Microbiology: Lab 06

Protection of the Central Nervous System

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

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

What is the Gram Stain method?

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

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

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

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

Hans: Where do we find the Teichoic acids?

Hans: Where are the lipopolysaccharides found?

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

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

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

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

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

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

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

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

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

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

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

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

Is the positive control properly stained?

Is the negative control properly stained?

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

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

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

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