Sakacin Q produced by Lactobacillus curvatus ACU-1: Functionality characterization and antilisterial activity on cooked meat surface

This work was conducted to evaluate the antilisterial activity of sakacin Q produced by Lactobacillus curvatus ACU-1 on the surface of cooked pork meat. A genetic re-characterization of the producer strain and a study of the structural genes involved in bacteriocin production were carried out as complementary data. Studies indicated that the bacteriocin was not attached to the producer cells favoring pre-purifications steps. Bacteriocin effectiveness was not compromised by adsorption to meat and fat tissues. Several ways of dispensing the bacteriocin onto the meat surface, namely cell culture, cell free supernatant (CFS), a mixture of both and freeze-dried reconstituted CFS, were investigated. The use of the latter was the most effective one to control Listeria growth within studied systems. L. curvatus ACU-1 and its bacteriocin presented promising technological characteristics that made them suitable for meat biopreservation.     

Bacteriocin-producing lactobacilli in Spanish-style fermented sausages: characterization of bacteriocins

Three bacteriocins were studied. Sakacin K, a bacteriocin from Lactobacillus sake CTC494 was purified to homogeneity by a four-step system involving ammonium sulphate precipitation, binding to a cation exchanger, hydrophobic interaction and reverse phase chromatography in FPLC (fast performance liquid chromatography) system. The peptide sequence was determined by Edman degradation. The first 30 amino acid residues from the N-terminus of sakacin K were identical to those of curvacin A from Lactobacillus curvatus LTH1174 and sakacin A from Lactobacillus sakei Lb706. The structural gene of sakacin K in Lb. sake CTC494 was located on a 60 Kbp plasmid (as has been previously reported) by curvacin A in Lb. curvatus LTH1174 and sakacin A in Lb. sakei Lb706. Plantaricin D, a bacteriocin-like compound isolated from Lb. plantarum CTC305 was purified and sequenced using the same procedure as described for sakacin K. The first 15 amino acid residues of plantaricin D were identical to those obtained from the bacteriocin inducer peptide (termed plantaricin A) of the bacteriocinogenic system in Lb. plantarum C11. The structural gene of the plantaricin D peptide was located on a similar EcoRl chromosomal fragment when compared to plantaricin A in Lb. plantarum C11. These two isolated bacteriocin-like peptides (sakacin K and plantaricin D) were purified from two new different strains obtained from fermented meat, confirming the ecological importance of these substances. Lactobacillus sakei CTC372, the third bacteriocinogenic strain selected in this study from fermented sausages, produced a bacteriocin named sakacin T. The bacteriocin is not found free in the supernatant of the cells. It is active against Listeria monocytogenes and Staphylococcus aureus. The genetic determinant of this bacteriocin was localized in a 84·4 Kbp plasmid by conjugative transfer and curing assays.     

Combined use of bacteriocin‐producing strains to control Listeria monocytogenes regrowth in raw pork meat

Avoiding the presence of Listeria in meat and dairy products is a major challenge for the food industry. In this work, a Lactobacillus curvatus strain producing the bacteriocin sakacin P and a Pediococcus acidilactici strain producing another bacteriocin, pediocin AcH, were used as starter cultures under laboratory conditions in a Listeria‐seeded raw‐pork‐meat matrix, which was then stored for 6 weeks at 4 °C. At 1 week intervals during the storage period, the antilisterial activity was evaluated. When either strain was added alone, the Listeria monocytogenes cfu count initially dropped from 10² cfu g^?1 to an undetectable level by the end of week 1 or 2, but this was followed by a rebound (regrowth) 1 week later. When both strains were added together to the meat matrix, rebound was delayed, Listeria remaining undetected from the end of week 1 to the end of week 5. A rebound was observed 6 weeks post‐inoculation, but fewer than 10 cfu g^?1 were counted. The use of more than one bacteriocin‐producing strain may thus overcome some of the problems limiting the effectiveness of bacteriocins in food systems.     

