Microscopic organisms, usually one-celled. Some kinds of bacteria cause dead animals to decay.
Unicellular prokaryotic microorganisms which generally possess rigid cell walls, multiply by cell division, and exhibit three principal forms: round or coccal, rodlike or bacillary, and spiral or spirochetal.
Unicellular microorganisms, ranging from 0.5 to 5 pm in size. They may be classified on the basis of their shape: spherical (coccus), rodlike (bacilli), spiral (spirillum), comma-shaped (vibrio), corkscrew-shaped (spirochaetes), or filamentous. Other classifications are based on whether or not they are: stained by Gram’s stain; aerobic or anaerobic; and autotrophic or heterotrophic.
Single celled microscopic organisms which usu- ally produce by splitting in two (called fission). There may be several shapes, that is, rods, spherical (cocci), filamentous, etc. Many types are infectious, but others are beneficial.
Any of a large group of microscopic organisms having round, rod-like, spiral, or filamentous unicellular or noncellular bodies that are often aggregated into colonies, are enclosed by a cell wall or membrane (procaryotes), and lack fully differentiated nuclei. Bacteria may exist as free-living organisms in soil, water, and organic matter, or as parasites in the live bodies of plants and animals.
Small unicellular microorganisms. Bacteria exist in many areas in the body, but they are usually restrained by the immune system. Many bacteria cause serious, life-threatening infections.
One-celled organisms that may be either harmless, beneficial, or harmful to the body.
A large group of single-celled microorganisms, some of which cause disease in humans. Bacteria, commonly known as “germs,” are one of the six principal types of infectious organisms, with the others being viruses, protozoa, rickettsia, fungi, and parasites. Infectious bacteria can enter the body in food, drink, or air; through a wound or opening in the skin; or through a natural opening in the body. Under favorable conditions, bacteria multiply rapidly by cell division. Bacteria are simple organisms that lack a true cell nucleus. Some bacteria have long, whip-like filaments called flagella that allow them to move, while others have short filaments (pili) that do not move but help the bacteria attach to tissue surfaces, such as the lining of the intestine. Many bacteria are surrounded by a protective capsule that help prevent them from being destroyed by the special white blood cells that attack invading microorganisms.
A group of microorganisms all of which lack a distinct nuclear membrane (and hence are considered more primitive than animal and plant cells) and have a cell wall of unique composition (many antibiotics act by destroying the bacterial cell wall). Most bacteria are unicellular; the cells may be spherical (coccus), rod-like (bacillus), spiral (e.g. Spirillum), comma-shaped (Vibrio), or corkscrew-shaped (‘spirochete). Generally, they range in size between 0.5 and 5 μm. Motile species bear one or more fine hairs (flagella) arising from their surface. Many possess an outer slimy capsule, and some have the ability to produce an encysted or resting form (endospore). Bacteria reproduce asexually by simple division of cells; incomplete separation of daughter cells leads to the formation of ‘colonies of different numbers and arrangements of cells. Some colonies are filamentous in shape, resembling those of fungi. Some bacteria may reproduce sexually by conjugation.
One celled microscopic organisms of a particular class (Schizomycetes). Some bacteria (pathogenic bacteria) are able to cause disease in animals. The singular is “bacterium.”
Bacteria (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 beneficial to the environment and other living organisms, but some cause harm to their hosts and can be lethal.
Single-celled microorganisms that can be either “friendly” or cause disease. Friendly bacteria are normally present in the body and protect it from harmful invading organisms.
Tiny, single-celled organisms, some of which can cause disease.
One-celled microorganisms that have both plant and animal characteristics.
A large group of single-cell microorganisms. Some cause infections and disease in animals and humans. The singular is bacterium.
Microscopic organisms that can live inside the human body. Some bacteria are health promoting, whereas others act as pathogens (disease-causing agents).
Microscopic single-celled organisms that are responsible for numerous diseases and infections.
Bacteria are microscopic, single-celled organisms that cannot be seen with the naked eye. The singular form of the term is bacterium. They are widely present in the air, soil, and water, with the majority of bacteria being harmless to humans. In fact, some bacteria, such as those residing in the intestine, are beneficial as they aid in the breakdown of food during digestion.
Bacteria that cause diseases are referred to as pathogens and are categorized into three primary groups based on their shape: cocci (spherical), bacilli (rod-shaped), and spirochaetes or spirilla (spiral-shaped).
Cocci, belonging to the group of spherical bacteria, are responsible for causing a diverse array of diseases. These include pneumonia, tonsillitis, bacterial endocarditis (inflammation of the inner lining of the heart), meningitis (inflammation of the membranes surrounding the brain and spinal cord), toxic shock syndrome, and various skin disorders.
