The use of enterocin CCM 4231 in soy milk to control the growth of Listeria monocytogenes and Staphylococcus aureus

The inhibitory effect of enterocin CCM 4231 (concentration 3200 AU ml-1) was used to control the growth of Listeria monocytogenes Ohio and Staphylococcus aureus in soy milk. The growth and bacteriocin (enterocin) production of producer strain CCM 4231 in soy milk was also checked. Bacteriocin production by CCM 4231 strain in soy milk was first detected after 2 h from the beginning of cultivation (100 AU ml-1). The stationary phase for CCM 4231 was reached after 6 h reaching 10.38 cfu ml-1 (log10) with a slight increase up to 24 h (10.43 cfu ml-1, log10), and the maximum bacteriocin production in soy milk (200 AU ml-1) was noted after 8 h of the beginning of cultivation with stability up to 24 h. The addition of enterocin CCM 4231 at 3200 AU ml-1 to a growing indicator strain, L. monocytogenes Ohio, in soy milk resulted in inhibition for 24 h. The high inhibitory effect of enterocin was found after 1 h and 2 h of its addition (in 5 h-6 h of cultivation), the difference between the experimental and the control samples (ES, CS) being 4.96 log cycles at 5 h and 5.15 log cycles at 6 h. Staphylococcus aureus was not fully inhibited, although a difference of 3.55 log cycles was found when ES and CS were compared at the end of cultivation (24 h). The pH was not influenced by enterocin addition. The inhibitory effect of enterocin CCM 4231 against L. monocytogenes Ohio in soy milk was probably bacteriocidal; while Staph. aureus was influenced bacteriostatically. In general, the observed inhibitory activity confirmed the possibility for further application of bacteriocins in food environments as the protective agents. Of course, legislation problems must be solved.     

Inhibition of Listeria monocytogenes by enterocin 4 during the manufacture andripening of Manchego cheese

The inhibitory effect of enterocin 4, a bacteriocin produced by Enterococcus faecalis INIA 4, on Listeria monocytogenes strains Ohio and Scott A during themanufacture and ripening of Manchego cheese was investigated. Raw ewe's milk wasinoculated with ca 10⁵ cfu ml⁻¹ of L.monocytogenes and with 1% of a commercial lactic starter, 1% of an Ent. faecalis INIA 4 culture, or 1% of each culture. Manchego cheeses were manufactured according tousual procedures. Listeria monocytogenes Ohio counts decreased by 3 log units after8 h and by 6 log units after 7 d in cheese made from milk inoculated with Ent. faecalis INIA 4 or with both cultures, whereas no inhibition was recorded after 60 d in cheese made frommilk inoculated with commercial lactic starter. Listeria monocytogenes Scott A wasnot inhibited by enterocin 4 during cheese manufacture, but decreases of 1 log unit after 7 d andof 2 log units after 60 d were achieved in cheese made from milk inoculated with bothcommercial lactic starter and Ent. faecalis INIA 4.     

Anti-Listeria effect of enterocin A, produced by cheese-isolated Enterococcus faecium EFM01, relative to other bacteriocins from lactic acid bacteria

Enterocin A produced by Enterococcus faecium EFM01 displayed a narrow antimicrobial spectrum, mainly directed against Listeria spp. In particular, the bacteriocin was extremely active against 13 Listeria monocytogenes strains. This high specificity of action of enterocin A for Listeria spp. relative to lactic acid bacteria, together with its broad range of activity from pH 4.0 to pH 9.0, are factors which may be of great interest with respect to the potential antilisterial use of this bacteriocin in fermented foods. Assessment of the effect of enterocin A concentration on the extent and kinetics of bactericidal activity on L. monocytogenes Lm 6 (107 cfu ml-1 in culture broth), suggested that viability losses of higher than 5 log10, and time intervals necessary for maximum loss of viability of less than 2 h, could not be obtained. Moreover, it was shown that both parameters are closely dependent on the Listeria strain used. On the other hand, at concentrations inducing destruction of approximately 2 log10 cycles, maximum loss of viability was achieved within time intervals which varied widely from one lactic acid bacteria bacteriocin to another.     

