Abstract:
Weissella confusa CP3-1, is gram-positive lactic acid bacteria, isolated from a
Thai fermented sausage. Previous report showed that it produced bacteriocin-like activity
against two foodborne pathogens i.e. Bacillus cereus and Staphylococcus aureus.
This study was then aimed at optimizing the percentage of yeast extract and incubation
time that provided the highest bacteriocinogenic activity prior to separation and
purification. Maximum of growth was found when CP3-1 was cultured in TSB with 5%
yeast extract for 24h (OD600 = 0.376 ± 0.024). Whereas the results of bacteriocin activity
showed that the filtrate of 2% YE started to exhibit highest inhibition against B. cereus
at 1.04 ± 0.06 BU/ml at 24 hour. During the growth pH was not different from the initial
pH (6.7-7.0). In contrast inhibition of S. aureus displayed in every percentage of yeast
extract, highest activity showed in the filtrate of 5% YE at 4.46± 0.17 BU/ml after 24 hour.
The second best was the filtrate of 1% YE which gave activity of 3.92± 0.19 BU/ml.
However, TSB added with 2% YE cultured for 24h was selected as an appropriate
medium to produce large scale bacteriocin due to the filtrate could inhibit both B. cereus
and S. aureus. Inhibition activities of filtrate from TSB with 2% YE against B. cereus was at 1.231
± 0.314 BU/ml and against S. aureus was 0.935 ± 0.197 BU/ml. Thereafter the filtrate
was precipitated by ammonium sulfate. An increase of activity was detected in both
40% and 60% ammonium salt precipitates. For B. cereus the activity was only found in
40% (NH4) 2SO4
precipitate at 3.313 ± 0.027 BU/ml, whereas S. aureus was found in
both 40% and 60% (NH4) 2SO4
precipitates at 3.364 ± 0.026 BU/ml and 3.389 ± 0.020
BU/ml, respectively. According to protein bands appeared in SDS-PAGE they became
more purified. Resuspended precipitates were then fractionated in Anion exchange chromatography
of DEAE-cellulose column. For 40% salt precipitate high protein peaks were detected in
the fraction of 5-12, while in 60% salt precipitate such peaks were found in the fraction
of 7-17. The 10th fraction of 40% salt precipitate had highest protein amount at 5.246
± 0.046 mg/ml and showed highest inhibition against B. cereus at 5.523 ± 0.185 BU/ml.
However the activity against S. aureus was found high in the 6th fraction at 6.578
± 0.098 BU/ml where the protein amount was 3.952 ± 0.026 mg/ml.
In addition the 9th fraction of 60% salt precipitate showed highest bacterioncin
activity against B. cereus at 4.392 ± 0.008 BU/ml with the protein content of 5.276
± 0.080 mg/ml, whereas the highest inhibition against S. aureus was found in fraction 14
with 3.305 ± 0.020 BU/ml where the protein amount was 6.820 ± 0.118 mg/ml. Purify
bacteriocin was determined approximate 3 kDa. An observation of bacteriocin mechanism on the scanning electron micrographs showed pore formation on B. cereus cell wall. Whereas morphological deform in S. aureus appeared that cocci shape altered into rod shape. These results occurred at 12 hour of
incubation and clearly observed at 24 hour which agreed to the pervious results on
bacteriocin activity test.