UAMS MICRO EXAM PRACTICAL
QUESTIONS AND ANSWERS WITH
COMPLETE SOLUTIONS 100%
CORRECT!!!
What is meant by the clinical microbiology term "nonfermenter"?
✔✔ Definition: Microorganisms that are unable to metabolize carbohydrates
(sugars) via fermentation under anaerobic conditions (as demonstrated by
negative fermentation reactions in OF tubes or TSI/KIA slants).
✔✔ Key Laboratory & Growth Characteristics:
Media Growth: Usually grow readily on routine laboratory media such as
Blood Agar (BAP), Chocolate Agar (CHOC), and most grow on
MacConkey (MAC) agar.
Oxygen Requirements: Mostly strict aerobes or facultative aerobes that
utilize oxidative metabolism.
Incubation Temperature: Optimal growth typically occurs at
$35^\circ\text{C}$.
Clinical Examples: Pseudomonas aeruginosa, Acinetobacter species, and
Stenotrophomonas maltophilia.
Which tests are ran to differentiate nonfermenters from enterics? -
ANSWER✔✔OF glucose test, oxidase reduction test, (most nonfermenters are +),
and growth on MAC (most are lactose =).
What do fermenters utilize for energy? How are nonfermenters different? -
ANSWER✔✔CHOs in both aerobic and anaerobic conditions. Nonfermenters
cannot break down CHOs under anaerobic conditions.
, Whats the difference between oxidizers and non-oxidizers? -
ANSWER✔✔Oxidizers metabolize CHOs in the air, while non-oxidizers cannot
use CHOs as an energy source at all.
What is the oxidative fermentation test (OF)? -ANSWER✔✔Test that determines
if MO is a fermenter, oxidizer, or non-oxidizer. It utilizes Hugh-Leifson OF
medium and turns yellow for acid conditions and green/blue for alkaline
conditions. OF medium contains a high concentration of glucose. Each MO is
tested in both aerobic and anaerobic conditions.
A fermenter will produce acid in open and closed tube such as E. coli. An oxidizer
will produce acid in an open tube only such as Pseudomonas aeruginosa. A non-
oxidizer (assacharolytic) does not metabolize glucose in either open or closed tubes
such as Acinetobacter lwoffii.
What is the nitrate reduction test? -ANSWER✔✔Test that determines if MO
contains nitrate reductase, which converts nitrate to nitrite (NO3 to NO2). Nitrite is
detected by adding reagents Sulfanilic acid (reagent A) and Dimethyl-alpha-
naphthylamine (reagent B). Pos nitrite will yield a red color and neg will have no
color change. If neg, determine if MO converted nitrite to nitrogen gas by adding
zinc to the tube.
What is nitrogen gas detection? -ANSWER✔✔Test that determines if MO can
convert nitrite to nitrogen gas (NO3 to NO2 to nitrogen gas). Add zinc to a neg
nitrite tube. Zinc reduced nitrate to nitrite. If tube is pos, there will be no color
change, indicating that nitrate has already been converted to gas by the MO. If neg,
red color develops, indicating that the MO did not convert nitrate to gas.
Pseudomonas aeruginosa morphology and characteristics? -ANSWER✔✔Large,
spready colonies with an iridescent sheen that are beta hemolytic. P. aeruginosa
has a corn chip or grape smell.
QUESTIONS AND ANSWERS WITH
COMPLETE SOLUTIONS 100%
CORRECT!!!
What is meant by the clinical microbiology term "nonfermenter"?
✔✔ Definition: Microorganisms that are unable to metabolize carbohydrates
(sugars) via fermentation under anaerobic conditions (as demonstrated by
negative fermentation reactions in OF tubes or TSI/KIA slants).
✔✔ Key Laboratory & Growth Characteristics:
Media Growth: Usually grow readily on routine laboratory media such as
Blood Agar (BAP), Chocolate Agar (CHOC), and most grow on
MacConkey (MAC) agar.
Oxygen Requirements: Mostly strict aerobes or facultative aerobes that
utilize oxidative metabolism.
Incubation Temperature: Optimal growth typically occurs at
$35^\circ\text{C}$.
Clinical Examples: Pseudomonas aeruginosa, Acinetobacter species, and
Stenotrophomonas maltophilia.
Which tests are ran to differentiate nonfermenters from enterics? -
ANSWER✔✔OF glucose test, oxidase reduction test, (most nonfermenters are +),
and growth on MAC (most are lactose =).
What do fermenters utilize for energy? How are nonfermenters different? -
ANSWER✔✔CHOs in both aerobic and anaerobic conditions. Nonfermenters
cannot break down CHOs under anaerobic conditions.
, Whats the difference between oxidizers and non-oxidizers? -
ANSWER✔✔Oxidizers metabolize CHOs in the air, while non-oxidizers cannot
use CHOs as an energy source at all.
What is the oxidative fermentation test (OF)? -ANSWER✔✔Test that determines
if MO is a fermenter, oxidizer, or non-oxidizer. It utilizes Hugh-Leifson OF
medium and turns yellow for acid conditions and green/blue for alkaline
conditions. OF medium contains a high concentration of glucose. Each MO is
tested in both aerobic and anaerobic conditions.
A fermenter will produce acid in open and closed tube such as E. coli. An oxidizer
will produce acid in an open tube only such as Pseudomonas aeruginosa. A non-
oxidizer (assacharolytic) does not metabolize glucose in either open or closed tubes
such as Acinetobacter lwoffii.
What is the nitrate reduction test? -ANSWER✔✔Test that determines if MO
contains nitrate reductase, which converts nitrate to nitrite (NO3 to NO2). Nitrite is
detected by adding reagents Sulfanilic acid (reagent A) and Dimethyl-alpha-
naphthylamine (reagent B). Pos nitrite will yield a red color and neg will have no
color change. If neg, determine if MO converted nitrite to nitrogen gas by adding
zinc to the tube.
What is nitrogen gas detection? -ANSWER✔✔Test that determines if MO can
convert nitrite to nitrogen gas (NO3 to NO2 to nitrogen gas). Add zinc to a neg
nitrite tube. Zinc reduced nitrate to nitrite. If tube is pos, there will be no color
change, indicating that nitrate has already been converted to gas by the MO. If neg,
red color develops, indicating that the MO did not convert nitrate to gas.
Pseudomonas aeruginosa morphology and characteristics? -ANSWER✔✔Large,
spready colonies with an iridescent sheen that are beta hemolytic. P. aeruginosa
has a corn chip or grape smell.