Inhibition of Listeria monocytogenes by piscicolin 126 in milk and Camembert cheese manufactured with a thermophilic starter

The effect of bacteriocin, piscicolin 126, on the growth of Listeria monocytogenes and cheese starter bacteria was investigated in milk and in Camembert cheese manufactured from milk challenged with 10(2) cfu ml(-1) L. monocytogenes. In milk incubated at 30 degrees C, piscicolin 126 added in the range of 512-2,048 AU ml(-1) effectively inhibited growth of L. monocytogenes for more than 20 d when challenged with approximately 10(2) cfu ml(-1) L. monocytogenes. At higher challenge levels (10(4) and 10(6) cfu ml(-1)), piscicolin 126 reduced the viable count of L. monocytogenes by 4-5 log units immediately after addition of the bacteriocin; however, growth of Listeria occurred within 24 h. The minimum inhibitory concentration (MIC) of piscicolin 126 against lactic acid cheese starter bacteria was generally greater than 204,800 AU ml(-1) , and the viable count and acid production of these starter cultures in milk were not affected by the addition of 2,048 AU ml(-1) piscicolin 126. Camembert cheeses made from milk challenged with L. monocytogenes and with added piscicolin 126 showed a viable count of L. monocytogenes 3-4 log units lower than those without piscicolin 126. Inactivation of piscicolin 126 by proteolytic enzymes from cheese starter bacteria and mould together with the emergence of piscicolin 126-resistant isolates was responsible for the recovery of L. monocytogenes in the cheeses during ripening.     

Partial characterization of bacteriocins produced by environmental strain Enterococcus faecium EK13

AIMS: The partial characterization of bacteriocins produced by an environmental strain Enterococcus faecium EK13, isolated from cattle dung water. METHODS AND RESULTS: A bacteriocin was partially purified by ammonium sulphate precipitation, followed by a SP-Sepharose column, reverse-phase chromatography and N-terminal region sequenced. The anti-microbial substance produced was found to be a heat-stable polypeptide with molecular mass 4.83 kDa, which was determined by N-terminal amino acid sequencing to be enterocin A. A second substance was specified by PCR as enterocin P. Bacteriocins were stable at 4 and -20 degrees C for long storage periods. The optimum of bacteriocin production was observed in the range of pH 5.0-6.5 at 30 and 37 degrees C. The most active substances are produced by strain EK13 in logarithmic growth phase and bacteriocins are produced after 1 h of fermentation. The highest activity detected in fermentation experiments was 51 200 AU ml(-1) and the most sensitive indicator strain was found to be Listeria innocua LMG 13568. Differences in bacteriocin activity against two indicators could be explained by more than one type of enterocin production by strain EK13, or with different mode of action or in different sensitivity of strains. CONCLUSION: Enterococcus faecium strain EK13 isolated from cattle dung water produces two bacteriocins, enterocin A and P, with an inhibitory effect against the strain of the genera Enterococcus, Leuconostoc, Lactobacillus, Streptococcus, Staphylococcus, Bacillus and Listeria (in different origin). SIGNIFICANCE AND IMPACT OF THE STUDY: Enterococcus faecium EK13 environmental strain is a new producer of enterocin A and P. The E. faecium EK13, isolated from cattle dung water, is presented with the further aim to utilize it for waste treatment by biotechnological processes.     

Isolation of a bacteriocin-producing Lactococcus lactis subsp. lactis and application to control Listeria monocytogenes in Moroccan jben

