microbio lab2 exam (all hw)

A bacterial culture is diluted 1:1000 in sterile DI water. The concentration of bacteria is then determined using a hemacytometer. The total number of cells counted in the 5 large square of the chamber was 625. What is the concentration of cells/ml?

(625 x 104 x 103) = 1.25 x 109 cells/ml 5

Nitrate A, and nitrate B reagents have been added to all tubes (A-E). Which tube or tubes need to have zinc added before the reduction of nitrate can be assessed? (Mark all that apply)

(all tubes that are not red)

Which culture(s) is/are positive for fermentation of lactose?

(only ones that are yellow/light)

Use pseudopods for movement

Amoeba

Barophile

An example would be bacteria growing at the bottom of a deep lake

Psychrophile

An organism that grows well at 5o C

Neutrophile

An organism that grows well at a pH of 7

Acidophile

An organism that requires a pH 3 for growth

Halophile

An organism that thrives in a high salt environment such as the ocean

This apparatus is typically used for growth of which type of organisms?

Anaerobes

Bacteriostatic

Antimicrobial that inhibits bacterial growth but does not kill

Bactericidal

Antimicrobial that kills bacteria

Sporicide

Antimicrobial that kills bacteria and their spores

What would you expect to occur if large amounts of carbon-rich and nitrogen-rich wastes are released into aquatic environments?

Bacterial populations will increase.

Why must the methylene blue reductase test be performed in a sealed tube?

Because oxygen will disrupt the ability to observe the results.

A student is shopping for antibacterial hand cleansers and is trying to decide which one to buy. One is a "waterless" hand gel containing 70% isopropanol and the other is a wipe that lists benzethonium chloride (a synthetic quaternary ammonium salt) as the active ingredient. Compare and contrast these cleansers in terms of the action of the antimicrobial ingredient and the level of disinfection (degerming, germistatic, germicidal).

Both are germicidal, although not to the same degree. The alcohol of the waterless hand cleaner is a germicide that disrupts cytoplasmic membranes and denatures proteins. It is not effective against bacterial endospores or fungal spores, and it has limited effect on nonenveloped viruses. The alcohol evaporates quickly, so the germicidal effect is short term. The waterless hand cleaner is an intermediate-level disinfectant and is not an effective degermer. Synthetic "quats" (quaternary ammonium compounds) disrupt cell membranes. They are effective against fungi, enveloped viruses, and most bacteria, but not against nonenveloped viruses, nor on endospores. Quats are low-level disinfectants that are germicidal for some microbes. The action of using and discarding the wipe provides some degerming effect.

Normal human microbiota; opportunistic pathogen

Candida albicans

An antimicrobial that inhibits cell wall synthesis will result in which of the following?

Cells become more susceptible to osmotic pressure.

Antiseptic

Chemical agent applied to living tissue to kill microbes

Use a short hair-like projections to facilitate movement

Ciliates

Dimorphic fungus that causes Valley fever

Coccocoides immitis

List two factors that may influence the efficacy of an antimicrobial agent.

Concentration of the agent Microbial burden (concentration of microbes) Age of the agent Temperature pH Presence of organic matter Evaporation Diffusability Time of exposure

Yeast found in pigeon feces that may cause serious infection in immunocompromised patients

Cryptococcus neoformans

Which image is depicting trypanosomes, the etiologic agent of African sleeping sickness?

D

Identify the helminth shown here

Dipylidium

Which column represents the minimal inhibitory concentration (MIC) of ketoconazole (keto)?

E (furthest right w an X)

Which of the following may induce dysentery? (Mark all that apply)

Entamoeba histolytica e. Balantidium coli

Which of the following helminths are examples of nematodes (round worms)? (Mark all that apply)

Enterobius vermicularis b. Trichinella spiralis

Based on the following data, which organism(s) is/are neutrophiles?

