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Old 09-11-2011
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Question catalase positive organisms and CGD

can someone help me understand why catalase positive organisms can survive in patients with CGD?and what s the relation between CGD and NADPH oxidase,SOD and myeloperoxidase deficiency?
quickly plz:sorry:
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Old 09-11-2011
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Quote:
Originally Posted by alanine40 View Post
can someone help me understand why catalase positive organisms can survive in patients with CGD?and what s the relation between CGD and NADPH oxidase,SOD and myeloperoxidase deficiency?
quickly plz:sorry:
NADPH oxidase & Myeloperoxidase function is to get rid of H2O2 which categorized under reactive oxidative species (ROS) which is a product of normal Metabolism. Catalase degrades H2O2 into H2O and O2. So Catalase is important in detoxification & it is found normally in Peroxisomes organelles in the Cell.
CGD patients has a problem in NADPH Oxidase function. So toxic H2O2 accumulates in the cell. Organisms that have Catalase will degrade H2O2 & can survive & spread. Whereas organisms that don't produce Catalase would be killed from the accumulated H2O2 in the Neutrophil cell
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Old 09-11-2011
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thanks my angel
but can tell me is CGD means deficiency of NADPH oxidase so in turnt MPO will be deficinet absolutely?i heard about a disease where NADPH oxidase is deficient but but MOP is present so these patients will be more lucky?
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Old 09-11-2011
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The lack of severe symptoms suggest that role of myeloperoxidase in the immune response must be redundant to other mechanisms of intracellular killing of phagocytosed bacteria.
Patients with MPO deficiency have a respiratory burst with a normal nitro blue tetrazolium (NBT) test because they still have NADPH oxidase activity, but do not form bleach due to their lack of myeloperoxidase activity. This is in contrast to chronic granulomatous disease in which the NBT test is negative(not positive) due to the lack of NADPH oxidase activity.(wikipedia)
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i want understand if catalase-positive organsims already degrade H2O2 why speacially they infect CGD patients while they can degrade H2O2 from normal patients?is it a a matter of quantity?less NADPH oxidase so bacteria overcome?more NADPH oxidase so bacteria beaten?
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NADPH oxidase and MPO are used by phagocytes to kill bacteria
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Old 01-19-2014
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To understand the reason, let us go back to the mechanism of resp. burst.

O2 to O2-( superoxide inoin) by NADPH oxidase.

O2- to H2O2 (Hydrogen peroxide) bY SOD superoxide dismutase.

H2O2 to HOCL (highly toxic to bacteria) MYLOPEroxidase.MOP

so the trick is here Luckliy most bacteria generate H2O2 from perixomes, and then MOp will rescue the whole sysytem by generating the toxic HCOL and kill them, whether are catase - ve or + ve.
but in GCD the bacteria who has + catalase it ll destroy the H2O2 to water, and it will survive, and catalase - ve H2O2 will be generated and no catalase to destroy THe H2O2 and the bateria will not survive. so these kds only can fight infection from catalase +ve infection.

+ve which will take care of themselve by destroying H2O2 on their own and survive the killing ).

Last edited by ranii; 01-19-2014 at 08:01 PM.
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Old 01-19-2014
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I think the previous poster has already said this.

But the O₂ dependent killing in the cell happens due to NADPH oxidase and MPO.
NADPH Oxidase (along with SOD) helps create reactive oxygen species (ROS) like superoxide and peroxide.
MPO helps create the halide i.e. HOCl (bleach).
Reactants used in the following order: NADPH Oxidase ➜ SOD ➜ MPO

So, a normal person with both NADPH Oxidase and MPO has both, i.e. ROS and bleach to help kill organisms. Please consider these as the 2 "arms" of O₂ dependent killing for this explanation.

In CGD, if NADPH oxidase is defective, we don't have H₂O₂ being produced by our neutrophils and monocytes. But aerobic bacteria will actually produce H₂O₂ as part of their metabolism, which can still be used in turn by the MPO (still working) to make the bleach and kills bacteria. But catalase +ve organisms can inactivate this H₂O₂ (that they are providing), so technically they make both enzymes i.e. NADPH oxidase and MPO useless.

Why do catalase +ve organisms not affect normal people?
Because the NADPH Oxidase arm is still present to create the ROS, which can produce H₂O₂ in neutrophils and monocytes in addition to the H₂O₂ that the bacteria itself is producing. This H₂O₂ can then be converted in to HOCl by MPO arm to kill catalase +ve organisms.

HTH.
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