MDS PREP
Which of the following is a killed viral vaccine?
1) Sabin vaccine for poliomyelitis
2) Salk vaccine for poliomyelitis
3) MMR vaccine for measles, mumps, rubella
4) Varicella-zoster
General Microbiology Answer: 2
The Salk vaccine for poliomyelitis is a killed viral vaccine, effectively preventing the disease by using inactivated poliovirus.
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 characteristic of the spore formation in C1. Perfringens?
1) Central or equatorial spores, giving the bacillus a spindle shape
2) Subterminal spores, causing the bacillus to appear club shaped
3) Oval and terminal spores, resembling a tennis racket
4) Spherical and terminal spores, resulting in a drumstick appearance
General Microbiology Answer: 3
C1. Perfringens forms subterminal spores, which cause the bacillus to appear club-shaped under the microscope. The tennis racket appearance is not a characteristic of C1. Perfringens spore formation.
Which of the following is a characteristic of amoebic dysentery?
1) More than 10 motions a day
2) Small, odorless stools
3) Dark red, copious stools
4) Presence of Charcot-Leyden crystals
Amoebic dysentery is characterized by more than 10 motions a day and the presence of Charcot-Leyden crystals.
What is the significance of HLA class I antigens in the context of graft rejection and cell mediated cytolysis?
1) They are only involved in cell-to-cell recognition in the immune system.
2) They are the principal antigens that induce an immune response in the host against transplanted tissues.
3) They have no role in graft rejection or cell-mediated immunity.
4) They are only involved in the innate immune response.
HLA class I antigens are the principal antigens that induce an immune response in the host against transplanted tissues.
What is the typical microscopic finding in amoebic dysentery?
1) Numerous pus cells
2) Abundant Charcot-Leyden crystals
3) Many motile bacteria
4) Abundant pyknotic bodies
The typical microscopic finding in amoebic dysentery includes numerous pus cells and abundant Charcot-Leyden crystals.
Which of the following is NOT a typical anaerobe found in human microbiota?
1) C1. Perfringens
2) C1. Tetani
3) C1. Difficule
4) C1. Botulinum
General Microbiology Answer: 2
C1. Tetani (Clostridium tetani) It is a spore-forming, gram-positive
bacillus that causes tetanus, a neurological disorder resulting from the
production of tetanospasmin, a toxin that affects the nervous system. It is
usually found in soil, dust, and manure, and enters the body through breaks in
the skin.
C1. Perfringens (Clostridium perfringens) is an anaerobic, gram-positive
bacillus commonly found in the gastrointestinal tract and soil. It can be a part
of the normal flora in the intestines and is also a pathogen, causing diseases
such as food poisoning and gas gangrene.
C1. Difficule (Clostridium difficule) is an anaerobic, gram-positive
spore-forming bacillus that is part of the human gut microbiota. It is notorious
for causing antibiotic-associated diarrhea and pseudomembranous colitis.
C1. Botulinum (Clostridium botulinum) is an anaerobic, spore-forming,
gram-positive bacillus found in various environments, including soil and water.
It is known for producing the neurotoxin that causes botulism, a rare but severe
form of food poisoning.
The destruction of microorganisms on living tissues, as long as there is contact between the tissues and the antimicrobial agent, denotes
1. sterilization
2. antisepsis
3. sanitization
4. none of the above
Microbiology
Answer: 2
The destruction of microorganisms on living tissues, as long as there is contact between the tissues and the antimicrobial agent, denotes antisepsis (option 2). Antisepsis refers to the application of antimicrobial agents to living tissues to reduce the possibility of infection, sepsis, or putrefaction.
Sterilization:
This is the process of completely eliminating all forms of microbial
life, including bacteria, viruses, fungi, and spores, from an object or
surface. Sterilization is typically achieved through methods such as
autoclaving (steam under pressure), dry heat, chemical sterilants, or
radiation. Sterilization is used for medical instruments, laboratory
equipment, and other items that must be free of all microorganisms.
Antisepsis:
Antisepsis refers to the application of antimicrobial agents to
living tissues to reduce the risk of infection, sepsis, or putrefaction.
Antiseptics are used on skin and mucous membranes to prevent infection
during surgical procedures, wound care, and other medical interventions.
Common antiseptics include alcohol, iodine solutions, and chlorhexidine.
Sanitization:
Sanitization is the process of reducing the number of microorganisms
on surfaces or objects to a level considered safe by public health
standards. This does not necessarily eliminate all microorganisms but
reduces them to a level that minimizes the risk of infection or disease.
Sanitization is commonly used in food service, public restrooms, and
other environments where hygiene is important.