Vibrio Health Dictionary

A severe infectious epidemic disease due to Vibrio cholerae... cholera

(Singular: bacterium.) Simple, single-celled, primitive organisms which are widely distributed throughout the world in air, water, soil, plants and animals including humans. Many are bene?cial to the environment and other living organisms, but some cause harm to their hosts and can be lethal.

Bacteria are classi?ed according to their shape: BACILLUS (rod-like), coccus (spherical – see COCCI), SPIROCHAETE (corkscrew and spiral-shaped), VIBRIO (comma-shaped), and pleomorphic (variable shapes). Some are mobile, possessing slender hairs (?agellae) on the surfaces. As well as having characteristic shapes, the arrangement of the organisms is signi?cant: some occur in chains (streptococci) and some in pairs (see DIPLOCOCCUS), while a few have a ?lamentous grouping. The size of bacteria ranges from around 0.2 to 5 µm and the smallest (MYCOPLASMA) are roughly the same size as the largest viruses (poxviruses – see VIRUS). They are the smallest organisms capable of existing outside their hosts. The longest, rod-shaped bacilli are slightly smaller than the human erythrocyte blood cell (7 µm).

Bacterial cells are surrounded by an outer capsule within which lie the cell wall and plasma membrane; cytoplasm ?lls much of the interior and this contains genetic nucleoid structures containing DNA, mesosomes (invaginations of the cell wall) and ribosomes, containing RNA and proteins. (See illustration.)

Reproduction is usually asexual, each cell dividing into two, these two into four, and so on. In favourable conditions reproduction can be very rapid, with one bacterium multiplying to 250,000 within six hours. This means that bacteria can change their characteristics by evolution relatively quickly, and many bacteria, including Mycobacterium tuberculosis and Staphylococcus aureus, have developed resistance to successive generations of antibiotics produced by man. (METHICILLIN-RESISTANT STAPHYLOCOCCUS AUREUS (MRSA)) is a serious hazard in some hospitals.

Bacteria may live as single organisms or congregate in colonies. In arduous conditions some bacteria can convert to an inert, cystic state, remaining in their resting form until the environment becomes more favourable. Bacteria have recently been discovered in an inert state in ice estimated to have been formed 250 million years ago.

Bacteria were ?rst discovered by Antonj van Leewenhoek in the 17th century, but it was not until the middle of the 19th century that Louis Pasteur, the famous French scientist, identi?ed bacteria as the cause of many diseases. Some act as harmful PATHOGENS as soon as they enter a host; others may have a neutral or benign e?ect on the host unless the host’s natural immune defence system is damaged (see IMMUNOLOGY) so that it becomes vulnerable to any previously well-behaved parasites. Various benign bacteria that permanently reside in the human body are called normal ?ora and are found at certain sites, especially the SKIN, OROPHARYNX, COLON and VAGINA. The body’s internal organs are usually sterile, as are the blood and cerebrospinal ?uid.

Bacteria are responsible for many human diseases ranging from the relatively minor – for example, a boil or infected ?nger – to the potentially lethal such as CHOLERA, PLAGUE or TUBERCULOSIS. Infectious bacteria enter the body through broken skin or by its ori?ces: by nose and mouth into the lungs or intestinal tract; by the URETHRA into the URINARY TRACT and KIDNEYS; by the vagina into the UTERUS and FALLOPIAN TUBES. Harmful bacteria then cause disease by producing poisonous endotoxins or exotoxins, and by provoking INFLAMMATION in the tissues – for example, abscess or cellulitis. Many, but not all, bacterial infections are communicable – namely, spread from host to host. For example, tuberculosis is spread by airborne droplets, produced by coughing.

Infections caused by bacteria are commonly treated with antibiotics, which were widely introduced in the 1950s. However, the con?ict between science and harmful bacteria remains unresolved, with the overuse and misuse of antibiotics in medicine, veterinary medicine and the animal food industry contributing to the evolution of bacteria that are resistant to antibiotics. (See also MICROBIOLOGY.)... bacteria

Curcuma spp.

Zingiberaceae

The genus Curcuma belonging to the family Zingiberaceae comprises of a number of species which are medicinally very important. Among them, the most important species are described below.

