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Lab exam 2

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created 3 years ago by rmgrahem

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What is chemically defined and give an example.

media is composed of exact amounts of chemically pure, specifically identified organic or inorganic components.

-glucose salt broth

-inorganic synthetic broth


What is complex media and give an example.

composed of organic materials that are not chemically pure and not specifically identified chemical components

-nutrient broth/agar

-tryptic soy broth/agar

-blood agar


What is enriched media and give an example.

Why is it necessary for growing fastidious bacteria?

-composed of general purpose media that has something added to help fastidious bacteria (those that require specific nutrients in order to grow, "picky eaters") to grow better

-blood agar, nutrient broth with yeast extract


What is the relationship between the amount of bacteria in a culture and the absorbance?

-directly related

-as the amount of bacteria increases, the amount of turbidity increases, therefore the absorbance is increased.


What is the relationship between the amount of bacteria in a culture and the transmittance?

-indirectly related

-100% transmittance would be your reading with zero cells


Would heterotrophic organisms grow well in inorganic salt media? Why or why not?

-heterotrophic organisms require organic compound for their energy and carbon source.

-without any organic molecules in the media, the bacteria will have nothing for energy or carbon.

-the bacteria will not grow in this media


Why is complex media generally used to cultivate microorganisms?

-it has lots of nutrients which would be required for the growth of most microorganisms.

-for most microbes, this is enough for growth


Describe the minimum, optimal and maximum growth temperatures.

minimal-the lowest temperature at which a bacterial population can survive

optimal-the temperature at which bacteria thrive (greatest rate of metabolism and reproduction)

maximum-the highest temperature at which a bacterial population can survive


list the temperature range for Psychrophiles

0oC - 15oC (with a range of -15o C - 20oC)


List the temperature range for Mesophiles

20oC - 40oC (with a range of 10oC - 50oC)


List the temperature range for thermophiles

45oC - 80oC (with a range of 45oC - 80oC)


List the temperature range for hyperthermophiles

80oC and up


Differentiate between aerobes, anaerobes, facultatives and microaerophiles

obligate aerobes-have the ability to live in oxygen and require oxygen for metabolism

obligate anaerobes-are not able to live in oxygen and do not require oxygen for metabolism

facultative-have to preference, growth is seen in both aerobic and anaerobic environments

microaerophiles-can grow in oxygen, but only require a small amount for metabolism


Describe how the anaerobic chamber achieves an anaerobic environment.

anaerobic chambers take oxygen out of the air, combine it with hydrogen, and produce water


Describe the indicator that an anaerobic environment is present

condensation on the inside of the container


What is fermentation?

anaerobic metabolism in which organic molecules are the end electron receptor


What is being distinguished in the carbohydrate fermentation test?

Whether the bacteria ferment this sugar to an acid, or an acid and a gas


What is the indicator used in the carbohydrate fermentation test?

phenol red indicator

-yellow when acidic and hot pink when basic


What is the appearance of a positive result for a carbohydrate fermentation to an acid? To a gas?


-a bubble is present in the durham tube


What is the appearance of a negative result for carbohydrate fermentation to an acid? To a gas?


-no bubble in the durham tube


What sugar is in the MR-VP broth?



What is being distinguished in the MR and VP test?

MR-fermentation results in mixed acids

VP-glucose fermentation results in acetoin production


What reagents are used in the MR and VP test?

MR-Methyl Red Indicator

VP-alpha naphthol, 40% potassium hydroxide


What is the appearance of a positive result for the MR and VP tests:

both are red


What is the appearance of a negative result for the MR and VP tests

both are coppery or have no color change


Explain why you would expect no growth on the LB/amp/-DNA plate

the bacteria is sensitive to ampicillin and ampicillin is present in the media


Explain why you would expect isolated colonies to grow on the LB/amp/+DNA plate.

-not all bacteria obtained the plasmid containing the ampicillin resistant gene, therefore you get isolated colonies instead of a lawn of growth


Explain the purpose of the arabinose on the LB/amp/ara/+DNA plate

Arabinose is a sugar that acts as an inducer to the gfp gene. When arabinose is present it removes the inhibitor from the section of the plasmid containing the gfp gene and allows transcription and translation to take place. The gfp gene produces the green fluorescent protein and causes colonies of bacteria to have a green fluorescent glow when exposed to UV light


Explain why you would expect a lawn of growth on the LB/-DNA plate

There is no ampicillin present in the media to inhibit the growth of the bacteria on the plate


What is selective media?

media that prevent the growth of one type of bacteria so that only one kind of bacteria grows on the plate


What is differential media?

media that differentiates one kind of bacteria from another by a color change


Can a media be both selective and differential?



