48 REPORT OF DEPARTMENT OF BACTERIOLOGY OF THE 
THE BACTERIAL FLORA OF CHEDDAR CHEESE.* 
H. A. HARDING AND M. J. PRUCHA. 
SUMMARY. 
1.— Recent developments in bacteriological technique have per- 
mitted a more intensive study of the flora of cheddar cheese than 
was previously possible. However, it is not yet certain that all the 
forms active in the cheese will grow upon our present culture 
media. 
2.— A quantitative and qualitative study of the bacterial flora 
-has been made during the ripening period in nine normal cheddar 
cheeses. Seven of these were manufactured under commercial con- 
ditions and represented four first-class factories. 
3.— The quantitative changes go through a similar cycie in all 
cases but different cheeses vary widely both in the total number of 
germs present and in the age at which the maximum content is 
attained. There is no evident connection between the number of 
bacteria present and the rate at which the cheese ripens. When 
commercially ripe, a cheddar cheese usually contains some millions 
of living bacteria per gram. 
4.— More than 300 pure cultures were isolated and finally re- 
duced to 33 groups according to the classification of the Society 
of American Bacteriologists. Ten of these groups disappeared 
from the cheese at once; representatives of 9 other groups were 
found in but single cheeses, although each group persisted for some 
time in the cheese where found; the remaining 14 groups are the most 
important members of the cheese flora. The Bacterium lactis acidi 
of Leichman, which includes 4 of these 14 groups, is the only spe- 
cies which was always found and it practically always included over 
gg per ct. of the total germ content. 
INTRODUCTION. 
The work here reported is a part of the investigation of cheese 
ripening which is being conducted jointly by the Dairy, the Chem- 
ical and the Bacteriological Departments of this Station. The re- 


* A reprint of Technical Bulletin No. 8. 
