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Relating to bacteria.
Farlex Partner Medical Dictionary © Farlex 2012


Relating to or caused by bacteria: a bacterial enzyme.

bac·te′ri·al n.
bac·te′ri·al·ly adv.
The American Heritage® Medical Dictionary Copyright © 2007, 2004 by Houghton Mifflin Company. Published by Houghton Mifflin Company. All rights reserved.


Relating to bacteria.
Medical Dictionary for the Health Professions and Nursing © Farlex 2012


(bak-ter'e-um) (-ter'e-a) plural.bacteria [L. bacterium, fr Gr. bakterion, a small staff]
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A one-celled organism without a true nucleus or cell organelles, belonging to the kingdom Procaryotae (Monera). The cytoplasm is surrounded by a rigid cell wall composed of carbohydrates and other chemicals that provide the basis for the Gram stain. Some bacteria produce a polysaccharide or polypeptide capsule, which inhibits phagocytosis by white blood cells. Bacteria synthesize DNA, RNA, and proteins, and they can reproduce independently but may need a host to provide food and a favorable environment. Millions of nonpathogenic bacteria live on human skin and mucous membranes; these are called normal flora. Bacteria that cause disease are called pathogens. bacterial (-al), adjective See: table


Shape: There are three principal forms of bacteria. Spherical or ovoid bacteria occur as single cells (micrococci) or in pairs (diplococci), clusters (staphylococci), chains (streptococci), or cubical groups (sarcinae). Rod-shaped bacteria are called bacilli, more oval ones are called coccobacilli, and those forming a chain are called streptobacilli. Spiral bacteria are rigid (spirilla), flexible (spirochetes), or curved (vibrios). See: illustration

Size: On average, bacilli measure about 1 µm in diameter by 4 µm in length. They range in size from less than 0.5 to 1.0 µm in diameter to 10 to 20 µm in length for some of the spirilla.

Reproduction: Binary fission is the usual method of reproduction, but some bacteria exchange genetic material with members of the same species or different species. Reproductive rate is affected by changes in temperature, nutrition, and pH. If the environment becomes unfavorable, some bacilli form spores, in which their genetic material is condensed and surrounded by a thick wall. Spores are highly resistant to heat, drying, and disinfectants. When the environment again becomes favorable, the spores germinate.

Mutation: Bacteria, like all living things, undergo mutations, and the environment determines which mutations are beneficial and have survival value. Certainly beneficial to bacteria, though not at all to humans, are the mutations that provide resistance to the potentially lethal effects of antibiotics.

Motility: None of the cocci are capable of moving, but most bacilli and spiral forms can move independently. Locomotion depends on the possession of one or more flagella, slender whiplike appendages that work like propellers.

Food and oxygen requirements: Most bacteria are heterotrophic (require organic material as food). If they feed on living organisms, they are called parasites; if they feed on nonliving organic material, they are called saprophytes. Bacteria that obtain their energy from inorganic substances, including many of the soil bacteria, are called autotrophic (self-nourishing). Bacteria that require oxygen are called aerobes; those that grow only in the absence of oxygen are called anaerobes. Bacteria that grow both with and without oxygen are facultative anaerobes. Most bacteria in the human intestines are anaerobic. See: infection, opportunistic

Temperature requirements: Although some bacteria live at very low or very high temperatures, the optimum temperature for most human pathogens is 97° to 99°F (36° to 38°C).


Enzyme production: Bacteria produce enzymes that act on complex food molecules, breaking them down into simpler materials; they are the principal agents of decay and putrefaction. Putrefaction, the decomposition of nitrogenous and other organic materials in the absence of air, produces foul odors. Decay is the gradual decomposition of organic matter exposed to air by bacteria and fungi.

Toxin production: Cell wall molecules called adhesins bind bacteria to the host cells. Once attached, the bacteria may produce poisonous substances called toxins. There are two types: exotoxins, enzymes that are released by bacteria into their host, and endotoxins, which are parts of the cell walls of gram-negative bacteria and are toxic even after the death of the cell. Exotoxins include hemolysins, leukocidins, coagulases, and fibrinolysins. Endotoxins stimulate production of cytokines that can produce widespread vasodilation and shock. See: endotoxin; sepsis

Miscellaneous: Some bacteria produce pigments; some produce light. Soil bacteria are essential for the nitrogen cycle in the processes of nitrogen fixation, nitrification, and denitrification.


Several methods are used to identify bacteria in the laboratory:

Culture: Bacteria are grown on various culture media; a visible colony containing millions of cells may be visible within several hours. A colony is usually composed of the descendants of a single cell. Each species of bacteria grows in colonies with a characteristic color, shape, size, texture, type of margin or edge, and particular chemical features. Groups of cells can then be examined under a microscope, usually with Gram's stain. In addition, colonies can be separated and antibiotics applied to assess their sensitivity to different drugs.

Hanging drop: Unstained bacteria in a drop of liquid are examined under ordinary or dark-field illumination.

Gram's stain: Gram-positive bacteria retain dye, turning purple; gram-negative bacteria can be decolorized by alcohol and colored red by a second dye; acid-fast bacteria retain the dye even when treated with an acid alcohol decolorizer. Bacteria are often described by a combination of their response to Gram's stain and their appearance. For example, “gram-positive staphylococcus” indicates a cluster of spheres that stain purple, whereas gram-negative bacilli are rod-shaped and pink.

