Advances in the trace analysis of muramic acid as a chemical marker for bacteria using gas chromatography tandem mass spectrometry

Detection and identification of bacterial components is important in assessing their pathogenic role within both clinical and environmental microbiology. Muramic acid can be used as a chemical marker for peptidoglycan derived from viable or non-viable bacteria and their remnants. Gas chromatography-tandem mass spectrometry (GC-MS/MS) is a state-of-the art technique for trace analysis within complex matrices. The studies described here were among the first in the field of microbiology to utilize GC-MS/MS for trace analysis.;Muramic acid had not been previously used in the detection of the total bacterial load within air. Two local agricultural environments were chosen for a prototype study to compare the concentration of airborne muramic acid to 3-hydroxy fatty acids found primarily in lipid A, a component of Gram-negative bacterial lipopolysaccharide. The levels of these chemical markers correlated, but not with the culturable bacterial population. In a more in-depth study, two elementary schools were chosen due to complaints of air quality from both staff and students. The muramic acid and 3-hydroxy fatty acid concentrations correlated well in one school but not in the other. Also, in contrast to the results from the first study, the levels of both chemical markers correlated with the levels of culturable bacteria. These results suggest non-culture based approaches and culture may provide complementary but independent measurements of airborne biopollution.;Initially, a triple quadrupole and later a more reliable tandem ion trap mass spectrometer were used in these studies. Ion traps were found to be extremely sensitive in identification mode but exhibited poor reproducibility for quantitation. Excellent reproducability was observed using the triple quadrupole. For the ion trap the mass spectrum can be dominated by a high mass ion (m/z 403). This is not the case for the triple quadrupole which required optimization primarily by decreasing fragmentation. These changes, which were essential in the use of the ion trap were later adapted to more effective use of the triple quadrupole. In conclusion, it is demonstrated that GC-MS/MS is a powerful tool for the trace analysis of muramic acid in complex samples.