Factors Controlling the Growth of Gram-Negative Bacteria in Vacuum-Packed Bologna

Gram-negative organisms were isolated from vacuum-packed bologna only after 7-8 weeks of storage at 5 C. These isolates were identified as Acinetobacter sp., Enterobacter hafniae , Enterobacter aerogenes , Serratia marcescens and Serratia liquefaciens . Nitrite tolerance tests on these isolates at pH 5, 5.5 and 6 showed that only Acinetobacter sp. may be controlled by nitrite and pH levels associated with bologna during the initial storage period. The nitrite tolerance of these organisms was linked to their ability to deplete nitrite at 5 C in broth cultures under anaerobic conditions. Associated growth experiments were done at 15 C in APT and BHI broths under anaerobic conditions. These studies with E. aerogenes and S. liquefaciens in the presence of Lactobacillus brevis or Lactobacillus buchneri showed varying degrees of inhibition of the gram-negative isolates. The major factor which appeared to influence this inhibition in both broth cultures and bologna was glucose levels.