Bacterial classification and identification (midterm)

Question 1

What are the taxonomic ranks of bacterial classification?

Answer 1

Kingdom/domain
Phylum/division
Class
Order
Family
Genus
species

Question 2

What methods are used to identify bacteria?

Answer 2

Phenotype: morphology, microscopy, biochemistry
Immunological/serological tests: specific Ig
Genotype: PCR
Bacteriophage typing

Question 3

What microscopic techniques are used to identify bacteria?

Answer 3

Hanging drop method (motility)
Simple staining, e.g. methylene blue
Gram stain (G+ and G–)
Ziehl–Neelsen stain (acid fast)

Question 4

What macroscopic techniques are used to identify bacteria?

Answer 4

Hemolysis
Pigment production
Colonial morphology

Question 5

Describe hemolysis on blood agar

Answer 5

β (complete): Staphylococcus aureus, Streptococcus pyogenes
α (partial): Streptococcus viridans, Streptococcus pneumoniae (pneumococcus)
γ (none): Enterococci

Question 6

Which bacteria perform complete (β) hemolysis?

Answer 6

Staphylococcus aureus
Streptococcus pyogenes

Question 7

Which bacteria perform partial (α) hemolysis?

Answer 7

Streptococcus pneumoniae (pneumococcus)
Streptococcus viridans

Question 8

Which bacteria perform no hemolysis (γ)?

Answer 8

Enterococci

Question 9

Describe pigment production

Answer 9

Endopigment: Staphylococcus aureus (yellow), Staphylococcus epidermidis (white)
Exopigment: Pseudomonas aeruginosa (green)

Question 10

Which bacteria release yellow endopigment?

Answer 10

Staphylococcus aureus

Question 11

Which bacteria release white endopigment?

Answer 11

Staphylococcus epidermidis

Question 12

Which bacteria release green exopigment?

Answer 12

Pseudomonas aeruginosa

Question 13

Outline colonial morphology

Answer 13

Colony form: pinpoint, circular, filamentous, irregular
Colony elevation: flat, raised, convex
Colony margin: smooth, irregular

Question 14

Outline microscopic colonial morphology

Answer 14

Diplococci: pairs
Streptococci: chains
Staphylococci: bundles/clusters
Sarcina: tetrads
Bacillus: like E. coli
Vibrio: comma shaped
Spirillum: spiral
Actinomyces: filamentous

Question 15

What types of diseases do spiral bacteria tend to cause?

Answer 15

Systemic diseases

Question 16

What types of diseases to filamentous bacteria tend to cause?

Answer 16

Chronic diseases

Question 17

What types of diseases do G+ bacteria tend to cause?

Answer 17

Skin infections

Question 18

Describe the Durham test

Answer 18

Glucose broth with Durham tubes
Red → yellow: acid fermentation
Red → yellow with gas: acid fermentation with gas production
Red: no acid fermentation

Question 19

Describe the IMViC/indole test

Answer 19

Production of indole from Trp, detected with Kovac’s reagent
Red/pink ring: positive
Yellow ring: negative

Question 20

What bacteria give a positive indole test?

Answer 20

E. coli

Question 21

What bacteria give a negative indole test?

Answer 21

Klebsiella

Question 22

Describe the methyl red reaction (MR) test

Answer 22

Detection of acid fermentation using methyl red
Yellow → red: positive
Yellow: negative

Question 23

What bacteria give a positive MR test?

Answer 23

E. coli

Question 24

What bacteria give a negative MR test?

Answer 24

Klebsiella

Question 25

Describe the Voges–Proskaur reaction (VP) test

Answer 25

Detection of acetyl methyl carbinol from glucose fermentation using KOH Yellow → pink: positive Yellow: negative

Question 26

What bacteria give a positive VP test?

Answer 26

*Klebsiella*

Question 27

What bacteria give a negative VP test?

Answer 27

*E. coli*

Question 28

Describe the H₂S test

Answer 28

Detection of sulfur reduction to H₂S using sulfide-indole-motility (SIM medium) and triple sugar iron agar (TSIA) Blackening: positive No blackening: negative

Question 29

What bacteria give a positive H₂S test?

Answer 29

Enterobacteriaceae, especially *Salmonella*, *Francisella*, *Proteus*

Question 30

What bacteria give a negative H2S test?

Answer 30

Most G– bacilli

Question 31

Describe the citrate utilization test

Answer 31

Detection of the enzyme citrase (citrate → OAA + acetate) using Simmons citrate agar Green → blue: positive Green: negative

Question 32

Which bacteria are differentiated by the citrate utilization test?

Answer 32

Presence of species of the Enterobacteriaceae family

Question 33

Describe the urease test

Answer 33

Detection of the enzyme urease (urea → NH3) by change in pH Yellow → pink: positive Yellow: negative

Question 34

What bacteria give a positive urease test?

Answer 34

*Proteus vulgaris*

Question 35

What bacteria give a negative urease test?

Answer 35

*E. coli*

Question 36

Describe the oxidase test

Answer 36

Detection of the enzyme oxidase using the oxidase reagent Colorless → purple: positive Colorless: negative

Question 37

What bacteria give a positive oxidase test?

Answer 37

*Pseudomonas*

Question 38

What bacteria give a negative oxidase test?

Answer 38

All Enterobacteriaceae members

Question 39

Describe the catalase test

Answer 39

Detection of the enzyme catalase (H₂O₂ → H₂O + O₂) using hydrogen peroxide Bubbling: positive No bubbling: negative

Question 40

What bacteria give a positive catalase test?

Answer 40

*Staphylococci*

Question 41

What bacteria give a negative catalase test?

Answer 41

*Streptococci*

Question 42

Describe the coagulase test

Answer 42

Detection of the enzyme coagulase (fibrinogen → fibrin) by adding fibrinogen and smearing with a slide or test tube Clot formation: positive No clot formation: negative

Question 43

What bacteria give a positive coagulase test?

Answer 43

*Staphylococcus aureus*

Question 44

What bacteria give a negative coagulase test?

Answer 44

Most *Staphylococci* except *S. aureus*