ASSOCIATIVE BACTERIAL ACTION IN THE PROPIONIC 

 ACID FERMENTATION.* 



By JAMES M. SHERMAN and ROSCOE H. SHAW. 



{From the Research Laboratories of the Dairy Division, United States Department 

 of Agriculture, Washington.) 



(Received for publication, January 13, 1921.) 



Among the most interesting problems in bacteriology are those 

 that have to do with the mutual relations of the organisms under 

 natural conditions. Numerous notations of effects, both beneficial 

 and detrimental, of one organism upon another are to be found in 

 bacteriological literature. The beneficial action on a specific organ- 

 ism of the associative growth of another organism is well illustrated 

 by such well known examples as the helpful effect on the tetanus 

 bacillus of associated aerobes; and the increased vigor of the lactic 

 acid fermentation when conducted in impure culture, which has been 

 studied extensively by Marshall and his associates. Antagonisms, 

 aside from those which may be readily explained upon a purely phys- 

 ical or chemical basis, have been noted in many connections. An 

 example of this nature is the recent report of Smith and Smith^ on 

 the inhibiting action of the paratyphoid organism upon the gas pro- 

 duction of Bacterium coli. 



In the present paper we wish to call attention to a beneficial asso- 

 ciative effect of greater magnitude than is frequently observed, and 

 which involves the little studied propionic acid fermentation. The 

 full details of this work will be included in a forthcoming paper on 

 the propionic acid fermentation of lactose. 



The propionic acid-producing organism used in these experiments 

 was of the type which has been tentatively designated as Bacterium 

 acidi propionici (d) and which has been shown to be the essential 

 organism for the production of "eyes" and the characteristic flavor 

 in Swiss cheese.^ The other organisms employed were Streptococcus 



* Published with the permission of the Secretary of Agriculture. 

 1 Smith, T., and Smith, D. E., /. Gen. Physiol., 1920, iii, 21. 

 ^ Sherman, J. M., /. Bad., 1921, vi, in press. 



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