THE INFLUENCE OF CARBON DIOXIDE ON BACTERIA

Abstract

(1) A study of high concentrations of CO2 as a possible germicidal or bacteriostatic agent was conducted with various organisms in ice cream, milk and on plain agar medium. In highly buffered menstrua such as ice cream, milk or buffered agar medium, the bacteriostatic or bactericidal effects of CO2 were negligible. Pure culture studies with various organisms showed that the inhibition obtained in poorly buffered media, under CO2, were analogous to those with the same organisms on an agar medium adjusted to corresponding pH. When 30-100% CO2 was supplied, considerable increase in pH was observed. By buffering the agar medium deleterious effects were greatly lessened or entirely prevented, depending on degree of buffering. (2) More than 100 species representing various bacterial groups were studied as to CO2 requirements. Growth inhibition was obtained by removal of CO2 from the cultural environment. Many organisms were actually killed in 24 hrs. under CO2-free conditions. The CO2 requirement of various strains and species varies within wide limits. Growth of many organisms is greatly facilitated by small increments of added CO2 (above ordinary atmospheric CO2). Lactobacillus acidophilus, Bad. pullorum, and Bad. pneumoniae are good examples.