Controlling Salmonella with plant-derived antimicrobials
Dr Mike Darre, Extension Poultry Specialist for the University of Connecticut presented data at the 2013 Egg Industry Issues Forum promoting the application of natural plant-derived antimicrobials as a possible approach to suppressing egg-borne Salmonella Enteritidis (SE).
In vitro assays demonstrated that a number of these compounds (trans-cinnamaldehyde, eugenol and caprylic acid) can inhibit Salmonella and depress up-regulation of genes influencing virulence. It is questioned whether these effects occur under commercial conditions or whether the relatively small quantifiable reduction noted is of any practical or epidemiologic significance, writes Simon Shane on Egg-Cite.com. Compounds tested reduced adhesion and invasion of oviduct epithelial cells by SE from 30% to 50% compared to controls under laboratory conditions.
Excretion of SE from hens (vaccination status unknown) subjected to challenge (dose not specified) persisted in faeces and in yolk for the duration of a ten-week trial. Incorporation of trans-cinnamaldeyde in feed significantly reduced recovery of SE from yolks and the surface of shells compared to untreated control hens. The recovery of SE from 40% of yolks and from 80% of the shell surface of eggs derived from controls, presumes high levels of both vertical trans-oviductal and transovarial transfer and intestinal colonization. These values are inconsistent with the literature.
The trial was based on inclusion of a pure reagent-grade trans-cinnamaldehyde at either 1.0% or 1.5% in diets to achieve the claimed inhibitory effect. Even if commercial product was available at 100% concentration, it would require 73,000 tons annually to supplement the feed of 180 million hens producing shell eggs each year in the US assuming a 1% inclusion level. Given that commercial-grade extracts are not available in the quantities and concentrations that would be required and costs are unknown, the entire prospect of using these plant-derived anti-microbials to inhibit Salmonella under commercial conditions appears either prohibitively expensive or impractical.
The justification for embarking on an experimental program without due regard to the economic realities appears narrow focused and oblivious to commercial realities. To infer that the research presented offers a practical solution or even a contribution to reducing vertical transmission of SE at a national meeting is premature. If there is any possible application, it would appear that the technology might be applied to organic production which functions with poorly justified restrictions on inhibitory feed additives. Under NOP rules a combination of vaccination, supplementation of feed with approved probiotics and prebiotics, biosecurity and refrigeration of eggs offers cost-effective protection to consumers.
The effect of including phytophenolics in hen diets on taste of eggs, composition of intestinal flora, potential residues of the compounds and their metabolites, production parameters and consumer response have not been evaluated. An important consideration is that a number of plant-derived compounds with anti-bacterial action including oregano inhibit the action of Salmonella Typhimurium live modified vaccine. This represents a contraindication for the purpose for which “natural plant-derived antimicrobials” are considered.
The presentation and approach by the research team at the University of Connecticut raises questions as to the overall conceptual appreciation of the needs of the egg production industry. It would appear that experiments are planned and carried out to determine the potential effectiveness and mechanism of action for compounds which ultimately may not have any commercial value or application. While basic research is to be encouraged, even if not supported financially, there is concern over linking preliminary results with the false or premature promise of resolving problems. In recent months university public relations departments have offered media the results of preliminary studies which lack substantiation or the prospect of commercial application. This is to the detriment of scientists achieving incremental improvements in proven modalities to control foodborne pathogens.
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