1. C. amada Roxb.

English: Mango ginger San: Amrardrakam, Karpuraharida Hin: Ama -haldi

Mal: Mangainchi

Tam: Mankayinci

Tel: Mamidi Allam

Mango ginger is cultivated in Gujarat and found wild in parts of West Bengal, U. P, Karnataka and Tamil Nadu. It is a rhizomatous aromatic herb with a leafy tuft and 60-90cm in height. Leaves are long, petiolate, oblong-lanceolate, tapering at both ends, glabrous and green on both sides. Flowers are white or pale yellow, arranged in spikes in the centre of tuft of the leaves. Lip is semi -elliptic, yellow, 3-lobbed with the mid lobe emarginate. The rhizomes are useful in vitiated conditions of pitta, anorexia, dyspepsia, flatulence, colic, bruises, wounds, chronic ulcers, skin diseases, pruritus, fever, constipations, strangury, hiccough, cough, bronchitis, sprains, gout, halitosis, otalgia and inflammations (Warrier et al, 1994). The fresh root possesses the smell of green mango and hence the name mango ginger. The rhizomes are used externally in the form of paste as an application for bruises and skin diseases generally combined with other medicines. Tubers rubbed with the leaf- juice of Caesalpinia bonduc is given for worms (Nadkarni, 1982).

The essential oil contains -pinene, -and -curcumene, camphor, cuminyl alcohol, myristic acid and turmerone. Car-3-ene and cis-ocimene contribute the characteristic mango odour of the rhizome. Rhizome is CNS active, hypothermic and it shows potentiation of amphetamine toxicity. Tuber is trypsin inhibitor and is effective against Vibrio cholerae (Husain et al, 1992). The rhizomes are bitter, sweet sour, aromatic, cooling, appetiser, carminative, digestive, stomachic, demulcent, vulnerary, febrifuge, alexertic, aphrodisiac, laxative, diurectic, expectorant, antiinflammatory and antipyretic (Warrier et al, 1994).

2. C. aromatica Salisb.

Eng: Wild turmeric; San: Aranyaharidra, Vanaharidra;

Hin: Ban-haridra, Jangli-haldi;

Ben: Ban Haland; Mal,

Tam: Kasturimanjal, Kattumanjal;

Tel: Adavi-pasupu;

Kan: Kadarasina

Wild turmeric or Cochin turmeric or Yellow zeodoary is found wild throughout India and cultivated in Bengal and Kerala. It is a perennial tuberous herb with annulate, aromatic yellow rhizome which is internally orange-red in colour. Leaves are elliptic or lanceolate- oblong, caudate-acuminate, 30-60cm long, petioles as long or even longer, bracts ovate, recurved, more or less tinged with red or pink. Flowers are pink, lip yellow, obovate, deflexed, sub-entire or obscurely three lobed. Fruits are dehiscent, globose, 3-valved capsules. Rhizomes are used in combination with astringents and aromatics for bruises, sprains, hiccough, bronchitis, cough, leucoderma and skin eruptions (Warrier et al, 1994). The rhizomes have an agreeable fragrant smell and yield a yellow colouring matter like turmeric, and the fresh root has a camphoraceous odour. The dried rhizome is used as a carminative and aromatic adjunctant to other medicines (Nadkarni, 1998).

Essential oil contains -and - -curcumene, d-camphene and p-methoxy cinnamic acid. The colouring matter is curcumin. Numerous sesquiterpenoids of germacrone and guaiane skeletons have been identified recently. Rhizome has effect on respiration. It is spasmolytic and shows antagonism of amphetamine hyperactivity. Rhizome is an anti-dote for snakebite and carminative (Husain et al, 1992).

3. C. longa Linn. syn. C. domestica Valeton.

Eng: Turmeric; San: Haridra, Varavarnini;

Hin: Haldi, halda;

Ben: Haldi;

Mal: Manjal, Pachamanjal, Varattumanjal;

Tam: Mancal;

Kan: Haldi, Arasina;

