McIntosh and Fildes’ Anaerobic Jar is a laboratory apparatus used for cultivation of strict anaerobic microorganisms. These microorganisms cannot grow in presence of oxygen. So, this jar is used to provide oxygen free condition for their growth.
It was introduced in 1916 by James McIntosh, Paul Fildes and William Bulloch. The jar is usually a strong cylindrical vessel. It may be made up of metal, heavy glass or transparent polycarbonate.
The jar has an airtight lid. The lid is fixed tightly by a curved metal bridge clamp and screw. It also has inlet valve, outlet valve, pressure gauge or manometer and thermometer.
The working of this jar is based on removal of air and replacement by suitable gas. Inoculated culture plates are kept inside the jar. Then the lid is closed tightly and air is removed with the help of vacuum pump.
All air is not removed from the jar. If complete air is removed, liquid medium may boil and agar may come out from the plate. So, about 6/7th part of air is removed only.
After this, hydrogen gas or a gas mixture is passed into the jar. The gas mixture may contain nitrogen, carbon dioxide and hydrogen. This helps to replace the removed air and produce anaerobic condition.
A palladium catalyst is kept inside the jar in a wire mesh cage. It is placed below the lid. The catalyst helps remaining oxygen to combine with hydrogen and form water.
Water may appear as condensation on the inner wall of the jar. This shows that oxygen has been removed. Thus, anaerobic condition is formed inside the jar.
An anaerobic indicator is also kept inside the jar. Methylene blue solution or Lucas semi-solid indicator may be used. It remains colourless in absence of oxygen and becomes blue if oxygen enters into the jar.
Principle of McIntosh and Fildes’ Anaerobic Jar
McIntosh and Fildes’ anaerobic jar is based on the principle of physical removal of air and chemical removal of remaining oxygen. It is used to produce oxygen free condition inside the jar.
In this method, the inoculated plates are kept inside the jar and the lid is closed tightly. Then a vacuum pump is attached and most of the atmospheric air is removed from the jar.
About 6/7th part of air is removed by evacuation. Complete removal of air is not done, because it may disturb the culture medium. After this, the jar is filled with hydrogen gas or a gas mixture containing nitrogen, hydrogen and carbon dioxide.
The remaining oxygen inside the jar is removed by palladium catalyst. This catalyst helps hydrogen to combine with residual oxygen. Water is formed as the end product of this reaction.
The formation of water or condensation on the wall indicates that oxygen is removed. Thus, anaerobic atmosphere is produced inside the jar for growth of strict anaerobic microorganisms.
Components of McIntosh and Fildes’ Anaerobic Jar
The following are the components of McIntosh and Fildes’ anaerobic jar-
- Jar body- It is a strong cylindrical container. It is made up of metal, heavy glass or transparent polycarbonate.
- Lid- It is a heavy metal or plastic disc present at the top of the jar. It closes the mouth of the jar.
- Gasket or O-ring- It is made up of rubber, silicone or plasticine. It is kept between the lid and rim of the jar for making airtight seal.
- Bridge clamp and screw- It is a curved metal strip with a screw. It is used to fix and tighten the lid on the jar.
- Outlet valve- It is a needle valve or tap. It is connected with vacuum pump for removing air from the jar.
- Inlet valve- It is also a needle valve or tap. It is used for passing hydrogen gas or anaerobic gas mixture into the jar.
- Pressure gauge- It is also called manometer. It is used to show the pressure inside the jar during evacuation and gas filling.
- Thermometer- It is used to measure the temperature inside the jar.
- Catalyst chamber- It is a wire cage or wire gauze envelope hanging below the lid. It holds the palladium catalyst safely.
- Palladium catalyst- It helps the remaining oxygen to react with hydrogen. Water is formed after this reaction.
- Electrical terminals- These are present mainly in older models. They are used for heating the catalyst to start the reaction.
- Indicator holder- It is a holder or side arm used for keeping chemical indicator. Methylene blue or Lucas semi-solid indicator is used to check anaerobic condition.
Operating Procedure of McIntosh and Fildes’ Anaerobic Jar
The following are the steps for operating McIntosh and Fildes’ anaerobic jar-
- Preparation of catalyst- The palladium catalyst is first reactivated by heating in dry oven. It is usually heated at 160°C for about 2 hours to remove moisture.
- Placing of catalyst- After heating, the catalyst is placed in the wire gauze cage attached below the lid.
- Loading of cultures- The inoculated culture plates or test tubes are placed inside the jar. A freshly prepared chemical indicator is also kept inside the jar.
- Indicator- Methylene blue indicator or Lucas semi-solid indicator is used. It is used to show whether anaerobic condition is formed or not.
- Sealing of jar- The lid is placed on the jar. The gasket should be clean and properly fitted.
