Submitted to: Feedstuffs
Publication Type: Popular Publication
Publication Acceptance Date: 7/10/2018
Publication Date: 10/1/2018
Citation: Richardson, K.E., Cox Jr, N.A., Cosby, D.E., Berrang, M.E., Hinton Jr, A. 2018. Stressors affect salmonella pH tolerance. Feedstuffs. 90(10):1-2.
Interpretive Summary: none
Technical Abstract: Previous studies have demonstrated that pre-enrichment media can become very acidic during the incubation of feed and feed ingredients and that those pH values can result in significant death and injury of the Salmonella. In a feed sample, the stress status of salmonellae may be genetically different than that of a viable culture of the same strain dependent on the stressor. Therefore, strains of Salmonella grown in a feed matrix prior to desiccation and heat exposure may respond differently to potential changes in pH within a pre-enrichment media which could affect recovery. The objective of this study was to evaluate the impact of stress (desiccation/heat exposure) on several Salmonella strains when subjected to pH changes that may occur during pre-enrichment. In this study an assortment of Salmonella serotypes were grown in either tryptic soy broth (unstressed) or in a meat and bone meal suspension which was subjected to dessication and heat exposure (stressed). This was done in order to stress the cultures and duplicate the stress that exists for salmonellae in feed and feed ingredients. Next, both stressed and unstressed cultures of each serovar were subjected to incubation in different pH solutions to determine their tolerance to acidic conditions. In the case of S. Typhimurium and S. Enteritidis, desiccation and heat exposure reduced their ability to tolerate acidic conditions with respect to cell death. It is interesting to note that the incidence of these two serotypes in feed is considered to be low. However, in the case of S. Senftenberg (one of the more common Salmonella isolates from feed) exposure to desiccation and heat increased its acid tolerance with respect to cell injury. This would suggest that the buffering capacity of the various pre-enrichment media used for feed and feed ingredients to maintain pH could bias the recovery serotypes of Salmonella isolated. Different serovars exhibit different pH tolerance and stressing them can further affect their pH tolerance. This highlights the need to consider the effects of pre-enrichment media on Salmonella isolation from feed. Future work will involve testing more serotypes and multiple strains within each serotype. The present methodology for detecting Salmonella in feed and feed ingredients has numerous weaknesses and needs to be re-evaluated and improved.