article · Heliyon
Twenty-three strains of Lactococcus lactis across three subspecies were isolated from raw cow milk to assess their probiotic and protective characteristics. The investigation evaluated their antibacterial activity against Staphylococcus aureus ATCC 29213, antioxidant properties, and profiles against 18 antibiotics. All strains exhibited antibacterial activity against the target pathogen, driven by nutrient competition and the production of active metabolites such as lactic acid, diacetyl, hydrogen peroxide, and proteins. Lactococcus lactis subsp. lactis showed the strongest inhibitory effects, led by strain Lc 26. In addition, all tested strains displayed moderate antioxidant activity ranging between roughly 11 percent and 26 percent. Antibiotic susceptibility testing confirmed that the strains remained sensitive to key therapeutic antibiotics, supporting their safety for potential use in food systems.
Staphylococcus aureus is a major cause of foodborne illness and clinical infection. Identifying naturally occurring lactic acid bacteria that inhibit this pathogen while offering antioxidant benefits presents opportunities for cleaner food preservation. Demonstrating that these milk-derived strains are sensitive to standard clinical antibiotics is an essential requirement for confirming they can be handled safely in food production without introducing hazardous resistance traits.
This early-stage laboratory research could enable dairy processors and starter culture producers to develop protective cultures or functional food additives targeting Staphylococcus aureus. Because the evaluations were conducted solely in laboratory culture media, the strains remain several stages away from commercial deployment, requiring food matrix validation, stability testing, and regulatory safety clearance before industrial use.
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BackgroundLactic acid bacteria (LAB) are utilized as a starter culture in the manufacturing of fermented dairy items, as a preservative for various food products, and as a probiotic. In our country, some research has been carried out, even if LAB plays a principal role in food preservation and improves the texture and taste of fermented foods, that is why we tried to evaluate their probiotic effect. The objective of this research was to determine the antibacterial activity of Lactococcus lactis (L. lactis) against Staphylococcus aureus (S. aureus) ATCC 29213, investigate their antioxidant activity, and characterize their sensitivity against 18 antibiotics.MethodsA total of 23 LAB (L. lactis subsp. cremoris, L. lactis subsp. Lactis diacetylactis, L. lactis subsp. lactis) were isolated from cow's raw milk. The antibacterial activity was performed using two techniques, competition for nutrients and a technique utilizing components nature, using the disk diffusion method. The sensitivity of the studied LAB to different antibiotics was tested on Man rogosa sharp (MRS) agar using commercial antibiotic disks. All strains of LAB were examined for their antioxidant activity. The antioxidant activity of L. lactis was tested by 2,2-diphenyl-1 picrylhydrazyl (DPPH).ResultsThe results showed that the MRS medium was more adapted than Muller Hinton Agar (MHA) to investigate the antibacterial activity of L. lactis against S. aureus ATCC 29213. Also, L. lactis exhibited a notable degree of antibacterial activity against S. aureus ATCC 29213. L. Lactis subsp. Lactis displayed higher antibacterial activities, followed by L. lactis ssp. lactis biovar. diacetylactis, and lastly, L. lactis ssp. cremoris against S. aureus ATCC 29213. Lc 26 among all strains of L. lactis showed a high potential antibacterial activity reaching 40±3 mm against S. aureus ATCC 29213. All strains of L. lactis showed a slightly moderate antioxidant activity (10.56±1.28%-26.29±0.05%). The results of the antibiotic resistance test indicate that all strains of L. lactis were resistant to cefotaxime, sulfamethoxazole-trimethoprim, and streptomycin and were sensitive to Ampicillin, Amoxicillin, Penicillin G, Teicoplanin, Vancomycin, Gentamicin 500, Tetracycline, and Chloramphenicol. These test results indicate that this strain falls within the criteria of not posing any harmful effects on human health. The important antibacterial properties recorded for all L. Lactis strains were derived from the production of antibacterial active metabolites, such as protein, diacetyl, hydrogen peroxide, and lactic acid, together with the fight for nutrients.ConclusionThis study suggests that the strains of L. lactis could be added as an antibacterial agent against S. aureus ATCC 29213 and can provide an important nutritional property for their antioxidant potential.
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DOI: 10.1016/j.heliyon.2024.e31957
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