Salmonella: Why it’s a chicken and egg thing

In a young bird’s first 24 to 48 hours, they’re pretty susceptible because their gut microbes are not well-developed. With probiotics and prebiotics, you can accelerate the development of the young bird’s gut microbes. When you establish a healthy gut microbial population, it serves as a barrier to prevent pathogens from establishing. It’s called competitive exclusion, which is sort of like saying, the neighborhood is already occupied and there’s no way for pathogens to buy a house.

Anything you can do to stack the deck against pathogens and support your good bacteria, that’s a win.

There are groups trying to get the USDA to declare Salmonella an “adulterant” in chicken, meaning contaminated chicken couldn’t be sold. After E. coli O157:H7 was declared an adulterant in beef, illnesses declined substantially. Would that be a good step?

I understand the desire to have it declared an adulterant, but it’s a complex issue. For one thing, you’re dealing with chickens versus cows, two different animal species. Also, Salmonella has quite a bit of range and adaptability. It’s so ubiquitous, I used to say, I could go out and isolate Salmonella from just about anywhere.

On top of that, there are over 2,500 serovars of Salmonella and not all of them make you sick. I think that gets lost in the discussion. In addition, the existence of Salmonella on a carcass is a real imprecise measurement. The question is, how much? If you have one Salmonella on a carcass, the risk of getting sick is essentially nil. But if there were a million Salmonella on the carcass, the risk is much higher. The problem is that we don’t have quantitative tests for Salmonella.

We don’t have tests to determine how much Salmonella is in our food?

Well, there are ways to do it, but they’re slow. You want instantaneous results, like the old science-fiction movies where you have the sensor that instantly gives you answers. We don’t have that yet. It takes us potentially at least three or four days to get an answer.

There’s a lot of research being done. We’ve got more rapid tests and we’re getting more and more precise on our quantitation. I think it’s on the horizon.

What’s the most important development you’ve seen in fighting these pathogens?

Whole-genome sequencing has been a game-changer, mostly because it allows you to more accurately pinpoint the source of an outbreak. It’s really revolutionized the science of identification. It’s like the forensic science stuff on these crime shows. The DNA from the person suffering from salmonellosis — can you find that strain in any of the food they ate? Then you go back to the farm and see: Is that same Salmonella there? Or did it get introduced somewhere else in the food supply chain? It allows you to more precisely trace the cause.

Whole-genome sequencing also helps us to understand these pathogens better. For example, because we know the entire genetic code, we can identify which genes make the bacteria virulent. Foodborne Salmonella and Campylobacter typically do not make adult chicken sick. So one fundamental question is, what makes them pathogens in people?

Salmonella contamination has been significantly reduced in some other countries, especially in eggs. Are the challenges somehow more insurmountable in the US? Too expensive? Too inconvenient?

All the above. The places where those pathogens have been effectively eliminated are much smaller countries, with smaller-scale production. For example, they do complete sanitation of trucks bringing feed into the farm. That’s an expensive, extensive process that just wouldn’t be practical here from an economic standpoint.

But there are interventions that would work here. For example, Great Britain went into a very extensive poultry-vaccination process that worked pretty well in eradicating Salmonella in eggs. Vaccines have been employed here, too, but part of the problem is vaccines are somewhat specific. Let’s say you create a vaccine that works on Salmonella Enteritidis. Salmonella Typhimurium can come in and fill that niche, and so now you’re going to have to create a second vaccine. So it’s sort of a moving target. Vaccination programs are very active now and more are being developed as we understand more about Salmonella.

What else would help?

You want what we call multiple hurdles — several interventions that are very different from each other mechanistically, so they attack the problem differently. We’ve done things like combining mild heat with organic acids, and it’s very effective.

What we really need is more investment, trying to figure out things like which probiotics work best, which combinations work best, so you can get that one-two punch: the probiotic to prevent the establishment of Salmonella and your essential oil to knock out any Salmonella already there. We need more science to do more investigations and to field-test this stuff on real farms and then have good detection and quantitation tools.

Where is the research headed?

Coming up with what I would call mechanistically better-defined interventions to where we know what they’re doing and how they work. Traditionally, producers have relied more on anecdotal reports; we’ve moved beyond that now, and the farmers and companies producing these products know we need peer-reviewed research. We’re in an era that’s exciting for me because I do that kind of mechanism-based research. Now there’s both governmental support and industry support.

What are you working on right now?

We’re doing microbiome mapping of poultry-processing facilities — mapping all the microbes that are found there — trying to identify what we call indicator organisms. These organisms are non-pathogenic, but they behave similarly to the way Salmonella behaves. The idea is they’re usually found in high numbers, and they’re very quantifiable, which makes them easier to detect and measure than Salmonella.

By monitoring these indicator organisms, you can determine whether your interventions are working. If the indicator organism went from, say, 2,000 down to 2, we know that if Salmonella were in there, the measure would work the same way against it.