Micro Exam 3

Choose the best description of how filtration works to control microbes.

A filter is a solid material containing small holes that only allows liquids to pass but restricts larger substances from passing to a sterile environment.

Most antiviral agents target extracellular viruses.

False

What is the best form of microbial control you could use for purifying a protein from genetically modified E. coli?

Filtration

Which of these techniques sterilizes on the basis of the size of the microbes to be removed?

Filtration

Which of the following microscopes typically uses dyes or antibodies?

Fluorescence microscope

Which of the following statements is false regarding the control of microbial growth by altering the availability of water?

Foods with a high sugar content such as honey, jams and jellies, and syrup, have a high aw value, which eliminates the growth of microbes.

Why are there far fewer antifungal agents than there are antibacterial agents?

Fungal cells are much more similar to human cells than are bacterial cells.

Which of the following stains would best determine if a bacterium has a single cell membrane plus a very thick cell wall or if a bacterium has a very thin cell wall in between two cell membranes?

Gram-stain

Why does treatment to combat HIV/AIDS typically involve drug combinations?

HIV frequently develops drug resistance.

Which microbial control method best describes the process of pasteurization?

Heat

Which best describes how heat controls microbes?

Heat denatures proteins and nucleic acids

Name all that are characteristics of transmission electron microscopes.

Highest practical magnification over 100,000 times, Uses electron beam for radiation source, Adjust current to magnetic lenses to change magnification

Which of the following is not true regarding the development of antimicrobial drugs?

Since the source of naturally-occuring molecules has been exhausted, only synthetic molecules are currently being designed and developed against pathogenic microbes.

Choose the characteristic of a microbe that would allow it to be controlled by filtration.

Size of microbe

Sulfonamides inhibit an enzyme necessary for production of purines and pyrimidines. What long-term impact would it have on a microbe if it were grown in the presence of sulfonamides?

The cell would cease to divide.

Ability to be distinguished from the surroundings

Contrast

The __________ reflects the time required to kill 90% of the microbes in a sample.

D value

List all the ways heat can be used to control microbes.

Denatures proteins, Denatures nucleic acids, Disrupts membranes

A school was closed after a high percentage of students suffered vomiting and diarrhea

Disinfection

Finally, the _________ uses a convenient test strip impregnated with increasing concentrations of the antibiotic.

Etest®

Which antimicrobial control method is best suited for heat-sensitive items such as disposable plastic Petri dishes and syringes?

Ethylene oxide

Which of these is a sterilizing gas?

Ethylene oxide

After performing a Gram stain of a mixed culture of Gram-positive and Gram-negative cells, you realize you forgot to apply the iodine in step 2. What would you expect to see if you observed the slide under the microscope after this omission?

Pink Gram-positive and pink Gram-negative cells

List all the different mechanisms by which antiviral medications work.

Preventing entry of the virus into the host cell Directly disrupting viral capsids Blocking viral nucleic acid synthesis Preventing the maturation of viral particles

What is the best form of microbial control you could use for a soft, plastic, surgical device that will melt at high temperatures?

Radiation

The ability to distinguish between two separate structures that are very close to one another

Resolution

Rationalize why HIV-positive patients are given a "cocktail" of drugs rather than a single antiviral agent to target the virus?

Reverse transcriptase, used by HIV for nucleic acid synthesis, cannot proofread for errors so mutations leading to multiple drug resistance are common.

The janitor cleans the bathrooms at the mall

Sanitization

What microscope would be the best to use to view cell surface features of a specimen?

Scanning electron

It should be noted that some cells act as persisters, resisting control methods, in a state considered ___________.

VBNC

Why are there far fewer antiviral agents than there are antibacterial agents?

Viruses enter host cells and make use of host components.

Name all of the following that can affect the resolution of a bright-field microscope.