AIM: Use of a bacteriocin-producing lactococcal strain to control Listeria monocytogenes in jben. METHODS AND RESULTS: A Lactococcus lactis strain isolated from lben was shown, by the spot technique, to produce a bacteriocin different from nisin. Inhibitory activity of the bacteriocin-producing strain against Listeria monocytogenes was investigated in jben, made from cow's milk fermented with the producer organism and contaminated with 104 or 107 cfu ml-1. Listeria counts were monitored during manufacture, and during conservation at room and at refrigeration temperatures. Results showed that the pathogen was reduced by 2.7 logarithmic units after 30 h of jben processing when the initial inoculum of 107 cfu ml(-1) was used. For the initial inoculum of 104 cfu ml(-1), the bacterium was completely eliminated at 24 h. Furthermore, the use of the bacteriocin-producing starter culture extended the shelf-life of jben by 5 days. CONCLUSIONS: In situ production of the lactococcal bacteriocin is an efficient biological means of controlling L. monocytogenes in jben and of allowing shelf-life extension. SIGNIFICANCE AND IMPACT OF THE STUDY: The proposed technology will essentially benefit minimally processed dairy products and those made with raw milk.     

Production of bacteriocin inhibitory to Listeria species by Enterococcus hirae.

A bovine intestinal bacterial isolate, identified as Enterococcus hirae, was found to produce a bacteriocin (designated hiraecin S) inhibitory to Listeria monocytogenes and other Listeria spp. Identification to species level was determined by comprehensive biochemical and morphological tests which were verified by DNA-DNA homology assays. The antimicrobial agent was inactivated by pronase and papain and was insensitive to catalase. The antimicrobial activity was not due to hydrogen peroxide or acid formation, nor was lysozyme or muramidase activity observed in cell-free bacteriocin preparations. Inhibition of selected gram-negative bacteria was not observed. Other enterococci were sensitive to the bacteriocin, and except for Listeria spp., no other gram-positive bacteria tested were inhibited.     

Production of bacteriocin inhibitory to Listeria species by Enterococcus hirae.

A bovine intestinal bacterial isolate, identified as Enterococcus hirae, was found to produce a bacteriocin (designated hiraecin S) inhibitory to Listeria monocytogenes and other Listeria spp. Identification to species level was determined by comprehensive biochemical and morphological tests which were verified by DNA-DNA homology assays. The antimicrobial agent was inactivated by pronase and papain and was insensitive to catalase. The antimicrobial activity was not due to hydrogen peroxide or acid formation, nor was lysozyme or muramidase activity observed in cell-free bacteriocin preparations. Inhibition of selected gram-negative bacteria was not observed. Other enterococci were sensitive to the bacteriocin, and except for Listeria spp., no other gram-positive bacteria tested were inhibited.     

Detection and characterization of a novel antibacterial substance produced by a Lactobacillus delbrueckii strain 1043

A novel antibacterial substance produced by a strain isolated from Bulgarian yellow cheese was characterized. The producer strain was identified by molecular typing to belong to the species Lactobacillus delbrueckii , which is a rare producer of bacteriocins. The inhibitory agent was heat stable and active against lactic acid bacteria species and several food-borne pathogens : Listeria monocytogenes , Staphylococcus aureus , Enterococcus faecalis , Escherichia coli , Yersinia enterocolitica and Y. pseudotuberculosis . Its sensitivity to amylolitic enzymes and lipase suggested that a lipid and carbohydrate moiety could be important for the activity. The amino acid content of the purified bacteriocin was estimated to 29 amino acids. The bacteriocin was shown to be small (3·6–6 kDa) by three different methods : HPLC gel-filtration, SDS-PAGE and amino acid contents.     

A "retrocidal" plasmid in Enterococcus faecalis: passage and protection

Enterococcus faecalis MC4 harbors a 130 kb conjugative, pheromone (cCF10)-responding plasmid, pAMS1, conferring chloramphenicol, streptomycin and tetracycline resistances. A plasmid-borne class IIa bacteriocin (MC4-1) determinant and cognate immunity gene were present, but not expressed in MC4. However, pAMS1 transfer to E. faecalis JH2-2 (but not to the non-isogenic OG1SS) generated the surprising ability to express bacteriocin activity against the plasmid donor, MC4. The bacteriocin target spectrum includes E. faecalis, Enterococcus faecium, Enterococcus gallinarum, Enterococcus hirae, and Listeria monocytogenes. Those donors unable to express bacteriocin or immunity could protect themselves from the "retrocidal" behavior of transconjugants by a switch to bacteriocin resistance at a frequency of approximately 10(-3). Reversion to sensitivity occurred at a relatively high frequency, suggestive of involvement of a phase variation event. These observations concerning a conjugative plasmid with novel "retrocidal" properties, coupled with a defense mechanism independent of plasmid-borne immunity functions, may relate to phenomena exploiting regulatory features with broader ecological and evolutionary implications.     

