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Any of the organic compounds possessing one or more basic amino groups and one or more acidic carboxyl groups. Of the more than 80 amino acids that have been found in living organisms, approximately 20 serve as the building blocks for proteins.…

An acute, infectious worldwide zoonotic disease (transmissible to humans) caused by the spore-forming bacterium Bacillus anthracis to which most animals, especially grazing herbivores, are susceptible. Anthrax is a serious, though rare, infectious…

An ongoing current event in which a large number of living species are threatened with extinction or are going extinct because of environmentally destructive human activities. The Earth is presently in the midst of a mass extinction event. In the…

The capability that a bacterium acquires to counteract an inhibitory chemical molecule or compound that was formerly effective in killing it or preventing its growth. Antibiotic resistance in bacteria (Fig. 1) is a hot topic in the media and in…

Programmed cell death triggered by extracellular signals or genetically determined events and carried out by physiological processes within the cell. Apoptosis is one of the major forms of cell death in multicellular organisms (necrosis is the other…

A group of diverse microscopic prokaryotic organisms that constitute one of the three domains of life. Taxonomists recognize three domains of cellular life: Archaea, Bacteria, and Eukaryota (also termed Eukarya or Eucarya) [Fig. 1]. The members of…

The classification, nomenclature, and identification of bacteria. Bacterial taxonomy is concerned with the naming of bacterial organisms and with organizing these names according to various criteria. Biologically, bacteria (Fig. 1) are prokaryotic…

A method for quantitatively determining the concentration, biological activity, or potency of a substance by its effect on the growth of a suitable animal, plant, or microorganism under controlled conditions. A bioassay (biological assay) is a…

A microbial (often bacterial) community that is enveloped by an adhesive substance (the glycocalyx) at the interface of a liquid and a surface. Biofilms (see illustration) are defined as highly structured communities of microorganisms that are…

Self-sustained circadian (approximately 24-hour) rhythms that regulate daily activities, including sleep and wakefulness. A biological clock is any physiologic factor that functions in regulating innate organismal rhythms. Biological clocks were…

A biochemical reaction involving the transfer of a negatively charged electron from one organic compound to another organic compound or to oxygen. Biological oxidation is an energy-producing reaction in living cells, and it is coupled with a…

Any of the genetically determined markers on the surface of cellular blood elements (red and white blood cells, and platelets). Blood groups (types) have medical, legal, and anthropologic importance. In medicine, the matching of ABO and Rh groups of…

Cells within a tumor that possess the capacity to self-renew and cause the heterogeneous lineages of cancerous cells that comprise the tumor. Cancer stem cells (CSCs) typically represent a small percentage of all cells in a tumor (rarely more than…

The science of the electrical activity of the heart. Cardiac electrophysiology is the branch of cardiology concerned with the mechanism, spread, and interpretation of the electric currents that arise within heart muscle tissue and initiate each…

Common pigments, typically of yellow, orange, or red hues, that serve in both light absorption and the protection against too much light in photosynthesis as well as in the vision process. Carotenoids comprise a class of labile, easily oxidizable,…

The cultivation of cells in the laboratory. Cell culture is the growth of living cells or microorganisms in a controlled artificial environment. Bacteria and yeasts may be grown suspended in a liquid medium or as colonies on a solid medium (usually…

A severe diarrheal disease caused by infection of the small bowel of humans with Vibrio cholerae. Cholera is an acute, infectious bacterial disease that results in serious, often fatal, gastrointestinal illness in humans. The causative agent is…

Any persistent pain occurring in the lumbar (lower) back, sometimes extending to the buttocks and legs, which has been present for at least 3 months. Chronic low back pain (CLBP) [Fig. 1] is usually a combination of musculoskeletal and neuropathic…

A genus of bacteria, including a number of important human pathogens, comprising large anaerobic spore-forming rods that usually stain gram-positive. Most species of the genus Clostridium are anaerobes, but a few will grow minimally in air at…

The internal structures and processes that are involved in the acquisition and use of knowledge, including sensation, perception, attention, learning, memory, language, thinking, and reasoning. The mental processes and behaviors that constitute…

A hereditary genetic disorder, resulting from mutations in the cystic fibrosis transmembrane conductance regulator gene, that severely damages the lungs, digestive system, pancreas, and liver. Cystic fibrosis is one of the most common…