Inflammation is part of the complex biological response of body tissues to harmful stimuli, such as pathogens, damaged cells, or irritants, is a protective response involving immune cells, blood vessels, molecular mediators. The function of inflammation is to eliminate the initial cause of cell injury, clear out necrotic cells and tissues damaged from the original insult and the inflammatory process, initiate tissue repair; the five classical signs of inflammation are heat, redness and loss of function. Inflammation is a generic response, therefore it is considered as a mechanism of innate immunity, as compared to adaptive immunity, specific for each pathogen. Too little inflammation could lead to progressive tissue destruction by the harmful stimulus and compromise the survival of the organism. In contrast, chronic inflammation may lead to a host of diseases, such as hay fever, atherosclerosis, rheumatoid arthritis, cancer. Inflammation is therefore closely regulated by the body. Inflammation can be classified as either chronic.
Acute inflammation is the initial response of the body to harmful stimuli and is achieved by the increased movement of plasma and leukocytes from the blood into the injured tissues. A series of biochemical events propagates and matures the inflammatory response, involving the local vascular system, the immune system, various cells within the injured tissue. Prolonged inflammation, known as chronic inflammation, leads to a progressive shift in the type of cells present at the site of inflammation, such as mononuclear cells, is characterized by simultaneous destruction and healing of the tissue from the inflammatory process. Inflammation is not a synonym for infection. Infection describes the interaction between the action of microbial invasion and the reaction of the body's inflammatory response—the two components are considered together when discussing an infection, the word is used to imply a microbial invasive cause for the observed inflammatory reaction. Inflammation on the other hand describes purely the body's immunovascular response, whatever the cause may be.
But because of how the two are correlated, words ending in the suffix -itis are sometimes informally described as referring to infection. For example, the word urethritis means only "urethral inflammation", but clinical health care providers discuss urethritis as a urethral infection because urethral microbial invasion is the most common cause of urethritis, it is useful to differentiate inflammation and infection because there are typical situations in pathology and medical diagnosis where inflammation is not driven by microbial invasion – for example, trauma and autoimmune diseases including type III hypersensitivity. Conversely, there is pathology where microbial invasion does not cause the classic inflammatory response – for example, parasitosis or eosinophilia. Acute inflammation is a short-term process appearing within a few minutes or hours and begins to cease upon the removal of the injurious stimulus, it involves a coordinated and systemic mobilization response locally of various immune and neurological mediators of acute inflammation.
In a normal healthy response, it becomes activated, clears the pathogen and begins a repair process and ceases. It is characterized by five cardinal signs:An acronym that may be used to remember the key symptoms is "PRISH", for pain, immobility and heat; the traditional names for signs of inflammation come from Latin: Dolor Calor Rubor Tumor Functio laesa The first four were described by Celsus, while loss of function was added by Galen. However, the addition of this fifth sign has been ascribed to Thomas Sydenham and Virchow. Redness and heat are due to increased blood flow at body core temperature to the inflamed site. Loss of function has multiple causes. Acute inflammation of the lung does not cause pain unless the inflammation involves the parietal pleura, which does have pain-sensitive nerve endings; the process of acute inflammation is initiated by resident immune cells present in the involved tissue resident macrophages, dendritic cells, Kupffer cells and mast cells. These cells possess surface receptors known as pattern recognition receptors, which recognize two subclasses of molecules: pathogen-associated molecular patterns and damage-associated molecular patterns.
PAMPs are compounds that are associated with various pathogens, but which are distinguishable from host molecules. DAMPs are compounds that are associated with host-related cell damage. At the onset of an infection, burn, or other injuries, these cells undergo activation and release inflammatory mediators responsible for the clinical signs of inflammation. Vasodilation and its resulting increased blood flow causes increased heat. Increased permeability of the blood vessels results in an exudation of plasma proteins and fluid into the tissue, which manifests itself as swelling; some of the released mediators such as bradykinin increase the sensitivity to pain. The mediator molecules alter the blood vessels to
Chlorhexidine known as chlorhexidine gluconate, is a disinfectant and antiseptic, used for skin disinfection before surgery and to sterilize surgical instruments. It may be used both to disinfect the hands of the healthcare providers, it is used for cleaning wounds, preventing dental plaque, treating yeast infections of the mouth, to keep urinary catheters from blocking. It is used as a powder. Side effects may include skin irritation, teeth discoloration, allergic reactions, it may cause eye problems. Use in pregnancy appears to be safe. Chlorhexidine may come mixed in water, or surfactant solution, it does not inactivate spores. Chlorhexidine came into medical use in the 1950s, it is on the World Health Organization's List of Essential Medicines, the safest and most effective medicines needed in a health system. Chlorhexidine is available over the counter; the wholesale cost in the developing world is about US$2.20–4.10 per liter of 5% solution. In the United Kingdom this amount costs the NHS about £4.80.
