TITLE:
Role of Lactic Acid Bacteria-Myeloperoxidase Synergy in Establishing and Maintaining the Normal Flora in Man
AUTHORS:
Robert C. Allen, Jackson T. Stephens Jr.
KEYWORDS:
Myeloperoxidase; Lactic Acid Bacteria; Hydrogen Peroxide; Hypochlorite; Singlet Oxygen; Selective Binding; Selective Microbicidal Action; Normal Flora
JOURNAL NAME:
Food and Nutrition Sciences,
Vol.4 No.11A,
November
27,
2013
ABSTRACT: Lactic acid bacteria (LAB)
are incapable of cytochrome synthesis and lack the heme electron transport
mechanisms required for efficient oxygen-based metabolism. Consequently, LAB
redox activity is flavoenzyme-based and metabolism is fermentative, producing lactic
acid, and in many cases, hydrogen peroxide (H2O2).
Despite this seeming metabolic limitation, LAB dominate in the normal flora of the mouth, vagina
and lower gastrointestinal tract in man. Myeloperoxidase (MPO) is produced by the
neutrophil leukocytes and monocytes that provide the innate phagocyte defense
against infecting pathogens. MPO is unique in its ability to catalyze the H2O2-dependent
oxidation of chloride (Cl-) to hypochlorite (OCl-). In
turn, this OCl- directly reacts with a second H2O2 to produce singlet molecular oxygen (), a metastable
electronic excitation state of oxygen with a microsecond lifetime that
restricts its combustive reactivity within a submicron radius of its point of
generation. Each day a healthy human adult produces about a hundred billion
neutrophils containing about 4 femtograms MPO per neutrophil. Inflammatory
states and G-CSF treatment increase both neutrophil production and the quantity
of MPO per neutrophil. After a short circulating lifetime, neutrophils leave
the blood and migrate into body spaces including the mouth, vagina, urinary
tract, and gastrointestinal tract. Greater than a hundred thousand neutrophils
are lavaged from the mouths of healthy humans; the quantity lavaged is proportional to the blood neutrophil count.
MPO selectively and avidly binds to most Gram-positive and all Gram-negative
bacteria tested, but LAB do not show significant MPO binding. Neutrophils
migrating to normal flora sites release MPO into the LAB-conditioned milieu
containing adequate acidity and H2O2 to support
extra-phagocyte MPO microbicidal action. In combination, LAB plus MPO exert a
potent synergistic microbicidal action against high MPO-binding microbes. This
LAB-MPO synergy provides a mechanism for the establishment and maintenance of
LAB in the normal flora of man.