Classification of bacteria

Question 1

What shape are bacilli ?

Answer 1

Rod shaped

Question 2

What shape are cocci ?

Answer 2

Round/Spherical

Question 3

What are the two structural types of cocci and what are their structures ?

Answer 3

Staphylococci and Streptococci.
Staphylococci are clusters
Streptococci are chains.

Question 4

Name the three sub categories of Streptococci and give examples for each.

Answer 4

Alpha haemolytic - Streptococci Pneumoniae
- Streptococci Viridans
Beta haemolytic - Streptococci Pyogenes
- Streptococci Agalactiae
Non haemolytic - Enterococci

Question 5

What does alpha haemolytic streptococci do to blood agar ?

Answer 5

Turns it green

Question 6

What does beta haemolytic streptococci do to blood agar ?

Answer 6

Turns it clear

Question 7

What test is used to distinguish Staphylococci ?

Answer 7

Coagulase test

Question 8

What strain of bacteria is coagulase positive ?

Answer 8

Staphylococci Aureus

Question 9

What are the three gram positive anaerobic bacilli ?

Answer 9

Clostridium tetani
Clostridium perfringens
Clostridium difficile

Question 10

Name the strict aerobic gram negative bacilli

Answer 10

Pseudomonas aeruginosa

Question 11

Name the gram negative diplococci

Answer 11

Neisseria meningitidis

Neisseria gonorrhoeae

Question 12

Name the small bacilli which is gram negative

Answer 12

Haemophilus influenzae

Question 13

There are two categories of large aerobic bacilli. What are they and give examples of each.

Answer 13

Gut commensals:
E.Coli
Proteus
Klebsiella

Gut pathogens:
E.coli 0157
Shigella
Salmonella

Question 14

What are the two microaerophilic bacteria ? Mention their shape too.

Answer 14

Campylobacter - small curved bacilli

Helicobacter - spiral bacilli

Question 15

Name the strict anaerobic gram negative bacilli

Answer 15

Bacteriodes

Question 16

Explain what colour gram positive bacteria are under the gram stain and why this is the case.

Answer 16

Gram positive bacteria take up the crystal violet stain, which appears purple when seen under the microscope. They have a thick peptidoglycan layer in the cell wall which retains the stain even after washing.

Question 17

Explain what colour gram negative bacteria are under the gram stain and why this is the case.

Answer 17

Gram negative bacteria take up the crystal violet stain. However they do not retain this stain after washing, because they have liposaccharides in their cell wall which dissolve from the alcohol used in the washing. Thus they don’t retain the stain and appear red/pink in colour.

Question 18

What are the three pathogens which cant be cultured well nor can be stained using the gram stain technique ?

Answer 18

Mycobacterium
Spirochaetes
Chlamydia

Question 19

What stain is used to see mycobacterium

Answer 19

ZN stain

Question 20

What causes TB and what causes leprosy ?

Answer 20

TB - mycobacterium tuberculosis

Leprosy - mycobacterium leprae

Question 21

What is the shape of spirochaetes and how are they diagnosed ?

Answer 21

They are long and spiral shaped bacteria.

They are diagnosed using serology

Question 22

How is Chlamydia diagnosed and why only that method ?

Answer 22

Using serology because they don’t grow in cell lines

Question 23

What are the groups of beta haemolytic bacteria, and which are the important ones ?

Answer 23

Groups A-G

Groups A, B and D are the important ones