Escherichia coli e. Staphylococcus aureus (no growth in the middle)

Select ALL statements that accurately reflect the process of filtration. (Mark all that may apply)

Filtration is beneficial in the preparation of products, such as serum, that cannot withstand high heat. b. Filtration methods may sterilize a product by removing bacteria, but might not remove viruses or proteins

Use a whip-like projection to facilitate movement

Flagellates

What is the key difference between yeast and mold?

Yeast is unicellular, while mold is multicellular

Does Saccharomyces cerevisiae stain Gram-positive or Gram-negative? Research and describe the composition of yeast cell walls. How does the composition compare to the cell walls of Gram-positive or Gram-negative bacteria?

Yeast stains gram positive but if the cell wall is ruptured, it will stain gram negative. That is why it is so important to follow directions and be careful with your specimen.---Saccharomyces cerevisiae stains Gram-positive. The cell walls of yeast, and other fungi, are made up of are made up of a layer of chitin, beta-glucan, and mannoproteins. The fungal cell wall is thick and rigid, similar to the cell wall of Gram-positive bacteria, which is why it retains the primary stain crystal violet. The Gram positive cell wall is composed of mainly peptidoglycan in addition to teichoic acids and a very small periplasm. Gram negative bacteria have a thin layer of peptidoglycan located within the periplasm. Because the Gram negatiive peptidoglycan layer is much thinner it readily decolorizes and will take on the safranin counterstain.

In many states, the legal limit for all bacteria present in pasteurized milk is not to exceed 20,000 CFU/mL. You have been away on vacation and left an unopened plastic jug of milk in your refrigerator. The "Sell By" date was three days ago. Instead of throwing it out, you decide to test it using your TCC Microbiology Kit. After completing a series of 10-fold dilutions 0.1ml was plated. Below is a table of the colony counts following 24 hours incubation at 37oC.

a) 230 x 104 x 10 = 2.3 x 107 cfu/ml b) This milk is well above the mandated 20,000 cfu/mL and therefore is not safe to drink by Public Health standards.

Which organism(s) can tolerate the 7.5% sodium chloride in this medium?

a,c (whichever actually has. growth)

Select ALL of these that are typical by-products of fermentation. (Mark all that apply)

a. Acid c. Carbon dioxide d. Ethanol

List two different chemical agents that are used to control microbial growth and their mode of action (be specific).

alcohol and its ability to denature proteins, enzymes, and lipids. this is why we use it to clean our tools for transfering bacteria. chlorine and its ability to denature enzymes, this is why it is used in water to clean.

Nitrification by bacteria is the biological oxidation of ...

ammonia to nitrite or nitrate.---Nitrification is the biological oxidation of ammonia to nitrite followed by the oxidation of the nitrite to nitrate. and is an important step in the soil nitrogen cycle.

Nitrate A, nitrate B and zinc have been added to all tubes shown. Which tube or tubes indicate a positive reduction of nitrate? (Mark all that apply)

b,c,d,e (all that are not red)

Select ALL of these that are example of eukaryotic microbes. (Mark all that apply)v

b. Entamoeba histolytica c. Chlamydomonas d. Trichinella spiralis f. Enterobius vermicularis

Select ALL of these that are characteristics of fungi. (Mark all that apply)

b. May reproduce through asexual and/or sexual mechanisms c. Exhibit dimorphism, and may be a yeast or a mold depending on the environment it inhabits d. May be unicellular or multicellular e. May be coenocytic (mutlinucleate) or have a single nucleus per cell

Which of the following are examples of ciliates? (Mark all that apply)

b. Stentor c. Balantidium coli e. Paramecium

Elements such as carbon, nitrogen, phosphorus and sulfur are recycled through both biotic and abiotic components of the ecosystem, in processes generally called ______ cycles.

biogeochemical

Which mode of reproduction is depicted here

budding

Which image is depicting the causative agent of toxoplasmosis?

c

The advantage of the plating method shown on the left over the plating method shown on the right is that the plating method on the left can be used to

d. quantify the number of organisms in a given bacterial sample.

