Bacilli can form reproductive cells called spores whose thick coats are highly resistant to adverse environmental conditions. When a better environment develops, the spores being to grow. Spores are difficult to kill because they are highly resistant to heat, drying, and disinfectant action. A group of bacteria growing in one place is called a colony. A colony is usually composed of the descendants of a single cell.
Colonies differ in shape, size, color, texture, type of margin, and other characteristics.
Each species of bacteria has a characteristic type of colony formation. Most bacteria, like all living organisms, have the ability to adapt their shape or functions when faced with changes in their environment, but there are limits to this ability. They can also mutate to adapt to potentially lethal agents such as antibiotics. The power of locomotion depends on the possession of one or more flagella, slender whiplike appendages that work like propellers. Putrefaction, the decomposition of nitrogenous and other organic materials in the absence of air, produces foul odors.