Clinical significance of infection pathogen resistance in a urological clinic for selection of antibacterial therapy regimes for the treatment of complicated urinary infections]

Data on changes of etiological structure of the complicated urinary tract infections treated at the Research Institute of Urology and Hospital No. 47 at the 5-year period (1996-2000) are given. It was shown that the most important microorganisms were the following: Enterobacter spp., E. coli, Proteus spp., Staphylococcus spp., Enterococcus faecalis. The correlation between frequency of the microorganisms isolation and their susceptibility to antimicrobial agents at different periods was analysed. The results of analysis allowed to elaborate algorithm of etiotropic therapy. Choice of the drug depends on pathogen susceptibility to antibiotics, bacteriuria level and clinical symptoms severity.     

Morphological changes induced in listeria monocytogenes V7 by a bacteriocin produced by Pediococcus acidilactici

Pediococcus acidilactici produces bacteriocin, which kills Listeria monocytogenes. The bactericidal mode of action of the bacteriocin against L. monocytogenes V7 was investigated by transmission electron microscopy. The bacteriocin was purified partially from the cell-free extract using Micro-Cel and cation-exchange chromatography, and the specific activity was increased 1,791 fold. The bacteriocin (6,400 AU/ ml) was inoculated with L. monocytogenes V7 and incubated for 0.5 h, 1 h, 3 h, and 6 h. The bacteriocin was found to destroy most of the cell wall and released most of the inclusions in the cells after 6 h of incubation. These results suggest that the bactericidal effect of the bacteriocin was due to bacterial lysis.     

Antimicrobial activity of extracts of the lichen Parmelia sulcata and its salazinic acid constituent

The antimicrobial activity of the acetone, chloroform, diethyl ether, methanol, and petroleum ether extracts of the lichen Parmelia sulcata and its salazinic acid constituent have been screened against twenty eight food-borne bacteria and fungi. All of the extracts with the exception of the petroleum ether extract showed antimicrobial activity against Aeromonas hydrophila, Bacillus cereus, Bacillus subtilis, Listeria monocytogenes, Proteus vulgaris, Yersinia enterocolitica, Staphylococcus aureus, Streptococcus faecalis, Candida albicans, Candida glabrata, Aspergillus niger, Aspergillus fumigatus, and Penicillium notatum. Salazinic acid did not show antimicrobial activity against L. monocytogenes, P. vulgaris, Y. enterocolitica, and S. faecalis but showed activity against Pseudomonas aeruginosa and Salmonella typhimurium as well. The MIC values of the extracts and the acid for the bacteria and fungi have also been determined.     

Characteristics and identification of enterocins produced by Enterococcus faecium JCM 5804T

AIMS: To screen bacteriocin-producing lactic acid bacteria (LAB) in 52 type and reference strains, which have not previously been studied, with respect to bacteriocins, and to characterize the presence of bacteriocins. METHODS AND RESULTS: Only Enterococcus faecium JCM 5804T showed bacteriocin-like activity. It inhibited the growth of Lactobacillus spp., Enterococcus spp., Clostridium spp., Listeria monocytogenes, and vancomycin resistant Enterococcus (VRE). However, it was not effective against Gram-negative strains, Weisella spp., Leuconostoc spp., Lactococcus spp., or methicillin resistant Staphylococcus aureus (MRSA). The inhibitory activity of Ent. faecium JCM 5804T was inactivated by proteinase K, trypsin, alpha-chymotrypsin, and papain, but not by lysozyme, lipase, catalase, or beta-glucosidase. The inhibitory activity was stable at 100 degrees C for 30 min, and had a pH range from 2 to 10. The molecular weight of the partially purified bacteriocin(s) was approx. 4.5 kDa, according to tricine-sodium dodecyl sulphate-polyacrylamide gel electrophoresis. Polymerase chain reaction and direct sequencing methods identified three different types of bacteriocins produced by Ent. faecium JCM 5804T, enterocin A, enterocin B, and enterocin P-like bacteriocin. CONCLUSION: Enterococcus faecium JCM 5804T produced three different types of bacteriocins, and they inhibited LAB and pathogens. SIGNIFICANCE AND IMPACT OF STUDY: This is the first report of enterocin A, enterocin B, and enterocin P-like bacteriocin, detected in Ent. faecium JCM 5804T among LAB type and reference strains.     

