lab 5-18: urease test

what is the purpose of the urease test?

to detect organisms which are capable of producing the enzyme urease

which bacteria produced a positive result?

klebsiella pneumoniae

what is the function of urease?

ureas is the enzyme that catalyzes the breakdown of urea. Urea gets broken down to produce carbon dioxide and ammonia

urease reaction:

urea —→ water + urease —→ ammonia + carbon dioxide

what is a buffer? why is a buffer used in the urea agar?

a buffer helps stabilize the ph. the buffer is added here so the plate does not change color if the organism exclusively utilizes peptone. The utilization of peptone produces ammonia waste, impacting the ph of the media.

how can two urease positive organisms take different amounts of time to turn the medium pink?

the differing time frame for turning the media pink can be due to their urease production rate. This means some can produce urease in larger amounts in a shorter amount of time, resulting in a quicker color change. Others are slower at producing urease, therefore the urea is being broken down in a longer time frame, producing a color changing after a longer incubation period.

a color change to pink indicates what about the ph? what is the ph indicator used in this media?

pink indicates an alkaline ph. the ph indicator in this media is phenol red.

what end product did we detect in this experiment? what effects does it have on the ph in the media?

with both carbon dioxide gas and ammonia as the end products of this experiment, we specifically detected the ammonia. this produces an alkaline environment in the media, making it pink

what is urea derived from?

urea is a byproduct of certain amino acids being broken

list 3 genera of bacteria known for producing urease:

1. proteus: causes UTI

2. klebsiella: pneumonia

3. helicobacter: cause of peptic ulcers. The helicobacter can neutralize acid in the stomach through ureas production to make it hospitable for it.

if there was no buffer included int he media, what color would the agar change if the organism utilized peptone?

the agar would become pink because the organisms are utilizing the peptone, which produces ammonia,

is the urea agar considered to be selective or differential?

the urea agar is considered differential. this media highlights the differences between the organisms through the phenol red ph indicator. The urea is another differential ingredient as it is the substrate that allows the urease to function which then produces ammonia highlighted by the phenol red.

how would you interpret an organism which turns yellow/orange after 24 hour incubation?

an orange/yellow incubation result would indicate acid formation. this could be due to fermentation. This would be a negative test for urease as ammonia was not produced

describe the appearance of your plate after 24 hours if you tested a rapid urease producer.

after a 24 hour incubation of a rapid urease producer would result in a pink plate.