A child comes with fever, cold, cough, membrane over tonsils, nasal swab is taken, culture should be done on which medium for earliest diagnosis

The symptoms and membrane over the tonsil are suggestive of infection with Corynebacterium diphtheriae. For the earliest diagnosis, the nasal swab should be cultured in Loeffler's serum slope. Loeffler's serum slope: diphtheria bacilli grow on this media very rapidly and colonies can be seen in 6-8 hours, long before other bacteria grow. Colonies are small, circular white opaque discs but enlarge on continued incubation and may acquire a distinctly yellow tint. Reference: Textbook of Microbiology; Anathanarayan and panicker's; 10th edition; Page no: 242