An antibiotic is a drug that kills or slows the growth of bacteria. Antibiotics are one class of antimicrobials, a larger group which also includes anti-viral, anti-fungal, and anti-parasitic drugs. They are relatively harmless to the host, and therefore can be used to treatinfections. The term, coined by Selman Waksman, originally described only those formulations derived from living organisms, in contradistinction to "chemotherapeutic agents", which were purely synthetic. Nowadays the term "antibiotic" is also applied to synthetic antimicrobials, such as the sulfonamides. Antibiotics are small molecules with a molecular weight less than 2000. They are not enzymes.
Unlike previous treatments for infections, which included poisons such as strychnine and arsenic, antibiotics were labelled "magic bullets": drugs which targeted disease without harming the host. Antibiotics are not effective in viral, fungal and other nonbacterial infections, and individual antibiotics vary widely in their effectiveness on various types of bacteria. Antibiotics can be categorised based on their target specificity: 'narrow-spectrum' antibiotics target particular types of bacteria, such as gram-negative or gram-positive bacteria, whilst 'wide-spectrum' antibiotics affect a larger range of bacteria.
The effectiveness of individual antibiotics varies with the location of the infection, the ability of the antibiotic to reach the site of infection, and the ability of the bacteria to resist or inactivate the antibiotic. Some antibiotics actually kill the bacteria (bactericidal), whereas others merely prevent the bacteria from multiplying (bacteriostatic) so that the host's immune system can overcome them.
Oral antibiotics are the simplest approach when effective, with intravenous antibiotics reserved for more serious cases. Antibiotics may sometimes be administered topically, as with eyedrops or ointments.
History
See also: Timeline of antibiotics
Antibiotics can also be classified by the organisms against which they are effective, and by the type of infection in which they are useful, which depends on the sensitivities of the organisms that most commonly cause the infection and the concentration of antibiotic obtainable in the affected tissue.
Classes of Antibiotics
Production
Main article: Production of antibiotics
Since the first pioneering efforts of Florey and Chain in 1939, the importance of antibiotics to medicine has led to much research into discovering and producing them. The process of production usually involves screening of wide ranges of microorganisms, testing and modification. Production is carried out using fermentation.
Side effects
Side effects range from slight headache to a major allergic reaction. One of the more common side effects is diarrhea, which results from the antibiotic disrupting the balance of intestinal flora, the "good bacteria" that dwell inside the human digestive system. Other side effects can result from interaction between the antibiotic and other drugs, such as elevated risk of tendon damage from administration of a quinolone antibiotic with a systemic corticosteroid.
Some antibiotics can interfere with the efficacy of birth control pills. Such effects were found to be unusual, and have been studied for a limited number of antibiotics.
Antibiotic misuse
Common forms of antibiotic misuse include taking an inappropriate antibiotic, in particular the use of antibacterials for viral infections such as the common cold, and failure to take the entire prescribed course of the antibiotic, usually because the patient feels better before the infecting organism is completely eradicated. In addition to treatment failure, these practices can result in antibiotic resistance.
In the United States, a vast quantity of antibiotics is routinely included as low doses in the diet of healthy farm animals, as this practice has been proved to make animals grow faster. Opponents of this practice, however, point out the likelihood that it also leads to antibiotic resistance, frequently in bacteria that are known to also infect humans, although there has been little or no evidence as yet of such transfer of antibiotic resistance actually occurring. Theoretically, though, there is a vast possibility that such resistances could be transfered through the bacterial plasmids.
Antibiotic resistance
Main article: Antibiotic resistance
One side effect of misusing antibiotics is the development of antibiotic resistance by the infecting organisms, similar to the development of pesticide resistance in insects. Evolutionary theory of genetic selection requires that as close as possible to 100% of the infecting organisms be killed off to avoid selection of resistance; if a small subset of the population survives the treatment and is allowed to multiply, the average susceptibility of this new population to the compound will be much less than that of the original population, since they have descended from those few organisms which survived the original treatment. This survival often results from an inheritable resistance to the compound, which was infrequent in the original population but is now much more frequent in the descendants thus selected entirely from those originally infrequent resistant organisms.
Antibiotic resistance has become a serious problem in both the developed and underdeveloped nations. By 1984 half the people with active tuberculosis in the United States had a strain that resisted at least one antibiotic. In certain settings, such as hospitals and some child-care locations, the rate of antibiotic resistance is so high that the normal, 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 inexorably to the rise of resistance to those drugs, and a never-ending ever-spiraling race to discover new and different antibiotics ensues, just to keep us from losing ground in the battle against infection. The fear is that we will eventually fail to keep up in this race, and the time when people did not fear life-threatening bacterial infections will be just a memory of a golden era.
