Abstract
A comparative study was performed to evaluate best practice culture media and enrichment broths for recovering Salmonella species from human stool samples. A total of 1297 human stools were collected and processed in this study. Evaluation of agar media was carried out by direct plating (DP), 1096 stool samples were inoculated on Modified Semisolid Rappaport-Vassiliadis (MSRV), Xylose-Lysine-Deoxycolate (XLD), MacConkey (MAC), and Hektoen Enteric (HE) agars. Evaluation of enrichment broths were carried out by enrichment all 1297 stool samples in Selenite broth (SB), Rappaport-Vassiliadis (RV) broth, and Buffered Peptone Water (BPW), followed by plating on MSRV, MAC, and HE agars. A total of 102 Salmonella-positive stools by DP, 85.3% (87/102) were recovered utilizing MSRV while recovery from XLD, MAC, and HE agars were 34.3% (35/102), 34.3% (35/102), and 29.4% (30/102) respectively. A total 299/1297 stools samples were Salmonella-positive on at least one plating medium after enrichment procedure were 77.3% (177/299) for SB, 86.0% (197/299) and 78.6% (180/299) for RV and BPW respectively. All Salmonella isolated in this study was nontyphi Salmonella. Presently, the data suggest that the use of MSRV over MAC, HE, and XLD agars for isolation nontyphi Salmonella species from human stools is more efficacious. Additionally, use of MSRV in combination with MAC and HE agars following enrichment in RV broth enhances recovery of nontyphi Salmonella species. However, RV broth is inhibitory to typhi Salmonella, thus use of MSRV medium in combination with MAC, HE or XLD agars in direct plating following enrichment in non-selective BPW is an alternate method for recovery of both typhi and nontyphi Salmonella species contaminated in human stool samples.
Highlights
Food-borne salmonellosis continues to be an important public health problem both in developed and developing countries [1]-[3]
In order to evaluate the performance of Modified Semisolid Rappaport-Vassiliadis (MSRV), XLD agar media, and enrichment broths (e.g., Buffered Peptone Water (BPW) and RV) with our standard method for Salmonella spp. detection (MAC and Hektoen Enteric (HE) agars and Selenite broth (SB) enrichment broth), a comparative study was conducted by direct plating for the isolation of Salmonella spp
0.5 mL of each stool suspension was inoculated into SB and BPW enrichment broths and incubated aerobically at 37 ̊C for 18 - 24 hours while inoculated RV broth was incubated at 42 ̊C for 18 - 24 hours, followed by subculture onto MacConkey agar (MAC), HE, and MSRV media and incubated as described above
Summary
Food-borne salmonellosis continues to be an important public health problem both in developed and developing countries [1]-[3]. Stuart and Pivnick used selective motility (SM) medium modified with selenite F broth to make a semisolid medium contained in motility tubes to isolate Salmonella spp. from stool specimens. Modified Semisolid Rappaport-Vassiliadis (MSRV) medium is a modification of Rappaport-Vassiliadis enrichment broth for detecting motile Salmonella spp. in food products and feces [12] [13]. The original study on MSRV medium revealed a semisolid could be used as a rapid and sensitive method for isolation of Salmonella spp. from food products following pre-enrichment or selective enrichment [14] [15]. In order to evaluate the performance of MSRV, XLD agar media, and enrichment broths (e.g., BPW and RV) with our standard method for Salmonella spp. detection (MAC and HE agars and SB enrichment broth), a comparative study was conducted by direct plating for the isolation of Salmonella spp. Samples were enriched in SB broth (routine standard medium), BPW and RV broths, and prior to plating
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