Influence of Environmental Factors on Bacteriocin Production by Human Isolates of Lactococcus lactis MM19 and Pediococcus acidilactici MM33.

The influence of temperature, initial pH, and carbon and nitrogen sources on bacteriocin secreted by Lactococcus lactis MM19 (MM19) and Pediococcus acidilactici MM33 (MM33) was evaluated. It was found that 30 and 45 °C were the growth temperatures for higher nisin and pediocin production by MM19 and MM33, respectively. The initial pH values for higher production of nisin and pediocin were 9 and 6, respectively. Glucose and wheat peptone E430 were found as suitable carbon and nitrogen sources, respectively, for highest nisin production by MM19 at 30 °C and initial pH of 9. In these conditions, nisin production could be increased by 6.7 times as compared to the control medium (de Man, Rogosa, and Sharpe--MRS broth). Similarly, fructose and pea peptone were suitable carbon and nitrogen sources, respectively, for highest production of pediocin by MM33 at 45 °C and initial pH of 6. In these conditions, pediocin production by MM33 was increased by three times as compared to the control medium (tryptone-glucose-yeast extract-TGE broth).

Partial Characterization of Bacteriocins Produced by Two New Enterococcus faecium Isolated from Human Intestine.

This study aimed at characterizing two novel bacteriocin-producing enterococcal strains isolated from human intestine. A total of 200 lactic acid bacteria were isolated from a woman stool sample. Two of them were selected for characterization due to their high antimicrobial activity against five strains of Listeria monocytogenes. The selected bacteria were identified as two different strains of Enterococcus faecium and designated MT 104 and MT 162. The bacteriocins produced by MT 104 and MT 162 were stable at different pH ranging from 2 to 11 and were active after different treatments such as heat, enzymes, detergents, and γ-irradiation. The two isolated strains exhibited some probiotic properties such as survival in simulated gastric fluid and intestinal fluid, lack of expression of bile salt hydrolase or hemolytic activity, adhesion to Caco-2 cells efficiently, and sensitivity to clinical antimicrobial agents. Thus, the two isolated strains of E. faecium could become new probiotic bacteria and their bacteriocins could be used for controlling L. monocytogenes in combination with irradiation for food preservation.