Effect of Various Media and Incubation Conditions on Recovery of Inoculated Salmonella from Poultry Feed

Abstract

Samples of commercially pelleted poultry feed (30 g) were inoculated with nalidixic acid-resistant marker strains of Salmonella heidelberg or S. montevideo at levels of 1 (low), 20 (medium), or 40 (high) cells/g of feed, then 100 ml of either a nonselective preenrichment medium (lactose broth) or a selective enrichment medium [selenite cystine (SC) or tetrathionate brilliant green (TT) broth] was added and incubated at either 37 or 43 C for 24 or 48 hr in different experiments. Four selective plating media [MacConkey with 100 ppm nalidixic acid, brilliant green (BG) sulfa, modified BG, bismuth sulfite] were then streaked. MacConkey agar with nalidixic acid served as a control to which the other three plating media were compared. After 24 hr incubation at 37 C, colonies with characteristics typical of Salmonella were selected from the plates and examined biochemically and serologically to determine if they were the marker organism. In this study, preenrichment was counterproductive, because the marker organisms were recovered much more often with direct enrichment in SC or TT broth than with reenrichment in lactose broth. The TT broth produced 135 positive recoveries, whereas only 88 positive recoveries were made with SC. No differences were observed between 37 and 43 C or 24 and 48 hr incubation of the selective enrichment media. Overall efficiency of the plating media for Salmonella recovery from feed, when compared to the control (MacConkey), was BG sulfa, 65%;modified BG, 64%; and bismuth sulfite, 40%. The most effective enrichment broth-plating medium combination was TT-BG sulfa, yielding 86% positive recoveries when compared to the control.

APPLICATION OF GENE AMPLIFICATION IN CONJUNCTION WITH A HYBRIDIZATION SENSOR FOR RAPID DETECTION OF SALMONELLA SPP. AND FECAL CONTAMINATION INDICATORS IN ANIMAL FEEDS

“…Present detection procedures require between 16 and 20 h for preenrichment and between 24 and 48 h for selective enrichment for Salmonella spp. (Cox et al 1982b;Waites 1997). PCR amplification and oligonucleotide probes have successfully detected both artificially seeded and naturally occurring Salmonella spp.…”

Comparison of Preenrichment to Direct Enrichment and the Effect of Pyruvate in Media for Recovery of Salmonellae in Feed

“…Salmonellae were recovered from only 7 of the 16 positive feed samples when preenrichment was used, whereas with direct enrichment in SC and TT Salmonellae were recovered from 14 of the 16 positive samples. Direct enrichment had also been found to be superior to preenrichment for recovery of Salmonellae from artificially inoculated poultry feed (Cox et al, 1982a), frozen broiler carcasses (Cox and -Mercuri, 1979), and frozen meat products (Cox et al, 1980). Smyser et al (1963) and Murphy (1969) were also unable to demonstrate greater recovery of Salmonellae from artificially inoculated poultry feed with lactose preenrichment.…”

“…Preenrichment is optional in a US Department of Agriculture (USD A, 1974) procedure for isolation of Salmonellae from animal feeds. Cox et al (1982a) found 4hat direct enrichment in TT or SC was superior to preenrichment in lactose broth (L) for recovery of Salmonellae artificially inoculated into feed samples. Brewer et al (1977) reported that the addition of 1% sodium pyruvate to their medium increased the recovery of heat-stressed Staphylococcus aureus.…”

Important Aspects of Salmonella in the Poultry Industry and in Public Health

“…1998), while Wyatt et al (1993) used buffered peptone water. Cox et al (1982) reported that preenrichment decreased the recovery of Salmonella spp. from artificially contaminated poultry feed when compared with direct enrichment.…”