<prompt> Which of the following is true about Corynebacterium diphtheriae?Loefflers serum is highly selective media for C. diphtheriaeElek gel is a precipitation testGram negative bacilli, non-motile, non capsulatedMetachromatic granules is produced on stain only by one strain of C. diphtheriae  <response>: Elek gel is a precipitation test. - Loefflers serum slope is an Enriched medium. - Selective medium for C. diphtheriae is tellurite blood agar eg. Mc Leods and Hoyles media or cystine - tellurite agar - Tinsdale medium. - Eleks gel is a precipitation test. It is an in vitro test for toxigenicity of the diphtheria bacillus. Refer to the image below - C. diphtheriae is gram positive, non-motile and non-capsulated, pleomorphic, non-sporing, slender rod- shaped bacilli. - All strains of C. diphtheriae show metachromatic granules on staining. Granules are composed of polymetaphosphate. Albes stain is used to demonstrate VolutinMetachromaticBabes Ernst granules of Corynebacterium diphtheriae. It contains toluidine blue O and malachite green. The bacilli are usually arranged in Chinese letter or cuneiform arrangement. Other stains : Neissers stain, Ponders stain. 