Abroad-spectrum antibiotic is anantibiotic that acts on the two major bacterial groups,Gram-positive andGram-negative,[1] or any antibiotic that acts against a wide range of disease-causingbacteria.[2] These medications are used when a bacterial infection is suspected but the group of bacteria is unknown (also calledempiric therapy) or when infection with multiple groups of bacteria is suspected. This is in contrast to anarrow-spectrum antibiotic, which is effective against only a specific group ofbacteria.[3] Although powerful, broad-spectrum antibiotics pose specific risks, particularly the disruption of native, normal bacteria and the development ofantimicrobial resistance. An example of a commonly used broad-spectrum antibiotic isampicillin.[3]
Antibiotics are often grouped by their ability to act on different bacterial groups. Although bacteria are biologically classified usingtaxonomy, disease-causing bacteria have historically been classified by their microscopic appearance and chemical function. The morphology of the organism may be classified ascocci,diplococci,bacilli (also known as "rods"), spiral-shaped or pleomorphic. Additional classification occurs through the organism's ability to take up theGram stain and counter-stain; bacteria that take up the crystal violet dye stain are referred to as "gram-positive," those that take up the counterstain only are "gram-negative," and those that remain unstained are referred to as "atypical." Further classification includes their requirement for oxygen (i.e., aerobic or anaerobic),patterns of hemolysis, or other chemical properties. The most commonly encountered groupings of bacteria include gram-positive cocci, gram-negative bacilli, atypical bacteria, and anaerobic bacteria.[4]
Empiric antibiotic therapy refers to the use of antibiotics to treat a suspected bacterial infection despite lack of a specific bacterial diagnosis. Definitive diagnosis of the species of bacteria often occurs throughculture of blood, sputum, or urine, and can be delayed by 24 to 72 hours.[5] Antibiotics are generally givenafter the culture specimen has been taken from the patient in order to preserve the bacteria in the specimen and ensure accurate diagnosis.[4] Alternatively, some species may be identified through a urine or stool test.[4]
There are an estimated 38 trillion microorganisms that colonize the human body.[6] As a side-effect of therapy, antibiotics can change the body's normalmicrobial content by attacking indiscriminately both the pathological and naturally occurring, beneficial or harmless bacteria found in the intestines, lungs and bladder.[7] The destruction of the body's normal bacterialflora is thought to disrupt immunity, nutrition, and lead to a relative overgrowth in some bacteria or fungi.[8] An overgrowth of drug-resistant microorganisms can lead to a secondary infection such asClostridioides difficile ("C. diff") orcandidiasis ("thrush").[3] This side-effect is more likely with the use of broad-spectrum antibiotics, given their greater potential to disrupt a larger variety of normal human flora.[7] The use ofdoxycycline inacne vulgaris has been associated with increased risk ofCrohn's disease,[9] although a later study indicated a link betweenacne vulgaris andIBS irrespective of the use of antibiotics.[10] Likewise, the use ofminocycline in acne vulgaris has been associated with skin and gut dysbiosis.[11]
Inveterinary medicine,co-amoxiclav, (in small animals);penicillin &streptomycin andoxytetracycline (in farm animals);penicillin andpotentiated sulfonamides (in horses).
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