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Overview of the use of the SOS response for genotoxicity testing. The SOS chromotest is a biological assay to assess the genotoxic potential of chemical compounds. The test is a colorimetric assay which measures the expression of genes induced by genotoxic agents in Escherichia coli, by means of a fusion with the structural gene for β-galactosidase.
The presence of an active β-galactosidase can be detected by X-gal, a colourless analog of lactose that may be cleaved by β-galactosidase to form 5-bromo-4-chloro-indoxyl, which then spontaneously dimerizes and oxidizes to form a bright blue insoluble pigment 5,5'-dibromo-4,4'-dichloro-indigo. This results in a characteristic blue colour in ...
A coliform is a gram negative, aerobic, or facultative anaerobic rod, which produces gas from lactose within 48 hours. The presence of some coliforms indicate fecal contamination. The term "IMViC" is an acronym for each of these tests. "I" is for indole test; "M" is for methyl red test; "V" is for Voges-Proskauer test, and "C" is for citrate ...
Escherichia coli (E. coli) can be distinguished from most other coliforms by its ability to ferment lactose at 44 °C in the fecal coliform test, and by its growth and color reaction on certain types of culture media. When cultured on an eosin methylene blue (EMB) plate, a positive result for E. coli is metallic green colonies on a dark purple ...
In E. coli, the lacZ gene is the structural gene for β-galactosidase; which is present as part of the inducible system lac operon which is activated in the presence of lactose when glucose level is low. β-Galactosidase synthesis stops when glucose levels are sufficient. [2] β-Galactosidase has many homologues based on similar sequences.
They are widely described among species of Enterobacteriaceae, mainly E. coli and K. pneumoniae. Detected in the 1980s they have since the early 2000s spread and are the now the predominant ESBL type in the world. They are generally clustred into five groups based on sequencing homologies; CTX-M-1, CTX-M-2, CTX-M-8, CTX-M-9 and CTX-M-25.
The TSI slant is a test tube that contains agar, a pH-sensitive dye , 1% lactose, 1% sucrose, 0.1% glucose, [2] and sodium thiosulfate and ferrous sulfate or ferrous ammonium sulfate. All of these ingredients are mixed together, heated to sterility, and allowed to solidify in the test tube at a slanted angle.
The lactose operon (lac operon) is an operon required for the transport and metabolism of lactose in E. coli and many other enteric bacteria.Although glucose is the preferred carbon source for most enteric bacteria, the lac operon allows for the effective digestion of lactose when glucose is not available through the activity of β-galactosidase. [1]