Tests for Carbohydrates Fermentation (F)

Question 1

The action of many spp of microorganisms on a carbohydrate substrates result to what?

Answer 1

It result in the acidification of the medium

Question 2

What are the components of a basal fermentation medium?

Answer 2

It typically includes:

1) Tryptichydrolysate of casein
2) Na chloride
3) Phenol red
4) Carbohydrate to be tested

Question 3

What is the purpose of tryptichydrolysate of casein (as component of a basal fermentation medium)?

Answer 3

It is the source of carbon and nitrogen

Question 4

What is the purpose of NaCl (as component of a basal fermentation medium)?

Answer 4

It serves as osmotic stabilizer

Question 5

What is the purpose of phenol red (as component of a basal fermentation medium)?

Answer 5

It serves as the indicator

Question 6

What is the concentration of the carbohydrate to be tested (as a component of a basal fermentation medium)?

Answer 6

0.5 - 1% concentration

Question 7

What is the procedure (or steps) of sugar fermentation test?

Answer 7

1) Inoculate TSI by stabbing the medium thru the butt or deep and the slant is streaked w/ a back and forth motion
2) Incubate overnight at 35 - 37 DC
3) Observe the color rxns (acid = yellow, alkaline = red)

Question 8

What are the results of sugar fermentation test?

Answer 8

1) Alkaline slant / alkaline butt: no sugars fermented
2) Alkaline slant, acid butt: only glucose is fermented, lactose and sucrose not fermented
3) Acid slant, acid butt: glucose and lactose (or sucrose in TSI) fermented

• negative carbohydrate fermentation, positive carbohydrate fermentation, fermentation and gas production

Question 9

What is the meaning of OF test?

Answer 9

Oxidative-Fermentative test

Question 10

True or False

Certain fermenting gram (-) bacteria metabolize glucose using aerobic respiration

Answer 10

False, because certain non-fermenting gram (-) bacteria metabolize glucose using aerobic respiration

Question 11

What are the products if certain nonfermenting gram (-) bacteria metabolize glucose using aerobic respiration?

Answer 11

It only produce a small amt of weak acids during Krebs cycle and Entner Doudoroff (glycolysis)

Question 12

What is the action of the increased concentration of glucose in the medium (in OF test)?

Answer 12

It enhances the production of these weak acids, this medium contains a reduced concentration of peptones

Question 13

What is the procedure (or steps) of OF test of carbohydrates (Hugh and Leifson’s)?

Answer 13

1) Inoculate 2 tubes of OF based medium w/ sugar by stabbing halfway to the bottom w/ the test organism
2) Overlay 1 tube w/ 1 cm of mineral oil
3) Incubate overnight at 35 - 37 DC
4) Interpret results

Question 14

What are the results of OF test of carbohydrates (Hugh and Leifson’s)?

Answer 14

1) Fermentation results: culture medium turned yellow from green
2) Oxidative: medium turns yellow near on the top only
3) Negative: no change of color to yellow

Question 15

What is the interpretation if the bacteria being tested via OF test (Hugh and Leifson’s) are the ff:

1) O- (or oxidative negative)
2) F- (or fermentation / fermentative negative)

Answer 15

Non Saccharolytic

Question 16

What is the interpretation if the bacteria being tested via OF test (Hugh and Leifson’s) are the ff:

1) O+ (or oxidative positive)
2) F+ (or fermentation / fermentative positive)

Answer 16

Fermentative

Enterobacteriaceae

Question 17

What is the interpretation if the bacteria being tested via OF test (Hugh and Leifson’s) are the ff:

1) O+ (or oxidative positive)
2) F- (or fermentation / fermentative negative)

Answer 17

Oxidative

Pseudomonas

Question 18

What are the components of the medium used in carbohydrate utilization test (cystine tryptic agar-based)?

Answer 18

The medium contains:

1) Cystine
2) Peptone

Question 19

What is the purpose of cystine and peptone (as components of the medium for carbohydrate utilization test)?

Answer 19

To supply the nutrients necessary to support the growth of fastidious microorganisms

Question 20

What is the meaning of CTA?

Answer 20

Cystine Tryptic Agar

Question 21

CTA media is supplemented w/ what?

Answer 21

It is supplemented w/ a 1% concentration of a sp carbohydrate w/c are used to detect fermentation rxns

Question 22

How is carbohydrate fermentation detected (in carbohydrate utilization test)?

Answer 22

It is detected by a visible color change of the medium due to the incorporation of the pH indicator dye, phenol red

Question 23

What happens when the carbohydrate present is metabolized by the organism (in carbohydrate utilization test)?

Answer 23

Organic acids are produced and the medium becomes acidified

Question 24

What is the action of the acid produced by carbohydrate fermentation (in carbohydrate utilization test)?

Answer 24

It causes a decrease in pH, causing a color shift in the medium from red-pink to yellow

Question 25

What is the procedure (or steps) of carbohydrate utilization test?

Answer 25

1) Inoculate tubes of CTA based medium w/ sugars by stabbing halfway to the bottom w/ the test organisms that are 18 - 24 hrs old
2) Incubate overnight at 35 - 37 DC
a. If testing for utilization, do not tighten cap
b. If testing for fermentation, tighten cap
3) Interpret results:
a. Yellow: (+), sugar is fermented
b. Orange-red: (-), sugar not fermented

Question 26

What is the indication of the presence of Neisseria meningitidis via carbohydrate utilization test?

Answer 26

Glucose: yellow
Maltose: yellow
Sucrose: orange-red

Question 27

What is the indication of the presence of Neisseria gonorrhoeae via carbohydrate utilization test?

Answer 27

Glucose: yellow
Maltose: orange-red
Sucrose: orange-red