MacConkey Agar without Crystal Violet and Salt is used for the isolation and differentiation of Gram-negative enteric bacilli from specimens containing swarming strains of Proteus spp, and is not intended for use in the diagnosis of disease or other conditions in humans. MacConkey Agar is based on the bile salt-neutral red-lactose agar of MacConkey. The original MacConkey medium was used to differentiate strains of Salmonella typhosa from members of the coliform group. Formula modifications improved growth of Shigella and Salmonella strains. These modifications include the addition of 0.5% sodium chloride, decreased agar content, altered bile salts, and neutral red concentrations. The formula modifications improved differential reactions between enteric pathogens and coliforms. MacConkey Agar without Crystal Violet and Salt is a differential medium that restricts swarming of Proteus spp., aiding in the detection and isolation of enteric microorganisms. Sodium Chloride is deleted from the medium to provide an electrolyte deficient medium preventing Proteus spp. from spreading. In addition, this medium does not contain crystal violet allowing Staphylococcus, Enterococcus, and Mycobacterium spp. to grow.