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The antibacterial activity of four bacterial standard strains that are naturally encountered in humans and animals was investigated by using bioactive compounds from commercial essential oils of Juniperus communis that were collected from the Western Romanian Carpathians. The Juniper communis essential oils, volatile compounds, were recognized through the GC–MS methodology by comparing identified spectra with those held in the NIST 02, Wiley 275 library. The ratio of each component was calculated based on the peak areas of the GC, without utilizing correction factors. The CLSI standardized micro-dilution was used to determine antimicrobial activity, employing 10−3 dilutions of fresh culture, with inoculums equivalent to a standard of 0.5 McFarland being prepared for testing. Four bacterial strains, Staphylococcus aureus (ATCC 25923), Escherichia coli (ATCC 25922), Pseudomonas aeruginosa (ATCC 27853), and Streptococcus pyogenes (ATCC 19615), were investigated, using 96-well micro-dilution plates. Over each micro-dilution well, the essential oils were poured, introducing gradually 2, 4, 8, and 10 µL/well, respectively. The results were expressed as ±SEM and analyzed by one-way ANOVA with Bonferroni’s multiple comparison test, considering the differences statistically provided when p < 0.05 or lower. The juniper essential oil originating from the Western Romanian Carpathians is rich in four main volatile compounds: β-pinene (34.02%), 1α-pinene (30.43%), p-cymol (20.25%), and β-myrcene (10.20%). The juniper communis essential oil reduced bacterial density for all four strains tested, but compared to Gram-negative bacteria, in our case; a considerably higher antibacterial effectiveness was detected for Gram-positives, with peak reduction of Staphylococcus aureus, recommending the Romanian essential oil as a beneficial antibacterial resource. more...