BAP plate

-enriched with 5% sheep's blood

-differential for type of hemolysis


MSA plate

-selective with 7.5% salt for salt tolerant bacteria (gram +)

-differential for mannitol fermentation

-indicator is Phenol Red

-pH <7 is yellow


EMB plate

-selective with Eosin and Methylene Blue for Gram- bacteria

-differential for lactose fermentation

-indicator is Eosin and Methylene Blue

-lots of acid accumulated=green metallic sheen


MAC plate

-selective with bile salts and crystal violet for Gram- bacteria

-differential for lactose fermentation

-indicator is neutral red

-pH <7 is pink precipitate


PEA plate

-selective with phenylethanol tolerance for gram+ bacteria


Starch hydrolysis (amylase)

-if starch is hydrolyzed by amylase (produced by bacteria), then no starch will be present around the bacteria

-reagent: iodine will detect starch in the media by producing a blue/black precipitate

-positive for starch hydrolysis: clear zone around the bacteria



-catalase (enzyme) breaks down hydrogen peroxide (substrate) into water and oxygen

-oxygen bubbles: effervescence is a positive result for catalase production


Phenylalanine Deaminase

Phenylalanine deaminase (enzyme) will work on phenylalanine by removing the amine group to produce phenylpyruvic acid and ammonia

-Reagent: ferric chloride combined with phenylpyruvic acid to produce a green color = a positive for phenylalanine deaminase enzyme


SIM: Hydrogen Sulfide (Sulfur)

-amino acids that are metabolized, theosulfates, sulfates and sulfites are reduced by the bacteria to produce hydrogen sulfide

-presence is a black precipitate in medium = positive result for H2S production


SIM: Indole

- Tryptophanase is the enzyme that hydrolyzes Tryptophan. Indole is a product of Tryptophan hydrolysis.

-Reagent: Kovac’s reagent - Dark pink color = positive for Indole production


SIM: Motility

-medium is semi-solid and allows the bacteria to move throughout the medium if it is motile.

-Motile bacteria will make the entire medium look cloudy or opaque.



-Urease (enzyme) breaks down urea (substrate) producing ammonia.

-Indicator: phenol red;

-Positive for urease production = hot pink


Simmon's Citrate

-Tests for the ability of the bacteria to utilize the citrate in the media as the sole source of carbon with the citrase enzyme.

-Bacteria that do this then use the ammonium hydroxide and ammonium phosphate as a sole source of nitrogen. When they break down the ammonium phosphate and ammonium hydroxide, they release ammonia. This raises the pH to produce a basic environment.

-Bromthymol blue in the medium is the indicator which will turn Prussian blue (KU blue) when it is basic and yellow when it is acidic. So a positive result for Citrate Utilization = Prussian blue (KU blue) color. A Negative result for Citrate Utilization = forest green color (no change in the color)


Define transient microbiota

This is the bacteria that have been picked up throughout the day as we are exposed to them. They have not (yet) colonized the body and if pathogens, have not breached the
physical barriers


Define normal microbiota

Normal microbiota are bacteria that have colonized the body (not just the skin). They are normally commensals which do not harm us, or mutualists which help us while they help themselves


Name 4 locations where normal microbiota is present on the host


-Upper Respiratory Tract

-Lower Respiratory Tract

-Digestive Tract (Oral Cavity, Large Intestine and Rectum)

-Urinary Tract (External Urethra)

-Genital Tract (Vagina).


Describe the ecological relationship between most normal microbiota and the host

Most are commensals (win/null (no affect) or have a mutualism (win/win) relationship. Some can be pathogenic, if given the opportunity (opportunistic pathogens).


Explain how normal microbiota can sometimes be an opportunistic pathogen

If microbiota crosses physical barriers into normally sterile compartments of the body, or if the host is immuncompromised, the microbe can cause disease


Use "texture" to describe a colony on a plate.

can be smooth, rough, shiny and/or dull


Use "shapes" to describe a colony on a plate:

-punctiform: a pin point small colony


-filamentous: fuzzy or thin extensions coming from the center


-rhizoid: root-like extensions come from the center

-spindle: football shaped


Use "elevation" to describe a colony on a plate




-pulvinate: like a water droplet on a surface

-umbonate: raised area in the center


Use "margin" to describe a colony on a plate

-even: entire, smooth regular edge

-undulate: wavy

-filamentous: thin filaments from the center

-lobulate: lobular extensions from center

-erose: serrated, like a blade

-curled: similar to a bullseye target



a chemical used to control microbes on an animate surface



chemicals used to control microbes on an inanimate surface


Give examples of antiseptics

-hydrogen peroxide




Give examples of disinfectants



What are the factors that affect the efficiency of the disinfectants and antiseptics?

