Micro-organisms antibiotics

The first of the antibiotics that found practical use as a therapeutic was penicillin. The success of penicillin initiated a vast screening process all over the world, which resulted in the isolation of a large number of antibiotic substances from various natural sources. Many of these compounds were produced by micro-organisms and prove to be lethal for other micro-organisms. Many of these compounds were also very toxic to humans and could not be used therapeutically. Nevertheless a large number of classes of useful compounds were produced. The chemical structures of members of some of the most important classes are shown in Figure 6.1. 

The major dasses of antibiotics are secondary metabolic products of micro-organisms. Many were discovered by empirically screening culture filtrates or cell extracts for antimicrobial activity. A range of techniques (examples are methods using, impregnated discs, porous cylinders, cut wells, see Figure 6.2) have been used to carry out such screening. 

Figure 6.3 Summary of the strategies available for improving yields and for diversifying the products made by antibiotic-producing micro-organisms.

Addition of antibiotics to the fermentation broth may be used to avoid problems associated with growth revertants (eg auxotrophic back mutation) ensure that genetic material (eg plasmid DNA) is maintained within the process micro-organism. 

Studies on marine micro-organisms, V. A new antibiotic, aplasmomy-cin, produced by a streptomycete isolated from shallow sea mud, Y. Okami, T. Okazaki, T. Kitahara, and H. Umezawa, J. Antibiot., 29 (1976) 1019-1025. 

Several mono-carba-oligosaccharidic alpha amylase inhibitors, such as acarbose and its homologs, amylostatins, trestatins, oligostatins, adipo-sins, and so on, have been isolated from cultures of micro-organisms, and considerable interest in the biochemistry and chemistry of this class of inhibitors has been stimulated. The characteristic core-structure for inhibitory action is composed of a trihydroxy(hydroxymethyl)cyclohexene moiety and a 4-amino-4,6-dideoxy-D-glucopyranose moiety, bonded by way of an imino linkage at the allylic position. A similar structural unit has been found in the antibiotic validamycins. 

In contrast to chemical agents, micro-organisms are dynamic and can adapt to situations like antibiotic or heat treatment and risks from specific micro-organisms may change over time. 

Antibiotics are used to treat bacterial infection [41]. Some antibiotics act directly on cell membranes of micro-organisms, with consequent alteration of permeability and leakage of intracellular components. Antibiotics affect cell membranes and thus also the liquid membrane, with the possibility of change in oscillation. 

A few other official antibiotics in BP (1993) may also be assayed by adopting the method stated above, but using specific micro-organism, definite final pH of the medium, pH of the phosphate buffer, potency of solution (U per ml) and the incubation temperature. A few typical examples are given in Table 20.1 below ... 

S. No. Antibiotic Micro-organism Medium Final pH Phosphate Buffer pH Potency of Solution U per ml Incubation Temperature (°C)... 

Antibiotics are routinely added to animal feed in conventional agriculture. This can have various effects on humans. Direct transmission of antibiotic residues in animal products to people may cause direct toxicity, i.e. allergies, or lead to the emergence of resistant strains of bacteria. Another threat is antibiotic-resistant forms of bacteria harmful to mankind that might appear in animals and pass from them to humans (Smith 1974), or may impart resistance to other bacteria by plasmid or transposon interchange (Franco et al. 1990). The resulting dmg-resistant and harmful micro-organisms can then not be treated successfully (Silverstone 1993). 

When considering antimicrobial therapy in a patient with fever, one should answer the following questions. First, is the fever caused by an infection If affirmative, data are needed to determine the severity of the infection, the site of infection, and the causal micro-organism(s). Second, when the cause of the fever is infectious, one should ask is treatment with antimicrobial drugs needed Many soft tissue infections including impetigo and decubital ulcers are best treated with local antiseptics and/or wound debridement without the use of antibiotics. If the chance to cure the infection with antimicrobial... 

Antibiotic/ micro- organism P. aeruginosa K. pneumoniae Acineto-bacter spp. S. aureus Staphylococcus spp. Candida... 

In the biochemistry of D-fucose and its derivatives, there are larger lacunae in our knowledge. The biosynthesis of D-fucose has not been examined, so that it is not yet known how this sugar is produced in the organisms that contain it (mainly plants and some micro-organisms). In plants, it occurs especially in the form of steroid glycosides, whereas, in micro-organisms, it has been particularly located in antibiotic substances. It has not been identified in animals. 

Antibiotics - these are substances, for example penicillin, originally produced by micro-organisms, which are used to kill bacteria. However, most antibiotics are now made in chemical laboratories, for example carbenicillin. 

The antibiotic tryptanthrin (21), originally isolated from a micro-organism... 

The structure and stereochemistry of chuangxinmycin (11a), a new antibiotic isolated from the micro-organism Actinoplanes tsinanensis, collected from a soil sample in Shantung Province, China, have been confirmed by synthesis (Scheme l).12a Chuangxinmycin contains a novel heterocyclic ring system, and is claimed to be effective in the treatment of septicaemia and urinary and biliary infections. 

The introduction of antibiotics into clinical medicine has brought about a whole range of unforeseen problems. Apart from potential toxicity and, with some antibiotics, such as penicillins, of hypersensitivity reactions, several micro-organisms (especially many types of bacteria) show high levels of resistance. Furthermore, transferability of resistance from resistant to sensitive cells of the same or different species or genus is a well-known phenomenon with potentially serious clinical consequences [6-8],... 

Antibiotics usually have a specific site or mode of action whereby they achieve a selective toxic effect against bacteria but not human host cells. In contrast, biocides frequently have multiple target sites in the bacterial cell and by their very nature are often toxic not only to bacteria and other micro-organisms but also to host cells [7,23,24], Thus, mutation at, or absence of, a normal target site (or the presence of an additional target site) may be responsible for producing resistance to antibiotics but not to biocides. 

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