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Bacterial oxygen requirement
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Introduction
• Bacteria in various environments have different behavior with oxygen according the enzymatic system which bacteria own.
• Oxygen Species is harmful if : 1- bacteria have no enzyme system to eliminate it. 2- Oxygen Species concentration is very high in media or air.
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Oxygen Species
• Singlet oxygen (O2) : is in high energy state and extremely reactive, exists in phagocytes.
• Superoxide free radical (O2-) & hydrogen
peroxide (H2O2): is so toxic to cell , formed in small amount in cellular respiration.
• Peroxide anion (O2-2) : used as antimicrobial
agent.• Hydroxyl radical (OH-) : the most active form,
form in the cytoplasm from respiration.
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Enzyme systems
1. Super oxide dismutase
Converts the superoxide ion to hydrogen peroxide in the existence of hydrogen ion
2
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2. Catalase : breaks up hydrogen peroxide to water and oxygen.
3. Peroxidase : converts hydrogen peroxide to water in presence of hydrogen ions (NADH).
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Other protective factors :
• ß –carotene : acts as anti-oxidant & is composed from simple lipids , quench singlet oxygen.
• Phenolic Glycolipids : scavengers of hydroxyl and superoxide anions (complex lipid).
• Dimethylsulfoxide : a hydroxyl radical scavenger.
• Tryptophan (A.A.) : a hydroxyl radical scavenger.
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Taxonomy
Bacteria are classified according to oxygen requirement into five classes :
1. Obligate aerobes : growth occurs only when high concentration of oxygen diffused into the medium.
2. Facultative anaerobes : grows in best where most oxygen is presented, but occur throughout tube.
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3. Obligate anaerobes : growth occurs only when there is no oxygen.
4. Aerotolerant anaerobes : growth occurs evenly, oxygen has no effect.
5. Microaerophiles : growth occurs only where a law concentration of oxygen has diffused into medium.
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class
Aspects
Obligate aerobes
Facultative anaerobes
Obligate anaerobes
Aerotolera -nt anaerobes
Microaerop-hiles
Energy source
cellular respiration
respiration, fermentation
fermentation, autotrophy
fermentation cellular respiration
aerobic
anaerobic
SOD enzyme
Peroxidase
catalase
example Bacillus, Pseudomonas
E. coli, Staphylococcus
Clostridium tetani,Bacteroides
Lactobacillus Campylobacter & Heliobacter pylori
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Methods for excluding oxygen
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supports aerobic & anaerobic bacteria• – Sodium thioglycollate and cyctine
removes O2 from the medium• – Resazurin as an oxidation reduction indicator
turns pink in presence of O2• Small amount of agar presented to retard gases
Fluid Thioglycollate Media (FTM)
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Gas Pack System : Anaerobic Jar
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Gas Pak Pouch
• Procedure for GasPak Pouch.
(a) Dispense GasPak liquid activating reagent into channel of pouch.
(b) Place plates inside the pouch.
(c) Lock in anaerobic environment with sealing bar and incubate.
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Candle jars
• The candle flame will consume most of the oxygen in the jar.
• Produce an elevated level of carbon dioxide.
• These conditions are ideal for the growth of campilophilic and microaerophilic organisms.
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CO2 Generating Packet
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Anaerobic Chambers
• The Vinyl Anaerobic Chambers provide a strict anaerobic atmosphere using a palladium catalyst and hydrogen gas mix of 5%.