STUDIES ON AEROBIC SPORE-BEARING NON- 

 PATHOGENIC BACTERIA 



Part II 



From the Laboratory of Hygiene and Bacteriology, Johns Hopkins University 

 SPORE-BEARING BACTERIA IN DUST 



BY C. A. LAUBACH 



Spore-bearing organisms from dust were obtained by rubbing 

 moist sterile swabs over various dust-laden surfaces, transfer- 

 ring the material thus obtained to melted agar and then heating 

 to 90°C. for fifteen minutes to destroy all non-sporulating bac- 

 teria. Plates were then poured in the usual way and different 

 colonies selected for study and identification. In many in- 

 stances the cultures had to be replated a number of times before 

 the purity of the strain was established, so closely do the spores 

 adhere to each other. In general the most prolific source of 

 the spore-bearing organisms was dust which had lain undisturbed 

 for long periods of time as in closets or on high shelves. Dust 

 particles circulating in the air seemed relatively free from spore- 

 bearing bacteria but an increase of these species was always 

 noted with an increased velocity of the wind. Dust from moist 

 surfaces allowed to dry down and from surfaces exposed to di- 

 rect sunhght contained few spore-bearers. Numerous strains 

 were obtained from the dust found on books. Some 312 cul- 

 tures were studied and the types (as established in accord with 

 results of the previous work on milk and on miscellaneous cul- 

 tures) were found to be distributed as follows. 



QO 



Bacillus cereus Frankland 



Bacillus subtilis (Ehrenberg) Cohn '1 



Bacillus vulgatus (Fliigge) Trevisan 46 



(Bacillus mesentericus vulgatus Fltjgge.) 



Bacillus megatherium De Bary 



493 



