Quantitative recovery of Listeria monocytogenes and select salmonella serotypes from environmental sample media.

Environmental sampling has become increasingly important in the food industry for monitoring the presence of specific pathogens such as Listeria monocytogenes and Salmonella enterica. Several microbiological media are available for storage and transport of environmental samples from the processing plant to the test laboratory. In this study, we quantified the survival of L. monocytogenes, S. Typhimurium, S. Enteritidis, and S. Typhi in environmental sampling media over several time and temperature combinations to determine optimum conditions for transport and storage. A cocktail of L. monocytogenes strains and Salmonella serotypes was separately added to tubes of Dey-Engley (D/E) Neutralizing Broth, Copan SRK solution, and Neutralizing Buffer and incubated at either -4, 4, 10, or 15 degree C. Counts were made of the bacterial load after 0, 12, 24, and 48 h. Neutralizing Buffer and Copan SRK solution were best at maintaining bacterial concentrations at all temperatures. D/E Neutralizing Broth, at 10 and 15 degrees C, allowed significant bacterial growth. This study helped validate the use of these 3 media for environmental sample transport and storage at cold holding temperatures and demonstrated that, at elevated temperatures (>4 degrees C), it is preferable to use Neutralizing Buffer or Copan SRK solution for quantifying microbial recovery.