CYSTINE HEART AGAR BASE

Description

Francisella tularensis is the cause of tularaemia, a plague-like disease of rodents and other small organisms. It was first described in humans in 1907. The organisms are strict aerobes; fresh isolates cannot be cultured on ordinary medium but require a complex medium containing blood, or tissue extracts and cystine. Several media formulations were employed to isolate this microorganism. Blood Dextrose Cystine Agar, described by Francis was found to be satisfactory for cultivating F.tularensis. Addition of 0.05% cystine and 1% dextrose to Heart Infusion Agar can also be employed for cultivation of F.tularensis. Subsequently haemoglobin was added to Cystine Heart Agar Base to develop a satisfactory cultivation medium for F.tularensis. This medium is also known as Cystine Glucose Blood Agar and is the most suitable medium for isolating F.tularensis. Hemoglobin provides additional nutrients and growth factors. This medium also supports growth of gram-negative cocci and other pathogenic microorganisms without additional enrichment. Cystine Heart Agar Base can be supplemented with Rabbit blood and antimicrobial agents. This medium is a nutritionally rich medium, which may also be used for cultivating many other organisms generally difficult to grow. Overgrowth by contaminating organisms can be reduced by incorporating 100-500 units penicillin per ml into the medium. F.tularensis is a Biosafety Level 2 pathogen that can be transmitted by aerosols or by penetration of unbroken skin. Wearing of gowns, gloves and masks is recommended for people handling suspected infectious material.