Immunofluorescence: Bacteria stained with fluorescein and examined under a microscope equipped with fluorescent light appearing yellow-green.

acetic acid bacteria

Any of a family of bacteria that oxidize alcohol and convert it to acetic acid (vinegar).

antibody-coated bacterium

1. A bacterium coated with an antibody that acts as an opsonin to make the bacterium more susceptible to phagocytosis.
2. A laboratory test using fluorescein-labeled antibodies to locate antigens with which the antibody links. See: opsonin

flesh-eating bacterium

A colloquial name given in the popular media to a rare invasive infection of the skin and underlying soft tissue by group A streptococcus. The infection is difficult to treat with antibiotics alone because it progresses rapidly through tissue planes. Emergency surgical debridement is required. See: necrotizing fasciitis

heterotrophic bacteria

Any of the bacteria that rely on organic compounds to grow and reproduce.

mucophob bacteria

Any of the bacteria that avoid, or cannot survive in, mucus.

probiotic bacterium

A bacterium that prevents illness, e.g., the Lactobacillus. species found in yogurt.
OrganismType and/or Site of Infection
Gram-Positive Bacteria
Clostridium difficilePseudomembranous colitis
Staphylococcus aureusPneumonia, cellulitis, boils, impetigo, toxic shock, postoperative bone/joints, eyes, peritonitis
Staphylococcus epidermidisPostoperative bone/joints, IV line–related phlebitis
Streptococcus pneumoniae (pneumococcus)Pneumonia, meningitis, otitis media, sinusitis, septicemia
Streptococcus pyogenesScarlet fever, pharyngitis, impetigo, rheumatic fever, erysipelas
viridans group streptococciEndocarditis
Gram-Negative Bacteria
Campylobacter jejuniDiarrhea (most common worldwide cause)
Escherichia coliUrinary tract, pyelonephritis, septicemia, gastroenteritis, peritonitis
Haemophilus influenzaePneumonia, meningitis, otitis media, epiglottitis
Klebsiella pneumoniaePneumonia, wounds
Legionella pneumophiliaPneumonia
Neisseria gonorrhoeaeGonorrhea
Neisseria meningitidis (meningococcus)Meningitis
Pseudomonas aeruginosaWounds, urinary tract, pneumonia, IV lines
Salmonella enteritidisGastroenteritis, food poisoning
Salmonella typhiTyphoid fever
Shigella dysenteriaeDysentery
Vibrio choleraeCholera
Medical Dictionary, © 2009 Farlex and Partners

Patient discussion about bacterial

Q. i have been in contact with someone whose in contact with bacterial meningitis. is this dangerous?

A. bacterial meningitis is one of the most lethal infections known. when people get infected by it they get a __ load of antibiotics and so are their families. but it all depends on what stage you had contact, and how close contact. in any way- he is probably under treatment now, no? if so, contact the doctors where he is hospitalized and ask them what is the protocol.

Q. What Causes Meningitis? I was told that meningitis is a very infectious disese. What causes meningitis?

A. Most cases of meningitis are caused by microorganisms, such as viruses, bacteria, fungi, or parasites, that spread into the blood and into the cerebrospinal fluid (CSF). Non-infectious causes include cancers, certain drugs and more. The most common cause of meningitis is viral, that is usually less severe. Bacterial meningitis is the second most frequent type and can be serious and life-threatening. Bacterial meningitis is a medical emergency.

Q. Why Is it Important to Not Use Antibiotics Often? Why is my doctor always so reluctant to prescribe me antibiotics?

A. Antibiotic resistance has become a serious problem in both developed and underdeveloped nations. By 1984 half of those with active tuberculosis in the United States had a strain that resisted at least one antibiotic. In certain settings, such as hospitals and some childcare locations, the rate of antibiotic resistance is so high that the usual, low-cost antibiotics are virtually useless for treatment of frequently seen infections. This leads to more frequent use of newer and more expensive compounds, which in turn leads to the rise of resistance to those drugs. A struggle to develop new antibiotics ensues to prevent losing future battles against infection. Therefore the doctors try to avoid using antibiotics when it is not necessary, and try to keep a certain limited use of these medications.

More discussions about bacterial
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References in periodicals archive ?
Mueller-Hinton agar (MHA) (Sigma-Aldrich) plates were swabbed with 0.1 ml of each culture suspension, and bacterially synthesized NPs (100 and 200 [micro]g/ml) were impregnated to a center well with a diameter of 8 mm.
Among these upregulated SLC genes, SLC15A3 had previously been found to inhibit chikungunya viral replication and to participate in bacterially derived MDP sensing [19, 20]; we therefore selected this gene as our candidate for further investigation.
Partial purification and substrate analysis of bacterially expressed HIV protease by means of monoclonal antibody.
The mineralogical and environmental implications of bacterially induced carbonate precipitation have been mentioned by several authors such as Folk (1993), Vasconcelos et al.
Efficacy of bacterially expressed dsRNA specific to different structural genes ofwhite spot syndrome virus (WSSV) in protection of shrimp from WSSV infection.
Habit of bacterially induced precipitates of calcium carbonate: examples from laboratory experiments and recent sediments.
The 173 amino acid polypeptide encoded 2 tryptic peptides isolated from a two-dimensional polyacrylamide electrophoretic gel of plasma from bacterially induced H.
The supplemented mice had more tumor polyps than did mice with normal diets, suggesting that the path from Western diets to colon cancer relies on this bacterially produced chemical.
Adsorption of Pb (II), Cu(II), Cd(II), Zn(II), Ni(II), Fe(II), and As(V) on bacterially produced metal sulfides, Journal of Colloid and Interface Science, 275: 61-71.
Sulfur oxidizing bacteria (Acidithio bacillus) oxidize S which results in P release from RP due to bacterially produced sulfuric acid during S oxidation phenomenon (Chi et al.
If bacterially infected colon cells can no longer repair damage to their DNA, mutations will accumulate, which will promote cancer growth.

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