Lactiplantibacillus plantarum, one of lactic acid bacteria (LAB), is found in various foods, including dairy products, meat, and vegetables, and most of these bacteria offer beneficial effects to humans and animals as potential probiotics with broad-spectrum antimicrobial activities. The aim of this study was evaluating the antibacterial efficacy of L. plantarum against some foodborne bacteria isolated from dairy products. This research involved 34 dairy products, including local and imported milk, cheese, and yogurt sold locally in Baghdad province, Iraq, during May 2022. For the isolation of L. plantarum, a special medium called MRS (de Man Rogosa and Sharpe) was applied. Colonies were purified and identified by routine bacteriological methods, Vitek2 system, and confirmed by the polymerase chain reaction (PCR) targeting the 16S rRNA gene followed by the amplicon sequencing. Other aerobic bacteria contaminating dairy products were also isolated onto sterile selective media specific for each microorganism, and the isolates were identified by routine diagnostics tests followed by verification with Vitek2 system. Then, the culture supernatant of L. plantarum was tested for its antagonistic activity toward foodborne bacteria by the use of agar well diffusion assay. The findings showed the isolation of 2 L. plantarum, 3 Pseudomonas aeruginosa, 4 Escherichia coli, one isolate of Bacillus subtilis, and another Staphylococcus hominis. The filtered supernatant of L. plantarum was significantly efficient in inhibiting the growth of the above bacteria. Each of E. coli and B. subtilis revealed zones of inhibition of 36 and 38 mm in diameter, respectively, while P. aeruginosa and S. hominis had inhibition zones diameters of 27 and 29 mm, respectively. This suggests that the L. plantarum supernatant possesses a broad-spectrum activity against foodborne bacteria. To conclude, locally made dairy products can hold different contaminating bacteria, which can be eliminated by using probiotics, such as L. plantarum, to avoid foodborne diseases onset.
