# Functional and Antimicrobial Properties of Propolis from Different Areas of Romania
## 4 Discussion
[61], who reported significant variability in antimicrobial potency based on these factors. The response of _L. monocytogenes_ to propolis extracts shows that chemical diversity affects bioactivity [62]. C1 showed the strongest inhibitory effect, while A, C2, and S were less active. H was the least active. Gram-negative bacteria were less susceptible overall, as observed in previous studies [20; 60]. The authors attributed this to the structural barriers of Gram-negative bacteria, particularly their outer membrane. For _S. enterica_ ATCC 25928, the A and C2 extracts were observed to exert the greatest inhibitory effect, while extract H demonstrated the least activity. Similar findings were reported by [PERSON] [62]. Propositions showed the greatest activity against _K. pneumoniae_ with extract S, with an inhibition halo of 7.2 mm, which is lower than the 18 mm reported by [PERSON] et al. [63]. The moderate inhibition observed in this study highlights the need to optimise extraction methodologies to enhance efficacy against this pathogen. The A and C2 extracts showed the most notable activity against _P. aeruginosa_, with inhibition zones of 11.5 and 11.1 mm. [PERSON] et al. [58] reported comparable outcomes with inhibition zones of \(\sim\)12 mm. The effects against _P. aeruginosa_ are consistent with the bacterium's resistance mechanisms. _E. coli_ inhibition zones were uniform across extracts, except for S and C2. These findings align with those of [PERSON] and [PERSON] [13] and [PERSON] et al. [20]. _A. baumannii_ was most inhibited by extract S and least inhibited by H extract. Similarly, [PERSON] et al. [63] reported inhibition zones of 16 mm, underscoring strain-to-strain variability. The antifungal activity against _C. albicans_ demonstrated the highest inhibition zones for C1 and A, while extract S exhibited the lowest activity. These findings are in accordance with those reported by [PERSON] et al. [64]. The MIC results for the five propolis extracts show variability in antimicrobial efficacy across different bacterial strains; Gram-positive and Gram-negative bacteria show significant variability, as documented in the literature. The discrepancies are likely due to the chemical composition of the extracts and the bacterial target. Among Gram-positive bacteria, _S. aureus_ showed the highest sensitivity, with extract C2 exhibiting an MIC of 0.25 mg/mL. This aligns with the findings of [PERSON] et al. [65], who reported a similar MIC of 0.2 mg/mL. [PERSON] et al. [66] noted lower values ranging from 62.5 to 125 mg/mL for red propolis. Alternatively, [PERSON] et al. [63] reported higher MICs between 1500 and 2500 mg/mL, reflecting strain variability. MRSA displayed reduced sensitivity, with extract C1 showing a MIC of 0.59 mg/mL. This value is higher than the MIC range of 80 to 100 mg/mL reported by [PERSON] et al. [67] but is within the upper limit reported by [PERSON] et al. [68], who documented values up to 1.25%. Against _E. faecalis_, extract C1 exhibited the greatest efficacy with a MIC of 0.75 mg/mL. This value is higher than those reported by [PERSON] et al. [69], who observed values between 0.12 and 0.25 mg/mL, and [PERSON] et al. [70], who documented MICs ranging from 14.0 to 210.0 mg/mL, likely reflecting differences in extraction methods, chemical composition, or bacterial strain sensitivity. For _L. monocytogenes_, extract C1 was the most potent with an MIC of 0.50 mg/mL, consistent with [PERSON] et al. [65], who observed 0.6 mg/mL for _L. innocua_. Extract H, the least effective sample, displayed a MIC of 5.63 mg/mL. In contrast to the observed efficacy of the propolis extracts against Gram-positive bacteria, the activity against Gram-negative bacteria was generally less pronounced, consistent with the established structural resistance of Gram-negative bacteria due to the presence of an outer membrane [71]. The extract C2 showed the highest efficacy against _E. coli_ (0.78 mg/mL), while H showed the weakest (11.25 mg/mL); results that align with previous studies [72; 73].