Chapter 1: Bacterial morphology, taxonomy, and Gram stain

Question 1

What are the 4 major shapes of bacteria?

Answer 1

1) Cocci - spherical
2) Bacilli - rods (short bacilli are called coccobacilli)
3) Spiral - comma, S, or spiral-shaped
4) Pleomorphic - lacking a distinct shape, like jello

Question 2

What are the 7(+1) classic Gram-positive bugs that cause disease in humans?

Answer 2

1) Streptococcus, 2) Enterococcus
3) Staphylococcus
4) Bacillus
5) Clostridium
6) Corynebacterium
7) Listeria
(8) Mycobacteria (weakly Gram+)

Question 3

What is the morphology of the classic Gram-positive bacteria? (hint: how do you remember the classification)

Answer 3

Of the Gram-positives, 3 are cocci and 4(+1) are rods. 2 are branching filamentous growth

Question 4

What Gram-positive bacteria are cocci? (3)

Answer 4

1) Streptococcus
(2) Enterococcus
3) Staphlococcus

Question 5

What Gram-positive bacteria are bacilli? (4+1)

Answer 5

1) Bacillus
2) Clostridium
3) Corynebacterium
4) Listeria
(5) Mycobacteria (weakly Gram+)

Question 6

Which Gram-positive bacilli form spores? (2)

Answer 6

1) Bacillus

2) Clostridium

Question 7

Which Gram-positive bacilli do not form spores? (2+1)

Answer 7

1) Corynebacterium
2) Listeria
(3) Mycobacteria

Question 8

What is the morphology of Streptococcus?

Answer 8

Gram-positive cocci that form strips

Question 9

What is the morphology of Enterococcus?

Answer 9

Gram-positive cocci that form strips

Question 10

What is the morphology of Staphylococcus?

Answer 10

Gram-positive cocci that form clusters

Question 11

What is the morphology of Bacillus?

Answer 11

Gram-positive rods that form spores

Question 12

What is the morphology of Clostridium?

Answer 12

Gram-positive rods that form spores

Question 13

What is the morphology of Corynebacterium?

Answer 13

Gram-positive rods

Question 14

What is the morphology of Listeria?

Answer 14

Gram-positive rods

Question 15

Which bacteria is weakly Gram-positive?

Answer 15

Mycobacteria

Question 16

Mycobacteria are weakly Gram-positive. What is a better stain for mycobacteria?

Answer 16

Acid-fast stain

Question 17

Acid-fast stain detects which bacteria? Why is it needed?

Answer 17

Mycobacteria, which is weakly Gram-positive.

Question 18

What Gram-negative bacteria are cocci? (2)

Answer 18

1) Neisseria2) Moraxella

Question 19

What Gram-negative bacteria are spirals? (1)

Answer 19

Spirochetes

Question 20

Which bacteria are the spirochetes? (3)

Answer 20

1) Borrelia (Giemsa)
2) Leptospira
3) Treponema

Question 21

What is the morphology of Neisseria?

Answer 21

Gram-negative diplococci

Question 22

What is the morphology of Moraxella?

Answer 22

Gram-negative diplococci

Question 23

What is the morphology of spirochetes?

Answer 23

Gram-negative spirals

Question 24

Can spirochetes be detected by Gram-stain? Why or why not?

Answer 24

Spirochetes have a gram-negative cell wall but are too small to be seen with the light microscope.

Question 25

How can you detect spirochetes?

Answer 25

Spirochetes must be visualized with a special darkfield microscope.Spirochetes have a Gram-negative cell wall but are too small to be seen with the light microscope.

Question 26

Which bacteria is neither Gram-negative nor Gram-positive so does not Gram-stain? Why not?

Answer 26

Mycoplasma lack a cell wall, so they are neither Gram-positive nor Gram-negative.

Question 27

What is the morphology of the Gram-negative bacteria? (hint: how do you remember the classification)

Answer 27

Of the Gram-negatives, 2 are cocci, 1 are spirals, 2 are pleomorphic, and the rest are rods.

Question 28

Which Gram-negative bacteria are pleomorphic? (2)

Answer 28

1) Chlamydia (Giemsa) | 2) Rickettsiae (Giemsa)

Question 29

What is the morphology of mycoplasma?

