Bacterial Categories

Category : cheese industry, Farming / Food production, food decay, food hygiene, food industry, Food Microorganisms, food poisoning, Miscellaneous
Bacterial Categoriesby Andrew Routledgeon.Bacterial CategoriesIn my last article on the subject of bacteria (shigella) I described some bacterial terminology in lay man’s terms to help you to understand the scientific terminology. Today I would like to touch a little upon the subject of how we categorize bacteria. There are many species of bacteria and the have evolved in many […]

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In my last article on the subject of bacteria (shigella) I described some bacterial terminology in lay man’s terms to help you to understand the scientific terminology. Today I would like to touch a little upon the subject of how we categorize bacteria. There are many species of bacteria and the have evolved in many different ways. Each has found a niche in the evolutionary ladder and they have adapted themselves to be able to live in a vast variety of different conditions. What I want to do is to go through some of the different conditions in which bacteria live and by which bacteria are categorized.

The first three categories I am going to describe relate to different temperature conditions in which bacteria can be found and by which they are categorized for having this quality.

Psicrophilic. Psicro in Greek means low. Psicrophilic bacteria are ones which prefer to function at low temperatures. Normally speaking, low temperatures means below 5 degrees Celsius. The advantage that these bacteria have by utilizing cold conditions is that there are very few other bacteria that can compete with them at this temperature. From a food hygiene perspective these are the bacteria which cause refrigerator spoilage. If you have ever notices a slightly slimy surface to food that is kept at low temperatures this sliminess can be caused by psicrophilic bacteria. Normally these are not considered to be pathogenic bacteria but if you are particularly sensitive eating food that has been affected by psychrophylic bacteria can cause mild to medium stomach upset.

Mesophilic. Mesophilic bacteria are once which prefer to perform their metabolic functions at a moderate temperature range. This means that this category of bacteria is active between temperatures of 10 degrees Celsius to 40 degrees Celsius. many processes in the food industry, particularly the cheese industry, and most fermentation processes occur within this temperature range. This is also the temperature at which the vast majority of pathogenic bacteria function and therefore this presents the need for close control of bacteria action within the cheese and fermentation industries. Mistakes in this area would definitely cost lives. It is also the temperature at which most bacteria attack our bodies.

Thermophilic. Thermophilic bacteria are bacteria which have developed the ability to operate their metabolic functions at high temperatures. Bacteria of this classification can survives in temperatures in excess of 100 degrees Celsius. Some bacteria of this classification are used in the food industry and some are found in nature. In processes of controlled rotting the development of thermophilic bacteria is undesirable because they will break the materials down too much. This can be caused in the manufacture of compost by giving too much food. By giving too much food the temperature rises, the desirable bacteria are killed as well as the worms and the thermophilic bacteria turn the entire compost heap into useless mush.

The next three categories that I would like to discuss refers to the chemical environment in which bacteria live with respect to levels of acidity. Bacteria have developed the ability to survive in a wide range of acidic or non acidic conditions. Many such bacteria by acting in different acidic or non acidic climates become desirable from an industrial point of view. Many industrial processes rely upon bacterial activity for the production of the end product. This is true of the food and non food industries. However, some conditions become the target zone of pathogenic bacteria.

Basophilic. Bacteria which thrive in a basophilic climate are bacteria which prefer to live in a base of alkali environment. The level of which depends upon the specific species of bacteria. Some pathogenic bacteria become pathogenically active in alkali environments particularly bacteria which break down the proteins in meat and fish. They have developed this ability because ammonia is produced in decomposing flesh which is an alkali. In saying that many industrial processes are dependant upon basophilic bacteria.

Normophilic. Normophilic bacteria are ones which perform their metabolic functions at a neutral PH level or there about. Bacteria wich are active within this climate include many types of pathogens. You may remember that we have already talked about the fact that most pathogenic bacteria cannot remain active when acidity levels are raised and PH is lowered. We can therefore state that a great many pathogens function in mesophilic, normophilic conditions. If you think about it this is logical because the acidic conditions within a body are more of less neutral. The bacteria have become suited to the environment in which they are designed to exist.

Acidophile. Bacteria which have developed to survive within an acidophile environment are ones which perform their metabolic function in a strong acid environment. Again, bacteria such as these have evolved in nature to continue the degradation of matter when conditions become too acidic for normophilc bacteria. This category of bacteria is also used extensively throughout industry for a great many purposes. Not many bacteria within this group are pathogens.

The third category of bacteria about which I would like to discuss with you refers to how the bacteria relates to the use of oxygen. by this I mean can the bacteria survive with or without the presence of oxygen. Most pathogenic bacteria exist in an anaerobic environment or can change from an aerobic environment to an anaerobic one depending on the environment in which it is trapped.

Obligate aerobic. An obligate aerobic bacteria is one which must have the presence of free oxygen around it. Many industrial processes rely upon bacteria of this category.

Obligate anaerobic. Obligate anaerobic bacteria are bacteria which for the most part cannot tolerate an oxygen rich environment and perform all their metabolic functions through fermentation. Some bacteria from this category are pathogens.

Facultative anaerobic bacteria are ones which can switch from an oxygen rich environment to an environment devoid of oxygen and back again as the need arises. Many pathogenic bacteria belong to this category. By belonging to this niche facultative anaerobic bacteria have ensured the ability to survive even when conditions change.

Now that you have this information look up different bacterial species on the Internet and see if you can distinguish pathogenic bacteria in several of the different categories stated here.


Andy has many years of experience in food preparation, Food Hygiene, Catering and staff Training

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