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Questionable Significance of a Study Purporting to Demonstrate that a Yeast Product can Suppress Salmonella Braenderup


A supplier of a widely used yeast supplement recently circulated a promotional circular demonstrating the apparent ability of feces from hens fed the product to suppress Salmonella Branderup in vitro. The obvious motivation for the in vitro study conducted by the company was to demonstrate apparent bactericidal or bacteristatic action of the supplement on Salmonella Braenderup as previously claimed for Salmonella Enteritidis.

EGG-NEWS consistently supports scientific advances and comments on research which may have practical implications for sustainability, flock health or safety. On the distaff side, EGG-NEWS will always question promotional claims which lack scientific substance or are based on supposition or speculation especially when appealing to the cupidity of those who are unable to evaluate data or are subject to coercive marketing.

The promotional release describes the evaluation as an “intestinal activity modifier model”. Basically hens were fed the yeast product and excreta was assayed for volatile fatty acid content. In addition, the effect of feces from treated hens compared to controls was evaluated for the ability to suppress Salmonella Braenderup in vitro.

The release demonstrated a statistically significant increase in volatile fatty acids, which is biologically plausible and consistent with administration of a prebiotic to hens. The significance of the increase in volatile fatty acids in relation to the probability of infection of a flock with Salmonella Branderup was not addressed. The ability of the increased volatile fatty acids content of the terminal intestinal tract to actually reduce the level of shell contamination with Salmonella Braenderup was beyond the scope of the study but obviously relevant to the real-world situation..

The second aspect of the in vitro evaluation was the claim that supplementing diets with the yeast product suppressed Salmonella Braenderup. There was no description of the procedure used but data demonstrated that the level of Salmonella Braenderup was reduced from 6.86 log to 5.92 log per gram of feces representing a 0.94 log reduction. Again, the practical or epidemiologic significance is questioned of a ten-fold reduction in the quantum of Salmonella Braenderup as a result of supplementing diets with the yeast product.

It is generally accepted in the U.S. egg industry that the problem of Salmonella Braenderup attributed to the farm in question was due to environmental and operational factors specific to the complex, leading to the limited outbreak among consumers. There is no evidence that Salmonella Braenderup is widely distributed in the U.S. egg industry as evidenced by the fact that only one egg-attributed outbreak has occurred over many decades of public health surveillance of Salmonella.

The epidemiologic significance of the in vitro study is obviously in question and a cynical approach would be to conclude that the manufacturer was stretching microbiology to promote a product of questionable value with respect to suppressing potential salmonellosis among consumers. 

It would have been more acceptable if the company in question had demonstrated that hens fed the supplement were refractory to intestinal colonization following challenge or that meaningful suppression of Salmonella Branderup could be achieved by dietary supplementation. The approach taken by the company would be more credible had the study been published in a peer reviewed journal.

Research conducted by Land-grant universities, institutes and the R & D departments of biopharmaceutical companies is intended to confirm safety and efficacy of products to suppress flock infection leading to foodborne diseases. Positive results, subject to peer review or FDA scrutiny allow compounds to be registered for a specific use. Commercial acceptability depends on demonstrated efficacy and cost-benefit. Performing studies of dubious scientific merit to   promote a product is sophistry and the principle is even more egregious when based on concern and fear arising from severe financial loss due to a pathogen of limited significance.

The draft of this editorial was submitted to a technical service veterinarian of the company concerned with an offer to post a rebuttal of the points raised. No response was obtained within two weeks-Editor.