SEL, a Selective Enrichment Broth for Simultaneous Growth of Salmonella enterica , Escherichia coli O157:H7, and Listeria monocytogenes

Abstract

Multipathogen detection on a single-assay platform not only reduces the cost for testing but also provides data on the presence of pathogens in a single experiment. To achieve this detection, a multipathogen selective enrichment medium is essential to allow the concurrent growth of pathogens. SEL broth was formulated to allow the simultaneous growth of Salmonella enterica, Escherichia coli O157:H7, and Listeria monocytogenes. The results were compared to those obtained with the respective individual selective enrichment broths, RappaportVassiliadis (RV) for S. enterica, modified E. coli broth with 20 mg of novobiocin/liter for E. coli O157:H7, and Fraser broth for L. monocytogenes, and a currently used universal preenrichment broth (UPB). The growth of each pathogen in SEL inoculated at 10 1 or 10 3 CFU/ml was superior to that in the respective individual enrichment broth, except in the case of RV, in which Salmonella cells inoculated at both concentrations grew equally well. In mixed-culture experiments with cells of the three species present in equal concentrations or at a 1:10:1,000 ratio, the overall growth was proportional to the initial inoculation levels; however, the growth of L. monocytogenes was markedly suppressed when cells of this species were present at lower concentrations than those of the other two species. Further, SEL was able to resuscitate acid-and cold-stressed cells, and recovery was comparable to that in nonselective tryptic soy broth containing 6% yeast extract but superior to that in the respective individual selective broths. SEL promoted the growth of all three pathogens in a mixture in ready-to-eat salami and in turkey meat samples. Moreover, each pathogen was readily detected by a pathogen-specific immunochromatographic lateral-flow or multiplex PCR assay. Even though the growth of each pathogen in SEL was comparable to that in UPB, SEL inhibited greater numbers of nontarget organisms than did UPB. In summary, SEL was demonstrated to be a promising new multiplex selective enrichment broth for the detection of the three most prominent food-borne pathogens by antibody-or nucleic acid-based methods.

Influence of milk product type and its initial contamination on the efficiency of different methods for detection of Salmonella Enteritidis, Listeria monocytogenes and Escherichia coli O157:H7

“…At the same time, the intentional inoculation by ≈30 live cells of E. coli O157:H7 resulted in > 1000 colonies detected both by classical ISO procedure, or IMS procedure (both on selective and non-selective broths; BPW and mTSB+Nb). Lower growth rate of E. coli O157:H7 after inoculation by such a small concentration as ≈10 live cells compared to ≈30 live cells, as well as compared to the growth rates of S. Enteritidis and L. monocytogenes, is in accordance with the results of Kim and Bhunia (2008). They found no growth of E. coli O157:H7 inoculated by ≈10 live cells into mEC+n (modified E. coli broth with 20 mg of novobiocin/L), whilst the same level of intentional contamination was detectable in the cases of S. Enteritidis and L. monocytogenes (on respective broths), where the small level of initial contamination did not play such important role.…”

A multipathogen selective enrichment broth for simultaneous growth of Salmonella spp., Vibrio parahaemolyticus, and Vibrio cholerae

“…Therefore, it is of great significance to identify and detect these 3 pathogens rapidly and accurately, both for industry food quality and public health laboratories worldwide (Malorny et al, 2004).Conventional detection methods for pathogen detection are labor intensive, time-consuming and difficult to operate (Eiler and Bertilsson, 2006). The sensitivity and specificity of modern pathogen detection methods have been improved significantly in recent years (Kim and Bhunia, 2008) and multipathogen detection on a single assay platform simplifies the detection procedure greatly and has become a worldwide tendency (Omiccioli, 2009). Thus, multiplex detection of Salmonella spp., V. parahaemolyticus, and V. cholerae is also an attractive subject to be investigated.…”

“…Recently, many researchers have attempted to develop multipathogen selective enrichment medium. Kim and Bhunia have successfully formulated a multipathogen selective enrichment broth for simultaneous growth of S. enterica, Escherichia coli O157:H7, and Listeria monocytogenes (Kim and Bhunia, 2008). However, the enrichment broth for concurrent growth of Salmonella spp., V. parahaemolyticus, and V. cholerae remains unexplored.…”

Salmonella Detection Methods for Food and Food Ingredients

“…For example, RapidChek® SELECT TM Salmonella (Strategic Diagnostics Inc.) employs a primary enrichment media supplemented with a bacteriophage cocktail as a selective agent, which reduces the level of background flora in high burden samples allowing Salmonella to grow with minimal competition. In addition, there is also the development of enrichment broths for the concurrent enrichment of pathogens thereby reducing laboratory workloads with respect to the preparation of sample homogenates since different enrichment broths would no longer be required, and multiple analyses could be performed from a single universal enrichment culture (Kim and Bhunia 2008). Amendments to media have also been performed such as the addition of novobiocin (Restaino et al 1977;Devenish et al 1986), and cycloheximide to decrease fungal overgrowth .…”