Keywords: Portable Culture Device, Staphylococcus aureus, Alkaline Phosphatase, Point of Control, Blue Phos.
In this work we present a test for presumptive identification of Staphylococcus aureus (S. aureus) from foods using a Portable Culture Device (PCD) especially for point of control testing in resource limited settings. PCDs are an alternative to traditional media plates. They are made of masking tape and paper and have a reservoir of medium for growth of culture. They are portable, cost effective and are useful for point of control testing in resource limited settings. Staphylococcal Food Poisoning (SFP) is one of the most common food borne diseases in underdeveloped countries and is caused by the ingestion of food contaminated with staphylococcal enterotoxins. The test described herein is based on detection of presence of alkaline phosphatase enzyme using chromogenic substrate BluePhos®. The test was standardised using known alkaline phosphatase producing culture, Staphylococcus aureus ATCC 25923, with respect to the time of incubation and limit of detection. Proof of concept studies were done using food samples spiked with known cell numbers of S. aureus ATCC 25923 and then the devices were used to test actual food samples. Cell numbers of 105 CFUmL−1 of S. aureus, which is a critical number for diagnosis of SFP could be detected within 5 hours as against 24 hours required by agar-based methods. The test is robust and cost effective. It does not need any sophisticated instruments or trained personnel as it is based on visual colour detection, hence ideal for resource limited settings.
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*Corresponding author: Ramnarain Ruia Autonomous College, Department of Microbiology, L. Nappo Road, Matunga, Dadar (East), Mumbai, Maharashtra-400019 Email: firstname.lastname@example.org