The present investigation was done to study the effects of Lactococcus lactis (L. lactis) subsp. lactis on the shelf life of the vacuum-packaged Oncorhynchus mykiss. Fish fillets were prepared and divided into 5 different treatment groups including control (distilled water), 2% and 4% supernatant, and 106 CFU/g L. lactis subspecies lactis. The pH, Thiobarbituric Acid Reactive Substances (TBARS), Total volatile Nitrogen (TVN), and Peroxide Value (PV) of the fillets were determined on days 0, 5, 10, and 15 while maintained at 4˚C. Protein expression and destruction were analyzed using the SDS-PAGE. The organoleptic assessment was done using five expert sensory panelists. Contents of TBARS, TVN, pH, and PV were increased throughout the storage period (P <0.05). An increase in the concentration of supernatant caused a significant decrease in the content of TBARS, TVN, pH, and PV (P <0.05). The highest and lowest contents of TBARS, TVN, pH and PV on 15th day were belonged to the control (3.367±0.04 mg MDA/kg) and pure bacteria (0.70±0.02 mg MDA/kg), control (87.20±6.40 mg/100g) and 4% supernatant (40.79±0.61 mg/100g), pure bacteria (6.23±0.04) and 4% supernatant (5.44±0.07) and control (12.22±0.01 meq/kg) and 4% supernatant (3.08±0.06 meq/kg) groups, respectively. Protein destruction was lower in the fillet samples treated with pure bacteria and 4% supernatant. The highest scores of the odor, flavor, texture, and color were obtained for fillets treated with 4% supernatant, pure bacteria, pure bacteria, and 4% supernatant and pure bacteria, respectively. The results revealed that treating O. mykiss fillets with 4% supernatant and 106 CFU/g of pure L. lactis subsp. lactis can extend the shelf life of O. mykiss fillets.

Mucosal surfaces of the body provide a universal entry portal for all known and emerging infectious pathogenic microbes. Therefore, it seems that special vaccination strategies are needed for vaccines that can hinder the entry capability of pathogenic microbes through the mucosal surfaces. Lactic acid bacteria are widely used in the food industry and are presently applied as delivery vehicles in many biological investigations. Among these bacteria, Lactococcus lactis is considered as a promising candidate for mucosal live vaccines to be used as an antigen delivery vector. This is an attractive alternative and a safer vaccination strategy against the pathogens, compared to other conventional methods. In this review, we summarized the applications of L. lactis as a mucosal vector of vaccine delivery for heterologous expression of proteins and its applications in biotechnology.

Needle free vaccines have a several advantages and very attractive way for vaccination. In a body, mucosal surfaces provide a universal entry portal for all the known and emerging infectious pathogenic microbes. Therefore, it seems, vaccination strategies need to be reorganized for vaccines that are hindering the entry capability of pathogenic microbes through mucosal surfaces. Lactic acid Bacteria (LAB) are widely used in the food industry and at the present, used as delivery vehicles for biological investigations. In this review, we summarized the Results of several studies which Lactococcus lactis (L. lactis) used as a live vector for vaccines. These bacteria are considered as promising candidates for heterologous expression of proteins and biotechnological usage. LAB are considered as promising candidates for heterologous expression of proteins and biotechnological usage. The results showed that these bacteria have an ability to deliver antigen to immune system. Therefore, developing mucosal live vaccines using lactic acid bacterium, L. lactis, as an antigen delivery vector, is an attractive alternative choice and a safer vaccination strategy against pathogens.

Nisin is the first FDA-approved food preservative produced by Lactococcus lactis at industrial scale. The negative effect of lactic acid produced by metabolism of Lactococcus lactis subsp. lactis, on nisin production, was removed by co-culture of Lactococcus lactis with Yarrowia lipolytica yeast. In the present study, the co-culture of Lactococcus lactis subsp. lactis and Yarrowia lipolyticawas performed for the first time inmolasses-based medium at 30° C, pH 6, 100 rpm, 0. 15 vvm was applied in a laboratory scale bioreactor. Nisin production was measured as 920 IU/mL. The results showed that co-culture fermentation increased biomass and nisin production up to 63% and 78%, respectively. Other factors such as extracellular proteolytic activity of the yeast should be taken into consideration, which in turn make the culture nutrients more available to the bacterium.

This study aimed to investigate the phenotypic and genotypic patterns of antibiotic resistance in two potential probiotic lactic acid bacteria, Lactococcus lactis subsp. cremoris (NABRII64 and NABRII66) isolated from the rainbow trout intestine. The phenotypic susceptibility pattern of the strains was studied based on the Minimum Inhibitory Concentration (MIC) of eight most commonly used antibiotics in medicine and veterinary including ampicillin, kanamycin, gentamicin, streptomycin, erythromycin, clindamycin, tetracycline and chloramphenicol. After comparing the MICs with standard values recommended by European Food Safety Authority (EFSA), the nature of the phenotypic resistance observed in bacterial strains was investigated by polymerase chain reaction (PCR) through plasmid DNA extraction. The results of phenotypic evaluation indicated the tetracycline resistance in both bacterial strains (MIC<4mg/L). Genotyping of antibiotic resistance genes including tet (S), tet (L), tet (M), tet (O), tet (W) and tet (K) indicated the presence of tet (S) and tet (M) resistance genes in plasmid DNA of both bacterial strains. These results exhibited the acquired resistance and the presence of two tetracycline resistance genes in the plasmid DNA of two bacterial strains, NABRII64 and NABRII66. However, further studies are required to understand the nature of the acquired resistance mechanism in the future.

This study evaluated the antimicrobial activities of two lactic acid bacteria, Lactococcus lactis subsp. lactis I23 and Lactococcus lactis subsp. lactis E91, against Brochothrix thermosphacta in pork meat during storage at ambient temperature (30oC) for 168 h. The LAB strains and the spoilage organism were inoculated on fresh pork samples at 1´106 CFUg-1. Results showed about 3 log reduction in the spoilage organism in LAB inoculated samples after 48 h of storage. The spoilage organism showed susceptibility to antimicrobial action of Lactococcus lactis subsp. lactis I23. There was reduction in the count of Enterobacteriaceae, and no detection of Staphylococcus in the samples inoculated with Lactococcus lactis subsp. lactis I23 strain. Count of Staphylococcus was between 2.04 and 3.11 log in the untreated samples, and detection was not observed until 72 h of storage. Conclusively, growth of Brochothrix thermosphacta was effectively controlled by nisin producing Lactococcus lactis subsp. lactis I23 in fresh pork meat and this could enhance the shelf life of the product.