Microbiology: Lab 06

Protection of the Central Nervous System

1 - Meninges 2 - Cerebrospinal Fluid 3 - Brain 4 - Spinal Cord

For how long will you drench the bacterial smear in crystal violet?

1 Minute (60 seconds)

For how long will you drench the bacterial smear in iodine?

1 Minute (60 seconds)

For how long will you drench the bacterial smear in safranin?

45 Seconds

For how long will you wash the bacterial smear with alcohol?

5-10 Seconds

What reagent is applied to decolorize the Gram-negative bacteria, and thus differentiate it from the Gram-positive?

95% Ethyl Alcohol

What is the Gram Stain method?

Staining method used to differentiate bacterial species into two groups

With you rinse off the glass slide with water or continue without washing?

Wash with water

Is the negative control properly stained?

Yes. it appears Gram-negative, with bacteria stained pink

What type of meningitis is the most dangerous? Fungal meningitis Autoimmune meningitis Viral meningitis Bacterial meningitis

Bacterial meningitis "Bacterial meningitis has high morality rates, and must be promptly treated with antibiotics."

How long does it take to perform and analyze the Gram stain? 1 - 2 hours 48 hours 24 hours A few minutes

A few minutes

Hans: Why is the bacterial cell well of such great importance? Antibiotics can target the cell wall All answers are correct The cell wall is involved in inducing disease in the infected host The cell wall is essential for bacterial viability

All answers are correct

What would most likely occur if you drenched the bacterial smear in alcohol for 1 minute?

All purple stain would escape as the cell wall of both Gram-positive and Gram-negative bacteria would dissolve

Figure 1: CSF sample with Gram-negative bacteria. The big circular pink structures (A) are human cells, while the small pink structures are Gram-negative bacteria (B) Which circle contains bacteria? A contains bacteria There are no bacteria present B contains bacteria

B contains bacteria

What morphological group do the bacteria in the CSF sample belong to? Cocci Bacilli Others

Cocci

How can the doctor rapidly determine if there are bacteria present in the cerebrospinal fluid (CSF)?

Collect a few milliliters of CSF and send it for a Gram stain

What is the primary stain used, that colors all bacteria purple?

Crystal violet

How are the Cocci in the CSF sample organized? Streptococci Diplococci Staphylococci

Diplococci

What reagent is used to fixate the crystal violet molecules in the bacterial cell wall?

Iodine

Hans: What is the outcome of a well-executed Gram stain?

Gram- positive appear purple, and Gram-negative appear pink

What would most likely occur if you applied alcohol for only one second?

Gram-negative bacteria would not decolorize like it should, and all bacteria would therefore remain purple (Gram-positive)

Hans: Do you know what two groups that i am talking about are named? Gram-visible and Gram-invisible Gram-positive and Gram-negative Gram-cocci and Gram-rods Gram-variable and Gram-constant

Gram-positive and Gram-negative

Hans: Where do we find the Teichoic acids?

Gram-positive bacteria

What is the secondary stain used, that colors the decolorized Gram-negative bacteria pink?

Safranin

Hans: Where are the lipopolysaccharides found?

The outer membrane of Gram-negative bacteria

How would you describe the bacteria found in the CSF sample? They appear Gram-negative They appear Gram-variable (both positive and negative) They appear Gram-positive

They appear Gram-negative

Why do we used positive and negative controls in the Gram stain? To exclude Gram-variable bacteria To determine if an unknown sample is Gram-positive or negative To verify that the Gram stain was performed properly To distinguish between Gram-positive and Gram-negative bacteria

To verify that the Gram stain was performed properly

Is the positive control properly stained?

Yes. It appears Gram-positive, with bacteria stained purple