Test 129  (Microbiology)

1.  The following substances are used in Gram staining:

a. iodine

b. crystal violet

c. alcohol

d. safranin

e. congo red
 

Answer
a.T   b.T   c.T   d.T   e.F
Crystal violet (purple), when applied to bacteria, 
attaches to negatively-charged groups in the cell wall, 
membrane and cytoplasm. The further addition of iodine strengthens this attachment. The addition of alcohol or acetone-alcohol decolourises the crystal violet 
and iodine but causing the stain to diffuse out of the cell. This diffusion is lower in Gram-positive cell walls 
because of the greater thickness and chemical composition (particularly teichoic acids). Safranin or neutral red is then used as a counterstain; this binds to free negatively charged groups that are not already binding to crystal violet

2. Antibiotic resistance in bacteria occurs through:

a. mutation

b. conjugation

c. phagocytosis

d. plasmid transfer

e. spore formation
 

Answer
a.T   b.T   c.F   d.T   e.F

3. Fungi differ from bacteria in that the former:

a. are eukaryotic

b. contain both DNA and RNA

c. contain cell walls

d. can reproduce sexually

e. can form spores
 

Answer
a.T   b.F   c.F   d.T   e.F
Both fungi and bacteria contain DNA and RNA, 
cell walls and ability to form spores. Fungi are 
eukaryotic (containing nuclear membrane) and 
bacteria are prokaryotic. Fungi can reproduce
sexually whereas bacteria reproduce through binary division.

4. Chlamydia:

a. possess a Gram negative cell wall

b. contain muramic acid in the cell wall

c. are obligate intracellular parasites

d. can not grow in inanimate media

e. appear as basophilic intracytoplasmic inclusion bodies 
    on Giemsa stain
 

Answer
a.T   b.F   c.T   d.T   e.T
Chlamydia possess a Gram-negative cell wall which lacks muramic acid and a peptidoglycan layer. They 
are obligate intracellular parasites which reproduce by the formation of elementary and reticulate bodies. .

5. The following organisms are common causes of endophthalmitis 
    following cataract surgery:

a. Staphylococcus aureus

b. Candidiasis albican

c. Streptococcal species

d. Bacillus species

e. Neisseria species
 

Answer
a.T   b.F   c.T   d.F   e.F
Streptococcus and staphylococcus species are the 
most common causes of endophthalmitis following 
cataract surgery. Bacillus species are common following trauma.

 

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