from indigenous fermented foods and human gut ... - Thapar University

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Chapter V Discussion
peptide was around 2.5 kDa as observed by Tricine-SDS-polyacrylamide gel electrophoresis.
The amino acid sequence of bacteriocin by Edman degradation was
TRSGNGVCNNSKCWNVGEAKENIAGIVISGKASGL. Based on available evidence, the
bacteriocin was ascribed to the Class IIa Pediocin like bacteriocins.
Moreover 20 pediocin like peptides have been characterized till date (Nes et al., 2001;
Nissen-Meyer et al., 1997). They have anti-Listeria activity and inactivate target cells by
permeabilizing the cell membrane (Moll et al., 1993; Chikindas et al., 1993). Pediocin-like
bacteriocins have similar sequences; especially in their N-terminal region. They all have a
disulfide bridge and a common YGNGV/L sequence “pediocin box” motif. Besides, they
have very similar amino acid sequences, especially in their cationic and hydrophilic N-
terminal half. The sequences of their hydrophobic/amphiphilic C-terminal half are somewhat
more diverse, and as a consequence the peptides have been grouped into three subgroups,
based on the sequence similarities and differences in the C-terminal half (Morisset et al.,
2004; Fimland et al., 2002). To understand the mechanism of inactivation, two important
food borne pathogens, S. typhimurium and S. flexneri 2a were chosen. The prevalence of both
the pathogens in the Indian subcontinent accords sufficient relevance in examining
inactivation methods using the purified bacteriocin. Analysis showed that the pathogens
treated with bacteriocin exhibited destruction of the cell membrane and extraction of cell
contents. Other studies have reported a change in cell shape from bacilli to coccoid, which
has been associated with a loss of infectivity (Rollins and Colwell, 1987). Though a shift to a
coccoid form was not observed by electron microscopy, in these sense previous reports have
indicated similar differences upon the transformation of bacillary forms to coccoid forms
through the processing or degradation of existing proteins (Takeuchi et al., 1998), it is
possible that bacteriocin changed the morphology of the pathogens from bacilli to cocci.