Ch. 9 Gram neg bacilli testing

Question 1

Oxidative pathway

Answer 1

• Aerobic
• glucose to pyruvic acid
• weak acid is neutralized by alkaline reactions from peptone breakdown
  
  • gives alkaline result (K)

Question 2

Fermentation

Answer 2

• Anaerobic
• acids produced from carbohydrate breakdown
• gives acid result (A)

Question 3

Triple Sugar Iron Test (TSI)

Answer 3

• Agar in tube contains glucose, sucrose, lactose, ferrous sulfate, phenol red
• all enterobacteriaceae use glucose up first
  
  • then lactose and/or sucrose after
• phenol red is pH indicator
  
  • red = high pH (alkaline)
  • yellow = low pH (acidic)
• slant is aerobic environment
• Deep/butt is anaerobic environment

Question 4

TSI results

Answer 4

• K/K (R/R) = no fermentation
  
  • probably a GNB non fermenter, like pseudomonas
• K/A (R/Y) = glucose only fermentation
  
  • first A/A, then glucose used up and peptones used
    
    • aerobic pathyway, so happens on slant
  • goes to K/A
• A/A (Y/Y) = lactose/fructose fermenter
• H2S produces black precipitate from ferrous sulfate
  
  • but acid produced first
• gas produces bubbles or splitting/raising of agar

Question 5

Kligler Iron Agar (KIA)

Answer 5

Similar to TSI but no sucrose in agar

Question 6

IMVC

Answer 6

• Indole
  
  • if indole produced
    
    • pos = red
  • uses Ehrlich’s or Kovac’s reagent
• Methyl Red
  
  • glucose to pyruvate
  • red = pos
• Voges - Proskauer
  
  • glucose to glycol; glycol goes to diacetyl
  • red = pos
• Citrate
  
  • citrate utilization as sole carbon source
  • leads to acid
    
    • pos = green color goes to blue

Question 7

PAD

Answer 7

Phenylalanine Deaminase test

green = pos

Question 8

DNase

Answer 8

• enzyme that digests DNA

Question 9

Oxidase

Answer 9

• detects cytochrome oxidase enzyme
  
  • used in electron transport system
• pos = purple

Question 10

Motility

Answer 10

Haze produced in gelatin tube as bacteria swim through media

Question 11

Nitrate to nitrite

Answer 11

• NO3 to NO2
• incubate broth with organism for 24hrs
  
  • then add NNDM
  • if nitrite is present red color appears from formation of red diazo complex
• no color = no nitrite formed
  
  • may be due to nitrate not being reduced or being reduced past NO2 to N2 or NO
• zinc dust is added to reduced nitrate still in tube
  
  • if red color is produced then no nitrate was converted tonitrite and test is negative
  • if no red color was produced then all nitrate was used and was reduced past NO2