Wavelength of light, quality of lens, magnification

However, if the agent does not kill bacteria, but merely prevents growth, it is termed _____________.

bacteriostatic

A key feature of penicillin is the _________ ring.

beta-lactam

To control microorganisms, a __________ must be evaluated for effectiveness.

biocide

Yet another use of heat is the sterilization of closed anaerobic containers in the ________ process.

canning

The Gram stain of a bacterial cell is based on the chemical properties of its ________.

cell wall

Penicillins are a group of antibiotics known for inhibiting ________ synthesis in _________.

cell wall; bacteria

Because of widespread resistance to penicillin, structurally related classes of antibiotics, the ____________, were developed.

cephalosporins

kills the microbe

cidal

Chemotherapeutic agents have different levels of activity and effectiveness, with some being _________ or strong enough to kill microbes while others are only ____________, inhibiting microbial growth.

cidal; static

The mechanism of this type of antibiotic is to block the formation of __________ in the complex polymer ____________.

cross-links; peptidoglycan

The proper sequence of reagents in the Gram stain procedure is _________.

crystal violet, iodine, ethanol, safranin

Foscarnet, a pyrophosphate analog, is used to treat _________ infections.

cytomegalovirus

The most effective method by which antibiotic resistance can be decreased in bacteria is _________.

decrease in antibiotic use

This is also its weak point, as penicillin-resistant pathogens contain the enzyme ____________ that destroys this ring.

penicillinase

Moist heat in excess of the normal growth curve alters cell structures; it denatures __________, degrades nucleic acids and disrupts the lipids in cell ___________. To attain the temperatures above 100°C sufficient to destroy endospores and prions, the autoclave employs steam under _____________.

proteins, membranes, pressure

On the other hand, low temperatures used in _________ or freezing inhibit the growth of most microorganisms, but do not kill the microbes.

refrigeration

Finally, if microbial populations are reduced just enough to meet public health standards, we call this process ____________.

sanitization

This term is used to describe compounds that cause greater harm to microbes than to the human host.

selective toxicity

When light generated by a lamp in a light microscope passes into a lens, the speed of the light _______ because the glass lens has a _______ refractive index than the air from which the light came.

slows; greater

The Food and Drug Administration uses the acronym "GRAS" to describe chemical preservatives. The ambiguity of the term "generally recognized as safe" may be questionable in light of the fact that __________.

sodium nitrite is toxic in animals and humans, and poses a probable cancer risk when combined with amines found in high-protein foods such as fish, fermented foods such as cheese and wine, as well as certain fruits and vegetables

keeps the microbe from dividing

static

If all of the microorganisms in a sample are killed by the biocide, including spores, we call this process ____________.

sterilization

At freezing temperatures, most bacteria ________.

stop growing, but are not dead

Despite numerous precautions, food-borne disease outbreaks continue to occur, resulting in about 48 million cases of food-related illness each year in the United States alone. Who needs to remain vigilant regarding the safety of our food supply? (Check all that apply.)

-Government regulatory agencies -Food producers -Food consumers

Identify all the ways that could help slow the emergence and spread of antimicrobial resistance.

-Have health care workers observe patients taking their antibiotic dose, to ensure compliance with the antibiotic regimen. -Encourage appropriate administration of drugs (don't overprescribe). -Administer two or three drugs simultaneously to prevent the emergence of resistance to one drug. -Educate patients on the proper use of prescribed drugs (don't skip a dose).

Cheese and beer are examples of fermented foods commonly consumed in the United States, but there are many other fermented foods consumed around the world. Identify the fermented foods from the ones listed below. (Check all that apply.)

-Miso -Kimchi -Tempeh

Pasteurization is the use of heat to kill both pathogens and spoilage organisms. It's commonly used for treatment of milk. For the high-temperature, short-time (HTST) process, milk is treated at ________.

72oC for 15 seconds

You are planning a cookout this weekend, so Friday night you defrost some hamburger meat on the countertop. The next morning, the cookout is postponed until the following weekend due to bad weather. You wonder if it is safe to put the meat back in the freezer and thaw it again next weekend. Select all statements that accurately apply to this situation.

-The bacteria in the ground beef were not killed upon freezing and resumed growing when the meat thawed at room temperature. -Ground beef is an especially good substrate for contaminants like E. coli O157:H7 because of the increased surface area. -By the time the ground beef is thawed the second time at room temperature, there most likely will be hundreds to thousands of times more bacteria than were present when it was originally frozen.

The distribution and metabolism of some antimicrobial drugs can be adversely affected by _________.

-the inability of specific tissue to absorb the drug -a low speed of uptake by the patient's body -the ability of the host to metabolize the drug quickly

Canned food available for sale at grocery stores have been subjected to a commercial canning process. If you bought a can of peas from the local grocery store and found the peas to be spoiled, it could explained by ______. (Check all that apply.)