In 2016 it was the 230th most prescribed medication in the United States with more than 2 million prescriptions. Chlorhexidine is used in disinfectants and pharmaceutical products. In endodontics, chlorhexidine is used for root canal irrigation and as an intracanal dressing, but has been replaced by the use of sodium hypochlorite bleach in much of the developed world. There is tentative evidence. CHG is active against Gram-positive and Gram-negative organisms, facultative anaerobes and yeasts, it is effective against Gram-positive bacteria. Higher concentrations are required for Gram-negative bacteria and fungi. Chlorhexidine is ineffective against adenoviruses; the effectiveness against herpes viruses has not yet been established unequivocally. Chlorhexidine, like other cation-active compounds, remains on the skin, it is combined with alcohols. Use of a CHG-based mouthwash in combination with normal tooth care can help reduce the build-up of plaque and improve mild gingivitis; such mouthwash has a number of adverse effects including damage to the mouth lining, tooth discoloration, tartar build-up, impaired taste.
Extrinsic tooth staining occurs when chlorhexidine rinse has been used for longer. Mouthwashes containing chlorhexidine which stain teeth less than the classic solution have been developed, many of which contain chelated zinc. Using chlorhexidine as a supplement to everyday mechanical oral hygiene procedures for 4 to 6 weeks and 6 months leads to a moderate reduction in gingivitis compared to placebo, control or mechanical oral hygiene alone. Chlorhexidine is a cation which interacts with anionic components of toothpaste, such as sodium lauryl sulfate and sodium monofluorophosphate, forms salts of low solubility and antibacterial activity. Hence, to enhance the antiplaque effect of chlorhexidine, "it seems best that the interval between toothbrushing and rinsing with CHX be more than 30 minutes, cautiously close to 2 hours after brushing.". Nepal was the first country in the world to use chlorhexidine to treat the umbilical cord of newborn babies, received a USAID Pioneers Prize for reducing the neonatal death rate.
Chlorhexidine is effective for poor countries like Nepal and its use is growing in the world for treating the umbilical cord. A 2015 Cochrane review has yielded high-quality evidence that within the community setting, chlorhexidine skin or cord care can reduce the incidence of omphalitis by 50% and neonatal mortality by 12%. Chlorhexidine gluconate is used as a skin cleanser for surgical scrubs, a cleanser for skin wounds, for preoperative skin preparation and germicidal hand rinses. Chlorhexidine eye drops have been used as a treatment for eyes affected by Acanthamoeba keratitis. CHG is ototoxic. CHG does not meet current European specifications for a hand disinfectant. Under the test conditions of the European Standard EN 1499, no significant difference in the efficacy was found between a 4% solution of chlorhexidine digluconate and soap. In the U. S. between 2007 and 2009, Hunter Holmes McGuire Veterans Administration Medical Center conducted a cluster-randomized trial and concluded that daily bathing of patients in intensive care units with washcloths saturated with chlorhexidine gluconate reduced the risk of hospital-acquired infections.
Whether prolonged exposure over many years may have carcinogenic potential is still not clear. The Federal Drug Administration in the USA recommendation is to limit the use of a chlorhexidine gluconate mouthwash to a maximum of six months. Once digested CHG is poorly absorbed into gastrointestinal tract. If aspirated into the lungs at high enough concentration, as reported in one case, it can be fatal due to the high risk of acute respiratory distress syndrome. At physiologic pH, chlorhexidine salts dissociate and release the positively charged chlorhexidine cation; the bactericidal effect is a result of the binding of this cationic molecule to negatively charged bacterial cell walls. At low concentrations of chlorhexidine, this results in a bacteriostatic effect, it is a cationic polybiguanide. It is used as its salts
Chlamydia trachomatis known as chlamydia, is a bacterium that can replicate only in human cells. It causes chlamydia, which can manifest in various ways, including: trachoma, lymphogranuloma venereum, nongonococcal urethritis, salpingitis, pelvic inflammatory disease. C. trachomatis is the most common infectious cause of blindness and the most common sexually transmitted bacterium. Different types of C. trachomatis cause different diseases. The most common strains cause disease in the genital tract, while other strains cause disease in the eye or lymph nodes. Like other Chlamydia species, the C. trachomatis life cycle consists of two morphologically distinct life stages: elementary bodies and reticulate bodies. Elementary bodies are infectious. Reticulate bodies are seen only within host cells. Chlamydia trachomatis is a gram-negative bacterium. Over the course of the C. trachomatis life cycle, the bacteria take on two distinct forms. Elementary bodies are 200 to 400 nanometers across, are surrounded by a rigid cell wall that allows them to survive outside of a host cell.
