Escherichia coli and the protective role of
Lactobacillus
casei
Esther van
Praag, Ph.D.
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Newborn rabbits are unique in the animal
world as their gastrointestinal tract is sterile and remains vastly devoid of
bacteria during the first weeks of their life (depending on the studies it varies
between a few days up to 3 weeks), even though the pH of the doe’s milk
ranges between 5 and 6.5, which would allow bacterial survival, growth, and
colonization. Rabbit milk, indeed, is rich in C8 and C10 fatty acids that
have bacteriostatic properties and inhibits growth of bacteria in the
digestive tract, of the newborn. These molecules are sometimes referred to as
"milk oil", and their activation needs two parameters, milk of the
mother and stomach of the suckling. This protects day-old newborn against the
growth of pathogen bacteria and to die of necrotizing enteritis or
generalized sepsis. Bacteria that are absorbed at the time of birth and via
the milk will survive the passage through the stomach and intestine and will
accumulate in the cecum and the final section of the digestive system (colon)
and rectum.
At the
age of 10-15 days, newborn rabbits become strong, inquisitive and leave the
nest. They start nibbling solid food (hay, fresh vegetables, pellets) as well as the hard feces of the doe. Up to the
age of 6 weeks, young rabbits gradually decrease milk intake. As a result: - The concentration of C8 and C10 fatty acids (milk
oil) decreases gradually in the anterior digestive system; - The pH of the stomach drops from about 5-6 down to
1-2, becoming a barrier for colonizing bacteria and killing ingested
bacteria; - Microorganisms that were ingested previously and
survived in the cecum and lower portion of the intestine and rectum will
start to multiply. Translocation (spread) of intestinal bacteria from the
rectum up to the upper portion of the small intestine (duodenum) becomes
possible. When the right bacteria are present, proper digestion and
fermentation of solid food becomes possible. This process takes a few days to
weeks. The
different stages of bacterial colonization of the digestive tract are very
important, but also very delicate. Indeed, microorganisms that develop inside
the GI tract depend on the type of diet, hay, stress. Colonization of yet
sterile portions of the intestine by pathogen bacteria may lead to organ
failure, necrotizing enteritis, diarrhea and (fatal) enteric trouble or
sepsis. It is
therefore important to keep the rabbits with the mother up to the age of 8
weeks, and not separate them to early, unless
needed. Once a healthy bacterial flora has colonized the GI tract, the
development of pathogen bacteria will be hindered. It is speculated that food
fermented by lactobacilli help keep homeostasis between Lactobacilli
sp., and other microbial flora of the GI tract, in animal species that host
this bacteria naturally. Orphaned
rabbit babies fed on alternative source of milk don’t get the protective C8
and C10 fatty acids, and often show increased sensitivity to enteric
infections. One of the bacteria that cause fatal enteritis is Escherichia
coli. A recent paper (2001, see ref) discusses the protective role of Lactobacillus
casei - a bacterium found in probiotic
preparation such as Protexin, Probiocin,
Benebac or Probios,
against a toxin producing strain of E. coli. This
particular strain has been shown to cause hemorrhagic colitis (inflammation
of the colon, accompanied by heavy bleeding), hemolytic-uremic syndrome
(fever, acute renal failure, dissolution of red blood cells, and low number
of platelet cells), and complications in the central nervous system. The
mucosal damage in the GI tract is severe though not equal, and correlates
with the number of observed pathogenic bacteria, and the concentration of the
toxin: more pronounced in the cecum, and colon, less in the small intestine. The
study showed that most of the infected rabbits developed diarrhea quickly.
