Antimicrobial Activity Of Cell-free Supernatant Research Articles

Improvement of antimicrobial activity of Pediococcus pentosaceus strain 2397 in suppressing Escherichia coli

Abstract. Riftyan E, Yusmarini, Rossi E, Pato U. 2024. Improvement of antimicrobial activity of Pediococcus pentosaceus strain 2397 in suppressing Escherichia coli. Biodiversitas 25: 2500-2506. Lactic acid bacteria exhibit antibacterial activity that suppresses spoilage and pathogenic bacteria. Due to their antagonistic action against foodborne pathogens such as Escherichia coli, LAB isolated from dairy products have attracted considerable attention as a potential food preservative. Furthermore, bioactive compounds generated by forming LAB biofilms may exhibit efficacy against pathogenic microorganisms and their toxin. Combining LAB biofilms and other LAB products, such as bacteriocins, could offer a significant method against pathogenic microorganisms and their biofilms. The aim of this study was to evaluate the effects of optimization of media composition and incubation conditions on the antimicrobial activities of cell-free supernatant (CFS) from Pediococcus pentosaceus strain 2397 to inhibit E. coli FNCC-19. The antimicrobial activity of CFS was determined using agar well diffusion method. The results revealed that antimicrobial activity of P. pentosaceus strain 2397 was enhanced by optimizing the media composition and incubation conditions. Pediococcus pentosaceus strain 2397 exhibited excellent antimicrobial activity against E. coli. In MRS, 5% (v/v) of P. pentosaceus strain 2397+2.0% (w/v) yeast extract with pH 7.0 showed an inhibition zone of 10.44 mm. Therefore, strain 2397 may be effective in producing bacteriocin as a preservative for food products.

Antimicrobial activity of cell-free supernatant derived from Ligilactobacillus animalis SWLA-1 in a novel ex vivo canine corneal infection model.

Canine bacterial keratitis is a corneal infection that causes various symptoms, including visual impairment, and necessitates eye removal in severe cases. Staphylococcus pseudintermedius is a pathogen that causes significant bacterial keratitis in canine patients. Moreover, multi-drug resistant Staphylococcus pseudintermedius (MDRSP) has been reported in both humans and animals. Regarding treatment failure against multi-drug resistant (MDR) pathogens with classic antibiotics, antimicrobial compounds derived from probiotics have been suggested as an alternative approach. Ligilactobacillus animalis SWLA-1 strain and its cell-free supernatant (CFS) have previously demonstrated potent antimicrobial activity against various MDR pathogenic bacteria. Based on this finding, we evaluated the anti-staphylococcal activity of CFS derived from Ligilactobacillus animalis SWLA-1 against MDRSP in a newly established ex vivo canine corneal infection model using fresh canine corneoscleral rims. Additionally, an in vitro cytotoxicity test using human keratocytes was performed. CFS significantly inhibited the growth of MDRSP in the novel ex vivo model and did not exhibit any significant toxicity against keratocytes in vitro. Based on these results, the antimicrobial compounds in CFS show potential as a novel approach for MDR staphylococcal keratitis treatment.

The Influence of Ph and Temperature on the Antimicrobial Activity Of Cell-free Supernatant of Lactobacillus plantarum Sn13t Isolated from Stingless Bee Honey (Galo-Galo)