This form can initiate a new infection. Reticulate bodies are 600 to 1500 nanometers across, are found only within host cells. Neither form is motile; the C. trachomatis genome is smaller than that of many other bacteria at 1.04 megabases, encoding 900 genes. A number of important metabolic functions are not encoded in the C. trachomatis genome, instead are scavenged from the host cell. In addition to the chromosome that contains most of the genome, nearly all C. trachomatis strains carry a 7.5 kilobase plasmid that contains 8 genes. The role of this plasmid is unknown, though strains without the plasmid have been isolated, suggesting it is not required for survival of the bacterium. Like other Chlamydia species, C. trachomatis has a life cycle consisting of two morphologically distinct forms. First, C. trachomatis attaches to a new host cell as a small spore-like form called the elementary body. The elementary body enters. Within the inclusion, C. trachomatis transforms into a larger, more metabolically active form called the reticulate body.
The reticulate body modifies the inclusion, making it a more hospitable environment for rapid replication of the bacteria, which occurs over the following 30 to 72 hours. The massive number of intracellular bacteria transition back to resistant elementary bodies, before causing the cell to rupture and being released into the environment; these new elementary bodies are shed in the semen or released from epithelial cells of the female genital tract, attach to new host cells. C. trachomatis are bacteria in the genus Chlamydia, a group of obligate intracellular parasites of eukaryotic cells. Chlamydial cells cannot carry out energy metabolism and they lack biosynthetic pathways. C. Trachomatis strains are divided into three biovars based on the type of disease they cause; these are further subdivided into several serovars based on surface antigens recognized by the immune system. Serovars A through C cause trachoma, the worlds leading cause of preventable infectious blindness. Serovars D through K infect the genital tract, causing pelvic inflammatory disease, ectopic pregnancies, infertility.
Serovars L1 through L3 cause an invasive infection of the lymph nodes near the genitals, called lymphogranuloma venereum. C. Trachomatis is thought to have diverged from other Chlamydia species around 6 million years ago; this genus contains a total of nine species: C. trachomatis, C. muridarum, C. pneumoniae, C. pecorum, C. suis, C. abortus, C. felis, C. caviae, C. psittaci. The closest relative to C. trachomatis is C. muridarum. C. trachomatis along with C. pneumoniae have been found to infect humans to a greater extent. C. trachomatis infects human beings. C. pneumoniae is found to infect horses and frogs. Some of the other species can have a considerable impact on human health due to their known zoonotic transmission. Clinical signs and symptoms of C. trachomatis infection and gonorrhea infection are indistinguishable. Both are common causes of urethritis. C. trachomatis is the single most important infectious agent associated with blindness. Elementary bodies are present in the semen of infected men and vaginal secretions of infected women.
When they come into contact with a new host cell, the elementary bodies bind to the cell via interaction between adhesins on their surface and several host receptor proteins and heparan sulfate proteoglycans. Once attached, the bacteria inject various effector proteins into the host cell using a type three secretion system; these effectors trigger the host cell to take up the elementary bodies and prevent the cell from triggering apoptosis. Within 6 to 8 hours after infection, the elementary bodies transition to reticulate bodies and a number of new effectors are synthesized; these effectors include a number of proteins that modify the inclusion membrane, called Inc proteins, as well as proteins that redirect host vesicles to the inclusion. 8 to 16 hours after infection, another set of effectors are synthesized, driving acquisition of nutrients from the host cell. At this stage, the reticulate bodies begin to divide. If several elemenary bodies have infected a single cell, their inclusions will fuse at this point to create a single large inclusion in the host cell.
