Commensal Health Dictionary

A chronic infectious condition caused by an anaerobic micro-organism, Actinomyces israelii, that often occurs as a COMMENSAL on the gums, teeth and tonsils. Commonest in adult men, the sites most affected are the jaw, lungs and intestine, though the disease can occur anywhere. Suppurating granulomatous tumours develop which discharge an oily, thick pus containing yellowish (‘sulphur’) granules. A slowly progressive condition, actinomycosis usually responds to antibiotic drugs but improvement may be slow and surgery is sometimes needed to drain infected sites. Early diagnosis is important. Treatment is with antibiotics such as penicillin and tetracyclines. The disease occurs in cattle, where it is known as woody tongue.... actinomycosis

The genus of Gram positive bacilli including Corynebacterium diphtheriae, the cause of diphtheria in humans. Genus also includes C. minutissimum, the cause of erythrasma in humans and the diphtheroids which are commensal corynebacteria making up part of the human respiratory tract normal flora.... corynebacterium

n. a genus of one of the largest parasitic *protozoans affecting humans (70 ?m or more in length). The oval body is covered with threadlike cilia (for locomotion). B. coli, normally living in the gut of pigs as a harmless *commensal, occasionally infects humans (see balantidiasis).... balantidium

n. a genus of mostly Gram-positive anaerobic spore-forming rodlike bacteria commonly found in soil and in the intestinal tract of humans and animals. Many species cause disease and produce extremely potent *exotoxins. C. botulinum grows freely in badly preserved canned foods, producing a toxin causing serious food poisoning (*botulism); an extremely dilute form of this toxin is now used to treat muscle spasm (see botulinum toxin). C. histolyticum, C. oedematiens, and C. septicum all cause *gas gangrene when they infect wounds. C. tetani lives as a harmless *commensal in the intestine but causes *tetanus on contamination of wounds (with manured soil). The species C. perfringens – Welch’s bacillus – causes blood poisoning, *food poisoning, and gas gangrene. Overgrowth of Clostridium difficile (often shortened to C. diff), a normal inhabitant of the human large intestine, is not uncommon as a complication of some antibiotic therapy and produces a specific condition – pseudomembranous colitis (see pseudomembrane) – which is life-threatening unless treated promptly and is becoming more common as a hospital-acquired infection.... clostridium

n. invasion of the body by harmful organisms (pathogens), such as bacteria, fungi, protozoa, rickettsiae, or viruses. The infective agent may be transmitted by a patient or *carrier in airborne droplets expelled during coughing and sneezing or by direct contact, such as kissing or sexual intercourse (see sexually transmitted disease); by animal or insect *vectors; by ingestion of contaminated food or drink; or from an infected mother to the fetus during pregnancy or birth. Pathogenic organisms present in soil, organisms from animal intermediate hosts, or those living as *commensals on the body can also cause infections. Organisms may invade via a wound or bite or through mucous membranes. After an *incubation period symptoms appear, usually consisting of either localized inflammation and pain or more remote effects. Treatment with antibiotics is usually effective against most infections, but there are few specific treatments for many of the common viral infections, including the common cold (see antiviral drug; interferon).... infection

n. any living thing that lives in (see endoparasite) or on (see ectoparasite) another living organism (see host). The parasite, which may spend all or only part of its existence with the host, obtains food and/or shelter from the host and contributes nothing to its welfare. Some parasites cause irritation and interfere with bodily functions; others destroy host tissues and release toxins into the body, thus injuring health and causing disease. Human parasites include fungi, bacteria, viruses, protozoa, and worms. See also commensal; symbiosis. —parasitic adj.... parasite

n. an intimate and obligatory association between two different species of organism (symbionts) in which there is mutual aid and benefit. Compare commensal; mutualism; parasite.... symbiosis