- Tightening of lid- The bridge clamp and screw are fixed tightly. This makes the jar airtight.
- Removal of air- The inlet valve is kept closed. The vacuum pump is connected with the outlet valve and air is removed from the jar.
- Vacuum reading- Air is removed until the pressure gauge shows about 600 mmHg vacuum.
- Filling with gas- The outlet valve is closed. The inlet valve is connected with hydrogen gas or anaerobic gas mixture.
- Gas replacement- The gas is slowly passed into the jar until the pressure becomes atmospheric level.
- Catalytic reaction- The jar is kept for about 20 to 30 minutes. During this time, hydrogen reacts with remaining oxygen in presence of palladium catalyst.
- Formation of water- Water is formed due to reaction between hydrogen and oxygen. Condensation may be seen on the inner wall of the jar.
- Heating in old model- In old jar with hot catalyst, electrical current is switched on to heat the catalyst during this step.
- Incubation- All valves are closed and gas connections are removed. The sealed jar is placed in incubator, commonly at 37°C.
- Incubation time- The cultures are incubated for required time, usually 48 to 72 hours.
- Checking of indicator- The chemical indicator is checked during incubation. It should remain colourless. Blue colour shows entry of oxygen inside the jar.
Uses of McIntosh and Fildes’ Anaerobic Jar
The following are the uses of McIntosh and Fildes’ anaerobic jar-
- Cultivation of anaerobic bacteria- It is used for growing strict anaerobic bacteria. Clostridium, Bacteroides and Fusobacterium can be grown by using this jar.
- Diagnosis of infections- It is used in diagnosis of anaerobic infections. Tetanus, botulism, gas gangrene, abscess and sepsis can be studied by this method.
- Isolation of pathogens- It is used for isolating anaerobic pathogens from clinical samples. Blood, cerebrospinal fluid, bone marrow, lung aspirate and pus may be used as specimen.
- Dental and abdominal abscess- It is used for culture of organisms from dental abscess, burn abscess and abdominal abscess.
- Culture of parasites- It is used for culturing Trichomonas vaginalis. This helps in diagnosis of trichomoniasis.
- Pharmaceutical quality control- It is used in pharmaceutical industry for detecting anaerobic contaminants. It is useful for checking injectable drug vials and other compounds.
- Food quality control- It is used in food industry for detecting spoilage organisms. It is useful in vacuum packed foods where anaerobic organisms may grow.
- Fermentation work- It is used in microbial growth for brewing and fermentation. It helps to maintain anaerobic condition required for some organisms.
- Bacterial research- It is used in laboratory research work. It helps to study anaerobic bacteria under controlled oxygen free condition.
Advantages of McIntosh and Fildes’ Anaerobic Jar
The following are the advantages of McIntosh and Fildes’ anaerobic jar-
- Efficient anaerobic condition- It produces complete anaerobic condition inside the jar. It is useful for growing strict anaerobic bacteria.
- Rapid removal of oxygen- Oxygen is removed quickly by evacuation and chemical reaction. So, sensitive organisms are not exposed to oxygen for long time.
- Good for obligate anaerobes- It is suitable for obligate anaerobes which cannot survive in presence of oxygen.
- Space saving- The jar is compact in size. It does not occupy much space in laboratory or incubator.
- Controlled condition- The pressure and anaerobic condition can be checked during use. So, the internal environment can be controlled properly.
- Reproducible result- It gives dependable and repeated result when the procedure is done correctly. It is useful in clinical diagnosis and quality control work.
- Useful in routine laboratory- It can be used for normal anaerobic culture work. It is simple to place culture plates inside and incubate them.
Limitations of McIntosh and Fildes’ Anaerobic Jar
The following are the limitations of McIntosh and Fildes’ anaerobic jar-
- Need of special equipment- It needs vacuum pump and gas cylinder for operation. These instruments may be costly and not available in every laboratory.
- Skilled handling- It needs proper training for use. Wrong sealing or wrong gas filling may lead to failure of anaerobic condition.
- Safety risk- Hydrogen gas is used in this jar. It may cause fire or explosion if not handled carefully.
- Risk in old models- In older jars, the catalyst is heated by electrical system. Sparking may occur and it can cause explosion in presence of hydrogen.
- Catalyst inactivation- Palladium catalyst may become inactive easily. Moisture, hydrogen sulphide and volatile organic compounds can reduce its activity.
- Regular maintenance- The catalyst needs regular reactivation. It is heated in dry oven at about 160°C for up to 2 hours before or after use.
- Leakage problem- The jar must be completely airtight. Leakage through valve, gasket or O-ring can allow oxygen to enter inside the jar.
- Culture failure- If oxygen remains inside or enters during incubation, strict anaerobes may not grow. So, the whole culture result may become wrong.
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