Development and characterization of an active polyethylene film containing Lactobacillus curvatus CRL705 bacteriocins

The development and characterization of a bacteriocin-containing polyethylene-based film is described, incorporating lactocin 705 and lactocin AL705, produced by Lactobacillus curvatus CRL705, and nisin. Three different procedures to obtain lactocin 705 and AL705 solution were evaluated, with the partially purified aqueous bacteriocin solution showing the highest inhibitory activity against indicator strains (Lactobacillus plantarum CRL691 and Listeria innocua 7). Pouch contact, soaking and a contact method were compared for incorporating bacteriocins onto PE-based films. Contact between the PE film and bacteriocin solution was the most effective, resulting in a more uniform distribution of bacteriocins on the film surface and using less active solution. The minimal inhibitory concentration of bacteriocin solution was 267 AU cm^?3 (lactocin 705) and 2133 AU cm^?3 (lactocin AL705), while the minimal contact time was 1 h. When relative inhibition area for antilisterial activity of the active films was compared, those treated with L. curvatus CRL705 bacteriocins displayed higher inhibitory activity than nisin-treated films. Functional properties of active PE-films containing lactocin 705 and AL705 showed no differences compared with non-active control films. Bacteriocin-active PE-based films are shown to be highly effective in inhibiting growth of Listeria. The potential use of commercially available packaging films as bacteriocins carriers may benefit active-packaging systems.     

Characterization of new bacteriocinogenic lactic acid bacteria isolated using a medium designed to simulate inhibition of Listeria by Lactobacillus sakei 2512 on meat

Bacteriocinogenic bacteria have been proposed to protect food products from Listeria contamination as bioprotective cultures. Lactobacillus sakei 2512 was demonstrated to inhibit the growth of Listeria on sliced cooked ham by challenge test. A liquid medium simulating ham, BHI5L200, was designed in order to select bioprotective strains for meat protection. Two strains were selected, from the 201 lactic acid bacteria screened, that produced bacteriocins at pH 5.8 in BHI5L200. The first one, Leuconostoc pseudomesenteroides 2733, produced a new bacteriocin which was purified and partially characterized. The second, Lactobacillus curvatus 2711, produced sakacin X and was shown to contain sakacin T and sakacin P structural genes. Co-culture experiments in BHI5L200 demonstrated that growth of Listeria was inhibited by L. sakei 2512 as well as by L. curvatus 2711.     

Impact of Lauric Arginate Application Form on its Antimicrobial Activity on the Surface of a Model Meat Product

This study evaluated the antimicrobial effect of N^α‐Lauroyl‐L‐arginine ethyl estermonohydrochloride (lauric arginate), sodium lactate, and sodium diacetate at various concentrations against Listeria innocua, Escherichia coli C600, and Lactobacillus curvatus (10² CFU/g) on “Lyoner style” sausage slices as a function of application form. We want to investigate if the results of a surface application of lauric arginate in various applications forms may differ from that of an in‐matrix application since different physicochemical processes occur at surfaces than in matrices. Lauric arginate was applied on the surface of meat emulsions as aqueous solution, as oil‐in‐water emulsion, and as solid lipid particles. The sausages slices were stored at 6 °C for 24 d and bacterial growth was assessed every 3rd day. The growth of L. curvatus was not impacted by lactate and diacetate at any tested concentration. In contrast, L. innocua and E. coli were inhibited over 24 d in the presence of ≥3.0 × 10³ μg/g diacetate. Aqueous lauric arginate solutions of 2.0 and 2.5 × 10³ μg/g were required for total inhibition of L. curvatus and L. innocua, respectively. The growth of E. coli was not affected by application of lauric arginate. The use of lauric arginate in an oil‐in‐water emulsion or solid lipid particles reduced antimicrobial effectiveness on the surface of Lyoner slices, which is in stark contrast to a previously conducted in‐matrix application of the same systems. Results were attributed to molecular interactions and mass transport processes that rendered lauric arginate less active when applied as emulsions or solid lipid particles. Results highlight the importance of understanding physicochemical properties when using interfacially active antimicrobials.     

Effects of curing sodium nitrite additive and natural meat fat on growth control of Listeria monocytogenes by the bacteriocin-producing Lactobacillus curvatus strain CWBI-B28

In realistic model meat systems, the separate and combined effects of fat content and sodium nitrite on the antilisterial activity of the bacteriocin of Lactobacillus curvatus CWBI-B28 were studied. In laboratory fermentations where Listeria monocytogenes was co-cultured at 4 °C with bacteriocin-producing CWBI-B28 in lean pork meat (fat content: 13%) without added nitrite, a strong antilisterial effect was observed after one week. The effect was maintained for an additional week, after which a slight and very gradual rebound was observed. Both added nitrite (20 ppm) and a high-fat content (43%) were found to antagonise this antilisterial effect, the Listeria cfu count reached after six weeks being 200 times as high in high-fat meat with added nitrite than in lean meat without nitrite. This antagonism could not be attributed to slower growth of the bacteriocin-producing strain, since CWBI-B28 grew optimally in fat-rich meat with 20 ppm sodium nitrite. Bacteriocin activity was also measured in the samples. The observed activity levels are discussed in relation to the degree of antilisterial protection conferred.     

