Investigations on the toxic effect of selective enrichment media on the growth of same Salmonella types
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Salmonellae have been and still are an important problem in the hygiene of food products and effective battle with these bacteria is dependent to a great extent on the possesion of laboratory methods guaranteeing their detection in the samples examined. The discovery of such methods has been the goal of the work of many investigators. Unfortunately, the methological problems in the course of these investigations on salmonellae have been found to be complicated. The results obtained depend on a variety of factors such as: type of the product examined, size of the sample, type of the enrichment media, time and temperature of incubation, and many other factors. (7, 15). According to some autors (3, 4, 6, 8, 11, 12, 13,) the enrichment media have the deciding influence on the effectiveness of the investigations. The most commonly used among these are: tetrationate bile brilliant green broth, sodium selenite broth (9), and selenite brilliant green medium (16). There are also numerous modifications of these depending on changes in proportion or addition of other chemical compounds such as, for example, cystine, dukitol, brilliant green, or others to selenite broth (10, 12, 16) or sodium sulfathiazole and novobiocine to tetrationate broth (3, 7). All of these enrichment media, containing inhibitors, naturally, influence unfavorably the growth of salmonellae to a certain degree. Supporting this view are the works of Smith (14) who found a toxic effect of the tetrationate broth and selenite broth on S. choleraesuis and S. abortusovis, Leifson (9) who noted the same in relation to S. choleraesuis and Banwart and Ayres (1), who showed a toxic activity of tetrathionate broth on S. paratyphi A. The toxic influence of selective media is probably sometimes so strong that better results may be obtained by using nutrient broth (17). This may be deducted from the observations of Hobbs ,(5) and also Galton et al. (2) made during the investigations of powdered eggs. The fact that the divergences between the growth requirements and the susceptibility to the toxicity of various media may be remarkable in particular types of Salmonella, led the authors to undertake their investigations on the toxic effect of the most commonly used enrichment media, with references to 16 types of these bacteria.
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