PoultryUSA - November 2017 - 3
Bacterial Peptidoglycans - Snicking Away at Animal Performance
N.E. Ward1 PhD and A. Cowieson2 PhD | DSM Nutritional Products | Parsippany, NJ1 and Kaiseraugst, Switzerland2
As animal production becomes more and more sophisticated,
previously unobserved factors that potentially hinder performance
become a bigger issue. Intestinal commensal bacteria - bacteria that
live together - fit this narrative.
Cell walls of nonpathogenic gram-negative bacteria are mostly
lipopolysaccharides. Peptidoglycans (PGN), or murein, are primary
components of gram-positive bacteria. In normal intestinal bacteria,
neither class causes disease. But fragments of their cell walls
which remain in the intestine as "intestinal rubbish" can push
This is particularly the case with PGN - a thread that unites bacteria
of virtually all types, regardless of species, type, or any other
classification. While necessary for the survival of bacteria, PGN can
snick away at bird performance and profits and not be noticed.
PGN undergoes constant growth and division in a manner similar to
bone reconstruction in animals. As much as a 50% turnover of PGN
occurs within one generation, according to researchers. This PGN
remains in the spent growth media and probably mimics a similar
phenomenon in the intestinal lumen.
Structure of a
What is a Peptidoglycan?
PGN is a massive polymer of amino acids (e.g., peptido-) and sugars
(e.g.,-glycan) unique to bacterial cell walls. The carbohydrate or sugar
constituents alternate from B-(1,4)-linked N-acetylglucosamine
(NAG) to N-acetylmuramic acid (NAM) crosslinked by short
peptides (Figure 1). Amino acids meld into a 2- or 3-dimensional
lattice to reinforce and give strength. PGN provides the bacteria with
structural support against osmotic pressure.
Figure 2. Gram-positive bacteria have a thick layer of peptidoglycan
(PGN), shown in red, outside the membrane. Gram-negative bacteria
have significantly less PGN inside the membranes.
And airborne PGN can be abundant in animal production facilities
and grain processing plants. PGN carried on dust particles is common
in swine farrowing and nursery production units. The repetitive
exposure of these aerial organic dust particles can be debilitating to
lung function in mice, according to Nebraska research.
When airborne sources are added to the G+ bacteria in the intestinal
tract, where 90% of the cell wall is PGN and 30 to 35% of cells
are dead, exposure to this cellular "rubbish" is quite high. It is this
constant source of rubbish that can physically interfere with normal
intestinal enzyme-substrate functions.
The High Cost of Excessive Mucin Secretion
Peptidoglycan Exposure Levels
In gram-positive (G+) bacteria, PGN is about 90% of the dry weight.
(Figure 2). G+ bacteria predominate in the intestinal tract. In the
turkey microbiome, for example, 77% of the microbes were G+
rods, while 14% were G-, and 9% were G+ cocci. In healthy swine,
71% of microbes were G+. This shows that G+ bacteria exist at a
disproportionately higher level in the intestinal tract.
Natural bacterial cell death generates an abundant source of PGN
in the intestine. In one study, 34% of total fresh fecal bacteria was
classified as dead. In another, 32% of fresh fecal bacteria was dead,
while an additional 20% was "injured." And although G+ lactococci
are resistant to gastric acidity (90 to 98% survival), only 10 to 30%
survive the duodenum. In fact, 60% of the feces mass is comprised
Intestinal mucous protects against potential pathogens and toxins, and
impedes their entry into the blood stream. There has been a growing
recognition that PGN and lipopolysaccharides act as intestinal
antagonists and stimulate mucin secretion. This can adversely affect
animal performance efficiency via the intestinal mucous barrier.
For example, about one-third of the amino acid content of mucin
is threonine. The gastrointestinal requirement for most essential
amino acids is 14 to 33% - but for threonine, this jumps to 61%
for gut-related functions and mucin production. Swine research finds
insufficient dietary threonine restricts intestinal mucin secretion.
Because mucin is essentially indigestible to the host, mucin
represents a net nitrogen loss to the animal. Thus, excessive
mucin synthesis and secretion fueled by antagonists like PGN is
In the End
The greatest threats to efficient and profitable animal performance
are those that go unobserved. They allow stressors to secretly
chip away at normal body processes, diverting nutrients away
from growth and efficiency. Peptidoglycans fit this category.
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