MDS PREP
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.
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.
In bacillary dysentery, what is the typical stool consistency?
1) Not adherent to the container
2) Adherent to the container
3) Watery
4) Mucous
In bacillary dysentery, the stool is typically adherent to the container due to the presence of mucus and pus.
Which of the following bacteriophage types of diphtheria bacilli are associated with avirulent strains?
1) Type I and II
2) Type IV and VI
3) Type III
4) Type VII
Type VII bacteriophage types of diphtheria bacilli are associated with avirulent strains.
Most bacterial endotoxins are composed of
1. pure carbohydrates
2. mucoprotein complexes
3. pure lipids
4. lipoprotein-polysaccharide complexes
Microbiology
Answer: 4
Most bacterial endotoxins are composed of lipoprotein-polysaccharide complexes
What does the Vi antigen of S. typhi confer upon the bacterium?
1) Resistance to antibiotics
2) Increased invasiveness
3) Resistance to phagocytosis
4) Resistance to acidic environment
General Microbiology Answer: 3the Vi antigen of S. typhi confers upon the bacterium Resistance to phagocytosis. The Vi antigen is a polysaccharide capsule that protects the bacteria from being engulfed and destroyed by phagocytic white blood cells, contributing to its virulence.
Which medium is suitable for the transport of Salmonella and Shigella?
1) Cary-Blair medium
2) Thiosulfate-citrate-bile salts-sucrose (TCBS) agar
3) Hektoen enteric (HE) agar
4) Blood agar
General Microbiology Answer: 1the medium suitable for the transport of Salmonella and Shigella is Cary-Blair mediumx. This medium is designed to maintain the viability of these organisms during transport and is selective for enteric pathogens by inhibiting the growth of other non-target bacteria. TCBS agar and HE agar are used for the selective isolation and growth of these organisms, while blood agar is a general purpose medium used for various bacteria.
What is a characteristic feature of Streptococcus viridans?
1) Capsulated, oval-shaped cells
2) Non-capsulated, round to oval cells in chains
3) Positive oxidase reaction
4) Negative oxidase reaction
Streptococcus viridans is characterized by non-capsulated, round to oval cells in chains and has a negative oxidase reaction.