BIO2071_Microbiology Laboratory Review Sheet Week 8 Exercise 21.5 Questions 1. Differentiate the microscopic morphology of streptococci and pneumococci as seen by Gram stain. 2. What type of hemolysis...

1. Differentiate the microscopic morphology of Streptococci and Pneumococci as seen by
Gram stain.
Gram staining can be defined as; an quite effective methodology to get an idea about the
morphology of microorganisms for instance; in case of Pneumococci we may observe lancet
shape organisms present in the form of pairs or in short chains whereas; Streptococci may reflect
a long chain arrangement usually.
2. What type of hemolysis is produced by S. pneumoniae?
Hemolysins are exotoxins that cause the destruction of erythrocytes. After inoculation of
bacteria onto blood agar there could be observed a zone around the budding colonies of microbes
and this zone may prove to be helpful in determination of the type of hemolysis performed via
microbial cells. For example; in case of S. pneumoniae, a greenish region could be found around
the bacterial colony which can result from the incomplete destruction of the erythrocytes and
referred as; alpha hemolysis.
3. How is S. pneumoniae distinguished from other streptococci with the same hemolytic
properties?
Following test may be performed for the purpose:
Bile Solubility
Streptococcus pneumoniae contains autolytic enzymes which might be induced with the
assistance of sodium deoxycholate (bile). When a drop of 2% sodium deoxycholate is added
to the exterior of a lonely colony of alpha-hemolytic streptococcus on sheep blood agar
then after incubation period of 30 minutes (during which cells are kept at 35° C) the colonies of
Streptococcus pneumoniae may get disappear.
4. What is the quelling reaction?
It’s used for the purpose of identification of Streptococcus pneumoniae in body fluids (or
in culture). For the experiment, a tiny drop of bacterial suspension is positioned on a glass slide
and mixed with a S. pneumoniae-specific antiserum. Subsequently, addition of Aq. methylene
blue suspension is performed so that, development of contrast could become possible. Afterward,
the slide is permitted to sit with a cover slip in position for approximately 10 minutes. If as a
consequence, the swelling of capsule could be noticed then it can confirm the presence of
Streptococcus pneumoniae.
5. What role does a bacterial capsule play in infection?
Capsule might perform numerous roles but, its most significant function is protecting the
bacterium from drying out and to save it from phagocytosis. Thus; capsule works as a key
virulence factor during the infection procedure of several pathogens for instance; Escherichia
coli and Streptococcus pneumoniae.
6. What kind of culture media and atmospheric and incubation conditions are best for
cultivating streptococci?
Streptococci is a Gram-positive catalase-negative microbe which can produce H2O2
through a flavoenzyme system so, could reflect better growth in presence of a source of
catalase for instance; Red Blood Cells. Its growth can also be induced via addition of choline and
reducing agents in defined media. In addition, its most strains need vitamin B complex, adenine,
guanine, uracil and 7-10 amino acids for the purpose of growth. Besides, the optimum pH for its
growth is 7.8 (range: 6.5–8.3).
7. Why is blood agar considered a differential medium?
A growth medium might be called differential if it can prove to be helpful in the detection
of specific microbes. Blood agar (BAP) may be used to get an idea about the presence of
clinically significant bacteria from throat and sputum cultures. Its differential nature is because
of presence of sheep blood in it. In fact, there are certain bacteria which can produce exotoxins
known as; hemolysins that may act on Red Blood Cells present in this medium and can lyse
them. This lytic reaction may indicate towards the presence of such microbes.
8. What is the function of a candle jar?
Candle jar contains a lid which works as a gas-tight seal in which a small white candle is...