Tel: Pasapu

Turmeric is cultivated all over India, particularly in W. Bengal, T. N and Maharashtra. It is a perennial herb, 60-90cm in height, with a short stem and tufts of erect leaves. Rhizome is cylindric, ovoid, orange coloured and branched. Leaves are simple, very large, petiole as long as the blade, oblong-lanceolate, tapering to the base upto 45cm long. Flowers are pale yellow, arranged in spikes concealed by the sheathing petioles and flowering bracts are pale green (Warrier et al, 1994). Turmeric occupies an important position in the life of Indian people as it forms an integral part of the rituals, ceremonies and cuisine. Due to the strong antiseptic properties, turmeric has been used as a remedy for all kinds of poisonous affections, ulcers and wounds. It gives good complexion to the skin and so it is applied to face as a depilatory and facial tonic. The drug cures diseases due to morbid vata, pitta and kapha, diabetes, eye diseases, ulcers, oedema, anaemia, anorexia, leprosy and scrofula. It purifies blood by destroying the pathogenic organisms. A paste of turmeric alone, or combined with a paste of neem (Azadirachta indica) leaves, is used to cure ringworm, obstinate itching, eczema and other parasitic skin diseases and in chicken pox and small pox. The drug is also useful in cold, cough, bronchitis, conjunctivitis and liver affections (Nadkarni, 1954; Kurup et al,1979; Kolammal, 1979). The rhizome is the officinal part and is an important ingredient of formulations like Nalpamaradi taila, Jatyadi taila, Narayana gula, etc. (Sivarajan et al, 1994).

Turmeric paste mixed with a little limejuice and saltpetre and applied hot is a popular application to sprains and bruises. In smallpox and chickenpox, a coating of turmeric is applied to facilitate the process of scabbing. The smoke produced by sprinkling powdered turmeric over burnt charcoal will relieve scorpion sting when the part affected is exposed to the smoke for a few minutes. Turmeric and alum powder in the proportion of 1:20 is blown into the ear in chronic otorrhoea (Nadkarni, 1998). “Haridra Khand”, a compound containing powdered turmeric, sugar and many other ingredients is a well-known preparation for cold, cough and flu, and for skin diseases. In Unani system, roasted turmeric is an ingredient of “Hab Narkachur”, used as antidysenteric for children (Thakur et al, 1989).

Essential oil contains ar-turmerone, and ar-curcumene as ma jor constituents. Some of the other compounds are -and -pinene, sabinene, myrcene, -terpinene, limonene, p- cymene, perillyl alcohol, turmerone, eugenol, iso-eugenol, eugenol methyl ether and iso- eugenol methyl ether. Curcumin and related compounds have also been reported as major constituents of the rhizomes. Recently a number of sesquiterpenes have been reported from C. longa, viz., the sesquiterpenoids of germacrane, bisabolane and guainane skeletons (Husain et al, 1992). The study of sesquiterpenes has revealed a new compound curlone (Kisoy et al, 1983). The crystalline colouring matter curcumin (0. 6%) is diferuloyl methane (Mathews et al, 1980). Stigmasterol, cholestrol, -sitosterol and fatty acids, mainly straight chain dienoic acids are reported (Moon et al, 1977). Curcumin, the colouring agent and major constituent of C. longa, is said to possess local as well as systemic antiinflammatory property which has been found to compare favourably with phenylbutazone (Srimal and Dhawan, 1973). An extract of the crude drug ‘akon’ containing the rhizomes exhibited intensive preventive activity against carbon tetrachloride induced liver injury invivo and invitro. The liver protecting effects of some analogs of ferulic acid and p-coumaric acid, probable metabolites of the curcuminoids have been also evaluated (Kiso et al, 1983). Curcumin is antiinflammatory. Rhizome is antiprotozoal, spasmolytic, CNS active, antiparasitic, antispasmodic, antibacterial, antiarthritic, anthelmintic, carminative, antiperiodic, emo llient, anodyne, laxative, diruretic, expectorant, alterative, alexertive, febrifuge, opthalmic and tonic.

