Why is HCL used in DNase test?
DNase-producing organisms depolymerize DNA into nucleotide fractions such as, mononucleotides and oligonucleotides. After incubation, DNase Test Agar requires addition of 1N HCl to the plate. HCl reacts with DNA (polymerized) in the medium, yielding free nucleic acid and a cloudy precipitate.
What does a positive DNase test mean?
Positive: Medium is colorless around the test organism. Negative: If no degradation of DNA occurs, the medium remains green.
What are 2 indicators that can be used in the DNase test?
DNase agar contains nutrients for the bacteria, DNA, and methyl green as an indicator. Methyl green is a cation which binds to the negatively-charged DNA. Deoxyribonuclease allows the organisms that produce it to break down DNA into smaller fragments.
Why does DNA agar turn cloudy when HCL is added?
Without DNAse enzyme, the HCL precipitates out the undestroyed DNA. The rest of the agar with the remaining DNA, which binds to HCL (hydrochloric acid) will have turned cloudy.
What function is the hydrochloric acid added to the DNase plates after incubation?
High molecular deoxyribonucleic acid enables the detection of deoxyribonuclease (DNase) that depolymerizes DNA. After incubation of the medium with the test strain, the plate is flooded with hydrochloric acid which precipitates the polymerized DNA, making the medium opaque.
What is the chemical reaction created by DNase?
A deoxyribonuclease (DNase, for short) is an enzyme that catalyzes the hydrolytic cleavage of phosphodiester linkages in the DNA backbone, thus degrading DNA.
What bacteria are DNase positive?
After application and penetration of hydrochloric acid into the medium, DNase positive organisms such as Staphylococcus aureus or Serratia marcescens will be surrounded by clear zones of depolymerized DNA while the medium farer away from the inoculation band will be opaque and whitish due to polymerized DNA.
Is M catarrhalis DNase positive or negative?
The DNase test distinguishes M. catarrhalis from all other gram-negative diplococci of human origin. Only N. ovis, a species isolated from sheep and cattle, produces DNase and fails to produce detectable acid from carbohydrates.
Why is DNase a virulence factor?
DNases have often been described as virulence factors in streptococci  or staphylococci . Indeed, it has been shown that DNase can help bacteria to escape from neutrophil extracellular traps (NETs) which are structures secreted by neutrophils to trap and kill bacteria .
Which bacteria are positive for DNase test?
Why is the plate flooded with HCL before reading?
After incubation of the medium with the test strain, the plate is flooded with hydrochloric acid which precipitates the polymerized DNA, making the medium opaque. Organisms that degrade DNA produce a clear zone around the growth area.
How do you detect DNase?
In this method, simply, bacteria is added to the broth medium containing DNA and followed for the DNA degradation caused by the DNase of bacteria by running in agarose gel. This method we called DNase Tube test showed DNA degradation as fast as in half an hour depending on the DNase activity of the bacteria.