Food Protection with Chemicals, and by Biocontrol 339
was observed also against L. monocytogenes when zinc and aluminum lactates or zinc and aluminum
chlorides were used with 100 IU/ml nisin, and the results showed that pretreatment with zinc lactate
sensitized the organism to nisin.
124 These findings point to the bacterial cell membrane as the target
for nisin, and this is further supported by the finding that nisin and vancomycin use the same target,
specifically, the membrane anchored cell wall precursor lipid II for which nisin has a high affinity.
21
Nisin was combined with lysozyme and EDTA in a gelatin coating to assess its effect on the spoilage
biota. The products tested were cooked ham and bologna sausage, and they were coated with 0.2 g
of 7% gelatin + 25.5 g/l lysozyme-nisin (1:3) + 25.5 g/l of EDTA. Each treatment was inoculated
(with 4–5 log 10 cfu) with six bacterial species, vacuum packaged, and stored at 8
◦ C for 4 weeks.
67 An
immediate reduction in numbers occurred in the antimicrobial gels and up to 4 log cfu/cm
2 for the four
Gram positives (Brochothrix thermosphacta, Lactobacillus sakei, Leuconostoc mesenteroides, and
Listeria monocytogenes) and further growth was inhibited during the 4 weeks. E. coli 0157:H7 was
reduced by 2 logs on ham, but the antimicrobials were ineffective against this species on bologna.
67
Using a Doehlert design, it was found that nisin and a w were synergistic and that cell numbers could
be reduced by 4–5 log cycles with 1,000 to 1,400 IU of nisin/ml at pH 5.5–6.5 and a w of 0.97 and
0.98.
31 The noted effect was not solute specific relative to a w control.
Other Bacteriocins
Two strains of Carnobacterium piscicola were added to cold-smoked salmon stored at 5
◦ C and
one was effective in reducing L. monocytogenes from 10
3 to <10 cfu/ml after 32 days.
138 This strain
was antilisterial by agar diffusion assay, and the nonbacteriocin producer prevented the pathogen
from growing on salmon. Another strain of C. piscicola was tested in cold-smoked salmon against
L. monocytogenes, and it was also found to be bactericidal to the pathogen within 21 and 12 days at
4 and 12
◦ C, respectively.
215 Cell-free extracts of the lactic were inhibitory to the pathogen by plate
assay. Two hundred food isolates and food industry cultures of L. monocytogenes were tested for their
susceptibility to the class IIa bacteriocins sakacin P 1 , sakacin A, and pediocin PA-1 along with nisin.
The 50% inhibitory concentrations (IC 50 ) were determined by plate assay with compounds at the
following ng concentrations: Pediocin PA-1 (0.10–7.34); sakacin A (0.15–44.2); and nisin (2.2–781).
None of the listerial strains were resistant to the class IIa bacteriocins,
102 and sakacin P 1 divided the
strains into two distinct groups.
ENDOLYSINS
Upon the maturation of newly formed bacteriophages inside their host bacterial cells, they effect
their own release by the consecutive use of two small hydrophobic proteins. Holins disrupt the cell
membrane and form holes through which endolysins can pass.
218 Endolysins target bonds in the
peptidoglycan, and upon the destruction of this cell barrier, the phage progeny is released. For a
review, see reference 205. In addition to their lysis of bacterial cells from within, endolysins from
Gram-positive bacteria also lyse bacteria exogenously (see reference 224). The production and use of
phage endolysins to control some foodborne bacterial pathogens have been demonstrated, and three
examples are outlined below.
An examination of the cell wall lysis system of Clostridium perfringens phage 3626 revealed that
it produces a holin and an endolysin. Holin function was demonstrated by its ability to substitute for
the deleted holin of phage lambda in a modified phage vector, and the endolysin gene (ply3626) was
was observed also against L. monocytogenes when zinc and aluminum lactates or zinc and aluminum
chlorides were used with 100 IU/ml nisin, and the results showed that pretreatment with zinc lactate
sensitized the organism to nisin.
124 These findings point to the bacterial cell membrane as the target
for nisin, and this is further supported by the finding that nisin and vancomycin use the same target,
specifically, the membrane anchored cell wall precursor lipid II for which nisin has a high affinity.
21
Nisin was combined with lysozyme and EDTA in a gelatin coating to assess its effect on the spoilage
biota. The products tested were cooked ham and bologna sausage, and they were coated with 0.2 g
of 7% gelatin + 25.5 g/l lysozyme-nisin (1:3) + 25.5 g/l of EDTA. Each treatment was inoculated
(with 4–5 log 10 cfu) with six bacterial species, vacuum packaged, and stored at 8
◦ C for 4 weeks.
67 An
immediate reduction in numbers occurred in the antimicrobial gels and up to 4 log cfu/cm
2 for the four
Gram positives (Brochothrix thermosphacta, Lactobacillus sakei, Leuconostoc mesenteroides, and
Listeria monocytogenes) and further growth was inhibited during the 4 weeks. E. coli 0157:H7 was
reduced by 2 logs on ham, but the antimicrobials were ineffective against this species on bologna.
67
Using a Doehlert design, it was found that nisin and a w were synergistic and that cell numbers could
be reduced by 4–5 log cycles with 1,000 to 1,400 IU of nisin/ml at pH 5.5–6.5 and a w of 0.97 and
0.98.
31 The noted effect was not solute specific relative to a w control.
Other Bacteriocins
Two strains of Carnobacterium piscicola were added to cold-smoked salmon stored at 5
◦ C and
one was effective in reducing L. monocytogenes from 10
3 to <10 cfu/ml after 32 days.
138 This strain
was antilisterial by agar diffusion assay, and the nonbacteriocin producer prevented the pathogen
from growing on salmon. Another strain of C. piscicola was tested in cold-smoked salmon against
L. monocytogenes, and it was also found to be bactericidal to the pathogen within 21 and 12 days at
4 and 12
◦ C, respectively.
215 Cell-free extracts of the lactic were inhibitory to the pathogen by plate
assay. Two hundred food isolates and food industry cultures of L. monocytogenes were tested for their
susceptibility to the class IIa bacteriocins sakacin P 1 , sakacin A, and pediocin PA-1 along with nisin.
The 50% inhibitory concentrations (IC 50 ) were determined by plate assay with compounds at the
following ng concentrations: Pediocin PA-1 (0.10–7.34); sakacin A (0.15–44.2); and nisin (2.2–781).
None of the listerial strains were resistant to the class IIa bacteriocins,
102 and sakacin P 1 divided the
strains into two distinct groups.
ENDOLYSINS
Upon the maturation of newly formed bacteriophages inside their host bacterial cells, they effect
their own release by the consecutive use of two small hydrophobic proteins. Holins disrupt the cell
membrane and form holes through which endolysins can pass.
218 Endolysins target bonds in the
peptidoglycan, and upon the destruction of this cell barrier, the phage progeny is released. For a
review, see reference 205. In addition to their lysis of bacterial cells from within, endolysins from
Gram-positive bacteria also lyse bacteria exogenously (see reference 224). The production and use of
phage endolysins to control some foodborne bacterial pathogens have been demonstrated, and three
examples are outlined below.
An examination of the cell wall lysis system of Clostridium perfringens phage 3626 revealed that
it produces a holin and an endolysin. Holin function was demonstrated by its ability to substitute for
the deleted holin of phage lambda in a modified phage vector, and the endolysin gene (ply3626) was