>This study aimed to measure the antimicrobial activity of Lactobacillus plantarum SN13T cell-free supernatant against bacterial pathogens at different pH and temperatures. L. plantarum SN13T was isolated from stingless bee honey (galo-galo). Some pathogenic bacteria were tested, namely Listeria monocytogenes VTO, Listeria monocytogenes, L. innocua, Staphylococcus aureus, Salmonella, Propionibacterium acnes, Pseudomonas, Klebsiella, Acinetobacter baumani, and Escherichia coli. Cell-free supernatant (CFS) L. plantarum SN13T had antimicrobial activity against pathogenic bacteria. The highest antimicrobial activity of CFS L. plantarum SN13T at pH 2 was against Salmonella bacteria (23.9 mm), and the smallest inhibition (10.2 mm) was against Acinetobacter baumani. While at pH 4, the highest antimicrobial activity of CFS was found in E. coli with an inhibition zone of 26.9 mm. CFS L. plantarum SN13T at different temperatures still had antimicrobial activity, even at more than 121oC. CFS L. plantarum SN13T produced the highest antimicrobial properties against Pseudomonas, both at 70, 100, and 121oC, while the lowest antimicrobial activity was shown against L. monocytogenes VTO.

ANTIBACTERIAL POTENCY OF CELL FREE SUPERNATANT PRODUCED BY LACTIC ACID BACTERIA ISOLATED FROM INDONESIAN FERMENTED FISH PRODUCTS AGAINST HISTAMINE-PRODUCING BACTERIA

The toxicity caused by high histamine content produced by histamine-producing bacteria (HPB) during the fermentation of scombridae fish group based fermented fish products is still a problem that requires a solution. This study aims to explore the potential of secondary metabolites in the form of cell free supernatant (CFS) produced by lactic acid bacteria (LAB) as antibacterial agents against HPB. The LAB was isolated from the fermented fishery products named bekasan, cincalok and fish sauce using MRS-Agar and fermented on MRS-broth for 48 hours. CFS was collected by centrifugation at 15,000 x g for 15 minutes, followed by heating at 100oC for 3 minutes and pH neutralization with 0.1N NaOH. Antimicrobial activity of CFS then tested on HFB namely Morganella morganii TK7, Citrobacter freundii CK1, and Klebsiella sp. CK13.2 (collection of the Laboratory of Fisheries Product Quality and Safety, Department of Fisheries UGM) using the macrodilution method. Isolation of LAB from all three products successfully isolated 34 isolates. The results of the antibacterial activity showed that 4 isolates namely GMCN 1.12, GMBK 2.6, GMBK 2.7, dan GMKI 2.1 were able to inhibit HFB growth more than 70%. The highest activity was shown by GMBK 2.7 which inhibits 98% against Morganella morganii TK7, 99% against Citrobacter freundii CK1, and 84% against Klebsiella sp. CK13.2. The antimicrobial activity was reduced after proteolytic enzymes were added suggesting that the bioactive compound came from peptide-based substances like bacteriocin.

16S rRNA metagenomic analysis reveals significant changes of microbial compositions during fermentation from ewe milk to doogh with antimicrobial activity

ABSTRACT The consumption of locally produced organic foods has become a popular trend in those seeking better health through diet. Despite their proposed health benefits, there are concerns regarding the safety of these foods, as they may contain pathogens due to poor hygienic conditions during production. This study aimed to explore the microbial inhibitory effects of ewe milk, yogurt, and doogh prepared by nomads from Ghasr-e-Shirin region in Iran, and to identify the bacterial community of these products using next-generation sequencing of 16S rRNA gene. The antimicrobial activity of cell-free supernatants (CFSs) of samples were evaluated against 3 fungi and 5 bacteria by agar disc diffusion and broth microdilution assays. The findings of this research showed that there is great diversity of bacteria in milk collected by nomads. The most dominant bacteria were Enterobacteriaceae (49.16%) in milk. However, non-lactic acid bacteria were overtaken by Lactobacillus delbrueckii (99.9%) in doogh and yogurt. The CFSs of yogurt and doogh showed growth inhibitory activity against the microorganisms used in this study.

