MDS PREP
Which of the following is NOT a method used to produce a recombinant hepatitis B vaccine?
1) Cloning the HBsAg gene in E. coli
2) Cloning the HBsAg gene in yeasts Saccharomyces cerevisae
3) Extracting and purifying HBsAg particles from infected human plasma
4) Using baculovirus vectors to produce HBsAg in insect cells
General Microbiology Answer: 1
While recombinant hepatitis B vaccines are produced using various methods, cloning the HBsAg gene in E. coli is not one of them. Instead, the gene is typically cloned in yeast or insect cells to produce the surface antigen for the vaccine.
Most viruses are
1. never destroyed by the application of moist heat
2 easily destroyed by the application of moist heat
3 difficult to destroy by the application of moist heat
4 never destroyed because they are not living
Microbiology
Answer: 2
The biologic standard used to test the efficiency of sterilization involves the use of
1. spores of Clostridium tetani
2. streptococcus pneumoniae
3 spores of a harmless bacillus
4. infectious hepatitis virus
Microbiology
Answer: 3
The biologic standard used to test the efficiency of sterilization typically
involves the use of spores of a harmless bacillus. This method is widely
recognized in the scientific community and is based on the principle that if a
sterilization process can effectively destroy the most heat-resistant
microorganisms, it is assumed to be capable of killing all other less resistant
microbes.
The choice of using spores of a harmless bacillus is rooted in the fact that
bacterial spores are the most heat-resistant forms of microbial life. Spores are
metabolically inactive, which makes them very hardy and capable of surviving in
adverse environmental conditions for extended periods. For sterilization
validation, scientists often employ a biological indicator that contains spores
of a known heat-resistant bacterium, such as Geobacillus stearothermophilus
(formerly Bacillus stearothermophilus) or Bacillus subtilis. These organisms are
chosen because they have well-characterized resistance profiles, and their
destruction indicates that the sterilization process has achieved the necessary
lethality to eradicate all microbial life forms, including vegetative bacteria,
fungi, and viruses.
Let's examine the other options provided:
1. Spores of Clostridium tetani: While C. tetani is a spore-forming bacterium,
its spores are not commonly used as a biological indicator for sterilization
efficiency. C. tetani is a pathogen that causes tetanus, a serious disease.
However, it is not typically used for this purpose because there are safer and
more universally accepted biological indicators available.
2. Streptococcus pneumoniae: S. pneumoniae is a bacterium that can cause
pneumonia and other infections, but it is not a spore-former. Moreover, it is
generally less resistant to heat and sterilization methods compared to
spore-forming bacteria. Thus, it is not suitable as a standard for testing
sterilization efficiency.
3. Spores of a harmless bacillus: As previously mentioned, this is the most
appropriate choice for a biologic standard in sterilization testing. These
spores serve as reliable and safe indicators of sterilization efficacy because
they mimic the resistance of pathogenic spores without posing the actual risk of
infection.
4. Infectious hepatitis virus: While viruses can be highly resistant to some
sterilization methods, they are generally more sensitive to heat than bacterial
spores. Moreover, using infectious viruses as biological indicators poses
significant biosafety risks and is not a standard practice in routine
sterilization testing. For viral resistance testing, specific viruses or
virus-like particles may be used, but these are not typically employed as the
primary biological indicators for sterilization validation due to the complexity
and high containment requirements of such testing.
Which of the following is NOT a direct method for diagnosing tuberculosis?
1) Smear examination
2) ELISA
3) Culture methods
4) Nucleic acid technology
General Microbiology Answer: 2ELISA: While ELISA (Enzyme-Linked Immunosorbent Assay) can be used to detect antibodies to the tuberculosis bacterium, it is not a direct method for diagnosing active TB infection. Direct methods include smear examination, culture, and nucleic acid technology, which detect the actual presence of the bacteria in the patient sample.
The chemical nature of bacterial exotoxins is, a
1. low molecular weight polypeptide
2. lipopolysaccharide complex
3. protein
4. complex carbohydrate
Microbiology
Answer: 2
The chemical nature of bacterial exotoxins is, a
lipopolysaccharide complex
Which of the following is a distinguishing feature of exotoxins?
1) Lipopolysaccharides
2) Heat stable
3) Actively secreted by cells
4) Obtained only by cell lysis
General Microbiology Answer: 3
Exotoxins are produced and secreted by bacteria into the surrounding environment. They are typically proteins that can cause damage to the host by disrupting cellular processes. This active secretion distinguishes them from endotoxins, which are part of the bacterial cell wall and are released upon cell lysis.
The period from disease initiation to disease detection in non-infectious disease is called -
1. Incubation period
2. Serial interval
3. Latent period
4. Lag time
Microbiology
Answer: 3
Incubation period: This term is typically used for
infectious diseases and refers to the time between exposure to the
infectious agent and the onset of symptoms.
Serial interval: This refers to the time between
successive cases in a chain of transmission, specifically in infectious
diseases.
Latent period: This is the time from the initiation of
the disease process (or exposure to a risk factor) until the disease is
detectable or until symptoms appear. In non-infectious diseases, this period
can be significant, as the disease may be developing without any noticeable
symptoms.
Lag time: This term can refer to various delays in
processes but is not specifically defined in the context of disease
initiation and detection.
What is the characteristic odor of cultures of proteus bacilli?
1) Fruity
2) Fishy or seminal
3) Sweet
4) Foul
General Microbiology Answer: 2Proteus bacilli are known for their characteristic swarming motility on agar and a distinctive odor, which is often described as fishy or seminal. This is due to the production of ammonia and indole as metabolic byproducts.