Dynamics of Salmonella Isolation with Modified Semi-Solid Rappaport-Vassiliadis Medium

Abstract

The effect of low Salmonella cell concentrations in combination with high numbers of competitive flora after pre-enrichment on subsequent isolation with motility enrichment in modified semisolid Rappaport-Vassiliadis (MSRV) was studied. Salmonella was always detected on MSRV if the cell concentration in the preenrichment culture was at least 60 per ml, even if they were outnumbered by competitive bacteria by a factor of 107. In a total of 52 experiments, Salmonella detection on MSRV directly after preenrichment was successful in 46 tests. Combination of direct motility enrichment with additional motility enrichment after 8 h in tetrathionate brilliant green (TBG) broth resulted in 49 positive tests, compared to only 33 positive results after enrichment in TBG for 24 h with subsequent plating on selective agars.

The prevalence of Salmonella enteritidis and other Salmonella spp. among Canadian registered commercial layer flocks

“…Number of flocks in which salmonellas were isolated from the feed samples Salmonellas were isolated from the feed samples of 21 of 295 (7-2 %) flocks. The serovars isolated from the feed samples were compared to those isolated from the faecal and/or eggbelt samples of the same flocks (Table 5).…”

“…Not only the eggbelt but also the faecal samples were pre-enriched in BPW because laying hens shed salmonellas only intermittently and in low numbers in the faeces [20], and about 102 of salmonellas per ml must be obtained by the end of the pre-enrichment period [21,22]. The samples were stomached and incubated at 37°C for 18-24 h. One-tenth of a ml of the BPW was then transferred with a sterile 1 ml pipette and inoculated at the periphery of a Modified Semisolid Rappaport Vassiliadis (MSRV) agar [21] plate.…”

“…Not only the eggbelt but also the faecal samples were pre-enriched in BPW because laying hens shed salmonellas only intermittently and in low numbers in the faeces [20], and about 102 of salmonellas per ml must be obtained by the end of the pre-enrichment period [21,22]. The samples were stomached and incubated at 37°C for 18-24 h. One-tenth of a ml of the BPW was then transferred with a sterile 1 ml pipette and inoculated at the periphery of a Modified Semisolid Rappaport Vassiliadis (MSRV) agar [21] plate. Overgrowth of salmonellas by competing organisms in the pre-enrichment medium was not considered to be an impeding factor in isolation of salmonellas because a few salmonella bacteria in the pre-enrichment culture are capable of motility and growth in MSRV medium even if they are outnumbered by competing bacteria by a factor of 107 [21].…”

“…The samples were stomached and incubated at 37°C for 18-24 h. One-tenth of a ml of the BPW was then transferred with a sterile 1 ml pipette and inoculated at the periphery of a Modified Semisolid Rappaport Vassiliadis (MSRV) agar [21] plate. Overgrowth of salmonellas by competing organisms in the pre-enrichment medium was not considered to be an impeding factor in isolation of salmonellas because a few salmonella bacteria in the pre-enrichment culture are capable of motility and growth in MSRV medium even if they are outnumbered by competing bacteria by a factor of 107 [21]. The inoculated MSRV medium was incubated overnight at 42°C for 18-24 h. A loopful of the semisolid agar was taken from the outer edge of migration and streaked onto MacConkey (MC) agar (Difco).…”

Comparision of the BAX® System with an in-house MSRV method for the detection of Salmonella in chicken carcasses and pork meat

“…The method using modified semisolid Rappaport-Vassiliadis (MSRV) agar as selective and differential enrichment medium for Salmonella can be stood out because of its simplicity, rapid response and serological confirmation of migrated cultures is obtained 48 h after the beginning of pre-enrichment (10,11) and low cost (32,33). The method has been validated by the Association of Official Analytical Chemists (AOAC) for cocoa products (AOAC 993-07) (9), for dried milk products (AOAC 995-07) (4) and recently in the Netherlands by the Animal Health Service in monitoring programs for the eradication of Salmonella at all levels of poultry meat production (14).…”