THE FLOCCULATION OF BACTERIA BY PROTEINS. 



By ARNOLD H. EGGERTH and MARGARET BELLOWS. 



{From the Department of Bacteriology , Eoagland Laboratory, Long Island 

 College Hospital, Brooklyn.) 



(Received for publication, April 18, 1922.) 



The effect of the addition of proteins on the stability of suspensoid 

 colloids has been the subject of numerous investigations. Ordinarily 

 the proteins act to increase the stability of the suspension, hence their 

 use as protective colloids. Under certain circumstances, however, 

 they have been found to produce flocculation instead of protection. 

 Neisser and Friedemann (1904) found that NaCl in a dilution inca- 

 pable of producing flocculation by itself can coagulate mastic sol if 

 one part of gelatin per million is present; blood serum, leech extract, 

 and bacterial extract behaved in the same manner. Walpole (1913) 

 reported that gelatin, albumin, and globulin, when added in high 

 dilutions to oil emulsions or gold or mastic sols increased their sensi- 

 tiveness to flocculation both by acids and salts. Brossa and Freund- 

 lich (1914) showed that dialyzed serum albumin, when added to 

 Fe(0H)3 sol, diminished the positive charge on the colloidal Fe 

 (011)3 and caused it to be flocculated by concentrations of salt that 

 were without effect upon the pure sol. 



In the present investigation, the effect of pure proteins on the 

 stability of bacterial suspensions at different H ion concentrations was 

 studied. Several species of bacteria were used, but the most in- 

 structive results were obtained with a strain of Bacterium colt. This 

 is because the point of optimum flocculation (the isoelectric point) 

 for this organism lies in a very acid range, which leaves a wide interval 

 between it and the isoelectric points of the different proteins studied. 

 According to Beniasch (1912), Bacterium coli is not agglutinable by 

 H ions. We have not found any recently isolated strains that would 

 agglutinate in any of the buffer mixtures used by Beniasch; but most, 

 though not all, strains of this organism will agglutinate in dilute acids 

 in the absence of salt, at reactions ranging from pH 1 .6 to 3.0. Putter 



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