Reduced antimicrobial potencies of Oxytetracycline, tylosin, sulfadiazine, streptomycin, ciprofloxacin and olaquindox due to environmental processes

The stability of oxytetracycline (OTC), tylosin (TYL), sulfadiazin (SDZ), streptomycin (ST), ciprofloxacin (CF) and olaquindox (O) was examined in environmentally relevant matrices, such as soil interstitial water and sewage sludge water. Compounds were assessed in both aerobic (OTC, TYL, SDZ, ST, and CF) and anaerobic experiments (OTC, TYL, and O) using analytical measurements (UV spectrophotometry or HPLC) combined with a growth inhibition pour plate assay using activated sludge bacteria. (OTC was additionally assessed using a soil bacterial assay.) This combination of results enabled the assessment of whether a loss in antibacterial potency was reflected in a similar reduction of substance concentration.

If a potency reduction is not reflected in a decreased substance concentration, the results may indicate the formation of less potent degradation products possessing the same chromophoric system (same UV absorbance maximum) as the parent compound. With the exception of ST and CF, the antimicrobial agents generally lost a considerable amount of their antimicrobial potency in aerobic experiments.

In the anaerobic experiments having either an experimental duration of 21 or 100 days only OTC retained potency. These results correspond well with the fact that several degradation products were encountered in the study for this compound.