Definition of Bacteria

Bacteria – single-cell microorganisms (microbes). Bacteria are the most ancient and primitive life forms known, with fossils dating back more than 3 billion years. A bacterium’s structure is very simple, consisting of a rigid cell wall that supports and contains the cytoplasm, fragments of RNA, and a single strand of DNA within a nonencapsulated (unbordered) nucleus.

Though bacteria are capable of independent existence, most require a symbiotic relationship with a host organism. The bacteria provide needed functions for the host in exchange for nutrients and safe haven.

Types of bacteria

Many types of bacteria exist in and on the body in just such a symbiotic partnership; these are part of the body’s normal flora. Bacteria in the gastrointestinal tract digest food, for example. Bifidobacterium bifidum, Lactobacillus acidophilus, and Saccaromyces boulardii are some of the more abundant bacterial families that reside in the small intestine.

However, when normal flora bacteria are able to establish themselves in tissues other than their natural habitat or their numbers become abundant, they cause infection. Escherichia coli, for example, are abundant normal flora in the colon, where they work to prepare the residue of digestion for elimination from the body.

E. coli also synthesize vitamin K, which is essential for coagulation (blood clotting). When E. coli escape from their habitat, however, they cause infections such as vaginitis or urinary tract infection (UTI).

The “Bad” E. Coli: O157:H7

The bacterial family Escherichia coli is extensive and ubiquitous-its many strains live in the gastrointestinal systems of nearly all animals. E. coli O157:H7, normal flora in cattle, is a family member of great notoriety for the potential of severe illness it presents in people.

The toxin this strain releases can destroy red blood cells in such volume that the kidneys fail, a condition called hemolytic uremic syndrome. E. coli O157:H7 enters the human food chain as a foodborne illness.

Bacteria that cause infection are pathogens

Most pathogenic bacteria exist in the natural environment, they are harmful to human health, and the immune system establishes mechanisms to stop, contain, or attack them should they enter the body.

Bacteria can cause infection and illness by destroying the cells they invade or by releasing toxins. antibiotic medications treat bacterial infections.

Bacteria Classification

Traditional classification systems view bacteria according to their physical (morphologic) characteristics because these are the traits perceptible with the use of a microscope, the first tool available for viewing microbes. These characteristics provide basic information about the particular bacterial family that is important to doctors when choosing antibiotic medications to treat bacterial infections.

Methods made available through advances in molecular medicine during the latter years of the 20th century, such as ribosomal analysis and DNA sequencing, allow improved understanding of how bacteria function both to support health and to cause illness.

Illnesses Caused by Bacterial Infection

appendicitisbacterial meningitis
cold soreconjunctivitis
gonorrheaherpes zoster
infectious arthritislegionnaires’ disease
listeriosislyme disease
mastoiditisnecrotizing fasciitis
orbital cellulitisosteomyelitis
pericarditisperitonsillar abscess
pneumococcal pneumoniarheumatic heart disease
rocky mountain spotted feverscarlet fever
septicemiastaphylococcal scalded skin syndrome
strep throattyphoid fever


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