DNase

Uses of:

It is used to differentiate S.aureus (DNase +ve) from other Staphylococci that do not produce such enzyme. The DNase test is particularly useful when plasma is not available to perform a coagulase test or when the results of a coagulase test are difficult to interpret.

DNase test distinguishes M. catarrhalis from all other gram-negative diplococci (e.g. Neisseria gonorrhoeae & Neisseria meningitidis) of human origin.

Sample type:

Colonies on agar plate .

Precautions:

sterile the loop before use .

Reject unlabeled specimen

Interfering factors:

Some MRSA strains do not give positive DNase test result and some strains of the coagulase-negative staphylococci such as Staphylococcus capitis may give weak reactions.

Serratia and Moraxella species also produce deoxyribonuclease.

1N HCl is bactericidal for Staphylococci. Once the HCl has been applied, the test must be read within 5 minutes and cannot be continued by re-incubation

Pre analytical errors:

Non sterilized loop

Sample preparation

Post errors:

Delayed report

Corrective action:

Sterile the loop to avoid contamination