The antimicrobial properties and biogenic amine production of lactic acid bacteria isolated from various fermented food products

Lactic acid bacteria (LAB) have been isolated from fermented foodstuff and pre-identified using API 50 CHL and confirmed by polymerase chain reaction method to investigate the protective properties against important foodborne pathogens of their cell-free supernatants (CFS) and neutralized cell-free supernatants (NCFS). The antimicrobial activity of CFS and NCFS was determined using agar well diffusion assay. Biogenic amine production of LAB strains were also monitored in tyrosine decarboxylase broth (TDB). The highest and lowest histamine production were obtained by Pediococcus pentosaceus (155.66 mg/L) and Lactobacillus plantarum (5.96 mg/L), respectively. CFS obtained from LAB isolates showed better antimicrobial effects against pathogens than NCFS. The CFS and NCFS obtained from L. plantarum showed a high antimicrobial effect against S. Paratyphi A with inhibition zone diameter 22.5 and 16.5 mm, respectively. The CFS and NCFS of L. raffinolactis showed strong antibacterial activities against Listeria monocytogenes, with zone diameter 23.5 and 24.5 mm. Practical applications Antimicrobial activity of cell-free and neutralized cell-free supernatants obtained from LAB strains was evaluated. Biogenic amine production of LAB strains were also monitored in tyrosine decarboxylase broth. All LAB isolates had the capacity to produce biogenic amines. Cell-free supernatants obtained from LAB isolates showed better antimicrobial effect against pathogens than neutralized cell-free supernatants. Our results showed that cell-free supernatants can be used as a bio-protective agent in the food industry.

Selection of Lactic Acid Bacteria Isolated from Fresh Fruits and Vegetables Based on Their Antimicrobial and Enzymatic Activities.

Lactic acid bacteria (LAB) are an important source of bioactive metabolites and enzymes. LAB isolates from fresh vegetable sources were evaluated to determine their antimicrobial, enzymatic, and adhesion activities. A saline solution from the rinse of each sample was inoculated in De Man, Rogosa and Sharpe Agar (MRS Agar) for isolates recovery. Antimicrobial activity of cell-free supernatants from presumptive LAB isolates was evaluated by microtitration against Gram-positive, Gram-negative, LAB, mold, and yeast strains. Protease, lipase, amylase, citrate metabolism and adhesion activities were also evaluated. Data were grouped using cluster analysis, with 85% of similarity. A total of 76 LAB isolates were recovered, and 13 clusters were formed based on growth inhibition of the tested microorganisms. One cluster had antimicrobial activity against Gram-positive bacteria, molds and yeasts. Several LAB strains, PIM4, ELO8, PIM5 and CAL14 strongly inhibited the growth of L. monocytogenes and JAV15 and TOV9 strongly inhibited the growth of F. oxysporum. Based on enzymatic activities, 5 clusters were formed. Seven isolates hydrolyzed starch, 46 proteins, 14 lipids, and 36 metabolized citrate. LAB isolates with the best activities were molecularly identified as Leuconostoc mesenteroides, Enterococcus mundtii and Enterococcus faecium. Overall, LAB isolated from vegetables showed potential technological applications and should be further evaluated.

Antimicrobial activity and storage stability of cell-free supernatants from lactic acid bacteria and their applications with fresh beef

