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Principle
- CESBL agar base is used for the identification of Extended-spectrum β-lactamase producing microorganisms. The CESBL-producing organisms are resistant to wide-spectrum antibiotics and cause serious health-related complications.
- The media is composed of peptone, chromogenic mixture, sodium chloride, phosphate buffering agent, and agar. Special peptone provides nitrogenous and long-chain amino acids. The chromogenic mixture contains chromogens and nutrients, the nutrients provide nitrogenous and carbonaceous compounds, vitamins, and essential nutrients.
- While the chromogenic substance used in this media are X-Glucoside, Red-β-D-galactopyranoside and isopropylthio-β-galactoside. X-Glucoside is a substrate for β-Glucosidase that, upon enzymatic action, gives an insoluble indigo-blue chromophore. Red-β-D-galactopyranoside is used for detection of beta-galactosidase.
- IPTG (isopropylthio-β-galactoside) is an inducer of β-galactosidase activity in bacteria and is suitable for use with X-gal or Red-gal to detect lac gene activity in E. coli or genetically modified microorganisms. Sodium chloride maintains osmatic balance and phosphates provide buffering capacity to the medium.
- The selectivity is provided by antibiotics like cephalosporins, cephamycins, monobactams, and carbapenems. The organisms resistant to wide-spectrum antibiotics produce β-lactamase enzyme.
- The β-lactamases are enzymes; provide multi-resistance to β-lactam antibiotics such as penicillins, cephalosporins, cephamycins, monobactams, and carbapenems (ertapenem), although carbapenems are relatively resistant to beta-lactamase.
- The Escherichia coli, produce ß-lactamase enzyme provided resistant to antibiotics and ß-galactosidase enzyme activity, cleave red-β-D-galactopyranoside and forms pink color colonies. Klebsiella cleaves X-glucoside, by producing ß-glucosidase enzyme, and results in the formation of blue colonies.
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