An antibiotic is a type of antimicrobial substance active against bacteria. It is the most important type of antibacterial agent for fighting bacterial infections, and antibiotic medications are widely used in the treatment and prevention of such infections. They may either kill or inhibit the growth of bacteria. A limited number of antibiotics also possess antiprotozoal activity. Antibiotics are not effective against viruses such as the common cold or influenza; drugs which inhibit growth of viruses are termed antiviral drugs or antivirals rather than antibiotics. They are also not effective against fungi; drugs which inhibit growth of fungi are called antifungal drugs.
Antimicrobial resistance (AMR) occurs when microbes evolve mechanisms that protect them from the effects of antimicrobials. All classes of microbes can evolve resistance where the drugs are no longer effective. Fungi evolve antifungal resistance. Viruses evolve antiviral resistance. Protozoa evolve antiprotozoal resistance, and bacteria evolve antibiotic resistance. Together all of these come under the umbrella of antimicrobial resistance. Microbes resistant to multiple antimicrobials are called multidrug resistant (MDR) and are sometimes referred to as a superbugs. Although antimicrobial resistance is a naturally occurring process, it is often the result of improper usage of the drugs and management of the infections.
Bacterial growth is proliferation of bacterium into two daughter cells, in a process called binary fission. Providing no event occurs, the resulting daughter cells are genetically identical to the original cell. Hence, bacterial growth occurs. Both daughter cells from the division do not necessarily survive. However, if the surviving number exceeds unity on average, the bacterial population undergoes exponential growth. The measurement of an exponential bacterial growth curve in batch culture was traditionally a part of the training of all microbiologists; the basic means requires bacterial enumeration by direct and individual, direct and bulk (biomass), indirect and individual, or indirect and bulk methods. Models reconcile theory with the measurements.
A biofilm comprises any syntrophic consortium of microorganisms in which cells stick to each other and often also to a surface. These adherent cells become embedded within a slimy extracellular matrix that is composed of extracellular polymeric substances (EPSs). The cells within the biofilm produce the EPS components, which are typically a polymeric conglomeration of extracellular polysaccharides, proteins, lipids and DNA. Because they have three-dimensional structure and represent a community lifestyle for microorganisms, they have been metaphorically described as "cities for microbes".
The Luria–Delbrück experiment (1943) demonstrated that in bacteria, genetic mutations arise in the absence of selective pressure rather than being a response to it. Thus, it concluded Darwin's theory of natural selection acting on random mutations applies to bacteria as well as to more complex organisms. Max Delbrück and Salvador Luria won the 1969 Nobel Prize in Physiology or Medicine in part for this work.
Staphylococcus haemolyticus is a member of the coagulase-negative staphylococci (CoNS). It is part of the skin flora of humans, and its largest populations are usually found at the axillae, perineum, and inguinal areas. S. haemolyticus also colonizes primates and domestic animals. It is a well-known opportunistic pathogen, and is the second-most frequently isolated CoNS. Infections can be localized or systemic, and are often associated with the insertion of medical devices. The highly antibiotic-resistant phenotype and ability to form biofilms make S. haemolyticus a difficult pathogen to treat. Its most closely-related species is Staphylococcus borealis.
Antibiotic sensitivity testing or antibiotic susceptibility testing is the measurement of the susceptibility of bacteria to antibiotics. It is used because bacteria may have resistance to some antibiotics. Sensitivity testing results can allow a clinician to change the choice of antibiotics from empiric therapy, which is when an antibiotic is selected based on clinical suspicion about the site of an infection and common causative bacteria, to directed therapy, in which the choice of antibiotic is based on knowledge of the organism and its sensitivities.
Stenotrophomonas maltophilia is an aerobic, nonfermentative, Gram-negative bacterium. It is an uncommon bacterium and human infection is difficult to treat. Initially classified as Bacterium bookeri, then renamed Pseudomonas maltophilia, S. maltophilia was also grouped in the genus Xanthomonas before eventually becoming the type species of the genus Stenotrophomonas in 1993.
A chemostat is a bioreactor to which fresh medium is continuously added, while culture liquid containing left over nutrients, metabolic end products and microorganisms is continuously removed at the same rate to keep the culture volume constant. By changing the rate with which medium is added to the bioreactor the specific growth rate of the microorganism can be easily controlled within limits.
In microbiology, the minimum inhibitory concentration (MIC) is the lowest concentration of a chemical, usually a drug, which prevents visible in vitro growth of bacteria or fungi. MIC testing is performed in both diagnostic and drug discovery laboratories.
Medical microbiology, the large subset of microbiology that is applied to medicine, is a branch of medical science concerned with the prevention, diagnosis and treatment of infectious diseases. In addition, this field of science studies various clinical applications of microbes for the improvement of health. There are four kinds of microorganisms that cause infectious disease: bacteria, fungi, parasites and viruses, and one type of infectious protein called prion.