Production of salami from beef, horse, mutton, Blesbok (Damaliscus dorcas phillipsi) and Springbok (Antidorcas marsupialis) with bacteriocinogenic strains of Lactobacillus plantarum and Lactobacillus curvatus

Lactobacillus plantarum 423, producer of bacteriocin 423, Lactobacillus curvatus DF38, producer of curvacin DF38, and a bacteriocin-negative mutant of L. plantarum 423 (423m) were evaluated as starter cultures in the production of salami from beef, horse, mutton, Blesbok (Damaliscus dorcas phillipsi) and Springbok (Antidorcas marsupialis). Growth of L. plantarum 423 and L. curvatus DF38 was best supported in Blesbok salami, as revealed by the highest growth rate during sweating, cold smoking and maturation, and final cell numbers after 70 days (1 × 10⁸ and 5 × 10⁷ cfu/g, respectively). Growth of Listeria innocua was the best suppressed in Blesbok salami fermented with L. plantarum 423 and L. curvatus DF38. Growth of L. innocua in horse salami was best suppressed when fermented with L. curvatus DF38. The final pH of salami fermented with L. plantarum 423 and L. plantarum 423m was slightly lower (4.4) compared to the pH of salami produced with L. curvatus DF38 (pH 4.7). No significant differences (P > 0.05) were recorded by a trained sensory taste panel amongst the three starter cultures regarding colour and venison like aroma. Horse, Blesbok and Springbok salami were rated significantly higher (P ? 0.05) in salami flavour than mutton salami, which was rated the lowest for this attribute. Blesbok salami was rated the highest for sour meat aroma, while beef salami was rated the lowest. Springbok salami was rated the highest in terms of oily mouth feel. Beef salami had the most compact structure and horse salami the softest structure of all meat types fermented. In general, salami produced with L. plantarum 423 yielded the best sour meat aroma, colour, texture, venison like flavour, sour meat flavour and oily mouthfeel and is considered superior to the L. plantarum mutant (strain 423m) and L. curvatus DF38.     

Modelling contributes to the understanding of the different behaviour of bacteriocin-producing strains in a meat environment

Bacteriocins from lactic acid bacteria are potent antibacterial agents that enable the producer cells to selectively and efficiently inhibit a part of the competing background flora, including several spoilage bacteria and foodborne pathogens. The use of bacteriocinogenic lactic acid bacterium strains, either as starters or as protective cultures, is very limited in the food industry, possibly because many questions about the in situ functionality of such strains remain unanswered. A modelling approach was developed to study the functionality of lactic acid bacterium bacteriocin producers in a meat environment. The kinetic properties of three potential bacteriocin-producing starter cultures for sausage fermentation, namely Lactobacillus sakei CTC 494, Lactobacillus curvatus LTH 1174, and Lactobacillus amylovorus DCE 471 were compared in MRS, used as a meat simulation medium. Moreover, the application possibilities of the bacteriocin-producing Enterococcus faecium RZS C5 strain were evaluated. It turned out that growth and bacteriocin production by Lb. sakei CTC 494 and Lb. curvatus LTH 1174 are adapted to the meat environment, whereas Lb. amylovorus DCE 471 is kinetically not able to dominate the meat fermentation process. Furthermore, the use of bacteriocin-producing enterococci as functional cocultures seems to be attractive.     