-underprocessing during canning -spoilage before canning -the entrance of contaminated water through the can seams during cooling

Wine making is a process by which juice from a fruit is fermented into an alcoholic beverage. Arrange the text in the proper order to to review the steps of the wine making process.

1. Grape pressing 2. Sterilization; yeast addition 3. Fermentation of must 4. Setting vat 5. Aging 6. Bottling

Cheese production is a process by which milk is fermented into a solid substance. Arrange the text in the proper order to review the steps of the cheese making process.

1. Lactic acid fermentation of milk 2. Milk proteins denatured at lower pH 3. Milk proteins coagulated with rennin to form curds 4. Curds are separated from whey by pressing 5. Ripening of cheese by further fermentation and drying

List all possible adverse effects of using antibiotic drugs correctly.

Allergic reaction, Toxic effects at high concentrations, Suppression of the normal flora

Choose the statement that correctly explains how an antibiotic that inhibits protein synthesis can be selective.

Antibiotics bind to the 70S bacterial ribosomes but not to the 80S eukaryotic ribosomes.

The Kirby-Bauer Disk Diffusion test is used to determine what?

Antimicrobial susceptibility

A dad takes care of his daughter's injury after she falls from her bicycle and scrapes her knee

Antisepsis

List which of the following organisms/agents have been demonstrated to kill bacteria.

Bacteriophages and Bdellovibrio bacteria

Which microbial control method best describes how an autoclave sterilizes material?

By heat

Which statement best parallels the observation: when a new predator enters an ecosystem then the prey organisms are significantly stressed (i.e., killed).

Introduction of bacteriophages into the body to treat an infection

Which of the following is not true of an effective antibacterial drug?

It should target the plasma membrane since this is the one structure that bacteria and host cells have in common.

How does high-oxygen modified atmosphere packaging preserve food?

It stimulates the formation of radical oxygen species in contaminating microorganisms

Choose the method of antimicrobial susceptibility testing that involves measuring and evaluating diameters of zones of inhibition around antibiotic disks placed on a culture of bacteria prior to incubation.

Kirby-Bauer test

Identify a microorganism used in probiotic food.

Lactobacillus

Approximate focal lengths for four different objective lenses are given below. Choose the lens that would provide the highest magnification.

Lens A: 1.3 mm

The apparent increase in size of an image

Magnification

Which of the following practices do you expect to see in a commercial establishment dedicated to body piercing?

Needles are factory-sterilized and used for only a single customer before disposal. The piercing environment is sanitized daily by wiping counters and furniture with a strong disinfectant.

Johnny buys a package of fresh-sliced ham from the deli and places it in his refrigerator. Unbeknownst to him, there are 10,000 E. coli cells on his ham. After three days under refrigeration, predict the number of E. coli cells that would be on his ham, using what you know about the effects of refrigeration on most microbes.

Slightly more than 10,000 Why? --> Refrigeration slows the growth of food spoilage microorganisms but it does not completely arrest growth.

A microbiologist is preparing nutrient broth tubes so she can batch culture E. coli

Sterilization

A young man arrives at the hospital with a Staphylococcus infection. A microbiologist at the hospital runs a disk diffusion test and obtains a zone diameter of 17 mm for clindamycin. The zone diameter interpretive standards for this drug-microbe combination are listed as: Resistant = <15, Intermediate = 15-20, Susceptible = >20. How should the results of this disk diffusion test be interpreted?

The Staphylococcus shows some susceptibility to the antibiotic clindamycin. It would not be recommended to use this antibiotic for this infection.

Your friend tells you that she is lactose intolerant, but can eat yogurt without developing the cramps and bloating that other dairy products trigger. Why is this the case?

The bacteria in yogurt ferment almost all of the lactose to lactate

In 2015, it was reported that several patients at UCLA medical center were infected with carbapenem-resistant Enterobacteriaceae (CRE) because of ineffective sterilization of equipment used for colonoscopy procedures. Which two of the following are important considerations when addressing this sterilization issue?

The complexity of the equipment and the need to disassemble multiple components for cleaning present challenges for disinfection. Organic matter like tissue samples must be removed before applying a disinfectant.

How does the addition of immersion oil provide better magnification than a high power lens alone?