Cross-resistance is when something develops resistance to several substances that have a similar mechanism of action. For example, if a certain type of bacteria develops resistance to one antibiotic, that bacteria will also have resistance to several other antibiotics that target the same protein or use the same route to get into the bacterium. A real example of cross-resistance occurred for nalidixic acid and ciprofloxacin, which are both quinolone antibiotics. When bacteria developed resistance to ciprofloxacin, they also developed resistance to nalidixic acid because both drugs inhibit topoisomerase, a key enzyme in DNA replication. Due to cross-resistance, antimicrobial treatments like phage therapy can quickly lose their efficacy against bacteria. This makes cross-resistance an important consideration in designing evolutionary therapies.
Etest is a way of determining antimicrobial sensitivity by placing a strip impregnated with antimicrobials onto an agar plate. A strain of bacterium or fungus will not grow near a concentration of antibiotic or antifungal if it is sensitive. For some microbial and antimicrobial combinations, the results can be used to determine a minimum inhibitory concentration (MIC). Etest is a proprietary system manufactured by bioMérieux. It is a laboratory test used in healthcare settings to help guide physicians by indicating what concentration of antimicrobial could successfully be used to treat patients' infections.
In macroeconomics, the balanced-growth path of a dynamic model is a trajectory such that all variables grow at a constant rate. In the standard exogenous growth model, balanced growth is a basic assumption, while other variables like the capital stock, real GDP, and output per worker are growing. Developing economies may adopt a strategy of unbalanced growth to rectify previous investment decisions, as put forward by economist Albert O. Hirschman.
A microbial consortium or microbial community, is two or more bacterial or microbial groups living symbiotically. Consortiums can be endosymbiotic or ectosymbiotic, or occasionally may be both. The protist Mixotricha paradoxa, itself an endosymbiont of the Mastotermes darwiniensis termite, is always found as a consortium of at least one endosymbiotic coccus, multiple ectosymbiotic species of flagellate or ciliate bacteria, and at least one species of helical Treponema bacteria that forms the basis of Mixotricha protists' locomotion.
An antimicrobial surface is coated by an antimicrobial agent that inhibits the ability of microorganisms to grow on the surface of a material. Such surfaces are becoming more widely investigated for possible use in various settings including clinics, industry, and even the home. The most common and most important use of antimicrobial coatings has been in the healthcare setting for sterilization of medical devices to prevent hospital associated infections, which have accounted for almost 100,000 deaths in the United States. In addition to medical devices, linens and clothing can provide a suitable environment for many bacteria, fungi, and viruses to grow when in contact with the human body which allows for the transmission of infectious disease.
Cell counting is any of various methods for the counting or similar quantification of cells in the life sciences, including medical diagnosis and treatment. It is an important subset of cytometry, with applications in research and clinical practice. For example, the complete blood count can help a physician to determine why a patient feels unwell and what to do to help. Cell counts within liquid media are usually expressed as a number of cells per unit of volume, thus expressing a concentration.
Virtual colony count (VCC) is a kinetic, 96-well microbiological assay originally developed to measure the activity of defensins. It has since been applied to other antimicrobial peptides including LL-37. It utilizes a method of enumerating bacteria called quantitative growth kinetics, which compares the time taken for a bacterial batch culture to reach a threshold optical density with that of a series of calibration curves. The name VCC has also been used to describe the application of quantitative growth kinetics to enumerate bacteria in cell culture infection models. Antimicrobial susceptibility testing (AST) can be done on 96-well plates by diluting the antimicrobial agent at varying concentrations in broth inoculated with bacteria and measuring the minimum inhibitory concentration that results in no growth. However, these methods cannot be used to study some membrane-active antimicrobial peptides, which are inhibited by the broth itself. The virtual colony count procedure takes advantage of this fact by first exposing bacterial cells to the active antimicrobial agent in a low-salt buffer for two hours, then simultaneously inhibiting antimicrobial activity and inducing exponential growth by adding broth. The growth kinetics of surviving cells can then be monitored using a temperature-controlled plate reader. The time taken for each growth curve to reach a threshold change in optical density is then converted into virtual survival values, which serve as a measure of antimicrobial activity.
Changestat is a continuous cultivation method that is used for acquiring quantitative data of a microorganism's metabolism at various environmental conditions within a single experiment. Every changestat always starts as a continuous cultivation experiment, but after reaching steady state, smooth and slow change of an environmental parameter is applied. Two most common changestat techniques are accelerostat (A-stat) and dilution rate stat (D-stat).
In vitro models for calcification may refer to systems that have been developed in order to reproduce, in the best possible way, the calcification process that tissues or biomaterials undergo inside the body. The aim of these systems is to mimic the high levels of calcium and phosphate present in the blood and measure the extent of the crystal's deposition. Different variations can include other parameters to increase the veracity of these models, such as flow, pressure, compliance and resistance. All the systems have different limitations that have to be acknowledged regarding the operating conditions and the degree of representation. The rational of using such is to partially replace in vivo animal testing, whilst rendering much more controllable and independent parameters compared to an animal model.
