MDS PREP
What is the typical color of Salmonella colonies on MacConkey agar, except for Sh. Sonnei?
1) Colorless
2) Pink
3) Red
4) Yellow
General Microbiology Answer: 1Salmonella species, excluding Shigella sonnei, which is lactose non-fermenting, will ferment lactose in MacConkey agar, turning the colonies pink due to the formation of acidic end-products
What is the effect of Actinomycin D on orthomyxoviruses?
1) Stimulates multiplication
2) Inhibits multiplication
3) No effect
4) Enhances stability
General Microbiology Answer: 2Actinomycin D is an antibiotic that inhibits RNA synthesis. In the case of orthomyxoviruses, it effectively inhibits their multiplication by preventing the transcription of viral RNA, thereby blocking the virus ability to replicate. Actinomycin D inhibits the multiplication of orthomyxoviruses by blocking RNA synthesis, which is crucial for viral replication.
Which of the following hepatitis viruses has a single-stranded RNA genome?
1) Hepatitis A
2) Hepatitis B
3) Hepatitis C
4) Hepatitis D
General Microbiology Answer: 1Hepatitis C virus (HCV) is known for its single-stranded RNA genome. This characteristic is crucial for its classification and understanding its replication cycle, which involves RNA-dependent RNA polymerase.
Which of the following statements about the fermentation of sugars by Anthracoid bacilli is true?
1) Anthracoid bacilli ferment glucose, maltose, lactose, and sucrose, producing acid and gas.
2) Anthracoid bacilli do not ferment glucose but ferment maltose, lactose, and sucrose.
3) Anthracoid bacilli only ferment glucose.
4) Anthracoid bacilli ferment glucose, maltose, and lactose, but not sucrose.
Anthracoid bacilli ferment glucose, maltose, lactose, and sucrose, producing acid and gas.
Which of the following is a characteristic microscopic feature of amoebic dysentery that distinguishes it from bacillary dysentery?
1) Presence of RBCs in the stool
2) Presence of pus cells in the stool
3) Presence of Charcot-Leyden crystals
4) Presence of ghost cells
General Microbiology Answer: 3
Amoebic dysentery, caused by the protozoan parasite Entamoeba histolytica, is characterized by the presence of ghost cells in the stool. Ghost cells are the remnants of red blood cells that have been phagocytosed by the amoeba. These cells are ingested and their cytoplasm is removed, leaving only the cell membrane, which gives them a "ghost-like" appearance under the microscope. This feature helps distinguish amoebic dysentery from bacillary dysentery, which is caused by bacteria such as Shigella species. Bacillary dysentery typically shows the presence of white blood cells (pus cells) and red blood cells in the stool, but not ghost cells.
What is the typical macroscopic appearance of the stool in cases of amoebic dysentery compared to bacillary dysentery?
1) Amoebic dysentery stool is small and odorless, while bacillary dysentery stool is copious and offensive.
2) Both amoebic and bacillary dysentery stools are copious and offensive.
3) Amoebic dysentery stool is dark red and acidic, while bacillary dysentery stool is bright red and alkaline.
4) Amoebic dysentery stool is bright red and alkaline, while bacillary dysentery stool is dark red and acidic.
Amoebic dysentery stool is typically dark red and acidic, while bacillary dysentery stool is bright red and alkaline.
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.
What type of antibodies are known as "coproantibodies"?
1) IgA
2) IgM
3) IgG
4) Antibodies found in feces
General Microbiology Answer: 4Copro antibodies are antibodies found in feces These are typically IgA antibodies that are produced in response to infections in the gastrointestinal tract, including typhoid fever. They can be detected in stool samples and are used in diagnostic tests.