The use of lactic acid bacteria (LAB) in the fermentation process to produce fermented foods has a long history. Furthermore, LAB are beneficial microorganisms known for their health-promoting characteristics. During fermentation, LAB have the capacity to produce significant amounts of bioactive substances, such as peptides, bacteriocins, lactic acid, exopolysaccharides (EPSs), enzymes, and others. Lactococcus lactis as one of the best-known and well-characterized species of LAB serves as a model organism for studying LAB. For a very long time, L. lactis has been used in milk fermentation, both in well-monitored industrial settings and on a small scale in traditional operations. Furthermore, L. lactis is a vital microorganism in the dairy food fermentation industry due to its role in acidification, flavor development, and the creation of various dairy products, including cheese, fermented butter, and others. The novelty of this review is the comprehensive and organized presentation of the main benefits of the use of L. lactis in milk fermentation processes including technological and safety features relevant for the dairy industry, probiotic potential, the ability to produce bioactive compounds (e.g., bacteriocins, GABA), and the recent development of such bacteria research methods like whole genome sequencing (WGS).

Safety is the most important criteria of any substance or microorganism applied in the food industry. The whole-genome sequencing (WGS) of an indigenous dairy isolate LL16 confirmed it to be Lactococcus lactis subsp. lactis with genome size 2,589,406 bp, 35.4% GC content, 246 subsystems, and 1 plasmid (repUS4). The Nextera XT library preparation kit was used to generate the DNA libraries, and the sequencing was carried out on an Illumina MiSeq platform. In silico analysis of L. lactis LL16 strain revealed non-pathogenicity and the absence of genes involved in transferable antimicrobial resistances, virulence, and formation of biogenic amines. One region in the L. lactis LL16 genome was identified as type III polyketide synthases (T3PKS) to produce putative bacteriocins lactococcin B, and enterolysin A. The probiotic and functional potential of L. lactis LL16 was investigated by the presence of genes involved in adhesion and colonization of the host’s intestines and tolerance to acid and bile, production of enzymes, amino acids, and B-group vitamins. Genes encoding the production of neurotransmitters serotonin and gamma-aminobutyric acid (GABA) were detected; however, L. lactis LL16 was able to produce only GABA during milk fermentation. These findings demonstrate a variety of positive features that support the use of L. lactis LL16 in the dairy sector as a functional strain with probiotic and GABA-producing properties.

Antimicrobial resistance was determined for 341 thermophilic Campylobacter jejuni isolates obtained from human clinical cases (n = 101), broiler products (n = 98), dairy cattle (n = 41) and wild birds (n = 101) with known multilocus sequence types (MLST) in Lithuania. The minimum inhibitory concentration (MIC) values for ciprofloxacin, tetracycline, gentamicin, ceftriaxone and erythromycin were determined with the agar dilution method. MIC values were compared with MLST types to find possible associations among isolation source, sequence type and resistance to antibiotics. The proportions of resistant strains were 94.2% (human), 95% (wild birds), 100% (broiler products) and 100% (dairy cattle) for one of the tested antibiotics. Most frequently, resistance to ciprofloxacin was observed (91.5%), followed by ceftriaxone with 60.4%, and tetracycline (37.8%). However only three C. jejuni strains were resistant to erythromycin (0.9%) and all tested thermophilic Campylobacter strains were sensitive to gentamicin. Most of the examined C. jejuni isolates (80.6%) showed resistance to at least one of three profiles: CIP+AXO (28.1%), TET+CIP+AXO (26.7%) and CIP (25.8%). Statistically significant differences in resistance to tetracycline were found between C. jejuni strains obtained from cattle (85.4%) and broiler products (64.3%) (P < 0.05). The majority (87.1%) of the tested strains from wild birds were resistant to ciprofloxacin (P < 0.05). The results showed that strains of novel ST’s showed significantly lower resistance to ceftriaxone (P < 0.05). The ST-21 (CC21) (78.8%) was identified with significantly higher multidrug resistance relatively to other tested ST’s in this study. Our results emphasize the high antimicrobial resistance of phylogenetically diverse C. jejuni strains isolated from different sources including specific genotypes of wild bird’s strains in Lithuania. The results support the opinion that not only broiler products but cattle and wild birds may be a reservoir of resistant C. jejuni and stipulate a risk of spread or resistant bacteria. There is increasing need for broad surveillance and control measures to track changes and pathways of antimicrobial resistance of C. jejuni in epidemiologically distinct populations.

The demand for healthy foods without artificial food additives is constantly increasing. Hence, natural food preservation methods using bioprotective cultures could be an alternative to chemical preservatives. Thus, the main purpose of this work was to screen the indigenous lactobacilli isolated from fermented cow milk for their safety and antifungal activity to select the safe strain with the strongest fungicidal properties for the development of bioprotective acid whey protein concentrate (AWPC) based fermentates and their coatings intended for fresh cheese quality maintenance. Therefore, 12 lactobacilli strains were isolated and identified from raw fermented cow milk as protective cultures. The safety of the stains was determined by applying antibiotic susceptibility, haemolytic and enzymatic evaluation. Only one strain, Lacticaseibacillus paracasei A11, met all safety requirements and demonstrated a broad spectrum of antifungal activity in vitro. The strain was cultivated in AWPC for 48 h and grew well (biomass yield 8 log₁₀ cfu mL⁻¹). L. paracasei A11 AWPC fermentate was used as a vehicle for protective culture in the development of pectin-AWPC-based edible coating. Both the fermentate and coating were tested for their antimicrobial properties on fresh acid-curd cheese. Coating with L. paracasei A11 strain reduced yeast and mould counts by 1.0–1.5 log₁₀ cfu mL⁻¹ (p ≤ 0.001) during cheese storage (14 days), simultaneously preserving its flavour and prolonging the shelf life for six days.

Recently, the number of reports on isolation of ciprofloxacin resistant Campylobacter jejuni has increased worldwide. The aim of this study was to determine the prevalence of resistance to ciprofloxacin and its genetic determinants among C. jejuni isolated from humans (n = 100), poultry products (n = 96) and wild birds (n = 96) in Lithuania. 91.4% of the C. jejuni isolates were phenotypically resistant to ciprofloxacin. DNA sequence analyses of the gyrA gene from 292 isolates revealed that a change in amino acid sequence, Thr86Ile, was the main substition conferring resistance to ciprofloxacin. This change was significantly associated with isolates from poultry products (P < 0.05) and humans (P < 0.05). A total of 26.7% of C. jejuni isolates from human (n = 47), poultry products (n = 30) and wild bird (n = 1), had a mutation from Ser at position 22, and six had an additional mutation from Ala at position 39. Eight isolates from poultry and two isolates from human, corresponding to 67.0% of isolates with MICs ≥128 μg/ml, showed missense mutations Thr86Ile (ACA → ATA) and Ser22Gly (AGT → GGT) together, whereas isolates without these mutations showed lower MIC values (from 4 to 64 μg/ml). Two hundred forty-five C. jejuni isolates showed one or more silent mutations, and 32.4% of examined isolates possessed six silent mutations. In addition to the ciprofloxacin resistant isolates harboring only Thr86Ile point mutation (110 isolates), the current study identified resistant isolates (n = 101) harboring additional point mutations (Ser22Gly, Ala39Ser, Arg48Lys, Thr85Ala Ala122Ser, Glu136Asp, Vall49Ile), and strains (n = 57) having only Glu136Asp point mutation. The study highlight the potential public health problem with elevated ciprofloxacin resistance in Campylobacters from poultry meat, wild birds and humans, and the need for extensive surveillance enabling to follow changes of antimicrobial resistance development in this species.