Answer 29

Neither Gram-positive nor Gram-negative because they lack a cell wall.

Question 30

What structure is composed of small circles of double-stranded DNA adjacent to bacterial DNA?

Answer 30

plasmid

Question 31

What is bacterial DNA?

Answer 31

single circle of double-stranded DNA

Question 32

What is the mechanism of action of erythromycin?

Answer 32

antibiotic that inhibits bacterial protein synthesis at the 50S subunit of the ribosome

Question 33

What is the mechanism of action of tetracycline?

Answer 33

antibiotic that inhibits bacterial protein synthesis at the 30S subunit of the ribosome

Question 34

What antibiotic inhibits bacterial protein synthesis at the 30S subunit of the ribosome?

Answer 34

tetracycline

Question 35

What antibiotic inhibits bacterial protein synthesis at the 50S subunit of the ribosome?

Answer 35

erythromycin

Question 36

Which bacteria do not Gram stain well? (6)

Answer 36

These Microbes May Lack Real Color 1) Treponema 2) Mycobacteria 3) Mycoplasma 4) Legionella 5) Rickettsia 6) Chlamydia

Question 37

Why doesn't Treponema Gram stain well?

Answer 37

it is a spirochete and too thin to be visualized

Question 38

Why doesn't mycobacteria Gram stain well?

Answer 38

high lipid content in cell wall

Question 39

Treponema doesn't Gram stain well. What is a better way to detect treponema? (2)

Answer 39

Darkfield microscopyFluorescent antibody staining

Question 40

Mycobacteria doesn't Gram stain well. What is a better way to detect mycobacteria?

Answer 40

Acid-fast stain : the carbolfuchsin detects the high lipid content in the cell wall

Question 41

Why doesn't mycoplasma Gram stain well?

Answer 41

It lacks a cell wall.

Question 42

Why doesn't Legionella Gram stain well?

Answer 42

It is predominantly intracellular.

Question 43

Legionella doesn't Gram stain well. What is a better way to detect Legionella?

Answer 43

silver stain

Question 44

What bacteria can be detected by acid-fast stain?

Answer 44

Mycobacteria(and weakly Nocardia)

Question 45

What bacteria can be detected by dark-field microscopy?

Answer 45

Treponemes (spirochetes)

Question 46

What bacteria can be detected by silver stain?

Answer 46

Legionella

Question 47

Why doesn't Rickettsia Gram stain well?

Answer 47

it's an intracellular parasite

Question 48

Why doesn't Chlamydia Gram stain well?

Answer 48

It's an intracellular parasite, and lacks muramic acid in its cell wall

Question 49

Which Gram-positive bacteria have morphology of branching filamentous growth? (2)

Answer 49

1) Actinomyces (anaerobic) | 2) Nocardia (weakly acid-fast)

Question 50

What is the morphology of Actinomyces?

Answer 50

Gram-positive branching filamentous growth

Question 51

What is the morphology of Nocardia?

Answer 51

Gram-positive (acid-fast)

Question 52

Which bacteria have unusual cell membranes and cell walls? (3)

Answer 52

1) Mycoplasma 2) Mycobacteria 3) Chlamydia

Question 53

What is unusual about the cell membrane of mycoplasma?

Answer 53

Mycoplasma cell membrane contain sterols

Question 54

The cell membrane of which bacteria contains sterols?

Answer 54

Mycoplasma

Question 55

The cell wall of which bacteria lacks muramic acid and is therefore not sensitive to penicillin?

Answer 55

Chlamydia

Question 56

Which bacteria lacks a cell wall?

Answer 56

Mycoplasma

Question 57

What is unusual about the cell wall of mycoplasma?

Answer 57

Mycoplasma doesn't have a cell wall.

Question 58

What is unusual about the cell membrane of mycobacteria?

Answer 58

It contains mycolic acid

Question 59

What bacteria contain mycolic acid in their cell membrane?

Answer 59

Mycobacteria

Question 60

What is unusual about the cell wall of mycobacteria?

Answer 60

high lipid content

Question 61

Which bacteria have a high lipid content in their cell wall and thus need to be detected by acid fast stain?

Answer 61

Mycobacteria