Question 1

Which of the following best describes the main purpose of aseptic technique in a microbiology laboratory?

Accepted Answer

To prevent the introduction of unwanted organisms or contaminants into an environment

Question 2

A microbiologist is preparing to transfer bacteria from a broth culture to a solid agar plate. Which of the following steps is essential to maintain aseptic conditions during this process?

Accepted Answer

Sterilizing the inoculating loop by flaming it before and after use

Question 3

Which of the following statements correctly differentiates between sterilization, disinfection, and sanitization?

Accepted Answer

Sterilization destroys all microorganisms, disinfection destroys vegetative microbes and viruses on inanimate surfaces, and sanitization mechanically removes microorganisms to safe levels

Question 4

A hospital technician is tasked with cleaning surgical instruments. Which method should be used to ensure all microorganisms, including spores, are destroyed?

Accepted Answer

Sterilization using autoclaving (moist heat under pressure)

Question 5

Which type of culture medium would you use to isolate a specific bacterium from a fecal sample containing a mixture of microorganisms, and why?

Accepted Answer

Selective medium, because it contains agents that inhibit unwanted microbes and favor the growth of the desired bacterium

Question 6

A microbiologist is using Xylose Lysine Deoxycholate (XLD) agar to culture stool samples. Which of the following observations would indicate that an organism produces hydrogen sulfide?

Accepted Answer

Colonies appear black

Question 7

Which of the following best describes the difference between complex (nonsynthetic) and chemically defined (synthetic) media?

Accepted Answer

Complex media contain at least one ingredient that is not chemically defined, while chemically defined media have a known, exact chemical composition

Question 8

A student is asked to identify an unknown bacterium using the Five I’s. Which step involves producing a culture by introducing the sample into a medium?

Accepted Answer

Inoculation

Question 9

Which of the following statements about the Gram stain is correct?

Accepted Answer

It is a differential stain that distinguishes between gram-positive (purple) and gram-negative (red/pink) bacteria

Question 10

A clinical sample is stained with carbolfuchsin and treated with acid-alcohol. The cells remain red after this process. What can be concluded about the organism?

Accepted Answer

It is an acid-fast bacterium

Question 11

Which of the following best describes the purpose of a negative stain in microbiology?

Accepted Answer

To visualize structures such as capsules by staining the background and leaving the organism unstained

Question 12

A microbiologist observes a bacterial culture on a slant with uniform growth along the line of inoculation. Which term best describes this growth pattern?

Accepted Answer

Filiform

Question 13

Which of the following culture media would be most appropriate for differentiating between bacteria that can ferment mannitol and those that cannot?

Accepted Answer

Mannitol salt agar (MSA)

Question 14

A laboratory technician is using a pour plate technique to determine the number of bacteria in a water sample. Which of the following best explains why colonies appear both on the surface and within the agar?

Accepted Answer

The inoculum is mixed with warm liquid agar before solidification, allowing bacteria to grow throughout the medium

Question 15

Which of the following is a physiological or biochemical characteristic commonly used to identify bacteria in the laboratory?

Accepted Answer

Hydrogen sulfide production

Question 16

A patient’s blood sample is tested for the presence of antibodies against a specific pathogen. The result is positive, and the antibody titer is measured. What does a high antibody titer indicate?

Accepted Answer

The patient has a high level of antibodies, suggesting recent or past exposure to the antigen

Question 17

Which of the following best describes the process of genetic analysis for microbial identification?

Accepted Answer

It uses DNA or RNA sequences, or DNA fragments produced by restriction enzymes, to differentiate strains

Question 18

A microbiologist is using transmission electron microscopy (TEM) to examine a bacterial sample. Which of the following is a key step in sample preparation for TEM?

Accepted Answer

Using metals to block the transmission of some of the electron beam and increase contrast

Question 19

A microbiologist observes a gelatin stab tube after incubation and refrigeration. The medium is liquefied only at the upper region near the walls of the tube. Which type of liquefaction is this?

Accepted Answer

Stratiform

Microbiological Laboratory Techniques: Aseptic Methods, Culture Media, Staining, and Identification

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