Quantification of Muramic Acid,a Marker for Bacterial Peptidoglycan,in Dust Collected from Hospital and Home Air-Conditioning Filters using Gas Chromatography — Mass Spectrometry

The development of standardized non-culture-based approaches capable of assessing microbial contarnination of airborne dust is sorely needed. Direct chemical analysis has previously been successfully used for measuring components unique to Gram-negative bacteria. In the present study, dust from primary filters of hospital air-conditioning intake systems (which filter incoming outdoor and recirculated air) and dust from secondary room filters (filtering primarily indoor air) were analyzed. Dust from home air-condition-ing filters (which also filter outdoor air, with recirculation) were also analyzed. Muramic acid is an aminosugar present in Gram-positive and Gram-negative bacterial cell walls and can serve as a measure of bacterial contamination in dust. Samples were analyzed by gas chromatography-mass spectrometry after hydrolysis and conversion of released sugars (including muramic acid) to alditol acetates. Primary hospital filters contained 26.3 ± 10.0 ng of muramic acid/mg dust while secondary filters contained 5.3 ± 5.4 ng/mg. The level of inuramic acid in home air-conditioner dust was 31.7 ± 13.4 ng/mg. This study of dust collected from air-conditioners demonstrates the feasibility of chemical assessment of the microbial contamination of indoor air.