CHAPTER 4 MICROBIO

You are determining the number of colony forming units (CFUs) for Susan, who has a urinary tract infection (UTI). You added 1 mL of Susan's urine sample to 99 mL of diluent, and spread 0.1 mL of that dilution on a culture medium. After appropriate incubation, you count 143 colonies on the plate. What was the concentration of bacteria in the original urine sample?

1.43 × 105 cells/ mL

If you are asked to make 200 mL of Thayer-Martin agar, who much sheep's blood would you add to the medium? Recall that this complex medium contains 5% sheep blood.

10 mL

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

3 hr

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 he sample?

320,000

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

35-40ºC

In addition to the few Shigella colonies that are noted, there are also abundant salmon pink colonies, around which the medium has turned yellow, losing its original blue color. You know that hektoen enteric agar must contain ________.

A pH indicator

A halophilic, aerobic mesophile has a generation time of 20 minutes. You place 1 × 104 of these organisms on an appropriate solid medium, and incubate the plate for 100 minutes. Select the FALSE statement.

After incubation, a colony on the plate contains 5 × 104 cells.

The solidifying agent use most successfully in bacterial nutrient media is

Agar

The causative organism of gonorrhea is Neisseria gonorrhoeae, a fastidious, Gram-negative diplococcus. What does fastidious mean in this context?

An organism with complex nutritional requirements

Organisms that use CO2 ad their source of carbon are called

Autotrophs

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?

B) A spectrophotometer can measure absorbance as an indicator of cell number, but can't discriminate between a live cell and a dead one. The presence of dead cells keeps the absorbance high even into the death phase.

Bacteria on fish caught in the Atlantic Ocean would

Be psychrophiles AND would continue to grow while the fish is in the refrigerator

Prokaryotic cells divide by a process known as

Binary fission

Which statement about biofilms are true?

Biofilms may protect organisms against harmful chemicals.

In some labs, samples containing suspected L. pneumophila are cultured on traditional BCYE medium as well as BCYE medium lacking L-cysteine. How would L. pneumohila be identified in this situation?

Compare the two plates. Colonies that grow on traditional BYCE medium but not on BYCE medium lacking cysteine are likely L. pneumophila.

During which phase of the bacterial growth curves does the total number of viable (live) cells decline?

Death

The colonies of interest in this case are the blue-green presumptive Shigella colonies. However, growth on hektoen enteric agar is not sufficient for definitive identification. Further tests are needed. First, the lab technicians need to prepare larger numbers of Shigella from your patient's stool sample, and then they need to ensure that they are culturing a single species. The methods used to do this are ________, followed by ________.

E) enrichment culture; streak plating

Differential media only allow 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 bacteria

FALSE

One would expect most strict anaerobic organisms to have superoxide dismutase

FALSE

There are five stages of growth in an open system of culture.

FALSE

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

Heterotrophs

Shigella species and Salmonella species are classified as facultative anaerobes. You know that given this information, the bacteria in your patient's fecal culture will grow best

In the presence of oxygen

Late log phase of the bacterial growth curve

Is characterized by the production of secondary metabolites

Clostridium paradoxum grows optimally at 55°C, pH 9.3; it will not grow in the presence of O2. Please select the TRUE statement about this organism.

It is an obligate anaerobe

L. pneumophila is widespread and is found in various water sources, including hot tubs, water cooling towers, swimming pools, grocery store misters, and shower water. Select the FALSE statement regarding the organism, given this information.

It is an obligate anaerobe.

What would be true about an organism called Bacillus fastidiosus

It might be expected to be very strict in its growth requirements

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

Late log phase

In nature, bacteria

May adhere to surfaces by means of pili and slime layers

A hot tub (with water temperature of 104ºF or 40ºC) 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

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

Need for cooler temperatures

Thayer-Martin agar typically contains a combination of antibiotics: vancomycin, colistin, nystatin, and trimethoprim. Please select the TRUE statement.

