Effect of Oxygen Concentration on Food Microbes

All living beings do respire. To respire oxygen is taken up by the body. Respiration is the oxygenation break down of the complex large molecules into simple small molecules. Microbes also do respiration in order to gain energy and also to survive. Hence in the presence of adequate oxygen levels microbes carry out their body functions efficiently. Microbes vary in their oxygen requirement. Some may need high oxygen levels where as for some it may be very low or they may grow in the absence of oxygen. Hence if we can control the oxygen level in the food environment then we are able to prevent food spoilage and microbial interactions with the food.

Aerobic microorganisms need Oxygen to do respiration. Hence aerobes grow on the top of the medium. Because top surface of the medium touches the atmosphere where oxygen is present. Hence aerobes grow near to the atmosphere in the medium.

Ex: Penicillium sp. ,Pseudomonas fluorescens

Facultative anaerobes can survive both in the presence of oxygen and in the absence of oxygen. Hence they can grow all over the medium even at the bottom of the test tube.

Ex: Escherichia coli, Salmonella sp., Staphylococcus aureus

Microaerophiles need oxygen for respiration but they need lesser amount of oxygen than aerobes. Hence they grow somewhat below to the top surface where oxygen is present in lower levels.

Ex: Campylobacter sp.

Obligate anaerobes are the microorganisms that do not need oxygen or survive without oxygen. They only survive in oxygen absent environments.

Ex: Clostridium botulinum

The test tube which contains obligate anaerobes is sealed with a plug. That is to ensure no oxygen is gone inside the test tube hence this confirms that it contains only obligate anaerobes. Whereas other 3 tubes are covered with a cotton wool. Thus it facilitates the air movement into the medium.

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