Food Protection with Chemicals, and by Biocontrol 335
Lactic antagonism
The phenomenon of a lactic acid bacterium inhibiting or killing closely related and food-poisoning and
food spoilage organisms when in mixed culture has been observed for more than 80 years. Commonly
referred to as lactic antagonism, the precise mechanisms are yet unclear. Among factors identified
are the production of antibiotics, H 2 O 2 , diacetyl, and bacteriocins in addition to pH depression and
nutrient depletion. Lactic antagonism, thus, is an example of microbial interference.
In one study, a pediocin-producing strain of Lactococcus lactis was genetically enhanced to produce enough pediocin to control growth of L. monocytogenes in ripening Cheddar cheese. In control
cheese, the pathogen increased to about 10
7 /g after 2 weeks and then decreased to about 10
3 after
6 months but in the experimental cheese, the pathogen decreased to 10
2 /g within 1 week and then
to only 10/g within 3 months.
24 Propionibacterium freudenreichii subsp. shermanii produces an illdefined, multicomponent inhibitory system when cultured in pasteurized skim milk that is effective
against Gram-negative bacteria and molds in cottage cheese. One such product is Microgard. Reuterin
(3-hydroxypropionalaldehyde) is produced by Lactobacillus reuteri from glycerol. At a concentration
of 100 AU/g, a 5-log reduction of E. coli 0157:H7 was achieved in raw ground pork after 1 day at
7
◦ C.
53 When used alone, Reuterin at 4 AU/ml inhibited the growth of E. coli and 8 AU/ml inhibited
L. monocytogenes. This inhibitor was even more effective in combination with lactic acid.
53
Lactobacillus reuteri and allyl isothiocyanate (AITC, at ca. 1,300 ppm) alone and in combination
were tested for their effectiveness against a five-strain mixture of E. coli 0157:H7 in ground beef at 4
◦ C
for 25 days. The E. coli inoculum levels were 3- and 6-log 10 cfu/g, and 250 mM glycerol/kg of meat
was added. E. coli was killed in meat with the two levels of glycerol before day 20 by L. reuteri.
133
AITC completely eliminated the 3-log 10 inoculum of E. coli 0157:H7 and at the higher concentration,
it effected a >4.5-log 10 cfu/g reduction after 25 days.
To study the protective effect of a lactic organism, Lactobacillus casei and its culture permeate were
tested on ready-to-use salad vegetables at 8
◦ C.
199 After 6 days of storage, 3% culture permeate reduced
APC from 6 to 1 log 10 cfu/g, and suppressed coliforms, enterococci, and Aeromonas hydrophila.
Coliforms were reduced by about 2 logs and fecal coliforms by about 1 log by the use of 1% lactic
acid.
199 The inhibitory principal produced by a Staphylococcus equorum strain has been identified
as a macrocyclic peptide antibiotic, micrococcin P 1 , and the bacterium was effective in inhibiting
L. monocytogenes on the surface of a soft cheese.
28 Another antilisterial compound, coagulin, was
isolated from a strain of Bacillus subtilis and placed in the pediocin family of bacteriocins.
115
The efficacy of five lactic acid bacteria to control L. monocytogenes in pasteurized milk was assessed
by inoculating the pathogen at ca. 10
4 cfu/ml with incubation at 30
◦ C. The lactics employed were
Lactococcus lactis, Leuconostoc cremoris, Lactobacillus plantarum, L. delbrueckii subsp. bulgaricus,
and Streptococcus salivarious subsp. thermophilus.
151 An inhibition of 89–100% was achieved with
final pH of 4.17–4.21 at 30
◦ C or 37
◦ C. Complete inhibition was achieved by the two lactobacilli
after 20 hours at 37
◦ C and 64 hours at 30
◦ C. In another study, 49 isolates of lactic acid bacteria from
ready-to-eat products were screened on agar spot plates against L. monocytogenes.
4 The three most
effective isolates were identified as Lactobacillus casei, Lactobacillus paracasei, and Pediococcus
acidilactici. Using MRS broth incubated at 5
◦ C for 28 days, a 3.5-log reduction of L. monocytogenes
was found while in frankfurters, a 4.2–4.7 log reduction occurred. In cooked ham stored at 5
◦ C for 28
days under vacuum packaging, a 2.6-log reduction was noted.