Another example of selection is Staphylococcus aureus, which could be treated successfully with penicillin in the 1940s and 1950s. At present, nearly all strains are resistant to penicillin, and many are resistant to nafcillin, leaving only a narrow selection of drugs such as vancomycin useful for treatment. The situation is worsened by the fact that genes coding for antibiotic resistance can be transferred between bacteria, making it possible for bacteria never exposed to an antibiotic to acquire resistance from those which have. The problem of antibiotic resistance is worsened when antibiotics are used to treat disorders in which they have no efficacy, such as the common cold or other viral complaints, and when they are used widely as prophylaxis rather than treatment (as in, for example, animal feeds), because this exposes more bacteria to selection for resistance.
Beyond antibiotics
Unfortunately, the comparative ease of finding compounds which safely cured bacterial infections proved much harder to duplicate with respect to fungal and viral infections. Antibiotic research led to great strides in our knowledge of basic biochemistry and to the current biological revolution; but in the process it was discovered that the susceptibility of bacteria to many compounds which are safe to humans is based upon significant differences between the cellular and molecular physiology of the bacterial cell and that of the mammalian cell. In contrast, despite the seemingly huge differences between fungi and humans, the basic biochemistries of the fungal cell and the mammalian cell are much more similar; so much so that there are few therapeutic opportunities for compounds to attack a fungal cell which will not harm a human cell. Similarly, we know now that viruses represent an incredibly minimal intracellular parasite, being stripped down to a few genes worth of DNA or RNA and the minimal molecular equipment needed to enter a cell and actually take over the machinery of the cell to produce new viruses. Thus, the great bulk of viral metabolic biochemistry is not merely similar to human biochemistry, it actually is human biochemistry, and the possible targets of antiviral compounds are restricted to the relatively very few components of the actual virus itself.
References
# The Merck Manual of Medical Information - Home Edition, Robert Berkow (Ed.), Pocket (September, 1999), ISBN 0-671-02727-1.
External links
- [http://www.genomenewsnetwork.org/categories/index/drugs/resist.php Antibiotic News from Genome News Network (GNN)]
- [http://www.eff.org/Misc/Publications/Bruce_Sterling/FSF_columns/fsf.15 Bruce Sterling's Bitter Resistance]
- [http://www.jaapa.com/issues/j20040601/articles/antibiotics0604.html JAAPA: New antibiotics useful in primary care]
- [http://www.isracast.com/tech_news/090605_tech.htm A new method for controlling bacterial activity without antibiotics] - Research conducted at the Hebrew University
Antibiotic resistance is the ability of a microorganism to withstand the effects of an antibiotic.
Antibiotic resistance naturally develops via natural selection through random mutation and plasmid exchange between bacteria of the same species. Antibiotic resistance can also be introduced artificially into a microorganism through transformation protocols. If a bacterium carries several resistance genes, it is called multiresistant or, informally, a superbug.
Causes
Antibiotic resistance is a consequence of evolution via natural selection. The antibiotic action is an environmental pressure; those bacteria which have a mutation allowing them to survive will live on to reproduce. They will then pass this trait to their offspring, which will be a fully resistant generation.
Several studies have demonstrated that patterns of antibiotic usage greatly affect the number of resistant organisms which develop. Overuse of broad-spectrum antibiotics, such as second- and third-generation cephalosporins, greatly hastens the development of methicillin resistance, even in organisms that have never been exposed to the selective pressure of methicillin per se. [Thus the resistance was already present.] Other factors contributing towards resistance include incorrect diagnosis, unnecessary prescriptions, improper use of antibiotics by patients, and the use of antibiotics as livestock food additives for growth promotion.
Resistant pathogens
Staphylococcus aureus (colloquially known as "Staph aureus") is one of the major resistant pathogens. Found on the mucous membranes and the skin of around a third of the population, it is extremely adaptable to antibiotic pressure. It was the first bacterium in which penicillin resistance was found -- in 1947, just four years after the drug started being mass-produced. Methicillin was then the antibiotic of choice. MRSA (methicillin-resistant Staphylococcus aureus) was first detected in Britain in 1961 and is now "quite common" in hospitals. MRSA was responsible for 37% of fatal cases of blood poisoning in the UK in 1999, up from 4% in 1991. Half of all S. aureus infections in the US are resistant to penicillin, methicillin, tetracycline and erythromycin.
