Microbial Burden of Commercial Aircraft Cabin Air

The microbial burdens of 69 cabin air samples collected in-flight aboard commercial airliners were assessed via culture-dependent and molecular-based microbial enumeration assays. Cabin air samples from each of four separate flights aboard two different carriers were collected via air-impingement. Microbial enumeration techniques targeting DNA, ATP, and endotoxin were employed to estimate total microbial burden. The total viable microbial population ranged from 0 to 3.6 × 10⁴ cells per 100 liters of air, as assessed by the ATP-assay. When these same samples were plated on minimal medium, anywhere from 2 to 80% of the viable population was cultivable. Five of the 29 samples examined exhibited higher cultivable plate counts than ATP-derived viable counts, perhaps a consequence of the dormant nature (lower concentration of intracellular ATP) of cells inhabiting these air cabin samples. Ribosomal DNA sequence analysis showed these samples to consist of a moderately diverse group of cultivable bacteria, including human pathogens. Enumeration of ribosomal genes via quantitative-PCR indicated cellular densities of 5 × 10¹ to 10⁷ cells per 100 liters of air. Each of the aforementioned strategies for assessing microbial burden has its strengths and weaknesses; this publication serves as a testament to the power of their use in concert.