The immersion oil has the same refractive index as glass; by placing a drop of oil between the glass slide and the lens, this eliminates two refractive surfaces.

A fellow student carries out the Gram stain on a mixed culture containing Gram-negative rods and Gram-positive cocci. On completion he finds purple cocci and clear (no color) rods when viewing the prepared slide with a microscope. From the following, choose the best reason for these results.

The student forgot to add the counterstain.

What would be the best technique to prepare and view the internal structures of fungal hyphae?

Transmission electron microscopy

The dilemma facing government agencies that regulate food is to find a balance between fresh, healthy, minimally-processed foods, and prevention of debilitating outbreaks of food-borne illness.

True

The ___________, however, is the temperature change needed to kill 90% of the microbes in a sample in a specific length of time.

Z value

The antibacterial drug mechanism of action that would have the highest therapeutic index is _________.

a drug that targets peptidoglycan cross-linking

The class of antimicrobials that would have the most selective toxicity is _________.

antimicrobials that inhibit cell wall synthesis

If these agents are used on skin or tissues, the term __________ is used.

antiseptic

Above 100°C (212°F) most bacteria _________.

are destroyed

For example, those compounds that kill bacteria are called ________.

bactericides

As the magnification on a bright-field microscope increases, the amount of light that reaches the eye ________.

decreases

The ________ of the zone of inhibition is always measured in _________.

diameter; mm

During incubation, antimicrobials applied to the bacterial lawn become increasingly _________ as they diffuse out of the disk into the medium.

diluted

The are several ways to measure these concentrations, including ______________ tests where a series of drug concentrations is tested.

dilution susceptibility

However, if only those organisms likely to cause disease are killed, inhibited, or removed, this is termed _____________.

disinfection

Another important method is the _________ assay, where a ring of inhibition is seen around a piece of filter paper containing the antibiotic. The ___________ method is the most common assay of this type.

disk diffusion; Kirby-Bauer

When comparing time exposure, ________ heat is generally less effective than moist heat, but is a necessary control measure for items that cannot be exposed to steam, such as powders and oils. Microbiology students are no stranger to incinerating their ____________ in lab.

dry, inoculating loop

The ripening process during cheese production _________.

employs metabolic activities of other microbes to produce texture and flavor changes in the cheese over time

The death of microbial populations is typically ___________ and plotted as log values.

exponential

With ideal environmental factors, the reproduction rate of many bacterial species is ________.

extremely rapid

And further, those compounds that kill fungi are called __________.

fungicides

Exposing organisms to a range of temperatures will direct their survival, from fostering optimum growth with the shortest _____________, to complete sterilization of all microbial life, including bacterial ____________, the most difficult microbial structures to kill, and ______________, nonliving proteins that require the highest temperature for destruction.

generation time, endospores, prions

The area of clearing around the disks is called the zone of _________.

inhibition

The drug azidothymidine (AZT) _________.

inhibits replication of the viral nucleic acid

Depth filters work differently than membrane filters to sterilize fluids. The difference is that _________.

membrane filters have smaller pores, but depth filters have complex passages that retain microbes while letting the fluid through. Both methods are efficient

This term is used to describe the lowest concentration of a drug effective at preventing growth of particular microbes.

minimal inhibitory concentration (MIC)

The lowest concentration that prevents microbial growth is the ____________ concentration, while the lowest level that can kill microbes is the ____________ concentration.

minimal inhibitory; minimal lethal

This term is used to describe drugs that are effective against only a limited variety of microbes.

narrow-spectrum drug

This process was advanced in the case of milk _________, where slightly lower temperatures are applied yet still effective in killing potential pathogens.

pasteurization

A Z value has units of __________.

temperature

Another ancient method is the use of high _________ when cooking to kill many microbes present in food.

temperature

The main environmental factors that affect microorganism growth include chemical inhibitors, oxygen, pH, nutrients, moisture, and ________.

temperature

After conducting the Gram stain on a mixed culture containing Gram-positive rods and Gram-negative cocci, all the cells were purple in color. This was most likely because ________.

the cells were not decolorized enough with alcohol or acetone

A D value has units of __________.

time

Similar to bactericides, compounds that kill viruses are called __________.

viricides

Many common methods of food preservation have been utlilized since ancient times, such as salting, which lowers __________ and inhibits microbial growth.

water activity