Microbiology and Parasitology Lecture 6

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Questions and Answers

What is the purpose of heat fixing in smear preparation?

To kill the organism (correct)

To adhere the specimen to the slide

To dry the smear

To accept the dye

What is the characteristic of a negative stain?

It stains the background

It is repelled by the negative cell wall (correct)

It is an acid dye

It is a basic dye

What is the purpose of a simple stain?

To distinguish between bacterial groups

To provide an environment suitable for growth

To kill the organism

To show the morphology of bacteria (correct)

What is essential for successful identification of microbe?

Correctly handling the specimens Signup and view all the answers

What is the main difference between a simple stain and a differential stain?

The number of reagents used Signup and view all the answers

What is the function of Auxochrome in staining?

To allow the dye to form salt compounds that adhere to cells Signup and view all the answers

What is the purpose of Gram stain?

To distinguish between bacterial groups Signup and view all the answers

What is the purpose of macroscopic colonial morphology in phenotyping?

To examine the growth pattern of the bacteria Signup and view all the answers

What is the concentration of agar in solid media?

1 - 2% Signup and view all the answers

What is the purpose of culture media?

To provide an environment suitable for growth Signup and view all the answers

What type of stain is used to identify special structures such as capsule?

Special Stains Signup and view all the answers

What is a physical requirement for growth?

Temperature Signup and view all the answers

What type of medium is used to identify microorganisms based on their ability to utilize a specific substrate?

Differential medium Signup and view all the answers

What is the result of combining Benzene and Chromophore?

Chromogen Signup and view all the answers

Why is labeling the slide important in slide preparation?

To keep track of the samples Signup and view all the answers

Which of the following transport media is used for stool samples?

Carry Blair Transport Medium Signup and view all the answers

What is an inorganic nutrient required for growth?

Phosphate Signup and view all the answers

What is the purpose of the citrate utilization test?

To show ability to utilize a specific substrate Signup and view all the answers

Which of the following is NOT a type of bacterial classification?

Classification based on habitat Signup and view all the answers

What is the purpose of the H2S production test?

To test for metabolism of proteins and amino acids Signup and view all the answers

Study Notes

Bacterial Identification

Successful identification of microbe depends on: using aseptic techniques, correctly handling specimens, quickly transporting the specimen to the lab, and culturing and isolating quickly.
Three types of identification methods: phenotyping, serological, and molecular.

Phenotyping

Microscopic observation
Macroscopic colonial morphology
Culture media for growth
Biochemical tests

Stains

All dyes are salts that ionize
Cationic and anionic dyes
Staining techniques: single dyes, multiple dyes
Chemical makeup of stains: benzene, chromophore, auxochrome
Chromogen: a colored compound formed by combining benzene and chromophore

Staining Methods

Negative Stain: acid dye, (-) chromogen, repelled by (-) cell wall, cells appear colorless against a dark background
Simple Stain: one reagent used, soak smear 30-60 seconds, rinse with H2O, background stained, bacteria stained, basic dye, (+) chromogen
Differential Stains: two or more reagents, distinguish between bacterial groups or specific structures

Gram Stain

Time frame: 1 minute, 1 minute, 15 seconds, 1 minute
Rinse with water between each step
Example: Gram stain, Acid Fast Stain

Culture Techniques

Used to support the initial growth and isolation of microorganisms
Culture media: food material or substances required for growing microorganisms in vitro
Provide an environment suitable for microorganism growth

Culture Media

Classification based on agar concentration or consistency:
- Fluid (broth) media: 0% agar
- Semisolid media: 0.4-0.5% agar
- Solid media: 1-2% agar (1.5%)
- Diphasic media: agar portion and broth portion
Classification based on nutritional component or ingredients:
- Simple or Basic medium
- Complex medium
- Synthetic or defined medium
- Special medium (enriched, enrichment, differential, selective, or indicator and transport medium)

Biochemical Tests

Use: identification of microorganisms
Classification:
- Test for metabolism of carbohydrates: sugars fermentation test and O/F test
- Test for specific break down of product: MR & VP
- Test to show ability to utilize a specific substrate: citrate utilization test
- Test for metabolism of proteins and amino acids: H2S production test, indole production test
- Test for enzymes: catalase, oxidase, urease

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Description

This quiz covers the identification methods of bacteria, including phenotyping, serological, and molecular methods, as part of the first year nursing faculty curriculum. It is based on Lecture No. 6 by Rasha Zeinalabdein, M.Sc. in Microbiology.