Micriobiology Lab practical test prep

Why is is important to use aseptic techniques when inoculating tubes and media plates?

It is important in order to reduce the risk of contamination in hopes of a "pure colony."

How does the procedure for using the microscope differ using the high dry power as opposed to low power?

Using high dry power involves using the fine adjusting knob and the low power uses the coarse adjustment knob

How does loss of light affect the resolution of a specimen?

The less light while viewing a specimen will not allow for as good of resolution as possible, also making it harder to find specific characteristics

What is the purpose of using immersion oil?

Immersion oil ensures that there is no air between the slide and the lens. It has the same refractive index as the glass so images don't get scattered before hitting your eye. Ultimately creating a more clear resolution without light escaping from traveling outside of the oil.

What 2 things can be adjusted to control the amount of light passing into a specimen?

The iris diaphragm and the light intensity adjuster both control the amount of light passing into a specimen.

Describe how to properly care for a microscope after immersion oil has been used

After using oil immersion, one must ensure that the oil doesn't get on any other lenses. Isopropanol alcohol and lens paper are used to clean all oil off of the lens and the slide to keep optimal optical quality. The plastic cover is put back over the whole microscope and placed back in storage.

Why must we stain bacteria before examining them with a microscope?

Staining bacteria allows us to examine the shape and internal arrangement of the bacteria that would otherwise be colorless and unidentifiable.

What component of a stain gives bacteria their color?

The chromophore group

What advantage does knowing the morphology and arrangement of a culture provide?

Helps physicians describe a specific antibiotic and other medications that are particular to that morphology/arrangement.

Why must you use water when preparing a smear from a solid culture?

because otherwise the culture wouldn't spread to the slide.

What is a differential stain?

It is a stain for microorganisms that helps distinguish between bacteria, often based on color differences

How can the age of the cell culture affect the results of a gram stain?

If a culture is 24 hours or older, the cells lose their ability to retain the dye in a gram stain

Which is the most critical step in the gram staining procedure?

The decolorization, or alcohol wash, is the most important in gram staining because without it, gram negative and gram positive bacteria would look the same.

How can the results of a gram stain on a bacterial culture help a physician decide which antibiotic to use against that bacterium?

It can help determine because gram positive bacteria are affected by simple antibiotics such as penicillin and can be killed by some hand soaps. Gram negative bacteria are more resistant to antibiotics like penicillin.

Can a bacteria cell produce more than one spore?

No, a cell must lyse in order to produce an endospore

Why is heat required to stain endospores?

Heat allows the dye to penetrate the cell wall of the endospore

What is the advantage to the bacteria to produce endospores?

Endospores protect the bacteria and its necessary components from being damaged

Can bacteria survive with a capsule?

Yes, the capsule merely protects the bacteria and doesn't kill the bacteria

What are the advantages of a capsule to bacteria cells?

Capsules protect the cell from being phagocytized and help keep the bacteria alive longer.

After performing the Acid Fast Stain what is the color of cells lacking mycolic acid?

Cells lacking mycolic acid are blue after the stain

How does a layer of mycolic acid contribute to these bacteria ability to cause disease?

The mycolic acid creates a protective waxy layer, making the bacteria less sensitive to antibiotics

When performing a streak plate why is it necessary to flame the loop between each streak pattern?

You flame the loop between each streak pattern so that you don't end up with too much bacteria

How can you confirm that your isolated colony came from a single type of bacteria cell?

by looking at the color and morphology under a microscope or by growing that colony on a new plate

If you were asked to isolate bacteria from a water sample which of these isolation techniques would you use and why?

I would use spread plating to isolate bacteria from a water sample because it makes it easier to see the different colonies.

When performing the spread plate technique why is it important to burn of all the alcohol from the glass rod before attempting to spread the bacteria on the plate?

It's important because otherwise the alcohol could mix with the bacteria and potentially kill it or denature some proteins and it sterilizes the rod at a lower temperature, reducing burn risks.

What is a complex media?

It is a media with nutrient rich substances like peptone but in which you don't know the chemical composition completely.

What is the primary goal of selective media?

It is to inhibit the growth of a certain group of microbes or encourage growth of very few microbes

Besides MacConkey Agar, what other media(s) would be useful for isolating E. coli from a stool sample?

Eosin methylene Blue agar (EMB)

Explain why a pH indicator can be useful in determining whether or not fermentation of a substrate has occurred

A pH indicator gives the differences between organisms that ferment in an acidic solution compared to those who cannot ferment in an acidic solution

Why, particularly in clinical laboratories, are selectively differential mediums employed most often?

It takes less time to diagnose and identify the pathogen

Describe what 3 minimal components would be necessary in a medium designed to show a difference between an organism that ferments X->Y. X has a neutral pH, and Y is highly acidic.

