Behavior of Enterobacter Species and Hafnia Species in Skimmilk During Fermentation by Lactic Acid Bacteria

Abstract

Enterobacter cloacae, Enterobacter aerogenes and two strains of Hafnia sp. were cultured individually in skimmilk together with Streptococcus lactis, Streptococcus cremoris or with one of two commercial lactic starter cultures. Incubation was at 21 or 32 C, and the lactic culture inoculum was 0.25, 1.0 or 2.0%. Growth of E. cloacae and E. aerogenes was markedly inhibited by S. lactis and S. cremoris at 32 C, and less so at 21 C. The commercial starter cultures were less inhibitory than the individual lactic streptococci. An increase in inoculum of lactic acid bacteria was accompanied by an increase in inhibition of Enterobacter sp., especially at 32 C. Both strains of Hafnia were inhibited more by S. lactis than by S. cremoris and the commercial starter cultures. Incubation at 32 rather than 21 C and increasing the amount of added lactic starter culture increased inhibition of Hafnia sp. All of the test coliforms were partially or completely inactivated toward the end of the 15-h incubation, provided the necessary conditions prevailed.