From 24 to 72 hours after infection
Metronidazole, marketed under the brand name Flagyl among others, is an antibiotic and antiprotozoal medication. It is used either alone or with other antibiotics to treat pelvic inflammatory disease and bacterial vaginosis, it is effective for dracunculiasis, giardiasis and amebiasis. It is an option for a first episode of mild-to-moderate Clostridium difficile colitis if vancomycin or fidaxomicin is unavailable. Metronidazole is available by mouth, as a cream, by injection into a vein. Common side effects include nausea, a metallic taste, loss of appetite, headaches. Seizures or allergies to the medication may occur; some state that metronidazole should not be used in early pregnancy, while others state doses for trichomoniasis are safe. It should not be used. Metronidazole began to be commercially used in 1960 in France, it is on the World Health Organization's List of Essential Medicines, the most effective and safe medicines needed in a health system. It is available in most areas of the world.
The pills are inexpensive, costing between 0.01 and 0.10 USD each. In the United States, it is about 26 USD for ten days of treatment. In 2016, it was the 71st most prescribed medication in the United States, with more than 11 million prescriptions. Metronidazole is used to treat: bacterial vaginosis, pelvic inflammatory disease, pseudomembranous colitis, aspiration pneumonia, fungating wounds, intra-abdominal infections, lung abscess, amoebiasis, oral infections, giardiasis and infections caused by susceptible anaerobic organisms such as Bacteroides, Clostridium, Peptostreptococcus, Prevotella species, it is often used to eradicate Helicobacter pylori along with other drugs and to prevent infection in people recovering from surgery. Metronidazole is bitter and so the liquid suspension contains metronidazole benzoate; this requires hydrolysis in the stomach and so may be unsuitable in people with diarrhea or feeding-tubes in the duodenum or jejunum. Drugs of choice for the treatment of bacterial vaginosis include clindamycin.
The treatment of choice for bacterial vaginosis in nonpregnant women include metronidazole oral twice daily for seven days, or metronidazole gel intravaginally once daily for five days, or clindamycin intravaginally at bedtime for seven days. For pregnant women, the treatment of choice is metronidazole oral three times a day for seven days. Data does not report routine treatment of male sexual partners; the 5-nitroimidazole drugs are the mainstay of treatment for infection with Trichomonas vaginalis. Treatment for both the infected patient and the patient's sexual partner is recommended if asymptomatic. Therapy other than 5-nitroimidazole drugs is an option, but cure rates are much lower. Oral metronidazole is a treatment option for giardiasis, the increasing incidence of nitroimidazole resistance is leading to the increased use of other compound classes. In the case of Dracunculus, metronidazole just eases worm extraction rather than killing the worm. Initial antibiotic therapy for less-severe Clostridium difficile colitis consists of metronidazole, vancomycin, or fidaxomicin by mouth.
In 2017 the IDSA recommended vancomycin and fidaxomicin over metronidazole. Vancomycin by mouth has been shown to be more effective in treating people with severe C. difficile colitis. Entamoeba histolytica invasive amebiasis is treated with metronidazole for eradication, in combination with diloxanide to prevent recurrence. Metronidazole has been used in women to prevent preterm birth associated with bacterial vaginosis, amongst other risk factors including the presence of cervicovaginal fetal fibronectin. Metronidazole was ineffective in preventing preterm delivery in high-risk pregnant women and, the incidence of preterm delivery was found to be higher in women treated with metronidazole. Common adverse drug reactions associated with systemic metronidazole therapy include: nausea, weight loss, abdominal pain, headache and metallic taste in the mouth. Intravenous administration is associated with thrombophlebitis. Infrequent adverse effects include: hypersensitivity reactions, dizziness, glossitis, dark urine, paraesthesia.
High doses and long-term systemic treatment with metronidazole are associated with the development of leucopenia, increased risk of peripheral neuropathy, central nervous system toxicity. Common adverse drug reaction associated with topical metronidazole therapy include local redness and skin irritation. Metronidazole has been associated with cancer in animal studies; some evidence from studies in rats indicates the possibility it may contribute to serotonin syndrome, although no case reports documenting this have been published to date. Metronidazole is listed by the US National Toxicology Program as reasonably anticipated to be a human carcinogen. Although some of the testing methods have been questioned, oral exposure has been shown to cause cancer in experimental animals and has demonstrated some mutagenic effects in bacterial cultures; the relationship between exposure to metronidazole and human cancer is unclear. One study found an excess in lung cancer among women, while other studies found either no increased risk, or a statistically insignificant risk.