This left vancomycin as the only effective agent available at the time. However, VRSA (Vancomycin-resistant Staphylococcus aureus) was first identified in Japan in 1997, and has since been found in hospitals in England, France and the US. VRSA is also termed GISA (glycopeptide intermediate Staphylococcus aureus) or VISA (vancomycin intermediate Staphylococcus aureus), indicating resistance to all glycopeptide antibiotics.
A new class of antibiotics, oxazolidinones, became available in the 1990s, and the first commercially available oxazolidinone, linezolid, is comparable to vancomycin in effectiveness against MRSA. Linezolid-resistance in Staphylococcus aureus was reported in 2003.
Enterococcus faecium is another superbug found in hospitals: penicillin resistance was seen in 1983, vancomycin resistance (VRE) in 1987 and linezolid resistance (LRE) in the late 1990s.
Penicillin-resistant pneumonia (or pneumococcus, caused by Streptococcus pneumoniae) was first detected in 1967, as was penicillin-resistant gonorrhea. Resistance to penicillin substitutes is also known beyond S. aureus. By 1993 Escherichia coli was resistant to five fluoroquinolone variants. Mycobacterium tuberculosis is commonly resistant to isoniazid and rifampin and sometimes universally resistant to the common treatments. Other pathogens showing some resistance include Salmonella, Campylobacter, and Streptococci.
In November, 2004, the Centers for Disease Control and Prevention (CDC) reported an increasing number of Acinetobacter baumannii bloodstream infections in patients at military medical facilities in which service members injured in the Iraq/Kuwait region during Operation Iraqi Freedom and in Afghanistan during Operation Enduring Freedom were treated. Most of these showed multidrug resistance (MRAB), with a few isolates resistant to all drugs tested. [http://www.cdc.gov/mmwr/preview/mmwrhtml/mm5345a1.htm]
Alternatives to antibiotics
Prevention
Wash hands properly to reduce the chance of getting sick and spreading infection. Wash fruits and vegetables thoroughly. Avoid raw eggs and undercooked meat, especially in ground form.
Do not demand antibiotics from your physician; if antibiotics are not prescribed, there is a reason.
When given antibiotics, take them exactly as prescribed, and complete the full course of treatment; do not hoard pills for later use, or share leftover antibiotics.
Vaccines
Vaccines do not suffer the problem of resistance because a vaccine enhances the body's natural defenses, while an antibiotic operates separately from the body's normal defenses. Nevertheless, new strains may evolve that escape immunity induced by vaccines.
While theoretically promising, anti-staphylococcal vaccines have shown limited efficacy, because of immunological variation between Staphylococcus species, and the limited duration of effectiveness of the antibodies produced. Development and testing of more effective vaccines is under way.
Phage therapy
Phage therapy is a more recent alternative that can cope with the problem of resistance.
- [http://www.cc.nih.gov/hes/vre.html Vancomycin Resistant Enterococcus - Guidelines for Healthcare Workers]
- [http://antibiotic.org Alliance for the Prudent Use of Antibiotics]
- [http://www.stoptriclosan.com StopTriclosan.com]
- [http://www.mrsaresources.nailtechsecrets.com/OveruseofAntibiotics.htm Overuse of Antibiotics]
Category:AntibioticsCategory:Microbiology
Μεσολιθική
Ως Μεσολιθική περίοδος ορίζεται εκείνη η μεταβατική περίοδος ανάμεσα στην Παλαιολιθική και τη Νεολιθική. Οι άνθρωποι της Μεσολιθικής είναι είναι οργανωμένες ομάδες κυνηγών τροφοσυλλεκτών, οι οποίες εμφανίστηκαν περίπου το 10000 π.Χ., όταν το κλίμα έγινε θερμότερο κατά την εκπνοή της τελευταίας Παγετώδους. Στη δυτική Ευρώπη οι Μεσολιθικές κυνηγετικές κοινωνίες συνυπήρξαν χρονικά με τις καλλιεργητικές Νεολιθικές κοινωνίες της Ασίας.
