MDS PREP
What reaction is tested by adding concentrated sulfuric acid to a 24-hour peptone water culture?
1) Indole reaction
2) Cholera red reaction
3) Nitrate reduction
4) Coproantibody reaction
General Microbiology Answer: 2The reaction tested by adding concentrated sulfuric acid to a 24-hour peptone water culture is Cholera red reaction, This reaction tests for the presence of cholera vibrios, which produce hydrogen sulfide gas when their culture is acidified with sulfuric acid. The gas reacts with the ferric chloride present in the medium to produce a characteristic red color.
Which of the following is a distinguishing feature of orthomyxoviruses?
1) Single linear RNA
2) 80-120 nm in size
3) Hemolysin present
4) Cytoplasmic replication
General Microbiology Answer: 2Orthomyxoviruses, which include the influenza viruses, are characterized by their single-stranded RNA genome. This feature distinguishes them from other virus families that may have different types of genetic material. Orthomyxoviruses are distinguished by their single linear RNA genome, which is essential for their replication and pathogenicity.
What is the primary mode of action of exotoxins?
1) Enzymatic
2) Non-enzymatic
3) Structural disruption
4) Inhibition of protein synthesis
General Microbiology Answer: 1
The primary mode of action of exotoxins is enzymatic, as they often act as enzymes that modify or damage host cell functions.
The main tool for detection of "cases" of tuberculosis is -
1. Sputum examination
2. Mantoux test
3. Chest X-ray
4. All of the above
Microbiology
Answer: 1
The main tool for the detection of "cases" of tuberculosis is 1.
Sputum examination.
Explanation of Each Option:
Sputum examination: This is the primary method for
diagnosing active pulmonary tuberculosis. Sputum samples are collected and
examined for the presence of Mycobacterium tuberculosis through
microscopy (e.g., acid-fast bacilli staining) and culture methods. It is
considered the gold standard for confirming active TB cases.
Mantoux test: Also known as the tuberculin skin test,
this test is used to determine if a person has been exposed to the
tuberculosis bacteria. However, it does not diagnose active TB; rather, it
indicates whether a person has been infected with the bacteria at some
point.
Chest X-ray: While chest X-rays are important for
identifying lung abnormalities associated with tuberculosis and can support
the diagnosis, they are not definitive for detecting the bacteria itself.
They are often used in conjunction with sputum examination.
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 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 causative agent of dentoalveolar abscess?
1) Prevotella intermedia
2) P. melaninogenicus
3) Porphyromonas gingivalis
4) Fusobacterium nucleatum
General Microbiology Answer: 2Prevotella intermedia and P. melaninogenicus (now known as Aggregatibacter actinomycetemcomitans) are both anaerobic bacteria that can be found in the oral cavity and are involved in the pathogenesis of periodontal diseases, including dentoalveolar abscesses. Fusobacterium nucleatum is another anaerobic bacterium commonly found in dental plaque and is associated with various oral infections, including dentoalveolar abscesses.
A bacterial disease with oral manifestations is
1. Herpes Measles
2. Measles
3. Diphtheria
4. Leishmaniasis
Microbiology
Answer: 4
Diphtheria serious bacterial infection that usually affects the mucous
membranes of the nose and throat.
Diphtheria signs and symptoms usually begin 2 to 5 days after a person becomes
infected. Signs and symptoms may include:
A thick, gray membrane covering the throat and tonsils
A sore throat and hoarseness
Swollen glands (enlarged lymph nodes) in the neck
Difficulty breathing or rapid breathing
Nasal discharge
Fever and chills
Tiredness
Skin (cutaneous) diphtheria
A second type of diphtheria can affect the skin, causing pain, redness and
swelling similar to other bacterial skin infections. Ulcers covered by a gray
membrane also may be a sign of skin diphtheria.