178
at pH values below 3.0, these organisms generally exhibit increased sensitivity. This
is why acid tolerance is one desirable property that is being used in selecting probiotic strains (Corcoran et al. 2005).
Probiotics can also activate the immune response by secreting immunoglobulins
like IgA, or increasing the number of natural killer cells, and even enhancing phagocytic activity of macrophages. With an increased secretion of IgA the number of
pathogenic organisms in the gut is lowered and improves the microflora. Aside from
its immunomodulating effects, probiotics might also be helpful in certain medical
conditions like inflammatory bowel disease (IBD). Probiotics also digest food and
compete for nutrients with pathogens. Probiotics decrease programmed cell death in
intestine and/or increase the production of mucin. Lactobacillus rhamnosus avoids
cytokine-induced cell death by preventing TNF. Lactobacillus species augment
mucin expression to block invasion and adherence Escherichia coli. Lactobacillus
rhamnosus prevents inflammation and intestinal epithelial cells’ apoptosis showing
mitogenic effects and thus mucosal regeneration. Probiotic bacteria are also competitors of harmful bacteria on epithelial cell receptors and mucus layers.
Lactobacillus casei increase secretory IgA levels of pathogen by activating B cell.
Lactobacillus casei down-regulates gene transcription responsible for proinflammatory effectors like cytokines and chemokines. This anti-inflammatory
effect is processed by the NF-κB cell pathway inhibition and I-κBα stabilization
specifically. Communication among bacteria occurs with help of signalling molecules or auto-inducers called quorum sensing. This facilitates the intestinal microbes
for colonisation (Markowiak and Slizewska 2017).
When probiotics compete for adhesion sites, they fight for cellular attachments.
Such as when pathogenic organisms enter the GI tract, some strains of bifidobacteria and lactobacilli act as “colonization barriers” (Lactobacillus rhamnosus strain
GG and Lactobacillus plantarum 299v). Both of these organisms do not allow
attachment of Escherichia coli to human colon cells because they already have
adhered to the mucosal epithelium. The synthesis of antimicrobial compounds is a
mechanism of action wherein probiotics modify the microbial flora. Probiotics
induce host cells to release peptides directly affecting pathogens and thus prevent
their epithelial attack. The following antimicrobial peptides released from the gut
epithelial cells are: defensins (hBD protein), bacteriocins, hydrogen peroxide
(H 2 O 2 ), nitric oxide and short chain fatty acids (SCFA) such as lactic acids, acetic
acids and cathelicidin. They exert antimicrobial activity against many bacteria,
fungi, viruses by lowering the luminal pH. Many types of lactobacilli and bifidobacteria produce these bacteriocins or other antimicrobial compounds. These bacteriocins are “compounds produced by bacteria that have a biologically active
protein moiety and a bactericidal action”. Upon the release of these compounds by
probiotic organisms a beneficial modification of the microflora happens. But not all
strains of these Lactobacilli or Bifidobacteria have antimicrobial compounds, and
some produce compounds that has no specific activity, so that both beneficial bacteria and pathogenic organisms may be negatively affected (Khalighi et al. 2016).
S. Palai et al.
at pH values below 3.0, these organisms generally exhibit increased sensitivity. This
is why acid tolerance is one desirable property that is being used in selecting probiotic strains (Corcoran et al. 2005).
Probiotics can also activate the immune response by secreting immunoglobulins
like IgA, or increasing the number of natural killer cells, and even enhancing phagocytic activity of macrophages. With an increased secretion of IgA the number of
pathogenic organisms in the gut is lowered and improves the microflora. Aside from
its immunomodulating effects, probiotics might also be helpful in certain medical
conditions like inflammatory bowel disease (IBD). Probiotics also digest food and
compete for nutrients with pathogens. Probiotics decrease programmed cell death in
intestine and/or increase the production of mucin. Lactobacillus rhamnosus avoids
cytokine-induced cell death by preventing TNF. Lactobacillus species augment
mucin expression to block invasion and adherence Escherichia coli. Lactobacillus
rhamnosus prevents inflammation and intestinal epithelial cells’ apoptosis showing
mitogenic effects and thus mucosal regeneration. Probiotic bacteria are also competitors of harmful bacteria on epithelial cell receptors and mucus layers.
Lactobacillus casei increase secretory IgA levels of pathogen by activating B cell.
Lactobacillus casei down-regulates gene transcription responsible for proinflammatory effectors like cytokines and chemokines. This anti-inflammatory
effect is processed by the NF-κB cell pathway inhibition and I-κBα stabilization
specifically. Communication among bacteria occurs with help of signalling molecules or auto-inducers called quorum sensing. This facilitates the intestinal microbes
for colonisation (Markowiak and Slizewska 2017).
When probiotics compete for adhesion sites, they fight for cellular attachments.
Such as when pathogenic organisms enter the GI tract, some strains of bifidobacteria and lactobacilli act as “colonization barriers” (Lactobacillus rhamnosus strain
GG and Lactobacillus plantarum 299v). Both of these organisms do not allow
attachment of Escherichia coli to human colon cells because they already have
adhered to the mucosal epithelium. The synthesis of antimicrobial compounds is a
mechanism of action wherein probiotics modify the microbial flora. Probiotics
induce host cells to release peptides directly affecting pathogens and thus prevent
their epithelial attack. The following antimicrobial peptides released from the gut
epithelial cells are: defensins (hBD protein), bacteriocins, hydrogen peroxide
(H 2 O 2 ), nitric oxide and short chain fatty acids (SCFA) such as lactic acids, acetic
acids and cathelicidin. They exert antimicrobial activity against many bacteria,
fungi, viruses by lowering the luminal pH. Many types of lactobacilli and bifidobacteria produce these bacteriocins or other antimicrobial compounds. These bacteriocins are “compounds produced by bacteria that have a biologically active
protein moiety and a bactericidal action”. Upon the release of these compounds by
probiotic organisms a beneficial modification of the microflora happens. But not all
strains of these Lactobacilli or Bifidobacteria have antimicrobial compounds, and
some produce compounds that has no specific activity, so that both beneficial bacteria and pathogenic organisms may be negatively affected (Khalighi et al. 2016).
S. Palai et al.