Η Μετάβαση
Η συγκεκριμένη αλλαγή είχε ως αποτέλεσμα την βαθμιαία εξημέρωση φυτών και ζώων και το σχηματισμό κοινοτήτων σε μόνιμες εγκαταστάσεις, σε διάφορες εποχές και τόπους. Και τούτο γιατί ενώ οι Μεσολιθικοί πολιτισμοί στην Ευρώπη διήρκεσαν σχεδόν μέχρι το 3000 π.Χ. οι Νεολιθικές κοινότητες αναπτύχθηκαν στη Μέση Ανατολή μεταξύ του 9000-6000 π.Χ. Στη μεσολιθική φάση ανάπτυξης του ανθρώπινου πολιτισμού, εντοπίζουμε το ενδιαφέρον μας στην ποικιλία των τεχνικών κυνηγίου, αλιείας και τροφοσυλλογής που αναπτύχθηκαν. Η ποικιλία πιθανολογείται ότι είναι το αποτέλεσμα της προσαρμογής των ανθρώπων στις βαθμιαίες κλιματικές αλλαγές που επέφερε η υποχώρηση των παγετώνων,η ανάπτυξη των δασών στην Ευρώπη και των ερήμων στη Β. Αφρική.
Χαρακτηριστικά
Χαρακτηριστικά αυτής της περιόδουν συνιστούν οι εκτεταμένες αλιευτικές -στη βάση τους- παραποτάμιες και παραλίμνιες εγκαταστάσεις, εκεί όπου αφθονούσαν δηλαδή τα ψάρια ως πηγή τροφής. Επίσης, οι μικρόλιθοι της Μεσολιθικής περιόδου είναι ακόμα μικρότεροι και περισσότερο επεξεργασμένοι απ' ό,τι στην ύστερη παλαιολιθική περίοδο. Σε αυτή την περίοδο αναπτύσσεται η χρήση του τόξου και η χρήση της κεραμεικής, αν και ενίοτε η παρουσία τέτοιων ευρημάτων σε μεσολιθικούς οικισμούς ερμηνεύεται ως αποτέλεσμα επαφής με νεολιθικές κοινότητες.
Πολιτισμοί
Ο Αζιλαίος πολιτισμός -ο πλέον πρώιμος αντιπρόσωπος του μεσολιθικού πολιτισμού στην Ευρώπη- με επίκεντρο την περιοχή των Πυρηναίων εξαπλώθηκε στις περιοχές της σημερινής Ελβετίας, του Βελγίου και της Σκωτίας. Διάδοχός του θεωρείται ο Ταρδενισιανός πολιτισμός, που απλώθηκε στις περισσότερες περιοχές της Ευρώπης. Στη συνέχεια αναπτύχθηκε ο Μαγκλεμοσιανός (Maglemosian) πολιτισμός στις περιοχές της Βαλτικής, που πήρε το όνομά του από περιοχή της Δανίας και έχει να επιδείξει προωθημένες τεχνικές στην κατασκευή χειροπελέκεων και οστέινα εργαλεία. Επίσης από περιοχή της Δανίας πήρε το όνομά του ο πολιτισμός Ertebolle που εκτείνεται χρονικά στο μεγαλύτερο τμήμα της ύστερης Μεσολιθικής. Ύστεροι πολιτισμοί της Μεσολιθικής, όπως ο Καμπινιανός (Campignian) και ο Αστούριος (Asturian), είναι πολύ πιθανό να είχαν επαφές με τις πρώιμες φάσεις ανάπτυξης της Νεολιθικής. Η Μεσολιθική περίοδος σε άλλες περιοχές εκπροσωπείται από τον Νατούφιο (Natufian) πολιτισμό στη Μ. Ανατολή, τον Βαντάριο (Badarian) και τον Γέρζειο (Gerzean) στην Αίγυπτο και τον Κάψιο (Capsian) στη Β. Αφρική. Ειδικότερα ο Νατούφιος πολιτισμός παρέχει τις πιο πρώιμες αποδείξεις της μετάβασης από τη Μεσολιθική στον νεολιθικό τρόπο ζωής.
Whacking off
Sexual slang is any slang term which makes reference to sex, sexuality, sexual activity, the sexual organs, or matters closely related to them. A quintessential example is the slang term fuck for sexual intercourse. Other common examples include the term blow job for Read More...
Archibald Campbell, 1st Baron Blythswood
Lt.-Col. Sir Archibald Campbell, 1st Baron Blythswood (22 February1835–8 July1908) was a Scottish politician.
Born Archibald Campbell Douglas (he dropped the Douglas from his name in 1838) in Florence, Italy, he was the son of deletion review). No further edits should be made to this page.