Which of the following measurement techniques would be useful to quantify a species of bacteria that is difficult to culture?

direct microscopic counts

Humans harness microbial ________ to preserve foods and retain caloric value.

fermentation

The mode of action of an antimicrobial agent refers to ...

how it exerts the antimicrobial effects upon microorganisms.

Culturing viruses is difficult because viruses ...

must be grown inside a living cell.

The process of heating foods to a moderately high temperature long enough to kill most heat-resistant, non-spore-forming pathogens is known as ________.

pasteurization

Generally, protozoans are described as ...

unicellular heterotrophic eukaryotes.

Used in food production

Saccharomyces cerevisiae

Which of the following statements is true of selective toxicity?

Selective toxicity takes advantage of structural and/or metabolic differences between host and pathogen.

Identify two strategies that some bacteria may utilize to survive extreme or less than optimal environments.

Some bacteria use enzymes to lower the activation energy needed to do their job. This way they can do more work with less energy. Other bacteria use a preprogrammed cell death strategy to maintain the healthy ones in order to prevent large amounts of stress on the organism.---Examples of acceptable answers: Specific enzymes that can tolerate high temperatures, ability to use sulfur as an energy source and endosperms, ability to form endospores.

Which of the following would you expect to be most resistant to UV light?

Spore forming bacteria

Non-motile, transmitted to new hosts through vectors

Sporozoans

Pathogenic black mold associated with poor indoor air quality

Stachybotrys chartarum

Predict the results of a MBRT if the milk tubes were contaminated with a strict aerobe? Would the results be the same or different if the milk was contaminated with a strict anaerobe? Explain your answer.

The results would not be the same, because if the tubes were contaminated with a strict anaerobe, there would be no change in color. If the tubes were contaminated with a strict aerobe, the blue milk will change back to white. Methylene blue is a dye that is blue when oxidized so that is how we would know what kind of bacteria would be in the tubes and what could happen if they were contaminated. Correct Answer: Incubation with a strict aerobe would result in growth stopping as soon as the oxygen is consumed, but the medium would still convert from blue to white and the test would be valid. Incubation with a strict anaerobe would not result in reduction of methylene blue since the anaerobe would not consume the oxygen.

What does the Kirby-Bauer test assess?

The susceptibility of an organism to a set of antibiotics

Select ALL of the TRUE statements regarding the microbe in this image. (Mark all that apply)

This image is depicting the pseudohyphae of C. albicans. c. The microbe shown here has chitin in its cell wall. d. The microbe shown here reproduces by budding.

Dermatophyte associated with Tinea pedis (athletes foot)

Trichophyton

Only prokaryotic organisms, mainly bacteria, are capable of nitrogen fixation.

True

Which of these would be the least likely to be removed by passage through a HEPA filter?

Virus

In the figure below, in which phase shows the most rapid rate of growth?

2 (steepest incline)

To determine the concentration of E. coli in a sample, a broth culture was placed into a cuvette and analyzed in a spectrophotomer. The OD600 reading was 0.3. What is the concentration of E. coli in the sample?

2 x 107 cfu/ml

A 1:10,000 dilution of a bacteriophage sample produced a plate with 230 plaques. Assuming 1.0ml of the bacteriophage dilution was mixed with 2 drops of bacteria, what is the concentration of bacteriophages in the original stock solution?

230 plaques x 1mL x 104 = 2.3 x 106 pfu/mL

If a microbiologist starts with 10 organisms at time 0, how many organisms will they have after 8 generations, assuming exponential growth?

2560

A specimen of urine is determined to contain 30 bacterial cells per microliter. How many cells would be present in a milliliter?

30,000

Which image is depicting the trphozoite form of Acanthamoeba?

A

a) What is the primary difference in terms of information obtained between a direct cell count and a viable cell count? Why is this important? b) Many of the quantitative methods discussed are popular because they enable the microbiology researcher to selectively count live cells only. Why do you think this might be an important or desirable feature in a medical or environmental research situation? Provide a scenario in which it might not be important to differentiate between live and dead cells when counting cell numbers.