Metronidazole is listed as a possible carcin
Granulocytes are a category of white blood cells characterized by the presence of granules in their cytoplasm. They are called polymorphonuclear leukocytes or polymorphonuclear neutrophils because of the varying shapes of the nucleus, lobed into three segments; this distinguishes them from the mononuclear agranulocytes. In common parlance, the term polymorphonuclear leukocyte refers to "neutrophil granulocytes", the most abundant of the granulocytes. Granulocytes are produced via granulopoiesis in the bone marrow. There are four types of granulocytes: Basophils Eosinophils Neutrophils Mast cellsExcept for the mast cells, their names are derived from their staining characteristics. Neutrophils are found in the bloodstream and are the most abundant type of phagocyte, constituting 60% to 65% of the total circulating white blood cells, consisting of two subpopulations: neutrophil-killers and neutrophil-cagers. One litre of human blood contains about five billion neutrophils, which are about 12–15 micrometers in diameter.
Once neutrophils have received the appropriate signals, it takes them about thirty minutes to leave the blood and reach the site of an infection. Neutrophils do not return to the blood. Mature neutrophils are smaller than monocytes, have a segmented nucleus with several sections. Neutrophils do not exit the bone marrow until maturity, but during an infection neutrophil precursors called myelocytes and promyelocytes are released. Neutrophils have three strategies for directly attacking micro-organisms: phagocytosis, release of soluble anti-microbials, generation of neutrophil extracellular traps. Neutrophils are professional phagocytes: they are ferocious eaters and engulf invaders coated with antibodies and complement, as well as damaged cells or cellular debris; the intracellular granules of the human neutrophil have long been recognized for their protein-destroying and bactericidal properties. Neutrophils can secrete products that stimulate macrophages. Neutrophils have two types of granules.
Primary granules contain cationic proteins and defensens that are used to kill bacteria, proteolytic enzymes and cathepsin G to break down proteins, lysozyme to break down bacterial cell walls, myeloperoxidase. In addition, secretions from the primary granules of neutrophils stimulate the phagocytosis of IgG antibody-coated bacteria; the secondary granules contain compounds that are involved in the formation of toxic oxygen compounds and lactoferrin. Neutrophil extracellular traps comprise a web of fibers composed of chromatin and serine proteases that trap and kill microbes extracellularly. Trapping of bacteria is a important role for NETs in sepsis, where NET are formed within blood vessels. Eosinophils have kidney-shaped lobed nuclei; the number of granules in an eosinophil can vary because they have a tendency to degranulate while in the blood stream. Eosinophils play a crucial part in the killing of parasites because their granules contain a unique, toxic basic protein and cationic protein.
These cells have a limited ability to participate in phagocytosis, they are professional antigen-presenting cells, they regulate other immune cell functions, they are involved in the destruction of tumor cells, they promote the repair of damaged tissue. A polypeptide called interleukin-5 interacts with eosinophils and causes them to grow and differentiate. Basophils are one of the least abundant cells in bone blood. Like neutrophils and eosinophils, they have lobed nuclei. Basophils have receptors that can bind to IgE, IgG, histamine; the cytoplasm of basophils contains a varied amount of granules. Granule contents of basophils are abundant with histamine, chondroitin sulfate, platelet-activating factor, other substances; when an infection occurs, mature basophils will be released from the bone marrow and travel to the site of infection. When basophils are injured, they will release histamine, which contributes to the inflammatory response that helps fight invading organisms. Histamine causes increased permeability of capillaries close to the basophil.
Injured basophils and other leukocytes will release another substance called prostaglandins that contributes to an increased blood flow to the site of infection. Both of these mechanisms allow blood-clotting elements to be delivered to the infected area. Increased permeability of the inflamed tissue allows f
Bacteria are a type of biological cell. They constitute a large domain of prokaryotic microorganisms. A few micrometres in length, bacteria have a number of shapes, ranging from spheres to rods and spirals. Bacteria were among the first life forms to appear on Earth, are present in most of its habitats. Bacteria inhabit soil, acidic hot springs, radioactive waste, the deep portions of Earth's crust. Bacteria live in symbiotic and parasitic relationships with plants and animals. Most bacteria have not been characterised, only about half of the bacterial phyla have species that can be grown in the laboratory; the study of bacteria is known as a branch of microbiology. There are 40 million bacterial cells in a gram of soil and a million bacterial cells in a millilitre of fresh water. There are 5×1030 bacteria on Earth, forming a biomass which exceeds that of all plants and animals. Bacteria are vital in many stages of the nutrient cycle by recycling nutrients such as the fixation of nitrogen from the atmosphere.