This study aimed to evaluate the effectiveness of cell-free supernatants (CFS) produced by selected strains of lactic acid bacteria (LAB) as antimicrobials in vitro against Escherichia coli, Staphylococcus aureus, Shigella sonnei, Pseudomonas fluorescens, Salmonella Typhimurium, or Listeria monocytogenes. The agar-well diffusion method was performed using CFS from sixteen LAB. Neutralization of CFS pH as well as treatment with proteinase K were utilized to determine the nature of CFS’ antimicrobial compounds. Then stability of the three most effective CFS during storage at various temperatures (15, 25, or 35 °C) was determined through agar-well diffusion assays each week for 20 weeks. In addition, antimicrobial activity of CFS from Lb. plantarum was tested in inoculated (E. coli, Staph. aureus, S. Typhimurium, or L. monocytogenes) beef pieces; using this CFS to marinate beef pieces. Furthermore, the effect on beef color (raw or grilled beef, marinated or not with Lb. plantarum CFS) was determined. CFS from Lb. plantarum, Lb. sakei, and Lb. rhamnosus were found to be the most effective, with inhibition halos greater than 20.2 ± 2.0, 20.8 ± 2.9, and 17.1 ± 3.6 mm, respectively. Antimicrobial properties were eliminated when pH was adjusted to 6.5 for most of tested CFS while only Lb. plantarum CFS maintained their antimicrobial activity, which was lost when treated with proteinase K; according to these results, the antimicrobial activity of tested CFS can therefore be mainly attributed to organic acids. Antibacterial activity was significantly (p < 0.05) reduced between time zero and after 20 weeks of storage at three studied temperatures; the greatest reductions in antibacterial activity were observed at 35 °C. Antimicrobial activity against L. monocytogenes was less affected by time and temperature for the three most effective CFS. Lb. plantarum CFS was effective in reducing the microbial load of inoculated bacteria in beef, mainly S. Typhimurium and L. monocytogenes. Meat color differences were important in raw beef; while on grilled meat, changes were scarcely detected.

Antimicrobial Activity of Goat Colostrum Against Bacterial Strains Causing Food Poisoning Diseases

The study was aimed to investigate the antimicrobial activity of bacterial isolates L.plantarum 3CT7 and 20CT8 from goat colostrum. The antimicrobial activity of cell-free supernatant was tested using a well-diffusion method on several indicators: temperature, time of storage, and pH. Antimicrobial activity was recorded in both isolates at pH 2.0; 4.0; 6.0 and 8.0, temperature at 0, 50 and 100 oC, and in cold storage for 0, 15, 30, 45 and 60 days. L.plantarum 7CT3 and L.plantarum 20CT8 have a bigger zone of inhibition than that of Pseudomonas spp. as compared to other bacteria. Testing the cell-free activity was aimed to investigate the metabolite inhibition by L.plantarum. The isolates were capable of inhibiting all pathogenic bacteria in the experiment (S. thypimurium, E. coli, and S. aureus) as evidenced from the similar zone of inhibition from 15.83 to 16.06 mm. Isolates (L. plantarum 7CT3 dan 20CT8) exhibit inhibitory properties against S.thypimurium, S. aureus, Pseudomonas spp.. and L. monocytogenes at 0, 50 and 100oC. L.plantarum 7CT3 and L.plantarum 20CT8 exhibit antimicrobial activity during cold storage. Both isolates grown in the range of pH from 2 to 8 could inhibit S. thypimurium, E. coli, S. aureus and Pseudomonas spp. In general, the two isolates are the potential antimicrobial activity with broad ranges of pH, temperature and storage time.

Production of Bacteriocin-like Substances by &amp;lt;i&amp;gt;Bacillus&amp;lt;/i&amp;gt; Spp. JY-1 in Soy Whey

Soy whey is a by-product from the processing of soybean products, which is generally discarded and considered as waste. In recent years, a large number of bacteriocins produced by bacteria have been described. However, the production of bacteriocins in soy whey has not yet reported. Bacteriocin-like substance producing B. spp JY-1 was isolated from Chinese traditional fermented soybean (douchi) in previous study. In present study, the antimicrobial spectrum, and the effect of enzymes, pH and heat on the antibacterial activity of bacteriocin-like substance produced by B. spp JY-1 were evaluated. Then, the effects of supplement of carbon and nitrogen sources on the production of bacteriocin-like substances in soy whey were also investigated. Results obtained indicated that bacteriocin-like substance in cell-free supernatant of JY-1 exhibited broad inhibitory spectrum both against some food-borne pathogens. The bacteriocin-like substance JY-1 was sensitive to trypsin and pepsin, but stable between pH 2.0-10, and heat resistance (65-105°C). In addition, the production of bacteriocin-like substance JY-1 started at the early exphonential phase and reached its maximum at the stationary phase. The antimicrobial activity of cell-free supernatant of JY-1 cultured in soy whey was observed. The supplement of soluble starch or beef extract in soy whey yielded a higher production of bacteriocin-like substance. The results indicated that the bacteriocin-like substance JY-1 may be a potential candidate for alternative agent to control important food pathogens, and the soy whey has potential for production of bacteriocins.