A direct cell count they count living a dead cells in their number, and for viable its only, well, viable cells! They have to be healthy cells. This is important to differentiate because you would not want to get those two numbers mixed up or you could really mess up your test/ experiment. This is important because if you are testing a patient who might have been exposed to a pathogen but come to find out, majority of the samples were not viable or healthy, the odds are that its less likely to have been able to survive long enough to harm the patient. However there still may be large quantities of this bacteria, but there could be no risk. This is why it could be crucial to count both direct cell count and viable, and to not get those numbers mixed up. Correct Answer: a) A direct cell count is quick, easy, and inexpensive; however, they often result in higher cell densities because only a small percent of cells growing in nature can be cultivated in a lab. This method can also give insight to cell size and morphology. Also, direct cell counts do not distinguish between live and dead cells so that can also lead to a higher density. Viable cell counts only account for cells that are able to reproduce once they are cultured. Viable cell counts dilute a sample down to a countable number (between 30-300) and then the total cell count is estimated and determined from the number found post-dilution. This is important because direct cell counts account for both living and dead cells whereas viable cell counts are estimated but are selective for only cells that are able to reproduce. It is important to know the difference so that you know which method is most appropriate to use for the information you are looking to obtain and to know how to interpret the data once you have collected your data. b) It may be important to know how many live cells there are if one is looking to see if there are potential pathogens in a sample. Pathogens are only dangerous if they are alive. If, for example, a researcher wanted to know if food was contaminated and could potentially make a consumer sick, only the presence of live pathogens could result in infection. When looking for fecal coliforms, it might not matter if the cells are alive or dead because they are simply being used as a indicator for other microbes.

Betadine is an example of which of the following groups of antimicrobial agents?

Halogens

Dimorphic fungus found as a mold in the environment but as a yeast in the lungs once inhaled

Histoplasma capsulatum

Select ALL elements that are essential for growth, reproduction, and maintenance of a bacterial cell. (Mark all that apply)

Hydrogen d. Carbon e. Nitrogen

The zone of inhibition around a ciprofloxacin disk is 19mm. How would you report the susceptibility of this organism to ciprofloxacin?

Intermediate (in the middle (look at numbers))

Sterilization

Killing of all microorganisms in/on surface or material

Organisms that are commonly used to produce yogurt include ...

Lactobacillus and Streptococcus

Which organism(s) is/are resistant to bacitracin?

Left (whichever side is touching growth)

Which of the following is NOT an effective means of sterilization?

Lyophilization

Describe two ways microorganisms that inhabit the soil contribute to the ecosystem as a whole.

Microorganisms are the only organisms that have the power to convert nitrogen gas into other substances for other organisms to use. Bacteria also uses phosphate mineralization to give back to plants to give back to animals. Most of the time it is not in a gaseous state so it is important for microorganisms to break it down so plants and animals can use it to survive.---Examples may include: transfer of carbon, any stage of nitrogen fixation, any stage of the sulfur cycle, decomposition/recycling of organic matter.

Mesophile

Most human pathogens are classified as this

In both fermentation and respiration,

NAD+ is regenerated from NADH. Glycolysis produces NADH; NADH must donate its electrons to regenerate NAD+ for glycolysis to continue. In fermentation, pyruvate accepts electrons from NADH. In respiration, pyruvate is further oxidized, generating additional NADH. The NADH produced donates electrons to an electron transport chain.

How would you classify the organism in the middle tube?

Obligate aerobe

Antibiotic source

Penicillium chrysogenum

what is this image?

Pseudohyphae of Saccharomyces cerevisiae

Both lactic acid fermentation and alcohol fermentation begin with which substrate?

Pyruvate

What color would you expect the Gram-positive bacterium Staphylococcus aureus be after an endospore stain?

Reddish-pink---The bacterium S. aureus does not form endospores, thus the cells would retain the counterstain safranin and be reddish-pink.

Disinfection

Reducing the number of viable organisms present in a sample