STAPHTEX LATEX TEST

Effective Date: 
Mon, 11/04/2013
Reviewed: 
Tue, 01/10/2017
Policy: 

The  StaphTex Latex Test is a slide agglutination assay for the qualitiative detection of coagulase (both clumping factor and protein A) to identify Staphylococcus aureus to the exclusion of other species of staphylococci. This test is for use on pure culture samples suspected of being S. aureus. The  StaphTex latex Test does detect methicillin resistant S. aureus (MRSA) strains that produce clumping factor and protein A.

 

Materials

Latex Reagent-suspended inert plasma-coated latex particles, with 0.1% Sodium Azide as preservative.

Timing Device

Disposable stirrer (toothpicks or wooden sticks, inoculating loops etc)

 

Quality Control

Test Latex particles daily using control strains Staph aureus ATCC 25923 and Staph epidermidis ATCC 12228.

Procedure: 
  1. Add a drop of the Latex Reagent to a well of the test card.
  2. Using a disposable stirrer, collect a visible amount of an isolated colony about 2mm in size from the overnight culture grown on 5% sheep blood.
  3. Emulsify the culture sample in the Latex Reagent on the card. Discard the stirrer in an appropriate biohazard container.
  4. Gently tilt and rotate the card in a complete circular motion for up to 45 seconds, or until agglutination is evident, whichever comes first. Positive reactions usually occur within 15-20 seconds.
  5. View the mixture on the card, using only a high intensity light source. Do not use a magnifying lens.
  6. Record the results. Dispose of the card into an appropriate biohazard container.

 

Key Points: 

Limitations

Some streptococci possess plasma protein-binding factors; and several species, such as members of the enterobacteriaceae, nonspecifically agglutinate latex particles. Therefore all colonies tested must be ascertained to be staphyloccus by gram stain/wet mount and catalase.
 

Strains of some Staph aureus which do not possess clumping factor and protein A may give negative results in the test. Additional biochemical tests may be necessary to assist in identification.

Occasionally a culture sample may cause Latex Reagent to appear stringy or speckled and not demonstrate typical agglutination. This result necessitates further biochemical testing to identify the organism.

False positive results may occur with Staph saprophyticus for protein A and therefore cause misidentification as Staph aureus.

Rough strains of Staph and yeasts frequently cause nonspecific reactions and should therefore be distinguished by morphological criteria.

Reaction times longer than specified might cause false positive results due to a drying effect.

 

References

StaphTex Latex test Package insert Copyright 2014 Hardy Diagnostics