The nutrient cycle includes the decomposition of dead bodies. In the biological communities surrounding hydrothermal vents and cold seeps, extremophile bacteria provide the nutrients needed to sustain life by converting dissolved compounds, such as hydrogen sulphide and methane, to energy. Data reported by researchers in October 2012 and published in March 2013 suggested that bacteria thrive in the Mariana Trench, with a depth of up to 11 kilometres, is the deepest known part of the oceans. Other researchers reported related studies that microbes thrive inside rocks up to 580 metres below the sea floor under 2.6 kilometres of ocean off the coast of the northwestern United States. According to one of the researchers, "You can find microbes everywhere—they're adaptable to conditions, survive wherever they are."The famous notion that bacterial cells in the human body outnumber human cells by a factor of 10:1 has been debunked. There are 39 trillion bacterial cells in the human microbiota as personified by a "reference" 70 kg male 170 cm tall, whereas there are 30 trillion human cells in the body.
This means that although they do have the upper hand in actual numbers, it is only by 30%, not 900%. The largest number exist in the gut flora, a large number on the skin; the vast majority of the bacteria in the body are rendered harmless by the protective effects of the immune system, though many are beneficial in the gut flora. However several species of bacteria are pathogenic and cause infectious diseases, including cholera, anthrax and bubonic plague; the most common fatal bacterial diseases are respiratory infections, with tuberculosis alone killing about 2 million people per year in sub-Saharan Africa. In developed countries, antibiotics are used to treat bacterial infections and are used in farming, making antibiotic resistance a growing problem. In industry, bacteria are important in sewage treatment and the breakdown of oil spills, the production of cheese and yogurt through fermentation, the recovery of gold, palladium and other metals in the mining sector, as well as in biotechnology, the manufacture of antibiotics and other chemicals.
Once regarded as plants constituting the class Schizomycetes, bacteria are now classified as prokaryotes. Unlike cells of animals and other eukaryotes, bacterial cells do not contain a nucleus and harbour membrane-bound organelles. Although the term bacteria traditionally included all prokaryotes, the scientific classification changed after the discovery in the 1990s that prokaryotes consist of two different groups of organisms that evolved from an ancient common ancestor; these evolutionary domains are called Archaea. The word bacteria is the plural of the New Latin bacterium, the latinisation of the Greek βακτήριον, the diminutive of βακτηρία, meaning "staff, cane", because the first ones to be discovered were rod-shaped; the ancestors of modern bacteria were unicellular microorganisms that were the first forms of life to appear on Earth, about 4 billion years ago. For about 3 billion years, most organisms were microscopic, bacteria and archaea were the dominant forms of life. Although bacterial fossils exist, such as stromatolites, their lack of distinctive morphology prevents them from being used to examine the history of bacterial evolution, or to date the time of origin of a particular bacterial species.
However, gene sequences can be used to reconstruct the bacterial phylogeny, these studies indicate that bacteria diverged first from the archaeal/eukaryotic lineage. The most recent common ancestor of bacteria and archaea was a hyperthermophile that lived about 2.5 billion–3.2 billion years ago. Bacteria were involved in the second great evolutionary divergence, that of the archaea and eukaryotes. Here, eukaryotes resulted from the entering of ancient bacteria into endosymbiotic associations with the ancestors of eukaryotic cells, which were themselves related to the Archaea; this involved the engulfment by proto-eukaryotic cells of alphaproteobacterial symbionts to form either mitochondria or hydrogenosomes, which are still found in all known Eukarya. Some eukaryotes that contained mitochondria engulfed cyanobacteria-like organisms, leading to the formation of chloroplasts in algae and plants; this is known as primary endosymbiosis. Bacteria display a wide diversity of sizes, called morphologies.
