infections
Overview of Bacteria
Classification of Bacteria
Bacteria can be classified in several ways: Scientific names:Bacteria, like other living things, are classified by genus (based on having one or several similar characteristics) and, within the genus, by species. Their scientific name is genus followed by species (for example,Clostridium botulinum). Within a species, there may be different types, called strains. Strains differ in genetic makeup and chemical components. Sometimes certain drugs and vaccines are effective only against certain strains. Bacteria may be classified by the color they turn after certain chemicals (stains) are applied to them. Gram staining is a commonly used staining process. Some bacteria stain blue. They are called . Others stain red. They are called Shapes:All bacteria may be classified as one of three basic shapes: spheres (cocci), rods (bacilli), and spirals or helixes (spirochetes). Need for oxygen:Bacteria are also classified by whether they need oxygen to live and grow. Those that need oxygen are called aerobes. Those that do not need oxygen and have trouble living or growing when oxygen is present are called anaerobes. Some bacteria, called facultative bacteria, can live and grow with or without oxygen. Tests That Detect Genetic Material in Microorganisms can determine differences in the genetic make-up (genotype) of bacteria. The body normally contains several hundred different species of bacteria but many trillions of individual bacteria. Most of these bacteria reside in the following places: On the skin and teeth In the spaces between teeth and gums In the mucous membranes that line the nose and nasal passages, throat, intestine, and vagina The species differ at each site, reflecting the different environment at each site. Many of them are anaerobes—that is, they do not require oxygen to live and grow. Usually, these anaerobes do not cause disease. Many have useful functions, such as helping break down food in the intestine. However, anaerobic bacteria can cause disease if the mucous membranes are damaged. Then, bacteria can enter tissues that are usually off-limits to them and that have no defenses against them. The bacteria may infect nearby structures (such as the sinuses, middle ear, lungs, brain, abdomen, pelvis, and skin) or enter the bloodstream and spread. 