WATT Poultry USA - February 2018 - 33
Peptidoglycans and Gastrointestinal Functionality in Broilers
PGN in the fragments of dead bacteria may constrain the performance of poultry,
possibly by hindering gut functionality and lowering intestinal efficiencies.
Mikkel Klausen1 PhD and Nelson E. Ward2 PhD | 1Novozymes A/S, Copenhagen, Denmark | 2DSM Nutritional Products Inc, Parsippany, NJ
Peptidoglycan (PGN) is a polymer in bacterial cell walls that
provides rigidity and shape to the cells, whether spherical, rods,
spiral or filamentous. PGN is sometimes called the exoskeleton
of bacteria for this reason. The polymeric structure of PGN is
unique, exclusive to bacterial cells, and is absent in all other
organisms. Further, as much as 90% of cell dry weight of
gram-positive bacteria can be PGN, in comparison to less than
10% for gram-negative bacteria (Malanovic and Lohner, 2016).
One of the most densely populated microbial habitats is
the gastrointestinal tract of animals. Just the intestines of
the world's broiler population account for an estimated
23 megatons of bacteria (Whitman et al., 1998). More than
half of human fecal mass is comprised of bacterial biomass,
where dead cells make up about one-third of the total mass
(Ben-Amor et al., 2005; Stephen and Cummings, 1980).
Dead bacterial biomass in the gut is largely overlooked in
research, which focuses narrowly on the living segment
of the microbiome despite the fact that both the live and
dead fractions likely impact gastrointestinal functionality.
Figure 1 illustrates the relative nature of live and dead bacteria,
and bacterial fragments, based on data available from studies.
To date, over 100 different types of PGN have been described
in the literature.
Muramidases and Broiler Performance
Muramidases (EC 18.104.22.168), also known as N-acetylmuramidase,
hydrolyze PGN between the N-acetylmuramic acid and
N-acetylglucosamine (Korzynska et al., 2010). Recently, a
novel muramidase added to feed significantly improved 42-day
weight gain and the feed conversion ratio (FCR) of broilers
(Lichenberg et al., 2017). No changes were detected in total
anaerobic bacteria, total aerobic bacteria, enterobacteria and
coliforms in the ceca of birds fed this particular muramidase.
Populations of Salmonella, Campylobacter and Clostridia
were also unaffected (Lichenberg et al., 2017). Because
muramidase specifically catalyzes the degradation of PGN -
and because live bacterial populations were unaffected with
this muramidase - these results suggest that the weight gain
and FCR improvements arise from the destruction of PGN
in the dead bacteria remnants.
In another study, this novel fungal muramidase improved
broiler performance when added to a pelleted corn/SBMbased diet (Yegani et al., 2018). In this 42-day trial, 1,280
Cobb broilers were vaccinated with a commercial coccidiosis
vaccine and raised in floor pens. Muramidase supplementation
significantly (P < 0.05) improved body weight gain by
5.0% and FCR by 2.5% (Table 1). Mortality was unaffected
(P > 0.05) by the treatment.
Figure 1. Graphic
representation of the
gut, showing living and
dead bacteria, and dead
Table 1. Impact of muramidase on 42-day broiler performance (abP<0.05).
Bacterial Cell Wall Debris
Bacterial debris in the small intestine includes remnants
derived from major microbial colonizers such as lactobacilli,
streptococci, enterobacteria, fusobacteria and eubacteria,
all of which contribute to the accumulation of cell wall
debris. Anaerobic species (Eubacterium spp., Clostridium spp.,
Lactobacillus spp., Fusobacterium spp.) and Bacteroides are
important sources of remnants in the cecum (Rehman et al., 2007).
PGN can represent a prominent component of this debris. This
heteropolymer consists of a sugar backbone with alternating
N-acetylglycosamine and N-acetylmuramic acid components.
Muramic acid is the connection point for peptide subunits
of four to five amino acids which are linked to other sugar
chains by peptide bridges of one to seven amino acids. Unique
compositional differences in PGN from different bacteria can
provide a 'fingerprint' by bacterial class. In general, PGN from
gram-negative bacteria are similar across different strains,
whereas PGN from gram-positive bacteria can be quite diverse.
Ultimately, bird performance was elevated by feeding
muramidase, presumably because gut function was enhanced
when excess debris was cleared, thus, preventing PGN
from causing adverse effects on animal performance (Ward
and Cowieson, 2017; Celi, 2017). This suggests that the
importance of this bacterial biopolymer has largely been
overlooked, and that it may impact bird performance more
than previously recognized.
Research has focused largely on the role of live bacteria in
the intestinal tract, with little recognition of the impact of
dead bacteria. PGN in the fragments of dead bacteria may
constrain the performance of poultry, possibly by hindering gut
functionality and lowering intestinal efficiencies. Muramidase
degrades PGN, and muramidase supplementation in feeds is
a novel means to improve weight gain and feed efficiency.
References available upon request.
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