RA2: Major Groups of Disease Causing Bacteria

Question 1

Major genera of gram positive organisms:

Answer 1

1. ) Gram pos cocci: staphylococcus, streptococcus, enterococcus
2. ) Gram pos rods/bacilli: clostridium, corynebacterium, listeria, bacillus

Question 2

Which gram pos organisms are spore forming?

Answer 2

• Clostridium = anaerobic rod

- Bacillus = aerobic rod

Question 3

Major genera of gram negative organisms:

Answer 3

1. ) Gram neg cocci: Neisseria (diplococcic)
2. ) Gram neg enteric bacilli/rods: Escherichia, Yersinia entercolitica, Salmonella, Shigella, Vibrio
3. ) Gram neg non-enteric bacilli/rods: Haemophilus, Pseudomonas, Klebsiella, Yersinia pestis

Question 4

Bacteria that don’t gram stain

Answer 4

1. ) Acid fast: mycobacterium, nocardia
2. ) Spirochetes: Borrelia, Treponema
3. ) No cell wall: mycoplasma
4. ) Obligate intracellular bacteria: Chlamydia, chlamydophila

Question 5

What is the Wright’s test used for?

Answer 5

• stain for Borrelia spirochetes

Question 6

What does catalase test distinguish?

Answer 6

• Staphylococcus from Enterococcus / Streptococcus species

Question 7

What does hemolysis on blood agar test distinguish?

Answer 7

• Used to distinguish between enterococcus and streptococcus species
• Results are: alpha, beta and gamma
  a. ) Alpha: enterococcus or streptococcus species
  b. ) Beta: streptococcus species
  c. ) Gamma: enterococcus species

Question 8

What does hemolysis on blood agar test with Optochin and bacitracin sensitivity tests help to distinguish?

Answer 8

• Hemolysis on blood agar to distinguish between enterococcus and streptococcus species with results
  a. ) Alpha: enterococcus or streptococcus species
  b. ) Beta: streptococcus species
  c. ) Gamma: enterococcus species
• Alpha bacteria are tested via optochin sensitivity
  a. ) Sensitive = Streptococcus pneumonia
  b. ) Resistant = Enterococcus
• Beta are tested via bacitracin sensitivity
  a. ) Sensitive = Streptococcus pyogenes
  b. ) Resistant = Streptococcus agalactiae

Question 9

What does the coagulase and Novobiocin sensitivity tests distinguish

Answer 9

• Coagulase distinguishes between staphylococcus species
  a. ) Coagulase pos = Staph aureus
  b. ) Coagulase neg = Staph epidermidis, staph saprophyticus
• Novobiocin test to distinguish between staph epidermidis and staph saprophyticus
  a. ) Novobiocin sensitive = Staph epidermidis
  b. ) Novobiocin resistant = Staph saprophyticus

Question 10

Use results from anaerobic growth, spore formation and motility tests to distinguish between gram positive rods/bacilli species

Answer 10

• Anaerobic growth test
  a. ) Growth pos = Clostridium (spore-forming)
  b. ) Growth neg = Bacillus, Listeria or Corynebacterium
• Spore formation test
  a. ) spore pos = Bacillus anthracis or cereus
  b. ) spore negative = Listeria or Corynebacterium
• Spore pos w/motility test
  a. ) Spore pos with motility = Bacillus cereus
  b. ) Spore pos w/o motility = Bacillus anthracis or Bacillus cereus
• Spore negative w/motility test
  a. ) Spore negative w/motility = Listeria monocytogenes
  b. ) Spore negative w/o motility = Corynebacterium diphtheria

Question 11

Differentiate between Neisseria species using maltose fermentation

Answer 11

• Maltose pos = Neisseria meningitidis

- Maltose neg = Neisseria gonorrhoeae

Question 12

Differentiate amongst Enterobacteriaceae family based upon lactose fermentation and h2s production/motility test

Answer 12

• Lactose fermentation
  a. ) Positive = E.coli of K.pneumoniae
  b. ) Negative = Salmonella, proteus, shigella, Y.pestis
• H2s production/motility test
  a. ) Positive = Salmonella, proteus
  b. ) Negative = Shigella, Y.pestis