Inhibition of Listeria monocytogenes in cold smoked salmon by addition of sakacin P and/or liveLactobacillus sakei cultures

Listeria monocytogenes is the causative agent of food-related listeriosis. It has the ability to grow in vacuum-packaged food at chiller temperatures and is relatively tolerant to salt and low pH, thus it is difficult to control its growth in food.Listeria monocytogenes was added to vacuum-packed cold smoked salmon together with known concentrations of the bacteriocin sakacin P or nisin and/or one of two isogenic strains of the lactic acid bacteriaLactobacillus sakei . The vacuum-packaged salmon samples were incubated at 10°C for 4 weeks. Of the isogenic L. sakei strains, one produced sakacin P and the other did not. Both sakacin P and nisin had an initial inhibiting effect on growth of L. monocytogenes. Addition of the sakacin P-producing or the non-producing L. sakei had a bacteriostatic effect on L. monocytogenes during the complete storage period. When the sakacin P-producing L. sakei culture was added to vacuum-packed cold smoked salmon together with sakacin P, a bacteriocidal effect on L. monocytogenes was observed.     

Application of the bacteriocinogenicLactobacillus sakeiCTC494 to prevent growth of Listeria in fresh and cooked meat products packed with different atmospheres

The production of sakacin K byLactobacillus sakeiCTC494 at different temperatures and pH was evaluated before its application as a bioprotective culture againstListeriain different meat-based food packaging systems, that is, oxygen-permeable film, under vacuum and under a modified atmosphere (20% CO₂: 80% O₂) and stored at 7°C. TheLactobacillusculture produced the bacteriocin at a range of temperatures from 4°C to 30°C and at initial pH from 5·5 to 6·5.Listeriainhibition in raw minced pork, poultry breasts and modelized cooked pork could not be achieved by the sole application of vacuum or a modified atmosphere. Inoculation ofLb. sakeiCTC494 or sakacin K inhibited the growth ofListeriato different extents in all the products studied in each system; the greatest inhibition being observed in the vacuum packaged samples of poultry breasts and cooked pork, and in the modified atmosphere packaged samples of raw minced pork. Addition of sakacin K resulted in immediate bactericidal action againstListeriain every product and atmosphere studied.     

Characterization of a multilayer film activated with Lactobacillus curvatus CRL705 bacteriocins

BACKGROUND: Bacteriocins produced by lactic acid bacteria offer enormous promise for food safety preservation. In this study an active multilayer film obtained by the incorporation of lactocin 705 and lactocin AL705, two bacteriocins produced by Lactobacillus curvatus CRL705 with antimicrobial activity against Lactobacillus plantarum CRL691 and Listeria innocua 7, respectively, was characterized for its potential application in active packaging technology. Film activity performance at different storage conditions, bacteriocins transfer into water and sunflower oil, and film surface properties were evaluated. RESULTS: Film activity against L. innocua 7 was maintained during 2, 4 and 6 weeks at 30, 10 and 5 °C respectively. At 30 and 10 °C, activity loss against L. plantarum CRL691 was observed on the second week of storage and after the fourth week at 5 °C. Results showed no significant difference for active multilayer film contact angle and seal properties compared to the control (without bacteriocins). A decrease in lactocin 705 inhibitory activity after sunflower oil contact was observed, while lactocin AL705 remained unaffected. After water contact, film activity was retained for both bacteriocins. CONCLUSIONS: As demonstrated by antimicrobial activity and physico‐mechanical properties retention, lactocin 705 and AL705 active multilayer film present potential for application in active packaging technology. Copyright © 2011 Society of Chemical Industry     

Development of an active wheat gluten film with Lactobacillus curvatus CRL705 bacteriocins and a study of its antimicrobial performance during ageing

Antimicrobial wheat gluten film was obtained at pilot scale by Lactobacillus curvatus CRL705 bacteriocins inclusion in the film-forming solution. Bacteriocins’ minimum inhibitory concentration for the film activation was 2133 AU cm^?3 (lactocin AL705) and 267 AU cm^?3 (lactocin 705). Mechanical and barrier properties as well as film ageing kinetics were not significantly affected by the addition of bacteriocins. The antimicrobial film performance during ageing was assessed. Film activity against Listeria innocua 7 and Lactobacillus plantarum CRL691 was observed over 50 days of ageing. Even when the release of bacteriocins from the film upon water contact was observed for both bacteriocins at the beginning of the ageing period, and anti-Listeria activity was delivered to the simulant up to the 15th day of ageing, film residual activity for both bacteriocins was observed over 50 days. The results confirm the potential of a gluten film doped with L. curvatus CRL705 bacteriocins as a carrier of bacteriocins to avoid Listeria and lactic acid bacterial growth, thus enhancing quality and safety in foods.     