Microbiological quality of wheat flour consumed in Morocco

Cereal products (soft and hard wheat) are a basic staple food in the Moroccan diet. A total of 60 samples of two types of wheat flours used for human consumption were collected; 30 samples among this collection were obtained from various households using Moroccan varieties of wheat produced in traditional flour mills. The rest of the samples were purchased from retail wheat flour sources in the Rabat and Sale city markets. Standard plate counts (SPC), total and faecal coliforms, Clostridium, Salmonella spp., Shigella spp., Staphylococcus aureus, Listeria monocytogenes, yeast, lactic acid bacteria, and molds, were carried out to assess the microbiological quality of wheat flour. Microbiological interpretation of the criteria was performed according to standards implemented by the Codex Alimentarius Commission. Most frequent counts, in traditional and industrial wheat flour, were total aerobic mesophilic bacteria with an average 4 × 104 and 2.5 × 104 cfu/g, respectively. The results showed higher coliform and fungi counts in house than in commercial samples. Pathogenic flora as Salmonella spp., Shigella spp., S. aureus, L. monocytogenes, and Clostridium were not detected in all investigated samples. Bacterial strains isolated from both flours belong to the following genera: Enterobacter spp., Serratia spp., Klebsiella spp., Pantoea spp., Leclercia spp., Proteus spp. The most frequent genus of the investigated isolates was Aspergillus (81 %). Microbial counts were lower than the limit laid down in the Codex Alimentarius, attributing to these flours a satisfactory microbiological quality.     

Enterocin 226NWC, a bacteriocin produced by Enterococcus faecalis 226, active against Listeria monocytogenes

F. VILLANI, G. SALZANO, E. SORRENTINO, O. PEPE, P. MARINO AND S. COPPOLA. 1993. Enterococcus faecalis 226, isolated from natural whey cultures utilized as starters in the manufacture of mozzarella cheese from water-buffalo milk, produces a bacteriocin designated enterocin 226NWC. The bacteriocin was isolated from culture supernatant fluids of the producer strain and was active against strains of the same species and Listeria monocytogenes, but not against useful lactic acid bacteria. Enterocin 226NWC is a protein with an apparent molecular weight of about 5800; it is relatively heat-stable and has a bactericidal mode of action. Listeria monocytogenes, growing in the presence of the enterocin 226NWC producer strain in broth and in reconstituted skim milk, was inhibited.     

Partial characterization of enterocin MR99 from a corn silage isolate of Enterococcus faecalis

AIMS: To assess the inhibitory activity on Gram-positive and Gram-negative bacteria of several species of enterococci recovered from a natural corn silage. METHODS AND RESULTS: The inhibitory activity of strains of Enterococcus faecalis (58), Enterococcus faecium (35), Enterococcus gallinarum (3) and Enterococcus casseliflavus (4) were studied employing indicator strains from various sources (clinical, food and ATCC). Enterococcus faecalis MR99, the only strain with inhibitory activity, inhibited other enterococci, Listeria spp., Staphylococcus aureus, Clostridium spp., Bacillus spp., Escherichia coli, Shigella sonnei and Shigella flexneri. The bacterium contained only one conjugative pheromone-responsive plasmid. The partially chromatography-purified MR99 enterocin (PPE) had a molecular weight of approx. 5000 Da and a pI of 6.2, was sensitive to proteolytic enzymes and could be extracted in benzene and butanol. It appeared stable to adjustment of pH 4.0, 5.0, 6.0, 7.0 and 8.0 and was resistant to heat. Inactivation was at 15 min at 121 degrees C. Enterocin MR99 was bactericidal on strains of Listeria monocytogenes, Staph. aureus, and bovine mastitis agents, it was bacteriostatic on E. coli. Although enterocins MR99 and AS48 have inhibitory activity on Gram-negative bacilli, PCR studies demonstrated a lack of relationship between them. CONCLUSIONS: The active component had a protein nature, was resistant to heat and presented a wide inhibitory spectrum. SIGNIFICANCE AND IMPACT OF THE STUDY: The biological properties of Ent. faecalis MR99 suggest that this strain merits further investigations so it can be applied in human and veterinary health programmes.     

