Anaerobic Culture Media Components Found to Abiotically Hydrolyse Amoxicillin Under Mesophilic Incubation Conditions

Antibiotics are widely used throughout anaerobic laboratory culturing with uses ranging from culture purification and the development of biofuels as well as a product for the development of novel therapeutics. Anaerobic culture media requires many additives to such as nutrients, oxygen scavengers, and indicators for optimal growth. Interactions between growth media and antibiotic additives are rarely considered during experimental design. This study aimed to explore the influence of common components used in anaerobic culture media on the structural stability and rate of decay of amoxicillin to disambiguate between biotic and abiotic decay. Tests were performed by incubating a mixture of 1.0mg/L, 5.0 mg/L or 10 mg/L amoxicillin with acetate buffer, phosphate buffer, carbonate buffer, glucose, NaCl, or l-cysteine at 35°C for 7 days in the absence of an anaerobic culture. The amoxicillin concentrations were measured using LC-UV. This study found that increasing nucleophilicity of the media components correlated to an increase in the rate of decay of amoxicillin. Most notably the oxygen scavenger l-cysteine decayed amoxicillin below the lower limit of detection within a single time point. This work suggests that the media composition has the potential to bias the sensitivity of microbial cultures to inhibitory additives as well as the potential collection of desired byproducts through abiotic decay.