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Antibiotic resistance tests: Bacteria are streaked on dishes with white disks, each impregnated with a different antibiotic. Clear rings, such as those on the left, show that bacteria have not grown—indicating that these bacteria are not resistant. The bacteria on the right are fully resistant to all but two of the seven antibiotics tested. [33]
In organic chemistry, Keller's reagent is a mixture of anhydrous (glacial) acetic acid, concentrated sulfuric acid, and small amounts of ferric chloride, used to detect alkaloids. Keller's reagent can also be used to detect other kinds of alkaloids via reactions in which it produces products with a wide range of colors.
Escherichia coli bacteria on the right are sensitive to two beta-lactam antibiotics, and do not grow in the semi-circular regions surrounding antibiotics. E. coli bacteria on the left are resistant to beta-lactam antibiotics, and grow next to one antibiotic (bottom) and are less inhibited by another antibiotic (top).
Keller's reagent can refer to two different reagents: Keller's reagent (metallurgy), used to etch aluminum alloys; Keller's reagent (organic), used to detect alkaloids
Nitrocefin is a chromogenic cephalosporin substrate routinely used to detect the presence of beta-lactamase enzymes produced by various microbes. Beta-lactamase mediated resistance to beta-lactam antibiotics such as penicillin is a widespread mechanism of resistance for a number of bacteria including members of the family Enterobacteriaceae, a major group of enteric Gram-negative bacteria.
Some bacteria are naturally resistant to certain antibiotics; for example, gram-negative bacteria are resistant to most β-lactam antibiotics due to the presence of β-lactamase. Antibiotic resistance can also be acquired as a result of either genetic mutation or horizontal gene transfer . [ 155 ]
Antibiotic resistant bacteria are able to transfer copies of DNA that code for a mechanism of resistance to other bacteria even distantly related to them, which then are also able to pass on the resistance genes, resulting in generations of antibiotics resistant bacteria. [11] This initial transfer of DNA is called horizontal gene transfer. [12]
Bacterial cell wall synthesis and the role of PBPs in its synthesis is a very good target for drugs of selective toxicity because the metabolic pathways and enzymes are unique to bacteria. [10] Resistance to antibiotics has come about through overproduction of PBPs and formation of PBPs that have low affinity for penicillins (among other ...