Inhibitory effects of Listeria selective enrichment media on growth characteristics of L. ivanovii

Abstract

Various standard methods by different food regulatory bodies have been proposed different selective enrichment to grow and isolate Listeria monocytogenes in food samples. Different studies have demonstrated a variety of enrichment strategies to effectively improve the isolation rate of Listeria. However, very limited research was dedicated to understand the kinetics of Listeria spp. growth under imposed sublethal stresses by common selective agents used in those conventional enrichment media. A comprehensive list of primary and secondary enrichment media (i.e., UVM, LEB, SEB, HFB, PB, DFB, BLEB, MOPS-BLEB and FB) were used to study L. ivanovii multiplication at 37oC incubation for 24 hr. The medium concentrations were varied at four levels; 25%, 50%, 100% and 200% to accentuate the inhibitory effect of indigenous selective agents. The net normalized growth rate and the total cell count were utilized to evaluate the lethality of each selective media and survivability of L. ivanovii. The toxicity of the media to L. ivanovii was escalated significantly and produced negative impact on growth as the strength of the enrichment medium concentration increased (25% to 200%). The negative growth effect was more pronounced for all secondary enrichment media used. Only did LEB and SEB return positive net growth rate and produce the least negative impact on the cell multiplicity.