Interpretation of the results from metabolic assays (Lab) Flashcards
What does it mean when halos form around the colonies in a starch hydrolysis test?
Amylase is produced and the organism is hydrolyzing starch
What does it mean when no halos form around the colonies in a starch hydrolysis test?
No amylase is present. No starch hydrolysis
What does it mean when the tube is blue in an oxidative-fermentation test?
The organism can’t use glucose and is using the peptone instead, which produces alkaline ammonia
What does it mean when the aerobic tube is yellow, but the anaerobic tube is green in an oxidative-fermentation test?
The organism does glucose oxidation only in the presence of O2
What does it mean when the both the aerobic and anaerobic tubes are yellow in an oxidative-fermentation test?
The organism does glucose fermentation with or without O2
What does it mean when the tube is yellow in a carbohydrate fermentation test?
The organism is fermenting the carbohydrate and producing acid
What does it mean when the tube is red in a carbohydrate fermentation test?
The organism is not fermenting the carbohydrate and is using the peptone instead, producing alkaline ammonia
What does it mean when the tube is red on the top and yellow in a carbohydrate fermentation test?
The organism was fermenting the carbohydrate, produced a bunch of acid, and used it up, then starting using the peptone in aerobic conditions and created ammonia, which changed the phenol red back to red
What does it mean when the tube is red in a methyl red test?
The organism is not producing acid, so it does not do mixed acid fermentation
What does it mean when the tube is yellow in a methyl red test?
The organism is doing mixed acid fermentation and is producing large amounts of acid
What does it mean when the tube is red in a Voges-Proskauer test?
The organism is doing butanediol fermentation and is producing acetoin
What does it mean when the tube is yellow in a Voges-Proskauer test?
The organism is not producing acetoin
What does it mean when the agar is green in a citrate test?
The organism can’t use citrate for fermentation, so doesn’t have citrate lyase and can’t grow
What does it mean when the agar is blue in a citrate test?
The organism has citrate lyase and can grow using citrate for fermentation
What does it mean when the bacterial smear is stringy in a KOH test?
Gram-negative. The membrane got destroyed and the DNA got released
What does it mean when the bacterial smear doesn’t do anything in a KOH test?
Gram-positive. The PG layer protected the membrane so the DNA stays in the cell
What does it mean when the test strip turns blue in an oxidase test?
Cytochrome C is present and ADMA oxalate got oxidized and turned blue
What does it mean when the test strip stays colourless in an oxidase test?
Cytochrome C is absent
What does it mean when the tube is yellow in an ONPG test?
Beta-galactosidase is present and lactose is being broken down
What does it mean when the tube is colourless in an ONPG test?
No beta-galactosidase and no lactose breakdown
What does it mean when the tube is red in an indole test?
Tryptophanase is present and indole is being produced
What does it mean when the tube is yellow in an indole test?
No tryptophanase and no indole
What does it mean when colonies are yellow on MacConkey agar?
They’re enteric and gram-negative, but don’t do lactose fermentation
What does it mean when colonies are pink on MacConkey agar?
Enteric and gram-negative and do lactose fermentation (acid caused the dye to be absorbed)
What does it mean when colonies are pink with pink haloes on MacConkey agar?
Enteric, gram-negative, and strong lactose fermenters that caused the bile salts to precipitate around the colonies
What does it mean when the organism doesn’t grow on MacConkey agar?
Is gram-positive and can’t tolerate the crystal violet, or is non-enteric
What does it mean when colonies are metallic green on EMB agar?
Gram-negative and do mixed acid fermentation, which caused the eosin to turn black
What does it mean when colonies are fish-eye on EMB agar?
Gram-negative and do some sort of fermentation that isn’t mixed acid, so they produce less acid and less eosin turns black
What does it mean when colonies are light pink on EMB agar?
Gram-negative and don’t do lactose fermentation, but do absorb the eosin
What does it mean when the organism doesn’t grow on EMB agar?
Gram-positive
What does it mean when bubbles are produced in a catalase test?
Catalase is present and the organism is part of the Micrococcaceae
What does it mean when no bubbles are produced in a catalase test?
Catalase is absent and the organism is a Streptococcaceae
What does it mean when gas is produced in a nitrate reduction test?
Positive for nitrate reduction. The organism is producing NO, N2O, or N2 from reducing nitrate
What does it mean when the tube turns red after adding sulfanillic acid and alpha-naphthylamine in a nitrate reduction test?
Positive for nitrate reduction. The organism is reducing nitrate to nitrite
What does it mean when the tube turns red after adding the zinc in a nitrate reduction test?
Negative for nitrate reduction. Nitrate is still present in the tube so the organism isn’t using it
What does it mean when the tube turns yellow after adding the zinc in a nitrate reduction test?
Positive for nitrate reduction. Nitrate is being reduced to some other byproduct that isn’t detected
What does it mean when the agar is discoloured green or brown around the colonies on blood agar?
Alpha-hemolysis. The organism produces hemolysins that reduce Hb but don’t lyse red blood cells
What does it mean when the agar is cleared around the colonies on blood agar?
Beta-hemolysis. The organism produces hemolysins that completely lyse red blood cells
What does it mean when the agar isn’t cleared or discoloured around the colonies on blood agar?
Gamma-hemolysis. The organism doesn’t produce hemolysins
What does it mean when colonies are yellow on mannitol salt agar?
The organism can tolerate high salt and ferments mannitol
What does it mean when colonies are pink on mannitol salt agar?
The organism can tolerate high salts but can’t ferment mannitol
What does it mean when the organism doesn’t grow on mannitol salt agar?
It can’t tolerate high salt