4
A number of other investigators have demonstrated the efficacy of various lactic acid bacteria
to inhibit foodborne pathogens in meats and meat products. A meat starter culture of Pediococcus acidilactici was shown to effect a 2.3-log reduction of E. coli 0157:H7, L. monocytogenes, and
Staphylococcus aureus during a salami fermentation after 24 hours compared to a 1.3-log reduction in
Lactic antagonism
The phenomenon of a lactic acid bacterium inhibiting or killing closely related and food-poisoning and
food spoilage organisms when in mixed culture has been observed for more than 80 years. Commonly
referred to as lactic antagonism, the precise mechanisms are yet unclear. Among factors identified
are the production of antibiotics, H 2 O 2 , diacetyl, and bacteriocins in addition to pH depression and
nutrient depletion. Lactic antagonism, thus, is an example of microbial interference.
In one study, a pediocin-producing strain of Lactococcus lactis was genetically enhanced to produce enough pediocin to control growth of L. monocytogenes in ripening Cheddar cheese. In control
cheese, the pathogen increased to about 10
7 /g after 2 weeks and then decreased to about 10
3 after
6 months but in the experimental cheese, the pathogen decreased to 10
2 /g within 1 week and then
to only 10/g within 3 months.
24 Propionibacterium freudenreichii subsp. shermanii produces an illdefined, multicomponent inhibitory system when cultured in pasteurized skim milk that is effective
against Gram-negative bacteria and molds in cottage cheese. One such product is Microgard. Reuterin
(3-hydroxypropionalaldehyde) is produced by Lactobacillus reuteri from glycerol. At a concentration
of 100 AU/g, a 5-log reduction of E. coli 0157:H7 was achieved in raw ground pork after 1 day at
7
◦ C.
53 When used alone, Reuterin at 4 AU/ml inhibited the growth of E. coli and 8 AU/ml inhibited
L. monocytogenes. This inhibitor was even more effective in combination with lactic acid.
53
Lactobacillus reuteri and allyl isothiocyanate (AITC, at ca. 1,300 ppm) alone and in combination
were tested for their effectiveness against a five-strain mixture of E. coli 0157:H7 in ground beef at 4
◦ C
for 25 days. The E. coli inoculum levels were 3- and 6-log 10 cfu/g, and 250 mM glycerol/kg of meat
was added. E. coli was killed in meat with the two levels of glycerol before day 20 by L. reuteri.
133
AITC completely eliminated the 3-log 10 inoculum of E. coli 0157:H7 and at the higher concentration,
it effected a >4.5-log 10 cfu/g reduction after 25 days.
To study the protective effect of a lactic organism, Lactobacillus casei and its culture permeate were
tested on ready-to-use salad vegetables at 8
◦ C.
199 After 6 days of storage, 3% culture permeate reduced
APC from 6 to 1 log 10 cfu/g, and suppressed coliforms, enterococci, and Aeromonas hydrophila.
Coliforms were reduced by about 2 logs and fecal coliforms by about 1 log by the use of 1% lactic
acid.
199 The inhibitory principal produced by a Staphylococcus equorum strain has been identified
as a macrocyclic peptide antibiotic, micrococcin P 1 , and the bacterium was effective in inhibiting
L. monocytogenes on the surface of a soft cheese.
28 Another antilisterial compound, coagulin, was
isolated from a strain of Bacillus subtilis and placed in the pediocin family of bacteriocins.
115
The efficacy of five lactic acid bacteria to control L. monocytogenes in pasteurized milk was assessed
by inoculating the pathogen at ca. 10
4 cfu/ml with incubation at 30
◦ C. The lactics employed were
Lactococcus lactis, Leuconostoc cremoris, Lactobacillus plantarum, L. delbrueckii subsp. bulgaricus,
and Streptococcus salivarious subsp. thermophilus.
151 An inhibition of 89–100% was achieved with
final pH of 4.17–4.21 at 30
◦ C or 37
◦ C. Complete inhibition was achieved by the two lactobacilli
after 20 hours at 37
◦ C and 64 hours at 30
◦ C. In another study, 49 isolates of lactic acid bacteria from
ready-to-eat products were screened on agar spot plates against L. monocytogenes.
4 The three most
effective isolates were identified as Lactobacillus casei, Lactobacillus paracasei, and Pediococcus
acidilactici. Using MRS broth incubated at 5
◦ C for 28 days, a 3.5-log reduction of L. monocytogenes
was found while in frankfurters, a 4.2–4.7 log reduction occurred. In cooked ham stored at 5
◦ C for 28
days under vacuum packaging, a 2.6-log reduction was noted.
4
A number of other investigators have demonstrated the efficacy of various lactic acid bacteria
to inhibit foodborne pathogens in meats and meat products. A meat starter culture of Pediococcus acidilactici was shown to effect a 2.3-log reduction of E. coli 0157:H7, L. monocytogenes, and
Staphylococcus aureus during a salami fermentation after 24 hours compared to a 1.3-log reduction in