MDS PREP
What is the primary mechanism of action of the PCR test in diagnosing HIV infection?
1) Amplification of viral RNA or DNA
2) Detection of specific antibodies to HIV
3) Detection of the HIV virus directly
4) Measurement of the immune response to the virus
General Microbiology Answer: 1
The primary mechanism of action of the PCR test in diagnosing HIV infection is the amplification of viral RNA or DNA, allowing for the detection of the virus.
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.
Which of the following is a characteristic of endotoxins that makes them distinct from exotoxins?
1) They are heat labile
2) They are actively secreted by bacterial cells
3) They are proteins
4) They are part of the bacterial cell wall
General Microbiology Answer: 4
Endotoxins are components of the outer membrane of Gram-negative bacteria and are released when the bacteria die or divide. This structural characteristic differentiates them from exotoxins, which are secreted by living bacteria.
What is a key characteristic of the colonies formed by Streptococcus pneumoniae?
1) Dome-shaped
2) Initially dome-shaped, later draughtsman colonies
3) Granular turbidity with a powdery deposit
4) Not typically seen in culture
Streptococcus pneumoniae colonies are initially dome-shaped and later develop draughtsman colonies.
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 role of the Vi antigen in the pathogenesis of typhoid fever?
1) It aids in colonization of the intestinal mucosa.
2) It confers resistance to antibiotics.
3) It is involved in the production of toxins.
4) It allows the bacteria to evade the host's immune response by inhibiting phagocytosis.
General Microbiology Answer: 4The role of the Vi antigen in the pathogenesis of typhoid fever is it allows the bacteria to evade the hosts immune response by inhibiting phagocytosis: The Vi antigen is a polysaccharide capsule found in some strains of S. typhi that helps the bacteria avoid phagocytosis by host immune cells. This contributes to the bacterias ability to survive and proliferate within the human body.
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.