X, no oxygen, pH indicator

biochemical ability

Why are pure cultures necessary for biochemical testing?

In order to achieve optimal results and prevent contamination of unwanted microbes in the culture

Why do you need to know the Gram reaction and morphology of an organism before performing biochemical testing?

To know which test to perform and to ensure a pure culture

Can you relate urease production to diaper rash in infants?

Yes, urease contributes to the wetness and diaper rash is a skin irritation caused by a wet diaper

What is fermentation? Deamination?

The chemical breakdown of a substance by bacteria, yeasts, or other microorganisms and gives off heat. Deamination is the removal of an amino group form an amino acid or other compound

Why is testing for enzyme a reliable identification tool?

It usually reflects the genetic capabilities of the cell

Which of the enzymes you tested for would be considered exoenzymes?

urease, amylase, and DNase

What types of bacteria did you recover from your nose?

S. aureus

What are nosocomial infections?

It is an infection that was acquired in a hospital or healthcare facility

What bacteria cause most nosocomial infections?

S. aureus

Which of the bacterial respiratory pathogens can you be immunized against?

Strep. agalactiae, strep. pneumoniae, Corynbacterium diptheriae, Bordatella pertussis, Klebsiella pneumoniae, and Mycobacterium tuberculosis

How could you distinguish Staph. epidermidis from Staph. aureus?

Diagnostically by coagulase, mannitol, fermentation etc. tests. Staph. epidermidis is a pathogen in infections of prosthetic devices and neurosurgical shunts and Staph. aureus forms boils, carbuncles, osteomyelitis, and pneumonia

What are the symptoms of acute epiglottitis?

Fever, severe sore throat, difficult and painful swallowing, drooling, anxious, and more comfort when sitting up

What is a sputum specimen?

One of saliva/mucus acquired via mouth

Some chemicals may have produced a zone of inhibition on the nutrient agar plate, but not on the blood agar plate. What explanation can you give for this result?

The presence of an organic material may alter/neutralize the affects of many antimicrobial chemicals

Some chemicals may have had a better result on E. coli and less on Staphylococcus. What difference between these 2 bacteria may have effected the results?

E. coli is gram negative, meaning that there is less soft surface than Staphylococcus.

Bacillus may have survived treatment with a chemical better than Staphylococcus or E. coli. What special structure may be imparting additional resistance?

An endospore may be imparting additional resistance

Does the filter paper efficacy testing method examine the effect of bacteriostatic agents, bactericidal agents, or both?

Both because the test is showing how the bacteria are inhibited. If either are being killed or simply kept from growing, the results would be visible in the zone.

What is an antibiotic?

A medicine that inhibits the growth of or destroys microorganisms

Can antibiotics be used to treat a viral infection?

No, antibiotics are only effective against microbial growth

What three morphological types of capsids found in viruses?

helical, polyhedral, or complex morphology.

For what viral diseases are immunizations available?

Rubella (German Measles) and Mumps, given with the measles vaccine in the "MMR" vaccine.

Influenza.

Varicella (Chickenpox)

Hepatitis A.

Rabies.

Is filtration a suitable sterilization method for viral contaminated material? Why or why not?

No, the viruses will pass through the filter

What are retroviruses? Cite some diseases associated with this group of viruses

Change genetic make up of cell. Reverse transcriptase

ex: HIV

What does "opportunistic" mean?

an organism, not normally pathogentic, taking advantage of a compromised host

What type of patient specimen would you collect for histoplasmosis?

Respiratory

Flegm from coughing.

Describe some infections associated with Candida albicans.

yeast infection

Skin and mucosal infections

What are some examples of nonspecific chemical defense agents other than lysozyme?

Interferon

Low pH, high salt, gastric juices

Why did you get different results with E.coli and the Micrococcus luteus in the lysozome experiment?

Microcuccus are G+ and lysed by lysozyme

E. coli are G- unaffected

Cite some examples of mechanical defense mechanisms.

1. Cilia in mucus membranes impedes invasion of microbes

2. Skin epithelial keratin barrier

3. Sneezing

4. Urine flow

Define antigen.

Any foreign substance that causes the body to produce antibodies or sensitized T cells

Define antibody.

A protein made by B cells and Plasma cells in reaction to a foreign substance or antigen.

What is the difference in a precipitation reaction and an agglutination reaction?

Precipitaion reaction-(invitro), fine cloudy reaction, liquid form in test tube

Agglutination-coagulation on slide or test tube, soluble

How can serological tests be used to verify the etiology of a disease?

Organisms are identified at the strain level

These exercises demonstrated "in vitro" antigen-antibody reactions. What type of

activities are associated with antibodies "in vivo?"

Invivo is an experiment using the whole living organism such as animal testing or clinical trials