Antimicrobial effect of selected lactic acid bacteria against microorganisms with decarboxylase activity

The main purpose of this study was to evaluate the antimicrobial activity of twenty-one bacteriocinogenic lactic acid bacteria (12 strains of Lactococcus lactis subsp. lactis, 4 strains of Lactobacillus gasseri, 3 strains of Lb. helveticus and 2 strains of Lb. acidophilus, LAB) against 28 Staphylococcus and 33 Enterococcus strains able to produce tyramine, putrescine, 2-phenylethylamine and cadaverine. The antimicrobial activity of cell-free supernatants (CFS) from tested LAB was examined by an agar-well diffusion assay. Nine out of twenty-one strains (33%) showed the inhibitory effect on tested enterococci and staphylococci, namely 9 strains of Lactococcus lactis subsp. lactis. The diameters of inhibition zones ranged between 7 mm and 14 mm. The biggest diameter of 14 mm inhibition was obtained with the CFS's from strains CCDM 670 and CCDM 731 on Enterococcus sp. E16 and E28. The cell-free supernatants from Lactococcus lactis subsp. lactis CCDM 71 and from Lactococcus lactis subsp. lactis CCDM 731 displayed the broadest antibacterial activity (52% inhibition of all tested strains). On the other hand, the cell-free supernatants from the screened Lactobacillus strains did not show any inhibitory effect on the tested Staphylococcus and Enterococcus strains. Nowadays, the great attention is given to the antibacterial substances produced by lactic acid bacteria. With the ability to produce a variety of metabolites displaying inhibitory effect, the LAB have great potential in biopreservation of food.

In vitro Characterization of Bacteriocin Produced by Lactic Acid Bacteria Isolated from Nem Chua, a Traditional Vietnamese Fermented Pork.

The aim of this study was to screen and In vitro characterize the properties of bacteriocin produced by lactic acid bacteria isolated from Vietnamese fermented pork (Nem chua). One hundred and fifty LAB were isolated from ten samples of Nem chua and screened for bacteriocin-producing lactic acid bacteria. Antimicrobial activity of bacteriocin was carried out by spot on lawn method against both gram positive and gram negative bacteria. One isolate, assigned as KL-1, produced bacteriocin and showed inhibitory activity against Lactobacillus sakei, Leuconostoc mesenteroides and Enterococcus faecalis. To characterize the bacteriocin-producing strain, optimum temperature, incubation period for maximum bacteriocin production and identification of bacteriocin-producing strain were determined. It was found that the optimum cultivation temperature of the strain to produce the maximum bacteriocin activity (12,800 AU/mL) was obtained at 30℃. Meanwhile, bacteriocin production at 6,400 AU/mL was found when culturing the strain at 37℃ and 42℃. The isolate KL-1 was identified as L. plantarum. Antimicrobial activity of cell-free supernatant was completely inhibited by proteolytic enzyme of trypsin, alpha-chymotrypsin and proteinase K. Bacteriocin activity was stable at high temperature up to 100℃ for 10 min and at 4℃ storage for 2 d. However, the longer heating at 100℃ and 4℃ storage, its activity was reduced.

