'Super shedders' responsible for most Salmonella infections

Salmonella control on poultry farms is a combination of good management practices and accurate feeding, but new evidence supports that, even with the same genetics, some birds are super shedders and thus, contribute to most of the infections.

New evidence supports that, even with the same genetics, some birds are Salmonella super-shedders and, thus, contribute to the majority of infections.| Kharkhan_Oleg, iStock.com
New evidence supports that, even with the same genetics, some birds are Salmonella super-shedders and, thus, contribute to the majority of infections.| Kharkhan_Oleg, iStock.com

Salmonella in poultry production poses great challenges for the food chain. Research teams around the world are focused on understanding bacterial behavior and the connection between pathogens, hosts and the environment. Just a short time ago, the general thinking was that all genetically similar birds will react the same when faced with an infection, e.g. the “homogeneity paradigm;” however, things are not that simple.

“New findings show that even if the bird’s genetics are the same, all birds are not equal in terms of infection,” said Philippe Velge, French national institute for agricultural research (Inra) specialist of bird infections - group leader, while presenting “Signaling, carriage and bacterial virulence” at an Inra-Itavi seminar. “Heterogeneity is the rule and a minority of birds shed much of the Salmonella" in the flock.

Notably, the team’s findings are not limited to Salmonella, but also apply to E.coli, Campylobacter, Eimeria.

“This changes a lot of things,” Velge said. “After a Salmonella infection, some animals will excrete a lot of bacteria in their [manure] when others will excrete none or very small amounts. Some may excrete as much as 1 million Salmonella by gram, while others excrete none. Identifying those super shedders early opens new options to deal with infections, to deal with the real reservoir of pathogenic bacteria.”

He estimates those super shedders account for between 5 and 10 percent of outbreaks.

This discovery will lead to new possibilities for taking appropriate action.

Inra Philippe Velge

Better understanding of Salmonella super-shedding birds will drive researchers to propose new innovative solutions to poultry farmers, reports Inra’s Philippe Velge. | Yanne Boloh

Introducing ‘good’ bacteria to ‘bad’ microflora

The battle against pathogens is being fought on many fronts. To control infections, poultry producers use vaccines — which are generally not expensive — but offer limited efficiency due to the wide diversity of bacterial strains. While antibiotics are effective, their use increases the risk of antibiotic resistance and contrasts with consumers' demand for more for antibiotic-free meat production. For more than 20 years, the feed industry has been developing antibiotic alternatives, which contribute to their feeding strategy, i.e. probiotics, plant extracts and essential oils. Geneticists have long been involved in building genetic resistance. Meanwhile, it’s in disease labs, like Velge’s in Tours, France, that the knowledge on super shedders has emerged.

Researchers are now focused on strategies to anticipate, prevent and control infections as early as possible, e.g. at the hatchery.

First, they must understand how Salmonella infects and persists in birds.

“In modern flocks, animals share the same genetics and the same environment thus we must find another explaining factor,” Velge said.

Recently, the European research project, Momir-PPC, has discovered new evidence to support that the microbiome is distinct between super shedders and low shedders.

 “We’ve been able to identify super-shedder chickens, to collect their intestinal flora, and to implant it in chickens of another flock before any Salmonella infections,” he said. “When chickens of one flock receive the intestinal flora of the super-shedder ones, those ones become super shedders in a large proportion — up to 96 percent versus 5 to 10 percent in the general population.”

The next step will be to determine flock sensitivity through its intestinal flora profile as early as possible. The Tours lab is focused on finding the “good bacteria” which, in the low shedders' microbiome, fights against Salmonella implantation.

“We’ll be able to propose a kind of “bacterial cocktail,” which will act as a barrier against Salmonella and confirm the best ways to administrate it,” Velge said. This cocktail will be generally administered as a feed additive in the feed and, if they are used to induct a “good flora” as soon as the hatchery; they may also sprayed it on the eggs, similar to some vaccines.

“Good health practices are and will stay the first line [of defense] against infection. But it is not that easy to control all farm hygiene precautions day after day,” he noted. 

Salmonella Identification

Researchers have determined that super-shedder birds excrete as much as 1 million Salmonella bacteria in one gram of their manure. | Philippe Velge

Phages and defensins in the fight against Salmonella

In the context of worldwide growing antibiotic resistance threat, the potential of bacteriophages might be a novel and innovative strategy to fight this critical issue.

“Phages are ancient arms against bacteria as they aim precisely at one bacteria strain,” says Catherine Schoulder, Inra researcher specialized in those bacterial viruses. “With antibiotic development, the occidental world had forgotten about them, but Eastern and Central European countries continued their research and are now even able to propose commercial solutions, which we must evaluate. Science and regulation will play a part in their role, but I’m quite sure phages might be more widely used in poultry future. Now, the scientific community is active to constitute phage libraries and to test phages to be sure no resistance or environmental damage will occur prior to any commercial launch.”  

Phages can be administered on the drinking water or sprayed in the building or even injected.

Small peptides, defensins, are another new idea, but less advanced.

“It is a longer-term solution,” said Schoulder. “A lot of the work is [still] in front of researchers to formulate commercial solutions and be sure of their stability. Probably, they will be administered to the birds through their drinking water.”

Defensins are small cysteine-rich proteins with antimicrobial action. Extraction and purification from bone marrow of AvBD2 and AvBD7 has shown their potential as they have a wide antimicrobial spectrum even against multi-resistant bacterial strains.

AvB7 has been tested on lethal Salmonella-infected mice and helped them survive. However, the mode of actions of those defensins is under scrutiny, as they seem to stimulate macrophages to produce other antimicrobial components as cytokines.

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