Bacterial cells are about one-tenth the size of eukaryotic cells
Gram-positive bacteria are bacteria that give a positive result in the Gram stain test, traditionally used to classify bacteria into two broad categories according to their cell wall. Gram-positive bacteria take up the crystal violet stain used in the test, appear to be purple-coloured when seen through a microscope; this is because the thick peptidoglycan layer in the bacterial cell wall retains the stain after it is washed away from the rest of the sample, in the decolorization stage of the test. Gram-negative bacteria cannot retain the violet stain after the decolorization step, their peptidoglycan layer is much thinner and sandwiched between an inner cell membrane and a bacterial outer membrane, causing them to take up the counterstain and appear red or pink. Despite their thicker peptidoglycan layer, gram-positive bacteria are more receptive to certain cell wall targeting antibiotics than gram-negative bacteria, due to the absence of the outer membrane. In general, the following characteristics are present in gram-positive bacteria: Cytoplasmic lipid membrane Thick peptidoglycan layer Teichoic acids and lipoids are present, forming lipoteichoic acids, which serve as chelating agents, for certain types of adherence.
Peptidoglycan chains are cross-linked to form rigid cell walls by a bacterial enzyme DD-transpeptidase. A much smaller volume of periplasm than that in gram-negative bacteria. Only some species have a capsule consisting of polysaccharides. Only some species are flagellates, when they do have flagella, have only two basal body rings to support them, whereas gram-negative have four. Both gram-positive and gram-negative bacteria have a surface layer called an S-layer. In gram-positive bacteria, the S-layer is attached to the peptidoglycan layer. Gram-negative bacteria's S-layer is attached directly to the outer membrane. Specific to gram-positive bacteria is the presence of teichoic acids in the cell wall; some of these are lipoteichoic acids, which have a lipid component in the cell membrane that can assist in anchoring the peptidoglycan. Along with cell shape, Gram staining is a rapid method used to differentiate bacterial species; such staining, together with growth requirement and antibiotic susceptibility testing, other macroscopic and physiologic tests, forms the full basis for classification and subdivision of the bacteria.
The kingdom Monera was divided into four divisions based on Gram staining: Firmicutes, Gracilicutes and Mendocutes. Based on 16S ribosomal RNA phylogenetic studies of the late microbiologist Carl Woese and collaborators and colleagues at the University of Illinois, the monophyly of the gram-positive bacteria was challenged, with major implications for the therapeutic and general study of these organisms. Based on molecular studies of the 16S sequences, Woese recognised twelve bacterial phyla. Two of these were both gram-positive and were divided on the proportion of the guanine and cytosine content in their DNA; the high G + C phylum was made up of the Actinobacteria and the low G + C phylum contained the Firmicutes. The Actinobacteria include the Corynebacterium, Mycobacterium and Streptomyces genera; the Firmicutes, have a 45 -- 60 % GC content. Although bacteria are traditionally divided into two main groups, gram-positive and gram-negative, based on their Gram stain retention property, this classification system is ambiguous as it refers to three distinct aspects, which do not coalesce for some bacterial species.
The gram-positive and gram-negative staining response is not a reliable characteristic as these two kinds of bacteria do not form phylogenetic coherent groups. However, although Gram staining response is an empirical criterion, its basis lies in the marked differences in the ultrastructure and chemical composition of the bacterial cell wall, marked by the absence or presence of an outer lipid membrane. All gram-positive bacteria are bounded by a single-unit lipid membrane, and, in general, they contain a thick layer of peptidoglycan responsible for retaining the Gram stain. A number of other bacteria—that are bounded by a single membrane, but stain gram-negative due to either lack of the peptidoglycan layer, as in the Mycoplasmas, or their inability to retain the Gram stain because of their cell wall composition—also show close relationship to the Gram-positive bacteria. For the bacterial cells bounded by a single cell membrane, the term "monoderm bacteria" or "monoderm prokaryotes" has been proposed.
In contrast to gram-positive bacteria, all archetypical gram-negative bacteria are bounded by a cytoplasmic membrane and an outer cell membrane. The presence of inner and outer cell membranes defines a new compartment in these cells: the periplasmic space or the periplasmic compartment; these bacteria have been designated as "diderm bacteria." The distinction between the monoderm and diderm bacteria is supported by conserved signature indels in a number of important proteins. Of these two structurally distinct groups of bacteria, monoderms are indicated to be ancestral. Based upon a number of observations including that the gram-positive bacteria are the major producers of antibiotics and that, in general, gram-negative bacteria are resistant to them, it h