What is Coagulase-Positive Staphylococcus aureus?
Food poisoning from coagulase-positive Staphylococci is caused by the presence of enterotoxins in ingested foods. Staphylococcus hyicus and Staphylococcus intermedius are common veterinary pathogenic strains, while Staphylococcus aureus is the most common human pathogenic strain. S. aureus is a Gram-positive bacteria, found commonly on human skin and mucous membranes, with around 50% of the population being carriers. It is a common cause of bacterial food poisoning.
Since S. aureus is easily destroyed by heat and common cleaning products, its presence in environmental monitoring and food samples can be a sign of inadequate sanitisation and disinfection practices. Enterotoxins produced by coagulase-positive Staphylococci are not usually detectable until the bacteria has reached a concentration of more than 105 CFU/g. However, once the toxins are produced, they are virtually impossible to eliminate.
How do we test for Coagulase-Positive S. aureus?
The traditional ISO method for coagulase-positive S. aureus involves plating samples onto Baird Parker agar with egg yolk and tellurite and incubating for 48 hours. S. aureus colonies typically have a smooth, circular, convex appearance ranging from grey to jet black. Plates with 20-200 colonies are selected for subsequent confirmation tests.
Enumeration and confirmation of coagulase-positive S. aureus is performed in two ways:
- Plating on Baird Parker RPF (Rabbit Plasma Fibrinogen) agar
Incubating for a further 24-48 hours and reading plates
- Incubating colonies in brain heart infusion broth for 24 hours
Adding 0.1 mL of culture to 0.3 mL rabbit plasma and observing coagulase reaction
In some cases, the fibrin halo can fade before plates are read at 48 hours of incubation. Therefore, it is now recommended that Baird Parker RPF plates are read at both 24 and 48 hours which adds to technician’s already heavy workload.
Save Time & Resources with EASY STAPH Agar
EASY Staph is an alternative method for the enumeration of coagulase-positive Staphylococci in human food products, animal feeds and environmental samples. EASY Staph agar provides coagulase-positive staphylococci results after 22 hours of incubation without the need for confirmation. This replaces the traditional 48 hours incubation in the ISO 6888-2 standard and subsequent confirmation steps, such as testing with rabbit plasma fibrinogen.
Spread Plate Instructions
- Add 0.1 mL of the sample to be tested to the surface of pre-poured EASY Staph plates
- Spread the inoculum with a sterile triangle/spreader
- Incubate the plates inverted at 37°C ± 1°C for 24 hrs ± 2 hrs
Pour Plate Instructions
- Transfer 1 mL of sample to the bottom of an empty sterile Petri dish
- Add approx. 15 mL of EASY Staph® agar, mix and allow to solidify
- Incubate the plates inverted at 37°C ± 1°C for 24 hrs ± 2 hrs.
Reading EASY Staph Plates
EASY Staph plates can be read after 22 to 72 hours of incubation for pour plate inoculation and spiral method and 22 to 48 hours for surface inoculation. Coagulase-positive Staphylococcus aureus colonies will be surrounded by an opaque halo of fibrin so no confirmation steps are needed.
The Benefits of EASY Staph:
- Method fully validated by AFNOR Certification
- Detection of all coagulase-positive staphylococci including enterotoxigenic strains
- Halo around positive colonies enables easy plate reading
- No need for confirmation steps or additional media
- Detection and enumeration in only 22 hours compared to 48+ hours for ISO method
- Plates can be inoculated using the pour plate or spread plate method
You can download the EASY STAPH Technical Datasheet for more information here
Or browse our EASY STAPH products here
Contact us below for a quote or to arrange a sample pack for evaluation.
