Transcript Bacterial oxygen requirement

Bacterial oxygen requirement
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.
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.
Enzyme systems
1. Super oxide dismutase
Converts the superoxide ion to hydrogen
peroxide in the existence of hydrogen ion
2
2. Catalase : breaks up hydrogen peroxide
to water and oxygen.
3. Peroxidase : converts hydrogen
peroxide to water in presence of
hydrogen ions (NADH).
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.
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.
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.
class
Aspects
Energy
source
Obligate
aerobes
Facultative
anaerobes
Obligate
anaerobes
Aerotolera - Microaerop
nt
-hiles
anaerobes
cellular
respiration
respiration,
fermentation
fermentation
, autotrophy
fermentation
cellular
respiration
Bacillus,
Pseudomonas
E. coli,
Staphylococcus
Clostridium
tetani,Bacteroides
Lactobacillus
Campylobacter &
Heliobacter
pylori
aerobic
anaerobic
SOD
enzyme
Peroxidase
catalase
example
Methods for excluding oxygen
Fluid Thioglycollate Media (FTM)
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
Gas Pack System : Anaerobic Jar
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.
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.
CO2 Generating Packet
Anaerobic Chambers
• The Vinyl Anaerobic Chambers provide a strict
anaerobic atmosphere using a palladium catalyst and
hydrogen gas mix of 5%.