4. C. zedoaria (Berg.) Rosc. syn. C. zerumbet Roxb; Amomum zedoaria

Christm.vEng: Round zedoary; San: Kachura, Shati;

Hin: Kakhur;

Ben: Sati;

Kan: Kachora

Mal: Manjakoova, Adavi-kacholam;

Tam: Kichilikizhangu, Nirvisham;

Tel: Kacheramu

The round zedoary or Zerumbet is mostly found in India and S. E. Asia. The plant has 4-6 leaves with 20-60cm long lamina. The leaf lami na is oblong-lanceolate, finely acuminate and glabrous on both the surfaces. Flower stalk is 20-25cm long, emerging before the leaves. Flowers are yellow, while the flowering bract is green tinged with red. Calyx is 8mm long, corolla tube is twice as long as the calyx. Capsule is ovoid, trigonous, thin smooth and bursting irregularly. Tubers are palmately branched and camphoraceous (Thakur et al, 1989). The identity of the plant sources of the drug Karcura is a matter of debate. There is difference of opinion among men of Ayurveda, as to whether Sati and Karcura are the same drug or different. Many authors consider them different and equate Sati with Hedychium spicatum Smith. and Karcura with C. zedoaria, both belonging to Zingiberaceae (Kurup et al,1979; Chunekar 1982; Sharma, 1983). Some others treat them to be the same and equate it with C. zedoaria (Kirtikar and Basu, 1918; Vaidya, 1936; Nadkarni, 1954; Kapoor and Mitra, 1979). However, the source of Karcura in Kerala in the recent times has been Kaempferia galanga of the same family. The rhizome of C. zedoaria is used as appetiser and tonic, particularly prescribed to ladies after childbirth. In case of cold, a decoction of long pepper (Piper longum), cinnamon (Cinnamomum verum), zedoary and honey is given. In Ayurveda it is an ingredient of “Braticityadi kwatha”, used in high fever (Thakur et al, 1989). Root is useful in flatulence and dyspepsia, and as a corrector of purgatives. Fresh root checks leucorrhoeal and gonorrhoeal discharges. Root powder is a good substitute for many foreign foods for infants. For worms, the juice from the tubers is given to children. Juice of the leaves is given in dropsy (Nadkarni, 1982). It is an odoriferous ingredient of the cosmetics used for the cure of chronic skin diseases caused by impure or deranged blood (Nadkarni, 1998).

Essential oil from rhizomes contains -pinene, d-camphene, cineole, d-camphor, sesquiterpenes and sesquiterpene alcohols (Husain et al, 1992). The novel sesquiterpenoids which have been isolated and characterised are cuzerenone, epi-cuzerenone, iso- furanogermerene, curcumadiol, curcumol, curcumenol, iso-curcumenol, procurcumenol, dehydrocurdione (Hikino et al, 1968, 1971, 1972), germacrone-4, 5-epoxide, germacrone, germacrone furanodienone, curcumenol, iso-curcumenol, curcumanolides A and B and curcumenone (Shiobara et al, 1985). The starch left after the extraction is purified and sold as a commodity of cottage industry in West-Bengal under the name ‘Shoti’ (Rao et al, 1928). Ethyl-p methoxy-cinnamate has been isolated from the alcoholic extract of the plant (Gupta et al, 1976). Rhizome is stomachic, diuretic, and carminative and gastrointestinal stimulant.

Other important species of Curcuma genus are

C. angustifolia Roxb. (Vellakoova)

C. caesia Roxb. (Black ginger)

C. leucorhiza Roxb.

C. pseudomontana Grah.

C. rubescens Roxb.

Agrotechnology: Curcuma species are tropical herbs and can be grown on different types of soils both under irrigated and rainfed conditions. Rich loamy soils having good drainage are ideal for the crop. The plant is propagated by whole or split mother rhizomes. Well developed, healthy and disease free rhizomes are to be selected. Rhizomes are to be treated with copper oxychloride fungicides and stored in cool, dry place or earthen pits plastered with mud and cowdung. The best season of planting is during April with the receipt of pre-monsoon showers. The land is to be prepared to a fine tilth during February-March. On receipt of pre- monsoon showers in April, beds of size 3x1.2m with a spacing of 40cm between beds are to be prepared. Small pits are to be taken in the beds in rows with a spacing of 25-40cm.