  1. concentration of the chemical
  2. length of exposure
  3. type of microbial population to be destroyed
  4. environmental conditions (temp & pH)

What does the zone of inhibition indicate about the bacteria's relationship to the chemical?

-the zone of inhibition is related to the sensitivity or resistance of the bacteria to an antibiotic

-the larger the zone, the more effective the antibiotic


Define antibiotic

a chemical produced by certain species of bacteria and fungi for the purpose of competing better with their competition. The term traditionally refers to the naturally acquired chemotherapeutic agents. However, so many of the naturally occurring antibiotics have been chemically changed in the laboratory that most of the antibiotics are truly “semi-synthetic” and not true antibiotics


Define chemotherapeutic

a general term that describes any chemical that can be used in the treatment or prevention of disease (it thus includes cancer chemotherapeutic agents as well as infectious disease chemotherapeutic agents).


What is the minimum inhibitory concentration (MIC) and how is it determined?

-the most dilute concentration of antibiotics that are still able to kill microbes.

-Two methods are used – the MIC test uses several tubes of serially diluted antibiotics (1:2, 1:4, 1:8, etc…), the same concentration/amount of bacteria is added to each tube and incubated. The MIC is then determined by looking at the most dilute solution that is still effective against the bacteria (no growth in the tube).

-The second method is the E-Test in which strips with increasing dilutions of the antibiotic on the back side of the strip are placed on an inoculated plate. Wherever the zone of inhibition crosses the strip, that indicates the MIC.


What conditions must be controlled to make the MIC test repeatable and accurate?

  1. Temperature and Time of Inoculation: 37˚C for 24-48 hours
  2. Concentration of Bacteria: 0.5 McFarland Turbidity
  3. Standard Concentration of Antibiotics: Standardized discs with antibiotics
  4. Type of media: Mueller Hinton Agar

What are the modes of action for the antibiotics used in our lab.

-azithromycin: 50S protein synthesis

-PCN: cell wall

-ciprofloxacin: nucleic acid-DNA

-sulfamethoxazole X trimethroprim: folic acid metabolism

-tetracycline: 30S protein synthesis


Name the 5 genera of Enterobacteriaciae bacteria tested for in this unknown lab.

Why are biochemical tests required to identify bacteria?

  1. Escherichia
  2. Pseudomonas
  3. Klebsiella
  4. Proteus
  5. Salmonella

The bacteria all are gram negative rods and without biochemical tests, they are difficult to distinguish.


Why are biochemical tests required to identify the genus of these bacteria?

The biochemical tests indicate a set of unique characteristics


How are fermentation tests used to identify bacteria?

The results of fermentation are unique to each genus and can help identify the microbe


What are the five I’s of the microbiology lab and how were they used in this lab?

  1. Inoculation – when the media was inoculated
  2. Isolation – when the streak plate was performed
  3. Incubation – when the bacteria was incubated after inoculation
  4. Inspection – when the gram stain was observed
  5. Identification – when the bacteria was identified using biochemical tests

What does ELISA mean?

Enzyme Linked Immunosorbent Assay


Why is it better to have and Enzyme-linked antibody rather than Substrate-linked antibodies in this test?

Enzymes are recycled and only one enzyme linked antibody would be enough to create a visible change in the well to indicate an antigen/antibody reaction had occurred. If only one Substrate-linked antibody was present, that would not be adequate to be able to create a visible change


Where did the primary antibody come from in an indirect ELISA test?

patient's serum (if present)


Why should the secondary antibody stick to the primary antibody in an indirect ELISA test?

It is an anti-IgG antibody and will attach to any antibodies still in the well.


Why is it necessary to switch tips or pipettes when removing serum from the wells of different rows (between patients’ serum or between different dilutions).

To prevent any false positives from mixing of patients’ serum.


Why is it necessary to wash between each step?

This is to wash away any antibodies or antigens that did not stick to the wells or to the known antibodies/antigens.


What type of diagnostic test is the Bactistaph Test?

Passive Agglutinations


What is the Bactistaph test testing for to identify Staph bacteria?

Protein A is a part of the Coagulase enzyme that helps determine if the bacteria is Staphylococcus aureus or not.


What type of diagnostic test is the Group A Strep Test?

It is a type of Direct ELISA test (Sandwich Capture).


How are Streptococcus bacteria classified?

The two main ways that they can be classified are their Lancefield group of Carbohydrate Chain (Group A, B, C, etc….), or by Hemolysis (Beta hemolytic, Alpha hemolytic).

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