Microbial and Physicochemical Characterization of the Horse Meat in Fermented Sausage

In this study, 150 lactic acid bacterial strains, originating from horse meat, were subjected to a step-by-step screening and characterization to search for potential protective cultures to be used in the meat industry. Strains were first tested for their homofermentation and salt tolerance. Second, the antibacterial capacities towards Listeria monocytogenes were determined in an agar spot test. In total, 50% of the tested strains were inhibitory towards Listeria monocytogenes. However, only 12 strains produced a bacteriocin. Finally, three strains with strong bacteriocin activity were competitively evaluated by comparing their growth rate, acidifying character and lactic acid production at 15°C under anaerobic conditions in a liquid broth. All three strains had a fast growth rate with rapid acidification caused by the production of high levels of lactic acid. Based on this Lactobacillus sakei was used as starter culture for producing sausage horse meat. In this study, fermentations were followed analyzing the microbiological and physicochemical aspects of this product. The sausages were characterized based on microbial activity of lactic acid bacteria that resulted in a product with a final pH of about 4.56. No Listeria monocytogenes, Salmonella spp. nor Sulfite reducing clostridia were ever isolated from the raw materials or the fermented sausages during the maturation, reflecting the safety of this product. The final water activity of the product was 0.85. Lactobacillus sakei was efficient in reducing amine production since this strain caused a quick pH drop during sausage fermentation.     

Enhancing the antilisterial effect of Lactobacillus curvatus CWBI-B28 in pork meat and cocultures by limiting bacteriocin degradation

This work focused on Listeria monocytogenes growth inhibition and growth rebound in raw and cooked pork meat inoculated with Lactobacillus curvatus strains. During storage of raw meat homogenates in the presence of the bacteriocin-producing strain Lactobacillus curvatus CWBI-B28wt, the Listeria monocytogenes cfu count was initially reduced to an undetectable level, but a growth rebound occurred after two weeks, coinciding with loss of 70% of the bacteriocin activity present at the end of week 2. The Listeria growth rebound was suppressed when proteolysis of bacteriocin was countered by the absence of proteases (bacteriocin addition to cooked meat) or the presence of 1% soy flour (added to provide competing substrates). Further experiments confirmed that bacteriocin is sensitive to the action of proteolytic enzymes isolated from both Lactobacillus curvatus CWBI-B28wt and the meat matrix. Bacteriocin proteolysis thus emerges as a cause of Listeria growth rebound.     

<Emphasis Type="Italic">Listeria</Emphasis> Inactivation by the Combination of High Hydrostatic Pressure and Lactocin AL705 on Cured-Cooked Pork Loin Slices

The effect of the bacteriocin lactocin AL705 in combination with high hydrostatic pressure (HHP) on the inactivation of Listeria innocua 7, a nonpathogenic indicator for Listeria monocytogenes, deliberately inoculated (ca. 6.4 log CFU/g) onto the surface of ready-to-eat (RTE) sliced cured-cooked pork loin, was evaluated. Nontreated pork slices (control) and treatments subjected to lactocin AL705 (105 AU/ml) and/or HHP (400 or 600 MPa) were prepared. L. innocua 7 was monitored at days 1, 20, and 40 of storage at 4 °C. The results showed a complete inhibition of L. innocua 7 after the combined treatment with lactocin AL705 and 600 MPa and no regrowing of cells up to 40-day storage. The treatment at 600 MPa alone was not enough to avoid regrowth of L. innocua. Ultrastructural cell damage was observed at the cytoplasm and cell membrane/wall levels with all treatments; however, complete cell lysis was observed only with the combined treatment. HHP in combination with lactocin AL705 provided a wider margin of safety as post-processing listericidal treatment of RTE cured-cooked meat products.     

