Abstract:

Enterobacter sakazakii is an opportunistic pathogen that can cause neonatal septicemia and cephalomeningitis and
necrotizing enterocolitis with mortality rate of 80%. Lactic acid bacteria with inhibitory activity against E. sakazakii were
isolated from the intestine of freshwater fish and pickles by double-layer agar diffusion method. The lactic acid bacterial
strain isolated from the intestine of common carp, named as LY-4, showed the highest inhibitory activity, which was mainly
derived from its cell-free culture supernatant (CFS). The CFS showed the strongest antagonistic activity when the strain was
cultured for 28 h. The antagonistic activity was lost entirely after treatment with pepsin, and degraded sharply to 76.44% and
54.38% by treatment with neutral protease and papain, respectively, but it was not sensitive to α-amylase, and was stable
at pH 3.0–4.5. The antagonistic activity remained basically unchanged after thermal treatment at temperatures between 40
and 80 ℃ for 2 h, but declined to 79.57% and 75.71% of its original value after incubation at 100 ℃ and 121 ℃ for 2 h,
respectively. The inhibitory substance was determined as a non-glycosylated bacteriocin, which was found to be the most
extractable with ethyl acetate. The minimum inhibitory concentration (MIC) of this bacteriocin was 6.0 mg/mL. The strain
LY-4 was identified as Lactobacillus plantarum by physiological and biochemical characteristics and 16S rDNA sequence.

Key words: lactic acid bacteria, Enterobacter sakazakii, common carp intestine, screening and identification, antagonism