Modified agar medium for detecting environmental salmonellae by the most-probable-number method.
Salmonellae in the environment remain a potential source of disease. Low numbers of salmonellae have been detected and enumerated from environmental samples by most-probable-number methods which require careful colony selection from a plated agar medium. A modified xylose lysine brilliant green medium was prepared to control the loss of selectivity caused by heating the brilliant green component. Added agar reduced colony spreading. The medium contained 47 g of xylose lysine agar base per liter; the agar content was adjusted to 2%, autoclaved, cooled to 50 degrees C, and then amended just before pouring to include H2S indicator and 7 ppm (7 ml of 1:1,000 brilliant green per liter) of unheated brilliant green dye. H2S-positive salmonellae were easily detected from sewage sludge compost to the exclusion of most other gram-negative bacteria. As a result, fewer non-salmonellae were picked for further most-probable-number analysis, greatly reducing the work load associated with the most-probable-number method. Direct plating was possible for enumerating salmonellae in laboratory composts containing ca. 10(3) or more salmonellae.
D000362:Agar; D001431:Bacteriological Techniques; D003470:Culture Media; D008239:Lysine; D000644:Quaternary Ammonium Compounds; D012475:Salmonella / Q000254:growth & development / Q000302:isolation & purification*; D013776:Tetrathionic Acid; D014994:Xylose
D003470:Culture Media; D000644:Quaternary Ammonium Compounds; D013776:Tetrathionic Acid; D000362:Agar; D014994:Xylose; C006798:brilliant green; D008239:Lysine