Questions for Microbiology (practical) Dr. Nabil El Aila General Microbiology

Biosafety 1- What are the classification of risk groups? 2- What are the biosafety levels? Give examples of microorganisms belong to each class? 3- What is the difference between Fume hoods and laminar flow hoods? 4- Explain the types of Biological safet y cabinet? Why we use them?

Microscopy 1- Mention the types of Microoscopes? 2- Discuss the principle and use of each microscope? 3-What are the components of compound microscope and the function of each?

Smear preparation and simple staining 1- What is the functional group of stain? 2- What are the types of dyes? 3- What are the types of staining techniques? 4- Why it is necessary to heat fix bacterial smears? 5- What would be the reason(s) for not finding any organisms on the slide?

Questions on Gram stain 1-What is the difference in the structure of the cell wall of Gram positive and Gram negative bacteria with drawing? 2- Discuss how cell wall structure determines the gram stain reaction of a bacterium? 3- What are the conditions when Gram positive bacteria can appear Gram negative? 4- Which are bacteria or bacteria component that cant be stained by Gram stain? 5- What are the positive and negative control of Gram stain? 6- Which is the most important step in Gram stain?

Questions on Gram stain 7- Why gram staining is classified as differential staining? 8- Why are direct gram stains ordered on clinical specimens? 9- What are the applications of Gram stain? 10- List all of the things that can go happen during the Gram- staining process that could lead to an incorrect or poor result? 11- Why is a gram stain performed on all Cerebrospinal fluid specimens and not ordinarily done on a) vaginas and b) stools?

Questions on Acid fast stain 1) Explain the significance of the acid fast stain? 2) Is a gram stain an adequate substitute for an acid-fast stain? 3) What are the colors of acid-fast and non acid-fast bacteria like (Escherichia coli and Staph aureus) at the end of the acid-fast stain? Explain in details? 4) Why is it best to use an old culture for acid fast stain? 5) What is the purpose of the counterstain in the acid- fast staining? 6) Why acid alcohol is used instead of ethyl alcohol in acid fast staining? 7) What are 2 examples of acid-fast pathogens and what disease they cause?

Questions on Special stain 1) In the Gram stain and the endospore stain, heat fixing is used. In the capsule stain the cells are not heat fixed. Why? 2) What is the importance of the capsule stain, the flagella stain and the endospore stain? 3) What is the purpose of the Congo red in the capsule stain? 4) What roles do capsules play in the life of bacteria? 5) Why don't capsules pick up the stain? 6) How does the negative stain work? 7) why doesn't a negative stain colorize the cells in a smear? 8) List any advantages of a negative stain over a simple stain

Questions on Special stain 9) Define the terms: endospore; vegetative form; germinate. 10) Describe the unusual characteristics of bacterial spore 11) Why is a bacterial endospore more difficult to stain then a vegetative cell? 12) What differences between young and old culture by endospore stain?

Questions on Culture media 1) What is general purpose of culture media in microbiology? 2) What are the different types of media? Explain each of these types and give examples? 3) How are media made selective? 4) How are the media sterilized? Which media are not autoclavable? 5) How are media solidified? What is the melting and solidifying point of the agar? 6) Why is agar preferred over gelatin? 7) What is biphasic medi? Give example?

Questions on Culture media 8) Name some lactose fermenters and non lactose fermenters? 9) Why Gram positive bacteria doesn’t grow in MacConkey agar? 10) Why are pH buffers added to the growth media for microbes? 11) In what size container would you sterilize 500ml of medium? 12) Why do you incubate the plate inverted?

Inoculation and transfer techniques of microorganism 1)When an agar plate is inoculated, why is the loop flamed between quadrants? 2) What is a mixed culture? What is a pure culture? 3) What is a bacterial colony? 4) Why is it necessary to isolate individual colonies from a mixture in the clinical lab? 5) Give two reasons for using aseptic technique. 6) List the possible sources of contamination that you should be concerned about while transferring bacteria from one culture to another. 7) How should agar plates be incubated? Why? 8) Where and how should a label be written on an agar plate?

Counting Bacteria 1) What are the methods used in bacterial counting? Expalin each of them? 2) What is the difference between pour plate and spread plate methods in isolating microorganisms? 3) What is the main advantage of pour-plate method over other methods of bacterial colony isolation? 4) When doing a plate count, why do we choose a plate with 30 – 300 CFU’s?

Counting Bacteria 5) You count 75 CFU’s on a given plate. The colonies on the plate were formed from 1 ml of original bacterial solution that was serially diluted to 1/100,000 of the original amount. How many bacteria are in the original solution? (Show the proper units.)

Bacterial Motility 1) What advantages does the hanging drop slide have over the motility test medium for determining motility? 2) What are the categories of bacterial flagellation? 3) Give examples of motile and non motile bacteria? 4) What the different between solid and semisolid media? 5) What advantage might motile bacteria have over non-motile ones? 6) What is the role of mordant in flagellar stain?