Bacteria are small infectious agents that fall into a category of living things called prokaryotes. Prokaryotes' genetic material, or DNA, is not enclosed in a cellular compartment known as a nucleus. Bacteria are among the Earth's earliest forms of life. In fact, they are thought to have helped shape Earth's early environment, eventually creating atmospheric oxygen that enabled the development of other more complex life forms.
Bacteria are divided into thousands of different species but are broadly classified by their shape. Rod-shaped bacteria are termed bacilli, ball-shaped bacteria are called cocci and spiral-shaped bacteria are known as spirochetes. Bacterial cells are further grouped by whether they form clusters, chains or other groupings when examined microscopically. Bacteria live on or in almost every surface, material and environment on Earth. Some bacteria possess long whip-like structures called flagellae that they rotate to move. Others secrete a slime layer to slowly move over surfaces, and still others are stationary. Some bacteria are photosynthetic, but most absorb nutrients from their environment in order to survive. A particular bacterium's ability to absorb nutrients and tolerate specific environmental conditions influences whether it is likely to colonize or infect humans.
A multitude of antibiotics have been developed to treat bacterial infections. Antibiotics work by preventing bacteria from performing essential functions such as putting their cell walls together, assembling essential cell proteins or making copies of their genetic material (DNA). In addition, highly effective vaccines have been developed to prevent bacterial infection. Examples of such vaccines include those directed against Streptococcus pneumoniae, the most common bacterial cause of pneumonia in adults, and Neisseria meningitidis, the most common cause of meningitis. Research is underway to develop vaccines to prevent the most common causes of hospital-acquired infections, which are often resistant to common antibiotics. Lyme & Other Tick-borne Illnesses Tuberculosis (TB)