Rationale: Muramic acid (bacterial peptidoglycan) is a TLR2 ligand and, similar to other TLR ligands, it could cause either protective or exacerbating effect on allergic asthma depending on the exposure dose. Muramic acid levels were measured in air and dust samples collected from a subgroup of 42 homes from the NIEHS-sponsored Cincinnati Childhood Allergy and Air Pollution Study. The relationships between muramic acid levels and various home characteristics were explored.

Methods: Air samples were collected by the Button Inhalable Aerosol Sampler for 24 hours and dust samples were collected by vacuuming of flooring. Muramic acid concentrations in the samples were measured by PITC modification, HPLC separation, and detection by absorbance at 254 nm. Temperature and relative humidity (RH) were measured with a portable hygrometer and surface moisture was measured by a protimeter. Environmental relative moldiness index (ERMI) was assessed by qPCR assays of molds in dust samples.

Results: The levels of muramic acid in air and dust samples (mean6SD) were 0.962.0 ng/m3 and 21.6631.8 ng/mg, respectively (the corresponding ranges were <LOD–12.3 ng/m3 and 0.1–153.7 ng/mg). Significant correlation (r50.41; p50.006) was observed between air and dust muramic acid levels. In the univariate analysis, number of occupants, temperature, RH, and ERMI were significantly associated with muramic acid levels. However, only ERMI was significantly associated with muramic acid levels in dust and air samples in the multivariate analysis.

Conclusions: Muramic acid in indoor air and dust correlate significantly. ERMI values were significantly associated with muramic acid levels in air and dust.