Bacilli, the group of rod-shaped bacteria, contribute to the development of various diseases. These include tuberculosis, pertussis (whooping cough), typhoid fever, diphtheria, tetanus, salmonellosis, shigellosis (bacillary dysentery), legionnaires’ disease, and botulism.
Spirochaetes, which belong to the smallest group of bacteria, are accountable for diseases such as syphilis, yaws, leptospirosis, and Lyme disease.
Bacteria that inhabit the human body flourish in environments that are warm and moist.
Certain bacteria are classified as aerobic, requiring oxygen to thrive and reproduce. Consequently, they are predominantly present on the skin or within the respiratory system. On the other hand, some bacteria are classified as anaerobic, thriving in environments devoid of oxygen, such as deep within tissues or wounds.
Certain bacteria exhibit limited mobility and are generally static within the body, moving only when carried by air or fluid currents. However, there are also highly motile bacteria, such as salmonella, which navigate through fluids by propelling themselves with whiplike tails known as flagella. Additionally, these bacteria can attach themselves to other cells using filamentous threads called pili.
Bacteria undergo reproduction through a process known as simple cell division, which can take place every few minutes under ideal conditions—such as the appropriate temperature and ample nourishment for all cells. Some bacteria have an alternative method of multiplication wherein each bacterium produces a spore, leading to the creation of a single new bacterium. These spores possess a robust protective membrane, enabling them to withstand high temperatures, dry environments, and nutrient deprivation.
Bacteria can enter the body through the respiratory system when inhaled in infected droplets that are spread through coughs and sneezes. Ingesting contaminated food can lead to bacterial infection in the digestive tract. Additionally, certain bacteria have the ability to cause diseases, including sexually transmitted infections, by invading the genitourinary system.
Bacteria can also infiltrate the body by penetrating the skin through multiple routes, such as hair follicles, superficial cuts and abrasions, burns, and deep, penetrating wounds.
Certain bacteria have the capability to release toxins, which are detrimental to human cells. These toxins can either destroy the cells or disrupt their normal chemical processes. In rarer cases, specific types of bacteria can directly invade and replicate within body cells, resulting in tissue damage as they propagate.
The body’s initial defense mechanisms against disease-causing bacteria involve the skin and the mucous membranes that line the respiratory, digestive, and genitourinary tracts. In addition, the eyes are safeguarded by an enzyme present in tears, while the stomach secretes hydrochloric acid, which effectively eliminates numerous bacteria present in food and water.
When bacteria manage to breach these protective barriers, the body’s immune system springs into action by dispatching different types of white blood cells to locate and eliminate the invading bacteria.
Immunity can also be induced through immunization. This process entails injecting a weakened form of the bacterium or its toxin into the body, triggering an immune response. Immunization has become a standard practice for various conditions, including diphtheria, tetanus, and certain types of meningitis.
In certain cases, the immune response alone is sufficient to facilitate recovery, and mild bacterial infections may not require any treatment. However, for more severe infections, antibiotic drugs serve as the primary form of treatment. Superficial infected wounds can be addressed by employing antiseptics.
Certain bacteria, including MRSA, are increasingly developing resistance to antibiotic treatment. In such situations, bacterial infections can pose significant challenges and may even become untreatable, posing a life-threatening risk.
Unicellular plant microorganisms. They are classified according to their characteristics: cocci are round-shaped; bacilli, rod-shaped; spirilla, spiral-shaped; and vibrios, shaped like a comma. Coca and bacilli may occur singly, grouped in pairs called diplococci; in a chainlike formation called streptococci; or in grapelike clusters called staphylococci. Bacteria are further divided into two main classes: aerobes, or aerobic bacteria, which need oxygen to survive; and anaerobes, or anaerobic bacteria, which flourish in the absence of oxygen. Some bacteria are static, while others can move, such as the vibrios, which can wriggle their tails like tadpoles. Bacteria are either parasitic and live on a live host, or saprophytic and live on a dead host. Only a very small percentage cause disease. These are called pathogenic, while the harmless ones are called nonpathogenic. Bacteria are further classified by whether they can be stained with Gram’s stain. If they retain the stain they are Gram positive, and if they do not retain the stain they are Gram negative. Some, like those causing tuberculosis, are called acid fast when even the use of acid fails to decolorize them. Those which cause fermentation are called zymogenic; those producing gas are aerogenic; and those producing pigment are chromogenie.