Antimicrobial potential of Leuconostoc species against E. coli O157:H7 in ground meat

Ground beef is risky by foodborne pathogens such as E. coli O157:H7 due to the cross-contamination during grinding. The objective of this study was to evaluate the antagonistic activities of Leuconostoc species isolated from ground beef product in order to limit the growth of E. coli O157:H7. While Leuconostoc has been known as spoilage bacteria, the Leuconostoc isolates showed antimicrobial activity on foodborne pathogens such as E. coli O157:H7, Salmonella, Staphylococcus aureus, Listeria monocytogenes, and meat-spoilage bacteria Brochothrix thermosphacta. Antimicrobial activity of cell-free supernatant (CFS) was evaluated by heat, enzyme, and pH adjustment and antagonistic activity by cell competitive growth. In addition, CFS concentration was screened for the presence of organic acids for the antimicrobial properties. Regulation of virulence genes was investigated by inhibition of locus of enterocyte effacement expression by CFS. The result showed that Leuconostoc isolates inhibited the growth of E. coli O157:H7 by active antimicrobial agent including organic acids and the growth of background microorganisms, and E. coli O157:H7 in ground beef was inhibited with the supplement of the CFS.

Antimicrobial activity and safety evaluation of Enterococcus faecium KQ 2.6 isolated from peacock feces.

BackgroundThe objective of this paper was to study antimicrobial activity and safety of Enterococcus faecium KQ 2.6 (E. faecium KQ 2.6) isolated from peacock feces.MethodsAgar well diffusion method was adopted in antimicrobial activity assay. Disk diffusion test was used to determine the antibiotic resistance. The identification and virulence potential of E. faecium KQ 2.6 were investigated using PCR amplification.ResultsThe results indicated that cell free supernatant (CFS) of the strain had the good antimicrobial activity against selected gram-positive and gram-negative bacteria. The biochemical characteristics of antimicrobial substances were investigated. The results indicated that the antimicrobial substances were still active after treatment with catalase and proteinase, respectively. Moreover, the stability of antimicrobial substances did not change after heat treatment at 40, 50, 60, 70 and 80°C for 30 min, respectively. The activity of antimicrobial substances remained stable at 4 and −20°C after long time storage. The antimicrobial activity of CFS was compared with that of the buffer with similar strength and pH. The inhibitory zone of the buffer was apparently smaller than that of CFS, which meant that the acid in CFS was not the only factor that was contributed to antibacterial activity of CFS. The antibiotic resistance and virulence potential were evaluated using disk diffusion test and PCR amplification. The results showed that E. faecium KQ 2.6 did not harbor any tested virulence genes such as gelE, esp, asa1, cylA, efaA and hyl. It was susceptible to most of tested antibiotics except for vancomycin and polymyxin B.ConclusionE. faecium KQ 2.6 may be used as bio-preservative cultures for the production of fermented foods.

Examination of Lactic Acid Bacteria to Secretion of Bacteriocins.

IntroductionBacteriocins produced by lactic acid bacteria (LAB) have the potential to cover a very broad field of applications, including the food industry and the medical sector. In the food industry, bacteriocinogenic LAB strains can be used as starter cultures, co-cultures, and bioprotective cultures, which would be used to improve food quality and safety. In the medical sector, bacteriocins of probiotic LAB might play a role in interactions, which take place in human gastrointestinal tract, and contribute to gut health. The aim of this study was the examine the effect of LAB antimicrobial activity.MethodsLAB were isolated from different commercial and home made products, such as kazy and sour cream. To screen for bacteriocin producing LAB, we used an agar diffusion bioassay, described in a previous study by Dr. Yang, with three modifications in cell-free supernatant (CFS). First we had a clear supernatant, second we adjusted the CFS to pH 6.0 to eliminate acids antimicrobial effects, and third the CFS pH 6.0 was treated with catalase to exclude the action of H2O2 and confirm action of bacteriocin-like substances. Pathogenic S.marcescens, E. coli, S.aureus cultures were used as indicators.ResultsScreening of 95 strains of LAB through deferred antagonism to six indicator cultures showed that all of the selected strains had a high value of antibacterial activity. However, CFS of only 50 strains retained their antimicrobial activity, and 10 of them lost this activity in the second modification of CFS with pH 6.0 to test culture S.marcescens, which confirmed the acidic nature of antimicrobial activity of CFS. Lb.rhamnosus (P-1), Lb.fermentum (N-6), and Lc.lactis (7M) lost antibacterial activity in the presence of the catalase. All modifications of CFS of three strains: Lb.pentosus (16al), Lb.pentosus (P-2), and Pediococcusacidilactici (8) retained inhibitory activity to E.coli and S. aureus. Supernatants of only Lactococcusgarvieae (10a) and Pediococcusacidilactici (25) extracted from homemade meat food kazy (Karaganda) and sour cream (Astana), respectively retained antibacterial activity to all three indicator cultures.ConclusionThe antibacterial activity (pH 6.0, added catalase) of Lactococcusgarvieae (10a) and Pediococcusacidilactici (25) to S. marcescens, E. coli, and S.aureus indicates these strains as promising strains for further use in the preparation of bacteriocins.