Finger rhizomes are to be planted flat with buds facing upwards and covered with soil or dry powdered cattle ma nure. The crop is to be mulched immediately after planting and 50 days after first mulching. Cattle manure or compost is to be applied as basal dose at 20-40t/ha at the time of land preparation or by spreading over the beds after planting. Application of NPK fertilizers is beneficial and found to increase the yield considerably. Weeding is to be done twice at 60 and 120 days after planting, depending upon weed intensity. Earthing up is to be done after 60 days. No major incidence of pest or disease is noticed in this crop. Leaf blotch and leaf spot can be controlled by spraying Bordeaux mixture or 0.2% Mancozeb. Shoot borers can be controlled by spraying 0.05% Dimethoate or 0.025% Quinalphos. Time of harvest usually extends from January-March. Harvesting is generally done at about 7-10 months after planting depending upon the species and variety. Harvested rhizomes are to be cleaned of mud and other materials adhering to them. Good fingers separated are to be used for curing (KAU, 1996).... curcuma

Bacteria can be stained with an iodine-based chemical dye called Gram’s stain (after the scientist who discovered the technique). Different bacteria react di?erently to exposure to the stain. Broadly, the bacterial specimens are stained ?rst with gentian violet, then with Gram’s stain, and ?nally counterstained with a red dye after a decolorising process. Bacteria that retain the gentian stain are called gram-positive; those that lose it but absorb the red stain are called gram-negative. Some species of staphylococcus, streptococcus and clostridium are gram-positive, whereas salmonella and Vibrio cholerae are gram-negative.... gram’s stain

Linn.

Family: Lythraceae.

Habitat: Native to Arabia and Persia; now cultivated mainly in Haryana and Gujarat; to a small extent in Madhya Pradesh and Rajasthan.

English: Henna.

Ayurvedic: Madayanti, Madayan- tikaa, Mendika, Ranjaka.

Unani: Hinaa, Mehndi.

Siddha/Tamil: Marudum.

Action: Leaves—astringent, antihaemorrhagic, antispasmodic, oxytocic, antifertility, antifungal, antibacterial. Used externally to treat skin infections (tinea); also as a hair conditioner.

The Ayurvedic Pharmacopoeia ofIn- dia indicated the use of the leaves in dysuria, jaundice, bleeding disorders, ulcers, prurigo and other obstinate skin diseases. The leaf is also recommended in giddiness and vertigo.

The leaves contain naphthoqui- nones, in particular lawsone; couma- rins (laxanthone, I, II and III); flavono- ids, luteolin and its 7-O-glucoside, acacetin-7-O-glucoside; beta-sitoste- rol-3-O-glucoside; all parts contain tannins.

Chloroform and ethanol extracts of leaves exhibit promising antibacterial activity against Shigella and Vibrio cholerae. Leaf extract shows antifun- gal activity against several pathogenic bacteria and fungi.

Henna paint is used as a medicament for treatment of hands and feet for mycosis. The antimycotic activity is due to lawsone, a naphthoquinone.

The ethanol-water (1 : 1) extract of the stem bark shows hepatoprotective activity CCl4-induced liver toxicity. Stembarkand root, probably due to the presence of isoplumbagin and lawsar- itol, exhibit anti-inflammatory activity experimentally.

Evidence shows Henna leaf might be able to decrease the formation of sickled cells in individuals with sickle cell anaemia. (Natural Medicines Comprehensive Database, 2007.)

Dosage: Leaves—5-10 ml juice. (API, Vol. IV.)... lawsonia inermis

Linn.

Family: Myrtaceae.

Habitat: Native to Central America; cultivated chiefly in Uttar Pradesh, Punjab, Bihar, Maharashtra, and Andhra Pradesh.

English: Guava

Ayurvedic: Peruka (non-classical), Amaruuda.

Siddha/Tamil: Koyya.

Action: Unripe fruit—antidiar- rhoeal. Leaves—used for dysentery, diabetes, cough and cold. Flowers— anthelmintic.

Guava juice may be helpful in regulating blood sugar in type 2 diabetes and syndrome X. (Sharon M. Herr.)

A residue obtained from methanolic fraction of unripe fruits was found to possess significant antidiarrhoeal activity. The fraction decreased gastric motility in an experimental animal model. The fraction was also found to inhibit significantly the growth of different strains of Shigella sp. and Vibrio cholerae.

In China and Taiwan, the leaf extract is administered for treating diarrhoea, dysentery, diabetes and inflammations. The leaf extract (containing quercetin) inhibits acetylcholine release in the gastro-intestinal tract which might account for us antidiarrhoeal activity. An extract of leaves with a little salt is given in relieve whooping cough.

In New Papua Guinea, decoction of new leaf tips is drunk to treat hepatitis.