Neisseria gonorrhoeae is not sensitive to the included antibiotics

Bacteria may be stored for several months

On a slant in the refrigerator, frozen in glycerol solution, AND freeze-dried

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 the presence and type of Gram positive cells. Identification isn't the main goal here- just a first step to work towards determine what Gram positive cells might be there. what might you do first to go about souring towards this goal?

Preform a Gram stain

All bacterial cells that result from the replication of a single original bacterial organism are referred to as a

Pure culture

Peptone

Refers to hydrolysate of proteins used in growth media

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

Robert Koch

The lab technicians culture the sample on Thayer-Martin agar. This complex medium contains 5% sheep blood and a combination of antibiotics. This medium is

Selective

A modification of the BCYE medium used to culture L. pneumophila is BCYE with DGVP. This medium contains glycine, polymixin B (an antifungal agent), and and vancomycin (antibiotic), as well as two dyes (bromocreson purple and bromthymol blue) that facilitate identification of the organism based on colony color. What type of medium is BCYE with DGVP?

Selective AND differential

You take a stool sample from Mrs. Thomas, and send it to the lab for analysis. You tell her that the technicians will do a variety of tests to confirm the identity of the organism causing her illness. The first thing that will be done is to inoculate some of her stool sample onto a medium called hektoen enteric (HE) agar. On this medium, Shigella species produce blue-green colonies, while Salmonella produces blue-green colonies with a black center, and most Gram-positive bacteria do not grow at all. You explain to Mrs. Thomas that this type of medium is called a(n) ________ medium.

Selective and differential

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

Steak-plate method

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 ManConkey agar plate (which contains lactose and a pH indicator that turns pink when acid byproducts are present)

A single bacterial cell may multiply to form a visible colony.

TRUE

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

TRUE

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

TRUE

Secondary metabolites may be antibiotics

TRUE

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 if 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.

You are culturing a new bacterium in the laboratory. You cannot find any glucose it the lab when you are making growth medium, so you decide to use honey instead. You add twice as much honey than is called for in the medium recipe, because you want to give the organism the best opportunity or growth. To your surprise, the organism does not grow on your modified medium. Select the most likely explanation.

The growth medium became hypertonic with the addition of so much honey; the bacteria underwent plasmolysis and died.

Chemoheterotrophs

Use preformed organic molecules as a carbon source AND as an energy source.

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 colony counts after incubation.

MacConkey Agar is

a selective and differential agar.

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

aerotolerant anaerobes

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?

all of the above

High concentrations of salt and sugar in foods

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

In the cultivation of microaerophilic and anaerobic bacteria,

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

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

buffers

Diagnosis of legionellosis depends partly on culture of the causative agent from medical samples. Typically, the organism is grown on buffered charcoal yeast extract (BCYE) agar. What essential component must this medium have to ensure growth of L. pneumophila?

cysteine

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 the

exponential (log) phase

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

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

Medically important bacteria are often

grown on agar containing blood AND grown at 37°C.

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

growth factors

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.

On HE medium, Shigella species produce blue-green colonies, while Salmonella produces blue-green colonies with a black center. There are two noticeable types of colonies growing on the hektoen enteric (HE) medium in Mrs. Thomas' test. One type of colony is greenish in color. This leads you to conclude that the bacteria in these colonies

is Gram-negative and is likely Shigella.

When doing experiments with bacteria

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

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

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

major elements

Organisms that require gaseous oxygen for metabolism are referred to as

obligate aerobes

Shake tubes are used to determine the

oxygen requirements for bacterial growth.

The optimum pH for growth of most species of bacteria is___

pH of 7

Candle jars are usually used to

provide an atmosphere with CO2.

Generally the proteins of thermophiles

resist denaturation

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

selective medium

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

Eosin methylene blue agar (EMB) is a selective and differential medium. The dyes in the medium inhibit most Gram-positive organisms. Gram-negative organisms such as the coliforms grow on this medium. Coliforms that are fecal in origin produce colonies with a metallic green color on EMB, while those that are non-fecal produce colorless colonies. You plate a urine sample onto an EMB plate and incubate it. Metallic green colonies develop. From this, you can conclude that

the sample contains bacteria that are Gram-negative AND are fecal in origin.