Bacterial resistance is a considerable public health risk, with projections of up to 10 million deaths per year by 2050. Resistant Staphylococcus aureus is one of the main multidrug-resistant hospital pathogens. Due to the low efficacy of many antimicrobials, there is growing interest in natural alternatives, such as pomegranate leaf extract ( Punica granatum ), which is rich in antimicrobial compounds such as punicalagin, ellagic acid, and tannins. To evaluate the antimicrobial activity of the hydroalcoholic extract of pomegranate leaf (HPE) against one sensitive strain ( S. aureus ATCC 33591) and nine resistant strains (ATCC 25904 and eight clinical strains – Ethics approval: CAAE 32572820.6.0000.5133). Leaves of P. granatum were collected, macerated in hydroalcoholic solution (50%), filtered, evaporated, and lyophilized. The eight clinical strains were tested for susceptibility with 18 antimicrobials. Minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) assays were performed using broth microdilution in Mueller-Hinton broth, with HPE concentrations ranging from 1000 to 7.8 μg/mL. Azithromycin (40 μg/mL) was used as a control. Inocula (5 × 10⁴ CFU/well) were prepared according to the 0.5 McFarland standard. Plates were incubated at 37°C for 24 h, and the MIC was defined as the lowest concentration visually inhibiting growth. For the MBC, 10 μL from wells without growth were plated on BHI agar. All tested strains were resistant (R) to benzylpenicillin and oxacillin, and most were resistant to clindamycin and erythromycin. Some showed intermediate susceptibility or resistance to rifampicin. Half of the strains were resistant to levofloxacin. Only one strain was resistant to trimethoprim/sulfamethoxazole, nitrofurantoin, and ciprofloxacin. HPE showed a mean MIC of 500 μg/mL with activity against four strains, including three resistant to at least one antimicrobial. It demonstrated microbiostatic action for four strains at the tested concentrations. The data indicate the promising potential of HPE as a microbiostatic agent against S. aureus , reinforcing the importance of investigating higher concentrations and the development of natural therapeutic formulations against resistant strains.
Martins et al. (Sun,) studied this question.