A bacteriocin-producing strain PI80 was isolated from
the gut of Penaeus indicus (Indian white shrimp) and
identified as Streptococcus phocae PI80. The bacteriocin
was purified from a culture supernatant to homogeneity
as confirmed by Tricine SDS-PAGE. Reverse-phase HPLC
analysis revealed a single active fraction eluted at 12.94min,
and MALDI-TOF mass spectrometry analysis showed the
molecular mass to be 9.244 kDa. This molecular mass does
not correspond to previously described streptococcal
bacteriocins. The purified bacteriocin was named phocaecin
PI80 from its producer strain, as this is the first report of
bacteriocin production by Streptococcus phocae. The
bacteriocin exhibited a broad spectrum of activity and
inhibited important pathogens: Listeria monocytogenes,
Vibrio parahaemolyticus, and V. fischeri. The antibacterial
substance was also sensitive to proteolytic enzymes: trypsin,
protease, pepsin, and chymotrypsin, yet insensitive to
catalase, peroxidase, and diastase, confirming that the
inhibition was due to a proteinaceous molecule (i.e., the
bacteriocin), and not due to hydrogen peroxide or diacetyl.
Phocaecin PI80 moderately tolerated heat treatment (up
to 70oC for 10 min) and resisted certain solvents (acetone,
ethanol, and butanol). A massive leakage of K+ ions from
E. coli DH5α, L. monocytogenes, and V. parahaemolyticus
was induced by phocaecin PI80, as measured by Inductively
Coupled Plasma Optical Emission Spectrometry (ICPOES).
Therefore, the results of this study show that phocaecin
PI80 may be a useful tool for inhibiting L. monocytogenes
in seafood products that do not usually undergo adequate
heat treatment, whereas the cells of Streptococcus phocae
PI80 could be used to control vibriosis in shrimp farming.

Keywords: Bacteriocin,, Streptococcus phocae PI80,, Listeria monocytogenes, anti-listerial activity, potassium ion (K+), efflux