. Shouldn't it start coming down as the closed batch culture enters death phase? what's the most likely thing that is happening?

When we establish a growth curve, we should actually plot the log of the number of viable cells vs time. However, a spectrophotometer can only measure absorbance. Absorbance is NOT the same as the number of viable cells. Many of the cells in the tube are most likely dead, but the machine can't discriminate between a live cell and added one. This keeps the absorbance high even into the death phase

MacConkey agar is

a selective agar and differential agar