TEST FOR STAPHYLOCOCCUS AUREUS

INTRODUCTION:

Staphylococcus aureus  literally "Golden Cluster Seed" and also known as golden staph,  It is a spherical bacterium, frequently living on the skin or in the nose of a person, that can cause a range of illnesses from minor skin infections, such as pimples, impetigo, boils, cellulitis and abscesses, to life-threatening diseases, such as pneumonia, meningitis, endocarditis, Toxic shock syndrome (TSS), and septicemia.

Staphyloccus aureus was discovered in Aberdeen, Scotland in 1880 by the surgeon Sir Alexander Ogston in pus from surgical abscesses.

PREPARATION OF CULTURE MEDIA:

Sodium hydroxide 1N: Dissolve 4.0 g of sodium hydroxide in water to make 100 mL.

Hydrochloric Acid 1N: Dissolve 8.5 ml of Hydrochloric Acid in water to make 100 mL.

Soyabean Casein Digest broth Medium (SCDM)/ Mannitol Salt Agar (MSA): Reconstitute dehydrated media as directed by the manufacturer and sterilize in an autoclave at 121°C for 20 minutes.

PROCEDURE:

Sample Preparation and Pre enrichment

Aseptically add 1g of specimen if it’s a solid or 1ml accurately measured, if the specimen is a liquid to make 100ml of Soyabean Casein Digest broth medium or transfer 10 ml (Quantity corresponding to not less than 1 g or 1 mL specimen) of sample from the Total aerobic microbial count sample preparation to make 100ml Soyabean Casein Digest broth medium unless otherwise described in the specific STP.

Negative Control: Take 100 mL of sterile Soyabean-Casein Digest broth Medium without any inoculation.

Positive Control: Add 1mL

Incubate the sample, negative control and positive control 30-35°C for 18 to 24 hours.

Examine the medium for growth.

Interpretation:

Negative control flasks should not show any growth.

Positive control growth should be present.

If growth is present (turbidity observed) in the sample flask, or the media difficult to observe the growth with sample (Likely some powders and capsules can alter the color and the clearness of the media) mix by gentle shaking and proceed to test for Staphylococcus aureus. If there is no growth in the sample flask, that indicates, sample meets the requirement for absence of Staphylococcus aureus.

Note: Incase of water sample add 1 ml sample in 9 ml Soyabean Casein Digest  broth medium for test and negative control with out adding anything and positive control by adding Staphylococcus aureus culture in 10 ml media. 

Selective Enrichment and Conformation test:

Add 15 to 20 mL of Mannitol-salt Agar medium into each petriplate.

Streak the surface of Mannitol-salt Agar medium by taking loopful of inoculum from sample.

Streak the surface of the selected medium with standard culture of Staphyloccus aureus.

Maintain a negative control by the omitting the sample and standard culture in respective plates.

Cover and invert the dishes and incubate at 30 to 35°C for 18 to 72 hours.

After incubation, examine the plates.   

3.3  Interpretation:  

3.3.1    If  the  colonies  on  the  sample  plate  does  not  match  with the colony characteristic given table-1, that indicates that the sample meets the requirements for the absence of Staphylococcus aureus. If the colonies on the sample plate matches with the colony characters given table-1 that indicates that the sample does not meets the requirements for the absence of Staphylococcus aureus. If require perform identification test.    

Table1.  Morphologic Characteristics of Staphylococcus aureus on

                                                Selective Agar Medium

General testing procedure, staphylococcus, aureus