Long-Range AirTransmission ofBacteria

Ina3-year investigation ofairborne bacteria atdifferent localities inSweden(3), samples werecollected fortnightly attwolocalities during 1969: acoastal station (Kapellskar) 60kmnortheastofStockholm, andacountry station inan agricultural district (Nartuna) 40km inland fromthecoastal station. Fortheairsamples, anAndersen sampler was used(2). Culture mediumwastryptone-glucose extract agar(CM127; OxoidLtd., London) with anaddition of0.5gofcycloheximide (Sigma Chemical Co., St.Louis, Mo.)perliter. Inthis report, theresults fromonesampling eventon18February 1969arepresented. On thatdate, unexpectedly highbacterial concentrations wererecorded atbothlocalities (Table 1). Nolocal activity explaining these highcounts wasobserved, butatboththesampling stations red-colored snowwasfalling during thesampling. On5March, snowsamples werecollected atbothlocalities. Thesnowprofile thenconsisted ofa2-cmuncolored layer atthetop,then a 6-cmcolored layer, andbelowthatanuncolored layer. Samples werecollected fromeach layer. Thesnowwasmelted at4°C,and1-ml portions werepassed through sterile membrane filters (Millipore MHWG 03700), whichwere thenincubated ontryptone-glucose extract agar at24°C(Table 2).Thebacteria collected from bothairandsnowsamples weredistinguished fromthecommonairborne flora byanumberof properties; e.g., theywererapidly growing and formedcolonies thatwerecolorless andhada slimy appearance. Furthermore, mostofthebacteria intheairsamples wereinaparticle size range'3.5,um. Onfurther investigation, these bacteria werefoundtobegram-positive, sporeforming rods(Table 1). Therewasnosignificant difference inmorphological appearance orother investigated properties ofthebacteria fromthe airsamples orthesnowsamples. Forafurther examination, 36colonies randomly selected from theairandsnowsamples weretyped. These bacteria wereallofthegenusBacillus, e.g., B. megaterium, B.pumilis, B.licheniformis, and