Pre-enrichment Media Research Articles

Further Studies on the Screening Technique for Determining Salmonella- Negative Samples of Pasteurized Dried Egg

A METHOD was described by Banwart et al. (1966, 1968) to detect Salmonella- negative samples of pasteurized dried egg products. The procedure included preparing tubes of mannitol purple agar and SIM agar and introducing them inverted into a lactose broth-egg mixture. During incubation, the mannitol was fermented or hydrogen sulfide (H2 S) was produced in the SIM agar if salmonellae were present. The determination of mannitol fermentation or H2 S production could be accomplished in tubes of media external to the lactose broth-egg system and would simplify the screening technique of Banwart et al. (1968). In the tests previously reported, lactose broth was the pre-enrichment medium. Nutrient broth was suggested as a replacement for lactose broth to pre-enrich food samples (Taylor et al., 1964).This research was conducted to determine if the mannitol-SIM inverted-tube system could be utilized in broths other than lactose and if tubes of mannitol and SIM inoculated external to…

Isolation of Salmonellae from food samples. V. Determination of the method of choice for enumeration of Salmonella.

Comparison of three methods by which salmonellae may be isolated and enumerated from dried albumen, direct inoculation of enrichment media, centrifugation of samples, and pre-enrichment in noninhibitory media, reveals pre-enrichment to be the method of choice. The superiority of pre-enrichment manifests itself in replicate aliquots of the same sample by producing a statistically significant increase in numbers of isolations of salmonellae and in empirical use with various albumen samples by consistently higher values of most probable numbers (MPN). The primary factor involved in this superiority appears to be the greater ability of small numbers of salmonellae to initiate growth in the nonselective mannitol purple sugar broth than in the inhibitory enrichment media. The method of analysis recommended entails inoculation of mannitol broth pre-enrichment medium, transfer of 24-hr culture aliquots to tetrathionate broth, and streaking on brilliant green agar for isolation of salmonellae.