Behaviour of Listeria monocytogenes in the presence of Listeria innocua during storage of minced beef under vacuum or in air at 0°C and 10°C

Minced beef was inoculated with low levels (1·2–1·7 log₁₀cfu g⁻¹) of Listeria monocytogenes or Listeria innocua, or a combination of the two strains. Inoculated samples were stored at 0 or 10°C under two packaging atmospheres (aerobic and vacuum) for up to 28 days and surviving organisms recovered on Palcam Agar. The only significant increases in numbers of Listeria spp. occurred in samples held at 10°C under aerobic conditions. In vacuum packs, growth of both strains was inhibited. Under aerobic conditions meat pH increased from an initial value of pH 5·85 to c. 8·85 within 28 days. The pH of vacuum packaged meat declined to c. 4·95 during the same period. These differences in pH may be related to differences in the nature and effects of different background microflora that were observed to develop under each of these packaging conditions.Pseudomonas spp. predominated in aerobically stored beef, whereas in vacuum packed beef lactic acid bacteria predominated. No significant differences were observed between the growth rates of Listeria spp. inoculated into beef mince in pure and mixed culture. This suggests that the more frequent prevalence of Listeria innocua than Listeria monocytogenes in meat and meat products is not due to overgrowth or inhibition of the pathogen (Listeria monocytogenes) by the non-pathogen(Listeria innocua) during low-temperature storage.     

Production,mode of action and sequencing of the corresponding gene of a bacteriocin produced by Lactococcus lactis 19.3

Lactococcus lactis 19.3 produces a bacteriocin with a wide inhibitory spectrum, including the food pathogen Listeria monocytogenes. The producing strain was able to grow and produce similar amounts of bacteriocin in MRS medium, cow's milk and soya milk, respectively. The mode of action of this bacteriocin was further investigated using two indicator strains, Lactobacillus delbrueckii subsp. bulgaricus LMG 6901^T and Listeria monocytogenes ATCC 1911‐1. The bacteriocin displayed a bactericidal effect, causing a rapid decrease of the cell viability. Bacteriocin treatment of the sensitive strains resulted in major morphological changes, including pore formation, as shown by scanning electron microscopy. Finally, the bacteriocin‐encoding gene was identified by sequencing. The presence of nisin gene was confirmed. Based on all our data gathered so far, L. lactis 19.3 is a good candidate for a starter or protective culture in the manufacturing of both fermented dairy and vegetarian food products.     

Isolation and characterization of anti-listerial and amylase sensitive enterocin producing Enterococcus faecium DB1 from Gajami-sikhae, a fermented flat fish in Korea

Bacteriocinogenic Enterococcus faecium DB1 was isolated from Korean gajami-sikhae, a lactic fermented flat fish. The antimicrobial spectrum of E. faecium DB1 was limited to Listeria monocytogenes, Lactobacillus curvatus, and Pediococcus acidilactici in agar well diffusion assay; while it was expanded to other Grampositive and negative bacteria by direct and deferred assays. Induction of enterocin DB1 by co-culturing with sensitive indicators was not detected. Inactivation of bacteriocin activity was observed after treatment of crude enterocin DB1 with proteolytic enzymes and α-amylase, but not with catalase, sodium dodecyl sulfate, Tween 20 and 80. The bacteriocin activity was retained in pH between 2.0 and 10.0, and after treatment at 121°C for15 min. Maximum activity (1,280 AU/mL) against L. monocytogenes KCTC 3569 was observed in MRS broth and remained for at least 16 hr. The molecular weight of partially purified enterocin DB1 was approximately 16.5 kDa, and mode of action is bactericidal. Enterocin DB1 production trait is linked to a chromosomal DNA.     

Antilisterial and amylase-sensitive bacteriocin producing Enterococcus faecium SH01 from Mukeunji,a Korean over-ripened kimchi

A bacteriocinogenic strain identified as Enterococcus faecium SH01 was isolated from mukeunji, a Korean traditional over-ripened kimchi with antimicrobial activities against Listeria monocytogenes KCTC 3569 and Lactobacillus curvatus KFRI 166. The maximum bacteriocin titer (1,280 AU/mL) was detected at the early stationary phase and was maintained for 28 h with no activity loss. The bacteriocin activity, which disappeared after treatment with the proteolytic enzymes α-chymotrypsin, pronase E, proteinase K, and trypsin, was partially inactivated using α-amylase. The activity of bacteriocin SH01 remained after heat treatment (121°C, 15 min) and exposure to pH values from 2–12. The molecular weight of crude bacteriocin SH01 was 3 kDa. The bacteriocin production phenotype (Bac⁺) was linked to a 6 kb plasmid. Bacteriocin SH1 production was not induced by the co-presence of viable cells, heat treatment, or a cell-free indicator supernatant. The mode of action of bacteriocin SH1 was bactericidal.