CHARM inhibition assay

The CHARM inhibition assay (CIA), Charm farm test (CFT), and Valio TlOl test are all simple multiresidue screening tests based on microbial inhibition (34, 35). The CIA test is actually a disc assay using Bacillus stearothermophilus and specially formulated agar media to increase the sensitivity to sulfonamides. The CFT is a tube assay using the same test organism in a specific formulation, which, along with the nutrients, is in a tablet form. To roughly identify penicillins and sulfonamides with the CIA and CFT tests, positive samples should be reanalyzed after the addition of penicillinase and p-aminobenzoic acid. 

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. 

Charm inhibition Direct assay B. ste rothermophilus 2.3 h at 64 C on Bromocresol Penicillineise or 34 o Q. 

The milk sample containing SDM residues was extracted with dichloromethane chloroform, and the organic layer was evaporated to just dryness. The residual fluid was dissolved with hexane, and SDM was reextracted into the phosphate buffer (171). The results of this procedure were compared to those from the FDA-recommended ELISA method, Charm inhibition, and Charm II assays. The HPLC method seemed to be more robust than the FDA methods because it allowed for easier calculation and interpretation of the results (172). Moreover, this method was found to be the most specific and had a sufficient LOD value (2 yug/kg) (171). 

A limited range of microbial inhibition assays has also been developed and is commercially available for the analysis of tissue samples (muscle, kidney, liver), egg, fish, and honey. These assays include the PremiTest, produced by DSM Food Specialities Ltd. (Delft, The Netherlands) the Explorer test, developed by Zeu Inmunotec (Zaragoza, Spain) and the kidney inhibition swab (KIS test), produced by Charm Sciences Inc. (Massachusetts, USA). 

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. 

---