Upon hydrolysis, ß-lactams form the respective open-ring form. This is recognized better by the antibody and allows for more sensitive detection.
Source: BAM, division Environmental Analysis
Contamination of waters with pharmaceutically active substances, especially antibiotics, is an alarming problem as it may support the evolution of antimicrobial resistant bacteria. Occurring in drinking water, this would pose a severe health risk for humans and animals. In order to control the water quality and assure the safety of its use as a source of drinking water, fast and cost-effective analytical methods for potential on-site analysis are needed.
Here, immunochemical methods, such as the enzyme-linked immunosorbent assay (ELISA), can be helpful but may also have certain pitfalls in store depending on the analyte. As shown here for a group of penicillins from the class of β-lactam antibiotics, hydrolysis of the β-lactam ring, i.e. the common structural feature of all penicillins, is a key factor in the immunochemical analysis as it influences recognition by the antibody. Interestingly, the hydrolyzed open-ring form is bound with higher affinity by the antibody than the parent drug which is why it can be detected more sensitively.
Hence, with the antibody used in this study, the limit of detection (LOD) in the immunoassay could be significantly reduced for the five tested penicillins by converting them into the respective open-ring form via hydrolysis. The greatest impact on the LOD was observed for penicillins G and V which form the respective open-ring form without any by-products. The aminopenicillins amoxicillin and ampicillin form one minor by-product each which is recognized less sensitively by the antibody and therefore limits the overall improvement of the LOD. The lowest LOD of all tested penicillins was found for carbenicillin with 0.2 nmol/L.
In addition to determining the starting concentration of the ß-lactam in the sample, its degree of hydrolysis can be estimated in an additional analysis step by comparing both the results with and without hydrolysis. This was shown for samples spiked with the most frequently prescribed ß-lactam antibiotic amoxicillin.
Pitfalls in the Immunochemical Determination of β-Lactam Antibiotics in Water
Alexander Ecke and Rudolf J. Schneider
published in Antibiotics, Vol. 10, Issue 3, page 298, 2021
BAM, division Environmental Analysis