Evaluation of antimicrobial activity of Pine natural extracts against Agri- and Food-related pathogenic bacteria

The natural extracts derived from Pine (Pinus halepensis, region Attica, Greece) needles, male cones, and pollen mixed with male cones, were prepared following a green procedure at all stages, using environmentally friendly methods and safe solvents. Seventeen bacterial strains, relevant to agriculture and food, were cultured under optimal conditions. Antibacterial activity was assessed using agar well diffusion to determine inhibition zones followed by broth microdilution method to determine the minimum inhibitory concentrations (MICs) and minimum bactericidal concentrations (MBCs). The highest inhibition zones were observed for pollen mixed with male cones extract against Listeria monocytogenes, while the lowest MIC values were recorded for pine needles extract against Staphylococcus aureus (7.50 ng/mL). The lowest MBC values were observed from the pollen mixed with male cones extract (0.35 mg/mL) against Bacillus cereus. Notably, the pine needles extract was showed antibacterial activity with MIC and MBC values ranging from 7.50 ng/mL - 7.69 mg/mL and 0.48 – 30.75 mg/mL, respectively against Escherichia coli, Vibrio harveyii, Staphylococcus epidermidis, S. aureus, L. monocytogenes, B. cereus, and Agrobacterium tumefaciens. Significant antibacterial activity was recorded for the pine male cones with pollen extract with MIC and MBC values ranging from 0.02 - 22.4 mg/mL and 0.35 – 22.4 mg/mL, respectively against S. aureus, L. monocytogenes, and B. cereus. The pine male cones extract inhibited B. cereus, L. monocytogenes, and S. aureus with MIC values ranging from 3.6 -14 mg/mL, though MBC values were not detected. The extracts show minimal antimicrobial activity against Pseudomonas aeruginosa, Serratia marcescens, Yersinia enterocolitica, Klebsiella aerogenes, Salmonella enterica, and Salmonella typhimurium. Notably, Citrobacter freundii, Klebsiella oxytoca, Serratia liquefaciens, and Citrobacter sakazakii exhibited resistance to all tested extracts. These findings suggest the potential of natural extracts, especially those from pine needles, as antimicrobial agents in the agricultural and food sectors.