ability of streptococci to survive 
PASTEURIZATION 
By S. Henry Ayers , Bacteriologist, and Wieuam T. Johnson, Jr., Scientific 
Assistant, Dairy Division , Bureau of Animal Industry 
INTRODUCTION 
In this paper the group name “ streptococcus” is used to designate 
bacteria which are spherical in form and which divide in one axis only, 
forming chains of from two to many cells. Among the pathogenic 
streptococci may be mentioned those causing inflammations and sup¬ 
purations, of which Streptococcus pyogenes is an example. Among the 
nonpathogenic streptococci is a certain species of acid-forming bacterium 
which has been described as Streptococcus lacticus . 
It is generally assumed that cocci do not form spores and the vegeta¬ 
tive cells would not be expected to withstand Pasteurization. It has 
been shown, however, in previous publications, 1 that certain strains of 
lactic-acid bacteria, which would be classified among the streptococci, 
were able to survive Pasteurization. These strains had a high thermal 
death point; to destroy one culture in milk it was necessary to heat for 
30 minutes at 75.6° C. (168 0 F.). 
Pennington and Walter 2 also found that streptococci in cream sur¬ 
vived Pasteurization, but they attributed this to the inefficiency of the 
Pasteurizing process. 
It is evident that certain varieties of streptococci are able to survive 
Pasteurization, while other varieties are probably always destroyed. 
Davis, 8 in a study of the streptococci in milk and their relation to septic 
sore throat, found that streptococci isolated from cases of sore throat 
were readily killed by heating at 6o° C. (140 °F.) for 30 minutes. 
Hamburger 4 found that a streptococcus isolated from a patient having 
septic sore throat was killed by heating to 62.8° C. (145 0 F.) for 20 
minutes. 
These results, together with the protection which proper Pasteurization 
seems to afford against epidemics of septic sore throat from milk supplies, 
1 Ayers, S. H., and Johnson, W. T., jr. The bacteriology of commercially Pasteurized and raw market 
milk. U.S. Dept. Agr. Bur. Anim, Indus. Bui. 126, 98 p., 16 fig., 1910. 
-A study of the bacteria which survive pasteurization. U. S. Dept. Agr. Bur. Anim. 
Indus. Bui. 161, 66 p., 30 fig., 1910. 
2 Pennington, Mary E., and Walter, Georgiana. A bacteriological study of commercial ice cream. In 
N. Y. Med. Jour., v. 86, no. 22, p. 1013-1018, 1907. 
* Davis, D. J. Bacteriologic study of streptococci in milk in relation to epidemic sore throat. In Joun. 
Amer. Med. Assoc., v. 58, no. 24, p. 1832-1854, 1912. 
4 Hamburger, L. P. The Baltimore epidemic of streptococcus or septic sore throat and its relation to a 
milk supply. In Bui. Johns Hopkins Hosp., v. 24, no. 263, p. 1-11, 8 fig., pi. 1, 1913. 
(3 21 ) 
Journal of Agricultural Research, 
Dept, of Agriculture, Washington, D. C. 
Vol. II, No. 4 
July is, 1914 
A—8 