Newborn rabbits treated with L. casei
developed diarrhea too, but symptoms were less severe (16% severe diarrhea
against 77.3% in the control group). The growth of the bacteria did not show
a difference in both groups up to day 4 after infection; at day 7, the number
of viable bacteria was 100 fold lower in the L. casei
treated group. The same is observed for the toxin concentration: it remained
stable after day 4 in L. casei treated
rabbits. Histopathologic
examination of cecum, intestine, and colon showed that the control group
suffered severe damage: Small intestine: - necrosis, -
vacuolation
of epithelial cells. Cecum: -
exfoliation of epithelial cells - pseudo-eosinophil (type of white blood cell)
infiltration, - mitotic activity. Colon: - exfoliation of epithelial cells necrosis None
of the above pathology has been observed in L. casei
treated rabbits. The pH
of the stomach and intestine are high in newborn rabbits, 5.1 and 6.5, respectively,
and no differences were observed between the 2 groups. (Those high values
probably help the L. casei bacterium survive
the gastric passage, and enable it to colonize the colon, cecum and large
intestine of young rabbits.) The concentration of lactic acid was slightly
higher in L. casei treated rabbits, as
compared to the control group. Interestingly,
volatile fatty acids, like lactic acid, are known for their potent
bactericidal activities, and are often added to the diet or to the water of
weaning animals, in order to reduce the development of pathogenic bacteria. Lactic
acid furthermore acts on the membrane of cells, affecting the rate of
exchange of H+ and Na+ ions, the activity of the plasma
membrane H+/ATPase activities, and the fatty acid composition of
the membrane. This leads to an acidification of the cytoplasm. In the case of
this particular E. coli strain, it was shown that a concentration of
3.2 mM lactic acid was needed to inhibit its
development, while less 1 mM was found in
vivo. The presence of lactic acid thus may not explain the differences
observed between the control, and L. casei
treated group. Lactobacilli and Bifidobacilli
are, moreover, known to increase the secretion of IgA (immunoglobulin
A or antibody that deactivates the activity of foreign bodies). This was
observed in the newborn rabbits too. Higher levels of toxin present in a
particular organ (i.e. colon) correlated to a higher the level of mucosal IgA
present. This study indicates that preventive
administration of L. casei to newborn
rabbits protects them from E. coli enteritis, by enhancing the
secretion of specific IgA. Protection by its production of lactic acid
is doubted in this case, since the in-vitro bactericidal needed 3 times
higher concentrations.
Acknowledgements
Thanks are due to Linda Bayley (USA) and the rescued
doe, and to Karen Comish (Israel) and Pepe feeding her
newborn baby. Further information
Anderson LC,
Rush HG, Glorioso JC. Strain differences in the
susceptibility and resistance of Pasteurella multocida to phagocytosis
and killing by rabbit polymorphonuclear
neutrophils. Am J Vet Res. 1984; 45(6):1193-8. Dinsmore JE, Jackson RJ, Smith SD. The
protective role of gastric acidity in neonatal bacterial translocation. J Pediatr Surg. 1997;32(7):1014-6. Glass RL, Troolin HA, Jenness R.
Comparative biochemical studies of milks. IV. Constituent fatty acids of milk
fats. Comp Biochem Physiol. 1967; 22(2):415-25. Harcourt-Brown
F. Textbook of Rabbit Medicine. Butterworth Heinemann, Oxford, 2002, p 55-56. Ogawa M,
Shimizu K, Nomoto K, Takahashi M, Watanuki M, Tanaka R, Tanaka T, Hamabata
T, Yamasaki S, Takeda Y. Protective effect of Lactobacillus casei strain Shirota on Shiga toxin-producing Escherichia
coli O157:H7 infection in infant rabbits. Infect Immun. 2001;
69(2):1101-8. Schley P.
Rabbit milk - composition and withdrawal of samples, Berl
Munch Tierarztl Wochenschr.
1975; 88(9):171-3. Van Camp JM, Drongowski
R, Gorman R, Altabba M, Hirschl
RB, Coran AG. Colonization of intestinal bacteria in the normal neonate:
comparison between mouth and rectal swabs and small and large bowel
specimens. J Pediatr Surg.
1994;29(10):1348-51. |
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