Streptomycin may interfere with muramic acid assay

The muramic acid assay, an important biomarker method used in microbial ecology, is a powerful tool for the identification and detection of bacteria. Bacteria can be exclusively detected without prior culture by searching for muramic acid. For example, trace concentrations of muramic acid have been used for trace detection of bacterial presence in peculiar environment (e.g. indoor air, lunar dust and clinical samples); moreover, changes in muramic acid concentrations have been used to track changes in bacterial abundance in terrestrial and oceanic samples. In this study, we followed a commonly published procedure for extraction of muramic acid from environmental samples, and found that the presence of streptomycin in a sample can strongly interfere with or misconstrue the determination of muramic acid. Specifically, 1 molar streptomycin will be approximately 1.3 times to the assayed value of 1 molar muramic acid. Streptomycin is widely applied for both ameliorative growth of advanced organisms in situ and bacteria-inhibited incubation in laboratory, so our findings may have implications for the significance of results from muramic acid assays, i.e. it is very risky or wrong to directly use muramic acid as bacterial marker in the presence of streptomycin. This suggests that the analysis of muramic acid in practical samples is potentially more complex than the analysis in isolated bacterial cells. In summary, while muramic acid remains a valid bacterial biomarker due to its unique bacterial origin, care must be applied in interpreting results from the assay when performed in the presence of certain antibiotics.