how to detect salmonella ?
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Charles A. Burke
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In enterocolitis, the organism is most easily isolated from a Stool sample. However, in the enteric fevers, a blood culture Is the procedure most likely to reveal the organism during The first 2 weeks of illness. Bone marrow cultures are often Positive. Stool cultures may also be positive, especially in Chronic carriers in whom the organism is secreted in the Bile into the intestinal tract. Salmonellae form non–lactose-fermenting (colorless) Colonies on MacConkey’s or EMB agar. On TSI agar, an Alkaline slant and an acid butt, frequently with both gas and H2S (black color in the butt), are produced. S. typhi is the Major exception; it does not form gas and produces only a Small amount of H2S. If the organism is urease-negative (Proteus organisms, which can produce a similar reaction. On TSI agar, are urease-positive), the Salmonella isolate can Be identified and grouped by the slide agglutination test Into serogroup A, B, C, D, or E based on its O antigen. Definitive serotyping of the O, H, and Vi antigens is performed by special public health laboratories for epidemiologic purposes. Salmonellosis is a notifiable disease, and an investigation to determine its source should be undertaken. In certain cases of enteric fever and sepsis, when the organism is difficult to recover, the diagnosis can be made serologically by detecting a rise in antibody titer in the patient’s serum (Widal test).