Selenite Broth (Selenite F Broth), 5 kg

Klett (1) first demonstrated the selective inhibitory effects of selenite and Guth (2) used it to isolate Salmonella Typhi . Leifson fully investigated selenite and formulated the media (3). Enrichment media are routinely employed for detection of pathogens in faecal specimens as the pathogens are present in a very small number in the intestinal flora. Selenite Broth is useful for detecting Salmonella in the nonacute stages of illness when organisms occur in the faeces in low numbers and for epidemiological studies to enhance the detection of low number of organisms from asymptomatic or convalescent patients (4). Casein enzymic hydrolysate provides nitrogenous substances. Lactose maintains the pH of medium. Selenite is reduced by bacterial growth and alkali is produced. An increase in pH lessens the toxicity of the selenite and results in overgrowth of other bacteria. The acid produced by bacteria due to lactose fermentation serves to maintain a neutral pH. Sodium phosphate maintains a stable pH and also lessens the toxicity of selenite. Enriched broth is subcultured on differential plating media such as Bismuth Sulphite Agar (M027), Brilliant Green Agar (M016), XLD Agar (M031) etc. Do not incubate the broth longer than 24 hours as inhibitory effect of selenite decreases after 6 - 12 hours of incubation (5). Storage and Shelf-life: Store below 30°C in tightly closed container and the prepared medium at 2 - 8°C. Use before expiry date on the label. References: 1. Klett A., 1900, Zeitsch Fu¨r Hyg. Und. Infekt., 33: 137. 2. Guth F., 1926, Zbl. Bakt. I. Orig., 77:487. 3. Leifson E., 1936, Am. J. Hyg., 24(2) : 423. 4. Kelly, Brenner and Farmer, 2003, Manual of Clinical Microbiology, 8th ed.,Lennett and others (Eds.), ASM, Washington, D.C. 5. Chattopadhyay W. and Pilford J. N., 1976, Med. Lab. Sci., 33:191.