Culture Methods Differ on the Isolation ofSalmonella EntericaSerotypes from Naturally Contaminated Swine Fecal Samples

Abstract

Abstract. Four culture methods (A, B, C, and D) were comparatively evaluated for their ability to isolate Salmonella enterica from pooled swine fecal samples (n ϭ 100). None of the methods was able to isolate Salmonella from all positive samples. The relative sensitivity of the culture methods evaluated was 82%, 94%, 95%, and 78% for methods A, B, C, and D, respectively. The comparison of sensitivities showed that methods B and C performed significantly better (P Ͻ 0.05) than methods A and D. Although relative sensitivities of methods B and C were equal, from the 89 positive samples concomitantly detected by both, 35 (39.3%) had different serotypes (no match) isolated by each method. On the basis of the results of this study, it was concluded that culture methods differ on the isolation of S. enterica serotypes from naturally contaminated swine fecal samples. Depending on the objective(s) of investigations on the ecology and epidemiology of S. enterica in swine populations, a method or a combination of methods should be considered for more reliable results.An incredible number of different culture methods for isolation of Salmonella have been published, but currently, there appears to be no consensus on what would be the best method. 12 As a consequence, confusing and contradictory results are frequently found in the literature.For years, 2 culture methods (methods A and B, described below) have been concomitantly applied in our laboratory routine for isolation of Salmonella from swine samples. 13 A recent study 3 compared these methods with another frequently applied culture method (preenrichment in buffered peptone water, followed by enrichment in Rappaport-Vassiliadis [RV] broth and isolation on Xylose-Lysine-Tergitol-4 [XLT-4] agar), reporting better results when isolation was conducted using method B. However, we felt that continuous im- Disclaimer: Mention of trade names or commercial products in this article is solely for the purpose of providing specific information and does not imply recommendation or endorsement of the U.S. Department of Agriculture. provement in the sensitivity of culture methods was necessary and should be persistently pursued. Therefore, culture methods C and D (described below) were developed and included in this study, whose objective was to comparatively evaluate 4 different culture methods (methods A, B, C, and D) and to assess their relative sensitivity for the isolation of Salmonella enterica from naturally contaminated swine fecal samples. The current knowledge of the effect of different culture methods on the isolation of different S. enterica serotypes from naturally contaminated samples is very limited. Most studies published to date have simply focused on the sensitivity of culture methods for the detection of positive samples presenting little information on the isolation of multiple serotypes. This information is crucial, particularly when trying to understand the complex ecology and epidemiology of Salmonella in livestock.To compare the culture methods for the isolatio...

Sensitivity of the ISO 6579:2002/Amd 1:2007 Standard Method for Detection of Salmonella spp. on Mesenteric Lymph Nodes from Slaughter Pigs

“…For instance, the Se of bacteriology on fecal samples has been reported to be as low as 9% (10) and higher than 90% (11,12). Thus, when more than one method is used within the same surveillance system, comparisons are likely to be biased (13).…”

“…It is well recognized that the Se of bacteriological culture varies with regard to factors such as the sample of choice (feces, lymph nodes, or tonsils), the type of sample (single or pooled), the amount of sample processed, or the combination of culture media used for isolation of the bacterium (7)(8)(9)(10)(11)(12). For instance, the Se of bacteriology on fecal samples has been reported to be as low as 9% (10) and higher than 90% (11,12).…”

Use of Pooled Samples for the Detection of Salmonella in Feces by Polymerase Chain Reaction

“…Finally, different cultivation methods performed on the same set of samples can yield different Salmonella serotypes. 17 Thus, a rapid, sensitive, and inexpensive method for the detection of Salmonella in fecal samples would enhance the efficiency of epidemiological studies of Salmonella. This initial screening method would ideally eliminate all Salmonella-negative samples from further analysis and result in the isolation of individual colonies from all Salmonella-positive samples.…”

“…3,17,21 When the goal of herd sampling is to identify efficiently the Salmonellapositive animals in the herd and to obtain Salmonella isolates from these animals, the costs of cultivation are further increased by the need for confirming all suspect Salmonella colonies. Bacteria such as Citrobacter and H 2 S-positive, lactose-negative Escherichia coli can have a similar appearance to Salmonella on certain agar media, and therefore require biochemical characterization of presumptive colonies of Salmonella when in fact no colonies of Salmonella are present on the agar plate.…”

Detection of Virulence invA Gene in the Salmonella Isolated from Fecal Samples of Poultry by Pcr Method

“…The majority of epidemiological studies of Salmonella still rely on conventional bacteriological culture methods to detect Salmonella in fecal samples . Culture-based methods for Salmonella are laborious and time-consuming, taking up to 7 days to complete, and are inefficient for epidemiological studies in populations with low prevalence of Salmonella, particularly because of the large number of samples that are typically required (Rostagno et al, 2005;Ward et al, 2005).Thus, a rapid, sensitive, and inexpensive method for the detection of Salmonella in fecal samples would enhance the efficiency of epidemiological studies of Salmonella. For accurate profiling of the prevalence of Salmonella spp, the use of invA gene specific PCR method is considered as an appropriate method.…”