Microbial receptors

Sineshchekov, O. A., V. D. Trivedi et al. (2005). Photochromicity of Anabaena sensory rhodopsin, an atypical microbial receptor with a cw-retinal light-adapted form. J. Biol. Chem. 280(15) 14663-14668. 

Assays for detection of antimicrobial residues in foods are based on the microbial growth inhibition, microbial receptor, and enzymatic colorimetric formats. 

More versatile than the growth-inhibition assays and potentially applicable to determining the presence of different antibiotic residues in different matrices are the microbial receptor CHARM I and II test assays (19, 20). The Charm I test, developed exclusively for -lactams in milk, constitutes the first rapid test recognized by The Association of Official Analytical Chemists (AOAC) with a test time of 15 min (19). The speed and sensitivity of this test permitted testing of milk tankers before they unloaded at the processing plant (21). In 1984-1985, the CHARM I test was further developed to test for antibiotics beyond -lactams to include tetracyclines, sulfonamides, aminoglycosides, chloramphenicol, novobiocin, and macrolides. The extended version has been referred to as CHARM II test. 

The CHARM II test for tissues is relatively fast, easy to perform, and requires limited laboratory equipment. However, for antibacterials with established tolerance levels, it can serve only as a screening test because the results are not quantitative and therefore should be supported by additional quantitative chemical methods. The microbial receptor assay, with its broad-spectrum capability, can enhance any existing monitoring system as a first-line monitoring test or as a confirmation for any program using microbial inhibition tests. 

Application of some kind of sample treatment may have the potential to improve substantially the detection of certain antibacterials in milk by microbial routine methods (59). Treatment, for example, of milk samples with ammonium oxalate solution prior to analysis can lead to lower limits of detection of tetracyclines by both microbial inhibition and microbial receptor assays. This is due to the fact that tetracycline residues tend to form chelates with divalent cations and bind to proteins, which reduce their antibacterial efficacy. However, the oxalate treatment causes splitting of complex and/or protein bonds without increasing the detection limits of other antibacterials commonly used in dairy cows. 

E Zomer, J Quintana, S Saul, SE Charm. LC-Receptorgram—a method for identification and quantitation of beta-lactams in milk by liquid chromatography with microbial receptor assay. J AOAC Int 78 1165-1172, 1995. 

Blood Group Protein Antigens as Microbial Receptors ... 

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