The effects of metabolite molecules produced by drinking water-isolated bacteria on their single and multispecies biofilms

The elucidation of the mechanisms by which diverse species survive and interact in drinking water (DW) biofilm communities may allow the identification of new biofilm control strategies. The purpose of the present study was to investigate the effects of metabolite molecules produced by bacteria isolated from DW on biofilm formation. Six opportunistic bacteria, viz. Acinetobacter calcoaceticus, Burkholderia cepacia, Methylobacterium sp., Mycobacterium mucogenicum, Sphingomonas capsulata and Staphylococcus sp. isolated from a drinking water distribution systems (DWDS) were used to form single and multispecies biofilms in the presence and absence of crude cell-free supernatants produced by the partner bacteria. Biofilms were characterized in terms of mass and metabolic activity. Additionally, several physiological aspects regulating interspecies interactions (sessile growth rates, antimicrobial activity of cell-free supernatants, and production of iron chelators) were studied to identify bacterial species with biocontrol potential in DWDS. Biofilms of Methylobacterium sp. had the highest growth rate and M. mucogenicum biofilms the lowest. Only B. cepacia was able to produce extracellular iron-chelating molecules. A. calcoaceticus, B. cepacia, Methylobacterium sp. and M. mucogenicum biofilms were strongly inhibited by crude cell-free supernatants from the other bacteria. The crude cell-free supernatants of M. mucogenicum and S. capsulata demonstrated a high potential for inhibiting the growth of counterpart biofilms. Multispecies biofilm formation was strongly inhibited in the absence of A. calcoaceticus. Only crude cell-free supernatants produced by B. cepacia and A. calcoaceticus had no inhibitory effects on multispecies biofilm formation, while metabolite molecules of M. mucogenicum showed the most significant biocontrol potential.

Antimicrobial activity of Lactobacillus reuteri DPC16 supernatants against selected food borne pathogens

Lactobacillus reuteri DPC16 is a human-isolated strain recently patented in New Zealand. The antimicrobial activity of cell-free supernatants from different fermentation processes, with or without glycerol supplementation was studied. When grown in just MRS broth, the cultural supernatant significantly inhibited the growth of selected food-borne pathogens, possibly due to acidic effect as this activity was pH-dependent. The cell-free supernatants from secondary fermentation of DPC16 resting cells in glycerol-supplemented media have shown very different antimicrobial activities. A very potent antimicrobial activity gradually developed during the fermentation process which was observed only when growing in MRS-glycerol broth (such supernatant is denoted MRSg). This strong antimicrobial activity was pH-independent, dose-dependant and affected both Gram-negative and Gram-positive pathogens. Reuterin detected in MRSg is believed to be responsible for these activities. The susceptibility of the selected pathogens (grown to stationary phase) to MRSg was tested and found that exposure to MRSg for 180 min led to a significant reduction in cell viability in all pathogens. These results suggest that this is a reuterin-producing strain, which has potent antimicrobial activity against both Gram-negative and Gram-positive pathogens. These findings have indicated a clear potential of this novel strain in industrial applications.