Evaluation of the antimicrobial activity of the acetone extract of the lichen Ramalina farinacea and its (+)-usnic acid, norstictic acid, and protocetraric acid constituents

The acetone extract of the lichen Ramalina farinacea and its (+)-usnic acid constituent showed antimicrobial activity against Bacillus subtilis, Listeria monocytogenes, Proteus vulgaris, Staphylococcus aureus, Streptococcus faecalis, Yersinia enterocolitica, Candida albicans, and Candida glabrata. Norstictic acid was active against Aeromonas hydrophila as well as the above microorganisms except Yersinia enterocolitica. Protocetraric acid showed activity only against the tested yeasts Candida albicans and Candida glabrata. The MIC values of the extract as well as of the three substances were determined. No antifungal activity of the acetone extract has been observed against ten filamentous fungi.     

Conjugal transfer of plasmid-borne bacteriocin production in Enterococcus faecalis 226 NWC

Enterococcus faecalis 226 NWC, isolated from natural whey cultures utilized as starter in water-buffalo Mozzarella cheese manufacture, produces a bacteriocin, designated Enterocin 226 NWC, which is inhibitory to Listeria monocytogenes. Plasmid analysis of E. faecalis 226 NWC showed a single 5.2-kb plasmid, pEF226. In conjugation experiments, pEF226 was transferred into a plasmid-free strain of E. faecalis JH2-2. The transfer required direct cell-to-cell contact and was not inhibited by DNase. The identity of conjugation was confirmed by digestion with SmaI restriction endonuclease and subsequent pulsed-field gel electrophoresis (PFGE) of the genomic DNA of E. faecalis 226, E. faecalis JH2-2 and of the isolates after the mating. The data indicate that the ability of E. faecalis 226 NWC to produce the bacteriocin is linked to the 5.2-kb conjugative plasmid pEF226.     

Bacteriocin production, plasmid content and plasmid location of enterocin P structural gene in enterococci isolated from food sources

AIMS: To characterize bacteriocin production, antimicrobial spectrum and plasmid content in bacteriocinogenic enterococci from foods. METHODS AND RESULTS: Bacteriocinogenic Enterococcus faecium (14 isolates) and Enterococcus faecalis (three isolates) showed two different patterns of bacteriocin production in liquid broth: exponential-phase and stationary-phase production. Bacteriocin concentrates from all enterococci were inactivated by trypsin, but seldom by heat (100-117 degrees C), extremes of pH (2.0 to 9.0) or reducing agents (such as dithiothreitol). All bacteriocin concentrates were active against Listeria innocua and Listeria monocytogenes, and most were also active against many Ent. faecalis and Ent. faecium isolates. Enterococci clustered in three main groups according to their plasmid content (which included plasmids from 2.0 to 53 kb). Several isolates from different foods showed almost identical plasmid profiles. The enterocin P structural gene (entP) was detected by hybridization on plasmids of c. 19, 26 and/or 35-38 kb. CONCLUSIONS: Enterococci from food show different patterns of bacteriocin production and different plasmid content in spite of carrying similar bacteriocin-encoding genes. SIGNIFICANCE AND IMPACT OF THE STUDY: This study provides information on the diversity of bacteriocinogenic enterococci from food sources carrying apparently similar enterocin genes.