¹Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA

Correspondence: K Venkateswaran, Biotechnology and Planetary Protection Group, Jet Propulsion Laboratory, M/S 89, 4800 Oak Grove Drive, Pasadena, CA 91109, USA. E-mail: kjvenkat@jpl.nasa.gov

²Current address: Lawrence Berkeley National Laboratory, Berkeley, CA, USA

³Current address: California Institute of Technology, Pasadena, CA, USA

⁴Current address: University of Idaho, Coeur d'Alene, ID, USA

Received 23 November 2007; Revised 10 January 2008; Accepted 11 January 2008; Published online 7 February 2008.

Abstract

Total microbial burden and diversity associated with commercial airliner cabin air was assessed by molecular methods in 125 air samples from the business-class sections of 16 domestic and international flights. Viable microbial burden within these cabin air parcels constituted only 1–10% of the total microbial population and ranged from below detection limits to 1.2 10⁴ cells m^–3 as determined with a validated ATP-based technology. Cultivable bacterial diversity was almost entirely limited to Gram-positive bacteria such as Staphylococcus and Bacillus. In contrast, cloning and sequencing 16S rRNA gene directly from the samples without cultivation indicated a significantly broader diversity, as sequences representing more than 100 species, and encompassing 12 classes of bacteria, were retrieved in varying abundance. Sequences of proteobacterial and Gram-positive lineage were retrieved most frequently (58% and 31% of all clone sequences, respectively), with Gram-positive and -proteobacterial sequences dominating international flight samples and - and -proteobacterial sequences comprising the largest portion of those retrieved from domestic flights. Significant differences in bacterial load and diversity were noted between samples obtained on domestic and international flights. The disparities observed in microbial abundance and diversity further underscore the immense value of state-of-the art molecular assays in augmenting traditional culture-based techniques.