Medical Microbiology: Bacteriology Questions With
Complete Solutions
alpha-hemolytic streptococci are the main cause of what?
Caries or cavities.
A patient with sickle cell disease usually gets osteomyelitis from
what pathogen?
Salmonella
What is a gram stain? What is the difference between gram (+)
and gram (-)?
1. Gram (+) is purple, Gram negative will stain pink or red, P
for purple and positive.
2. All gram stained bacteria are dead
3. We don’t look at bacteria when they are alive because they
are invisible, that is why we stain them.
Describe the process of gram staining.
stain with crystal violet iodine, rinsed in alcohol-acetone, then
stained with red dye (saffranin).
CIAS
,Describe the color changes when gram staining a gram (+) cell.
CIAS
At fixation it is white.
1. Primary stain is Crystal Violet - Purple
2. Mordant: Iodine- Purple
3. Decolorizer: Alcohol Acetone- Purple
4. Counterstain: Safranin- Purple
Describe the color changes when gram staining a gram (-) cell.
CIAS
1. Primary stain is Crystal Violet - Purple
2. Mordant: Iodine- Purple
3. Decolorizer: Alcohol Acetone- Colorless
4. Counterstain: Safranin- Red
,What is the difference between Gram positive and gram
negative?
1. Gram-negative bacteria are surrounded by
a thin peptidoglycan cell wall, which itself is surrounded by an
outer membrane containing lipopolysaccharide.
2. Gram-positive bacteria lack an outer membrane but are
surrounded by layers of peptidoglycan many times thicker than
is found in the Gram-negatives.
Name the bacteria types with unusual cell walls
1. Mycoplasma, Ureaplasma
-Contains sterols on the cell membrane
-No cell Wall
2. Chlamydia
-Cell wall lacks muramic acid- just a structural component of
cell walls.
3. Mycobacterium
-Cell wall contains mycolic acid which makes them less
susceptible to antibiotics.
What are fimbriae? What are they also called? What is their
function(s)? What bacteria use them?
, 1. Fimbriae AKA (pili) are hairlike structures on the outside of
bacteria; composed of protein subunits (pilin).
2. They allow attachment and are important for bacterial
pathogenesis (eg, E. coli attaching and N.
gonorrhoeae attaching to uroepithelial cells).
What bacteria use fimbriae? What are the functions of fimbriae?
Name the 2 types of fimbriae and how they work.
1. Only on Gram (-) bacteria (except Streptococcus) which is
gram (+).
2. There are 2 types of fimbriae, Somatic (adhesion-virulence
factor) and Sex (longer for conjunction, used to transfer DNA
from one cell to another)
What are the 2 types of fimbriae? What are their functions?
There are 2 types of fimbriae, Only on Gram (-)
bacteria (except Streptococcus) which is gram (+).
Somatic (adhesion-virulence factor)
Sex (longer for conjunction, used to transfer DNA from one cell
to another)
Complete Solutions
alpha-hemolytic streptococci are the main cause of what?
Caries or cavities.
A patient with sickle cell disease usually gets osteomyelitis from
what pathogen?
Salmonella
What is a gram stain? What is the difference between gram (+)
and gram (-)?
1. Gram (+) is purple, Gram negative will stain pink or red, P
for purple and positive.
2. All gram stained bacteria are dead
3. We don’t look at bacteria when they are alive because they
are invisible, that is why we stain them.
Describe the process of gram staining.
stain with crystal violet iodine, rinsed in alcohol-acetone, then
stained with red dye (saffranin).
CIAS
,Describe the color changes when gram staining a gram (+) cell.
CIAS
At fixation it is white.
1. Primary stain is Crystal Violet - Purple
2. Mordant: Iodine- Purple
3. Decolorizer: Alcohol Acetone- Purple
4. Counterstain: Safranin- Purple
Describe the color changes when gram staining a gram (-) cell.
CIAS
1. Primary stain is Crystal Violet - Purple
2. Mordant: Iodine- Purple
3. Decolorizer: Alcohol Acetone- Colorless
4. Counterstain: Safranin- Red
,What is the difference between Gram positive and gram
negative?
1. Gram-negative bacteria are surrounded by
a thin peptidoglycan cell wall, which itself is surrounded by an
outer membrane containing lipopolysaccharide.
2. Gram-positive bacteria lack an outer membrane but are
surrounded by layers of peptidoglycan many times thicker than
is found in the Gram-negatives.
Name the bacteria types with unusual cell walls
1. Mycoplasma, Ureaplasma
-Contains sterols on the cell membrane
-No cell Wall
2. Chlamydia
-Cell wall lacks muramic acid- just a structural component of
cell walls.
3. Mycobacterium
-Cell wall contains mycolic acid which makes them less
susceptible to antibiotics.
What are fimbriae? What are they also called? What is their
function(s)? What bacteria use them?
, 1. Fimbriae AKA (pili) are hairlike structures on the outside of
bacteria; composed of protein subunits (pilin).
2. They allow attachment and are important for bacterial
pathogenesis (eg, E. coli attaching and N.
gonorrhoeae attaching to uroepithelial cells).
What bacteria use fimbriae? What are the functions of fimbriae?
Name the 2 types of fimbriae and how they work.
1. Only on Gram (-) bacteria (except Streptococcus) which is
gram (+).
2. There are 2 types of fimbriae, Somatic (adhesion-virulence
factor) and Sex (longer for conjunction, used to transfer DNA
from one cell to another)
What are the 2 types of fimbriae? What are their functions?
There are 2 types of fimbriae, Only on Gram (-)
bacteria (except Streptococcus) which is gram (+).
Somatic (adhesion-virulence factor)
Sex (longer for conjunction, used to transfer DNA from one cell
to another)
