Cultivation of Bacteria-Culture Media and Method

The cultivation of bacteria plays an important role in medical and research purposes. The culture of bacteria allows variable bacteria to isolate, detect, and provide biomasses. It is done for an in-depth analysis of metabolic activity. On the other hand, bacteria can cause bacterial infections, which can be dangerous for human life. At the end of this study, knowledge about the types of microbial culture media, concepts of sterilisation of culture media, and methods of cultivation of anaerobic bacteria could be gained.

Types of microbial culture media 

Bacteria cultivation is a biological activity wherein microorganisms multiply themselves in a predetermined culture media under laboratory conditions. Whereas, microbial culture media are used to identify the types of microorganisms and their abundance in culture media are being tested precisely. It could be observed that MTCC has around 20000 microbial cultures. More than 80% of the microbial culture available in MTCC is of Indian origin. Culture bacteria are the initial step to study the morphology of bacteria. There are various procedures of cultivating bacteria, which are as follows:

• Isolation of bacteria
• Creating antigens for laboratory use
• To estimate viable counts
• Testing for antibiotic sensitivity
• Maintenance of stock culture
• To separate different types of bacteria with the help of microbial culture media
• Certain manipulation of cells and genetic studies of the cell also need that bacterium to be cultured in vitro.

There are various types of microbial culture media present and they are classified into six different groups as follows: 

• Basal media: This type of media is used for the culture of bacteria, which do not need enrichment of media. For example, Peptone water, nutrient agar, Nutrient broth are notable aspects. 
• Enriched media: This media is enriched by adding serum, eggs, or blood. For example, Lowenstein-Jensen media is the most known. 
• Selective media: This type of culture is used for the cultivation of a particular type of bacteria by preventing the growth of undesired bacteria and allowing the growth of desired bacteria. The example of selective media includes MacConkey agar. It contains bile salts and crystal violet, which interferes with the growth of gram-positive bacteria and favours the growth of gram-negative bacteria.
• Storage media: This type of media is used for the storage of bacteria for a longer period. For example, chalk cooked meat broth and Egg saline medium are notable.
• Indicator media: An indicator is included in the media wherein a particular bacterium causes changes in the indicator such as tellurite. For example, Blood agar and MacConkey agar are evident examples of indicator media.

Concepts of sterilisation of culture media

Sterilisation is defined as the process of deactivating, killing, or removing all forms of life in particular reference to microorganisms such as fungi, bacteria, unicellular eukaryotic cells, and spores. There are various methods by which sterilisation of culture media can be achieved. The processes include heat, chemicals, irradiation, high pressure, and filtration. The most common Sterilisation of culture media of bacteria is carried in a steam autoclave at a temperature between 121 to 134 degrees Celsius. The sterilisation of the cultural media cycle can be divided into four stages as follows: 

• Stage 1: 20-121 degrees Celsius chamber heat uptime
• Stage 2: 100-121 degrees Celsius heat penetration time of the media
• Stage 3: 121-121 degrees Celsius holding time at a prescribed temperature
• Stage 4: 121-80 degrees Celsius cool-down time for the chamber to reach 80 degrees Celsius. 

Methods of cultivation of anaerobic bacteria

There are mainly three methods of cultivation of anaerobic bacteria such as an atmosphere free of oxygen, an anaerobic indicator, and an anaerobic jar with a catalyst. 

• McIntosh–Fildes anaerobic jar: This jar is used to generate an anaerobic condition for the cultivation of anaerobic bacteria in a laboratory. The principle of this jar is evacuation and replacement, wherein the mixture of gas replaces inner gas with oxygen. This consists of 85% nitrogen, 10% hydrogen, and 5% carbon dioxide. 
• An anaerobic indicator: This is a sachet-containing test, which contains test strips saturated with resazurin solution. It checks the atmosphere in a shielded container whether it can be used for incubation or not.  

Conclusion

It can be concluded that there are six types of microbial culture media. The growth of bacteria depends on many factors such as temperature, pH level, moisture level, and oxygen level. On the other hand, sterilisation of culture media has resulted where four effective steps are required to sterilise cultural media. Summarization about the sterilisation methods such as chemicals, irradiation, high pressure, and filtration could be made. This report concludes the methods of cultivation of anaerobic bacteria, for example in India, Agar plate is widely used for the cultivation of anaerobic bacteria. In addition, McIntosh–Fildes anaerobic jar can be used to provide an anaerobic condition for cultivation of anaerobic bacteria.