Introduction to Bacteriology I

Question 1

What accounts for the purple staining of gram + organisms relative to gram -?

Answer 1

1. cell wall peptidoglycan layer is thicker in gram +–> teichoic acid cross-linkages–> resists alcohol decolourization step
2. magnesium ribonucleate in gram + cell wall–> affinity for crystal-violet-iodine complex
3. gram + cell wall less permeable bc less lipid

Question 2

What are the uses of the gram stain for microbes?

Answer 2

1. basis for empiric antibiotic therapy
2. identifying non-bacterial microbes (ex. fungi..yeast)
3. assessing specimen adequacy (may be contaminated with normal flora/cells)

Question 3

Describe Staphylococcus spp. in terms of : Gram stain, shape, respiration, pattern

Answer 3

• GP
• cocci
• Aerobic
• clusters

Question 4

What are the 2 major groups of important Staphylococcus species and examples of each

Answer 4

1. S. aureus:
   - MRSA
2. Coagulase-negative staphylococci:
   - S. epidermitidis
   - S. lugdunensis
   - S. saprophyticus

Question 5

Describe Streptococcus spp.:

What does it look most like?

Answer 5

• GP
• cocci
• aerobic
• chains

*looks like enterococcus

Question 6

List 2 major groups of Streptococcus spp. and examples of each:

Answer 6

1. Beta-hemolytic streptococci-red/orange halo:
   - S. pyogenes (Group A Strep) **short chains
   - S. agalactiae (Group B Strep)
2. Alpha-hemolytic streptococci- green halo:
   - S. pneumoniae **diplococci, lancet-shape
   - Viridans group strep **long chains

Question 7

Describe Enterococcus spp.:

Answer 7

• GP
• Cocci
• chains
• aerobic

Question 8

List important Enterococcus spp.:

Answer 8

• E faecium
• E faecalis
• Vancomycin-resistant E. faecium (VRE)
• Vancomycin-resistant E. faecalis (VRE)

Question 9

What 2 GP bacilli do we need to know? (both are aerobic)

Answer 9

• Corynebacterium spp.

- Bacillus spp.

Question 10

What do Corynebacterium look like (describe):

Answer 10

• GP
• Bacilli
• shaped like letters/palisades
• aerobic

Question 11

What are important Corynebacterium spp?

Answer 11

• C. jeikeium
• C. urealyticum
• C. diphtheriae (uncommon)
• ‘diphtheroids’

Question 12

Describe Bacillus spp.:

Answer 12

• GP
• Bacillus
• singular
• aerobic

Question 13

List important Bacillus spp. :

Answer 13

• B. anthracis (uncommon)

- other species part of normal skin flora

Question 14

Describe Escherichia coli

Answer 14

• GN
• Bacillus
• singular
• aerobic

Question 15

List important enterobacteriaceae (enteric GNs)

Answer 15

• Escherichia coli
• Klebsiella pneumoniae
• Enterobacter spp.
• Citrobacter spp.
• Proteus spp.
• Salmonella spp.
• Shigella spp.

Question 16

Describe Haemophilus spp.:

Answer 16

• GN
• coccobacilli
• singular
• aerobic

Question 17

List the one important Haemophilus spp.:

Answer 17

-H. influenzae

Question 18

Describe Neisseria spp.:

Answer 18

• GN
• Cocci
• Diplococci
• aerobic

*coffee bean shaped

Question 19

List the important Neisseria spp.:

Answer 19

• Neisseria meningitidis
• Neisseria gonorrhoeae
• non-pathogenic Neisseria spp.

Question 20

Describe Clostridium spp. :

Answer 20

• GP
• Bacilli
• pairs
• anaerobic

Question 21

List the important Clostridium spp.:

Answer 21

• C. tetani
• C. botulinum
• C. perfringens
• C. difficile

Question 22

Describe Becteroides spp.:

Answer 22

• GN
• Bacilli
• clusters
• anaerobic (strict i.e. die in O2)