Staphylococcus Latex Test

Latex particles are coated with fibrinogen (to which coagulase binds) and IgG (which binds with Protein A). When mixed with a suspension of S. aureus, the latex particles rapidly agglutinate to form visible clumps. No obvious agglutination occurs in the absence of coagulase/Protein A-positive staphylococci.

Kit contents (100 tests)

• Staph Latex Reagent (M43a, 5 mL, blue cap): latex particles coated with human fibrinogen and IgG. Preserved with 0.099% sodium azide.
• Positive control (M43b, 1 mL, black cap): inactivated preparation of S. aureus, preserved with 0.099% sodium azide.
• Disposable agglutination slides (25 pcs).
• Disposable mixing sticks (4 x 25 pcs).

Additional materials required (not supplied in the kit)

• Bacteriological loops.

The Staphylococcus Latex Test should be stored at 2-8 °C when not in use. The kit should not be used after the expiry date printed on the box.

Before using this product, refer to Precautions and Limitations. The controls specified in the Quality control section should be performed each time the kit is used.

Specimens

Select 1-2 isolated colonies grown for 18-24 hours at 35-37 °C on primary isolation medium such as 5% blood agar. The morphology of the colonies tested should resemble that of S. aureus. Pure single colonies should be tested to minimise the possibility of erroneous results. If necessary, isolate by streaking on to a new agar plate. Colonies with atypical morphologies can be tested for Gram-positive staining to maximise the probability that staphylococci have been selected for testing.

Test procedure

For the positive control protocol, see the Quality control section.

1. Mix the Staphylococcus latex by gentle inversion and add 1 drop to a circle of a clean, dry test slide.
2. Using a sterile loop, pick one colony of the organism to be tested and emulsify in the drop of latex reagent on the slide. Spread over the area of the circle with a mixing stick.
3. Gently rock the slide for up to 2 minutes and observe for agglutination.
4. After reading, discard used slides and mixing sticks into suitable disinfectant.

Interpretation of results

Agglutination within 2 minutes is a positive result and indicates the presence of S. aureus. No agglutination indicates the absence of S. aureus and of other coagulase/Protein A-positive strains of Staphylococcus.

Safety

1. The kit and its reagents supplied are intended for professional use only, to be used for industrial diagnostics only and not for use in clinical testing.
2. Sodium azide, which is used as a preservative in the kit reagents, can react with lead or copper plumbing to form potentially explosive metal azides. Dispose by flushing with a large volume of water to prevent azide build-up.
3. The IgG and fibrinogen used to sensitise the latex reagent are derived from human plasma which has been tested and found negative for the presence of antibodies to HIV-1, HIV-2 and HCV, and HBsAg. It should nevertheless be handled as though potentially infectious.
4. Appropriate precautions should be taken when handling or disposing of potential pathogens. Decontamination of infectious material can be achieved with sodium hypochlorite at a final concentration of 3% for 30 minutes. Liquid waste containing acid must be neutralised before treatment.
5. The positive control has been inactivated during the manufacturing process. However, it should be handled as though potentially infectious.

Procedural

1. The Staphylococcus Latex Test should be used according to the kit instructions.
2. Allow all reagents to reach room temperature before use.
3. Do not dilute any of the kit reagents.
4. Do not intermix reagents from different batches of kits.
5. Do not freeze any of the kit reagents.
6. Do not allow the latex reagent dropper to touch the positive control or bacterial samples.
7. Be careful only to record agglutination. Reactions that are "curdy" or "stringy" may not be true agglutination.
8. Ensure the slide is clean and dry prior to use.

1. Results should be interpreted in the context of all available clinical and laboratory information.
2. Test only pure, single colonies since mixed colonies may give erroneous results.
3. Cultures older than 30 hours may autoagglutinate.
4. Media with a high salt content, such as Mannitol Salt Agar, inhibit Protein A production and this may lead to false negative results.
5. Rough strains of Staphylococcus may cause false positive reactions. These strains are rare and distinguishable from smooth strains by their colonial morphology. If suspected, these can be confirmed by emulsifying in a drop of saline and examining carefully for a smooth suspension.
6. Stringy reactions on the slide may not be true positive reactions and further biochemical tests are required.
7. Some yeasts may cause false positive results.
8. All coagulase-positive strains of Staphylococcus will react with the Staphylococcus Latex Test, therefore S. aureus will not be distinguishable from S. intermedius and S. hyicus. However, the latter two strains are infrequently isolated from human sources and are more commonly found in animals or as saprophytes.
9. The Staphylococcus Latex Test is intended for the identification of presumptive S. aureus. Colonies giving positive results should be confirmed as S. aureus by biochemical tests.

The following controls should be performed each time the kit is used.

1. Positive control: Add one drop of positive control (M43b) to one circle on the test slide. Mix the Staphylococcus latex by gentle inversion, add 1 drop to the same circle and mix with a mixing stick. Do not allow the dropper to touch the positive control. Rock the slide gently. Within 2 minutes, agglutination, indicating a positive result, should be visible. If no agglutination is seen, a fresh kit should be used.
2. Negative control: Mix the Staphylococcus latex by gentle inversion and add 1 drop to a circle on the test slide. Using a known coagulase/Protein A-negative Staphylococcus, e.g., S. epidermidis, take one fresh colony of 18-24 hour growth and emulsify in the drop of latex reagent on the slide. Gently rock the slide for 2 minutes. No agglutination should occur.

Dispose of according to any local, national, or regional regulations.