THE INHIBITING EFFECT OF STREPTOCOCCUS LACTIS ON LACTOBACILLUS BULGARICUS

Abstract

The fact that certain species of bacteria have an inhibiting effect on the development of other species or varieties is too well known to need discussion. This effect is frequently observed on agar plates on which the development of the colonies of one species may be restricted or completely suppressed by a pre-ponderance of colonies of another variety. Marmorek (1902) has shown that a broth in which a hemolytic streptococcus has grown is unfavorable to the growth of this same organism or to that of any other hemolytic streptococcus. McLeod and Goven-lock (1921) have demonstrated that pneumococci inhibit such bacteria as coli, dysentery, and staphylococci, as well as other pneumococci, and that this inhibiting property may be destroyed by heating the cultures to 85°C. Gundel (1927) found that coli not only inhibited the growth of anthrax but under certain con-ditions completely destroyed it. He also found that this effect could be prevented by shaking the culture with such adsorbing materials as kieselguhr, charcoal, etc. It is usually assumed that the lactic streptococci and bulgaricus, which differ in their action on milk in degree rather than in kind, grow together satisfactorily and even have a mutually favorable action. However, if a bulgaricus culture is used to increase the acidity of ordinary buttermilk the action is slow and may even fail entirely. If milk is inoculated with equal quantities of lactic' and bulgaricus cultures or only slightly predominating 1 For the sake of brevity Streptococcw lactis cultures are referred to as lactic. 321 L. A. ROGERS quantities of lactic a typical bulgaricus fermentation will ensue. If, however, the lactic inoculation greatly predominates, the bulgaricus culture will be suppressed and the fermentation will be of the streptococcus type. These facts are shown in table 1. This inhibiting property is apparently common to lactic streptococci although some of the cultures used have been more effective than others in retarding the growth of bulgaricus.