Characteristic Features of bacteria

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Chapter: Pharmaceutical Microbiology : Structure and Function of Bacterial Cells

A few vital and cardinal characteristic features of ‘bacteria’ are as enumerated under : 1. Shape 2. Size 3. Reproduction 4. Formation of Colony 5. Mutation 6. Motility 7. Food and Oxygen Requirements 8. Temperature Requirements



A few vital and cardinal characteristic features of ‘bacteria’ are as enumerated under :


1. Shape

There are three principal forms of bacteria, namely :

(a) Spherical or Ovoid — bacteria occur as single cells (micrococci), or in pairs (diplococci), clusters (staphylococci), chains (streptococci) or cubical groups (sarcinae) ;

(b) Rod-shaped — bacteria are termed as bacilli, more oval ones are known as coccobacilli, and those forming a chain are called as streptobacilli ; and

(c) Spiral — bacteria are rigid (spirilla), flexible (spirochaetes) or curved (vibrios).


2. Size

An average rod-shaped bacterium measures approximately 1 μm in diameter and 4 μm in length. They usually vary in size considerably from < 0.5 to 1.0 μm in diameter to 10–20 μm in length in some of the longer spiral forms.


3. Reproduction

It has been observed that simple cell division is the usual method of reproduction, whereas cer-tain bacteria give rise to buds or branches that eventually break off. The growth rate is substantially affected on account of changes in temperature, nutrition, and other factors.


Importantly, bacilli can produce reproductive cells invariably termed as spores, whose relatively thick coatings are highly resistant to adverse environmental conditions. In the event of a better congenial environment the spores commence to grow. Besides, spores are difficult to kill as they are highly resistant to heat as well as disinfectant action.


4. Formation of Colony

A group of bacteria growing in one particular place is known as a colony. A colony is invariably comprised of the ‘descendants of a single cell’. It has been found that colonies differ in shape, size, colour, texture, type of margin, and several other characteristic features. Interestingly, each species of bacteria has a characteristic type of colony formation.


5. Mutation

Evidently, a majority of bacteria, like all living organisms, do possess the ability to adapt their shape or functions when encountered with distinct changes in their environment, but there are certain degree of limits to this ability. However, they may also mutate to adapt to some potentially lethal sub-stances, for instance : antibiotics.


6. Motility

It has been duly observed that none of the ovoid or spherical cocci are capable of moving, but certain bacilli and spiral forms do exhibit absolute independent movement. It is, however, pertinent to mention here that the power of locomotion exclusively depends on the possession one or more flagella, slender whiplike appendages which more or less work like propellars.


7. Food and Oxygen Requirements

Bacteria are of different types based upon their food and oxygen requirements as given below :

(a) Heterotrophic : require organic material as food,

(b) Parasites : feed on living organisms,

(c) Saprophytes : feed on non-living organic material,

(d) Autotrophic : i.e., self-nourishing–obtain their energy from inorganic substances, including most of the soil bacteria,

(e) Aerobes : essentially require oxygen for their very existence and growth, and

(f) Anaerobes : do not require oxygen for their existence and growth. e.g., most bacteria found in the GIT.


8. Temperature Requirements

Although some bacteria live at very low temperature or very high temperature ; however, the optimum temperature for a majority of pathogens is 37 °C (98.6 °F).


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