No more falling foul: NMR reveals poultry target

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  • Published: Dec 1, 2013
  • Author: David Bradley
  • Channels: NMR Knowledge Base
thumbnail image: No more falling foul: NMR reveals poultry target

Protecting against pathogens

Transmission Electron Micrograph of normal, wild type (top) and EPS cluster mutant (bottom) L. johnsonii. The mutant on the bottom has a much reduced EPS coat

NMR spectroscopy has defined the substances, two exopolysaccharides, that seem to be responsible for the protective effect of the microbe Lactobacillus johnsonii FI9785, which is known to inhibit Clostridium perfringens infection the in gut of poultry. The finding could point the way to a new veterinary drug for preventing the necrotic enteritis this infection causes and so reducing loss of stock to the disease on poultry farms as well as reducing the risk of associated food poisoning in people eating the birds.

A team at the Institute of Food Research (IFR) on the Norwich Research Park, in Colney, UK, has characterised the coat of a putative probiotic for use in poultry that could prevent infection by a common pathogen found in chickens.

Exclusion

Researchers had previously demonstrated that the microbe L johnsonii - a Gram-positive facultative anaerobic or microaerophilic rod-shaped bacteria - can exclude the often pathogenic microbe C perfringens from the guts of poultry. C perfringens is itself a Gram-positive, rod-shaped, anaerobic, spore-forming bacterium that is ubiquitous in nature being a normal component of decaying vegetation, soil marine sediment and even the intestinal tract. However, while it can sometimes be ingested without causing illness it is also the third most common cause of food poisoning in the Western world. Infection can lead to tissue necrosis, bacteraemia, emphysematous cholecystitis and gas gangrene, due to the bacterium's release of toxins. In poultry the microbe commonly causes necrotic enteritis in infected animals.

In IFR work, supported by the Biotechnology and Biological Sciences Research Council (BBSRC), the researchers previously found that L johnsonii synthesises a biochemical coat that plays an important role in allowing this strain to colonise the host gut. Now, in work published in The Journal of Biological Chemistry, they have used NMR spectroscopy to identify and characterize the components of the coat. This, they suggest, offers new insight into how these "good" bacteria might be used to combat C perfringens infection.

Unique strain

The coat, the researchers explain comprises two types of exopolysaccharides (EPS), which are long sugar-containing molecules that many bacteria use to encapsulate themselves; different bacteria use different EPS. The capsules they form may help the bacteria to cope with environmental stress, or aid colonisation and adhesion to host tissues.

Characterising the EPS structures in the L johnsonii strain is the first step to explaining how it might outcompete C perfringens," explains team member Arjan Narbad.

Earlier studies had homed in on the putative genes from L johnsonii thought to be involved making the biosynthetic machinery the bacteria utilizes to make its EPS. Knowing what genes are involved allows researchers to probe the biosynthesis itself in detail. Moreover, by disabling, or knocking out, the whole cluster of EPS genes, it is possible to cultivate bacteria with no EPS capsule. Subsequent analysis of the genes by graduate student Enes Dertli at IFR uncovered their potential roles in the capsule biosynthesis process but more research is needed to fully understand the system in detail and how it is regulated.

Nevertheless, the work shows that the structures of these two EPS molecules in this L johnsonii are unique to this strain. The team points out that additional structural features, such as the pattern of phosphorylation of the sugars, are likely to strongly influence the efficacy of bacterial adhesion in competition with the pathogen. Further, the team reasons that other biochemical modifications, such as acetylation, endow the microbe with the necessary armour to protect itself from the enzymes produced by gut bacteria that would otherwise destroy it.

The team is now taking this strain of L johnsonii through farm-scale trials to determine whether its use as a probiotic in poultry might combat the pathogen in a real-life livestock scenario.

Related Links

J Biol Chem, 2013, 81, 430-434: "Structure and Biosynthesis of Two Exopolysaccharides Produced by Lactobacillus johnsonii FI9785"

Article by David Bradley

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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