Guava seed oil contains very higher proporation of linoleic acid (75.52%) than sunflower, groundnut, olive, soybean and coconut oil. The seeds from Pakistan yield 9.25% of a fatty oil.

Vitamin C content of the ripe fruit ranges from 100 to 1000 mg/100 g. It is highest in the skin and in the flesh next to it.

Psidium cattleyanum Sabine is equated with Straberry Guava and is known as Seemai Koyya in Tamil Nadu and Pahari Payaar in Bengal. The fruit contains vitamin C 15-44 mg/100 g.

Smaller var. of Guava is equated with Psidium guineense Sw. It is found in Tripura.... psidium guajava

Linn. (also auct. non L.)

Synonym: S. senegalensis DC. S. hirtus Willd.

Family: Compositae; Asteraceae.

Habitat: Tropical parts of India, in rice fields, cultivated lands as a weed.

Ayurvedic: Mundi, Mundika, Munditikaa, Bhuukadamba, Alam- busta, Shraavani, Tapodhanaa.

(Mahamundi, Mahaa-Shraavani Is Equated With S. Africanus Linn.)

Unani: Mundi.

Siddha/Tamil: Kottakarthai.

Folk: Gorakh-Mundi.

Action: Juice—Styptic, Emollient, Resolvent. Also Used In Hepatic And Gastric Disorders. Seeds And Root—Anthelmintic. Decoction Is Used In Cough And Other Catarrhal Affections And Chest Diseases. Root Bark—Given In Bleeding Piles. Flowers—Blood Purifier, Alterative, Depurative.

The Ayurvedic Pharmacopoeia Of India Recommends The Dried Leaf In Cervical Lymphadenitis, Chronic Sinusitis, Migraine, Epilepsy, Lipid Disorders, Diseases Of Spleen, Anaemia, Dysuria.

The Drug Is Mostly Administered In The Form Of Its Steam-Distillate. Steam Distillation Of Fresh Flowering Herb Yields An Essential Oil Containing Methyl Chavicol, Alpha-Ionone, D-Cadinene, P-Methoxycinnamaldehyde As Major Constituents. A Bitter Alkaloid, Sphaer- Anthine, Has Been Reported In The Plant.

Capitula Contains Albumin, A Fatty Oil (Up To 5%), Reducing Sugars, Tannins, Mineral Matter, A Volatile Oil (0.07%), And A Glucoside. No Alkaloid Was Detected In The Inflorescence. The Glucoside On Hydrolysis Gave A Aglycone, Phenolic In Nature. The Unsaponifiable Matter Of The Fatty Oil Showed Beta-Sitosterol, Stigmas- Terol, N-Triacontanol, N-Pentacosane And Hentriacontane. The Essential Oil Is Active Against Vibrio Cholera And Mi- Crococcus Pyogenes Var. Aureus. The Flower Heads Gave Beta-D-Glucoside Of Beta-Sitosterol.

Eudesmanolides, Cryptomeridiol And 4-Epicryptomeridiol Have Been Isolated From Flowers.

Flowers Gave A Sesquiterpene Glyco- Side, Sphaeranthanolide, Which Exhibited Immune Stimulating Activity.

Dosage: Leaf— 3-6 G (Api, Vol Iii); Whole Plant—10-20 Ml Juice (Api, Vol. IV).... sphaeranthus indicus

The study of all aspects of micro-organisms (microbes) – that is, organisms which individually are generally too small to be visible other than by microscopy. The term is applicable to viruses (see VIRUS), BACTERIA, and microscopic forms of fungi, algae, and PROTOZOA.

Among the smallest and simplest microorganisms are the viruses. First described as ?lterable agents, and ranging in size from 20–30 nm to 300 nm, they may be directly visualised only by electron microscopy. They consist of a core of deoxyribonucleic or ribonucleic acid (DNA or RNA) within a protective protein coat, or capsid, whose subunits confer a geometric symmetry. Thus viruses are usually cubical (icosahedral) or helical; the larger viruses (pox-, herpes-, myxo-viruses) may also have an outer envelope. Their minimal structure dictates that viruses are all obligate parasites, relying on living cells to provide essential components for their replication. Apart from animal and plant cells, viruses may infect and replicate in bacteria (bacteriophages) or fungi (mycophages), which are damaged in the process.

Bacteria are larger (0·01–5,000 µm) and more complex. They have a subcellular organisation which generally includes DNA and RNA, a cell membrane, organelles such as ribosomes, and a complex and chemically variable cell envelope – but, unlike EUKARYOTES, no nucleus. Rickettsiae, chlamydia, and mycoplasmas, once thought of as viruses because of their small size and absence of a cell wall (mycoplasma) or major wall component (chlamydia), are now acknowledged as bacteria; rickettsiae and chlamydia are intracellular parasites of medical importance. Bacteria may also possess additional surface structures, such as capsules and organs of locomotion (?agella) and attachment (?mbriae and stalks). Individual bacterial cells may be spheres (cocci); straight (bacilli), curved (vibrio), or ?exuous (spirilla) rods; or oval cells (coccobacilli). On examination by light microscopy, bacteria may be visible in characteristic con?gurations (as pairs of cocci [diplococci], or chains [streptococci], or clusters); actinomycete bacteria grow as ?laments with externally produced spores. Bacteria grow essentially by increasing in cell size and dividing by ?ssion, a process which in ideal laboratory conditions some bacteria may achieve about once every 20 minutes. Under natural conditions, growth is usually much slower.

Eukaryotic micro-organisms comprise fungi, algae, and protozoa. These organisms are larger, and they have in common a well-developed internal compartmentation into subcellular organelles; they also have a nucleus. Algae additionally have chloroplasts, which contain photosynthetic pigments; fungi lack chloroplasts; and protozoa lack both a cell wall and chloroplasts but may have a contractile vacuole to regulate water uptake and, in some, structures for capturing and ingesting food. Fungi grow either as discrete cells (yeasts), multiplying by budding, ?ssion, or conjugation, or as thin ?laments (hyphae) which bear spores, although some may show both morphological forms during their life-cycle. Algae and protozoa generally grow as individual cells or colonies of individuals and multiply by ?ssion.

Micro-organisms of medical importance include representatives of the ?ve major microbial groups that obtain their essential nutrients at the expense of their hosts. Many bacteria and most fungi, however, are saprophytes (see SAPROPHYTE), being major contributors to the natural cycling of carbon in the environment and to biodeterioration; others are of ecological and economic importance because of the diseases they cause in agricultural or horticultural crops or because of their bene?cial relationships with higher organisms. Additionally, they may be of industrial or biotechnological importance. Fungal diseases of humans tend to be most important in tropical environments and in immuno-compromised subjects.

Pathogenic (that is, disease-causing) microorganisms have special characteristics, or virulence factors, that enable them to colonise their hosts and overcome or evade physical, biochemical, and immunological host defences. For example, the presence of capsules, as in the bacteria that cause anthrax (Bacillus anthracis), one form of pneumonia (Streptococcus pneumoniae), scarlet fever (S. pyogenes), bacterial meningitis (Neisseria meningitidis, Haemophilus in?uenzae) is directly related to the ability to cause disease because of their antiphagocytic properties. Fimbriae are related to virulence, enabling tissue attachment – for example, in gonorrhoea (N. gonorrhoeae) and cholera (Vibrio cholerae). Many bacteria excrete extracellular virulence factors; these include enzymes and other agents that impair the host’s physiological and immunological functions. Some bacteria produce powerful toxins (excreted exotoxins or endogenous endotoxins), which may cause local tissue destruction and allow colonisation by the pathogen or whose speci?c action may explain the disease mechanism. In Staphylococcus aureus, exfoliative toxin produces the staphylococcal scalded-skin syndrome, TSS toxin-1 toxic-shock syndrome, and enterotoxin food poisoning. The pertussis exotoxin of Bordetella pertussis, the cause of whooping cough, blocks immunological defences and mediates attachment to tracheal cells, and the exotoxin produced by Corynebacterium diphtheriae causes local damage resulting in a pronounced exudate in the trachea.

Viruses cause disease by cellular destruction arising from their intracellular parasitic existence. Attachment to particular cells is often mediated by speci?c viral surface proteins; mechanisms for evading immunological defences include latency, change in viral antigenic structure, or incapacitation of the immune system – for example, destruction of CD 4 lymphocytes by the human immunode?ciency virus.... microbiology