https://doi.org/10.17113/ftb.64.01.26.9194

Article in press

Chemical Characterization and Antibacterial Activity of Royal Jelly Against Multidrug-Resistant Pathogens

Mirna Mrkonjić Fuka^1*, Irina Tanuwidjaja¹, Valentina Odorčić¹, Slaven Jurić², Igor Jerković^3,4, Nikolina Udiković-Kolić⁵, Marko Vinceković² and Lidija Svečnjak⁶

¹Department Microbiology, Faculty of Agriculture, University of Zagreb, Svetošimunska 25, 10000 Zagreb, Croatia

²Department of Chemistry, Faculty of Agriculture, University of Zagreb, Svetošimunska 25, 10000, Zagreb, Croatia

³Department of Organic Chemistry, Faculty of Chemistry and Technology, University of Split, Ruđera Boškovića 35, 21000 Split, Croatia

⁴Mediterranean Institute for Life Sciences, University of Split, Meštrovićevo šetalište 45, 21000 Split, Croatia

⁵Division for Marine and Environmental Research, Ruđer Bošković Institute, Bijenička 54 10000 Zagreb, Croatia

⁶Department of Fisheries, Apiculture, Wildlife Management and Special Zoology, Faculty of Agriculture, University of Zagreb, Svetošimunska 25, 10000 Zagreb, Croatia

Copyright © 2024 This is a Diamond Open Access article published under CC-BY licence. Copyright remains with the authors, who grant third parties the unrestricted right to use, copy, distribute and reproduce the article as long as the original author(s) and source are acknowledged.

Article history:

Received: 14 May 2025

Accepted: 13 January 2026

Keywords:

multidrug-resistant bacteria; royal jelly; antibacterial activity; gas chromatography–mass spectrometry (GC-MS); Fourier-transform infrared (FTIR) spectroscopy; antioxidant capacity and bioactive compounds

Summary:

Research background. Given the known antibacterial properties of royal jelly (RJ), we hypothesized that RJ could inhibit priority multidrug-resistant (MDR) bacteria, including different strains of vancomycin-resistant Enterococcus faecium (VRE), methicillin-resistant Staphylococcus aureus (MRSA), carbapenem-resistant Klebsiella pneumoniae (CRKP), and Acinetobacter baumannii (CRAB). We further proposed that RJs antibacterial efficacy may be influenced by its chemical composition and by the inter- and intraspecies variability among MDR pathogens.

Experimental approach. RJ samples were collected from five beekeepers (RJ1–RJ5) in Mediterranean and continental regions of Croatia. Chemical profiling was performed using solid-phase microextraction gas chromatography–mass spectrometry (HS-SPME/GC-MS), Fourier-transform infrared (FTIR) spectroscopy, along with separate assays to measure antioxidant capacity (ABTS) and quantify the content of bioactive compounds. Antibacterial activity was assessed by agar well diffusion assay and by determining minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) against 20 MDR strains of VRE, MRSA, CRKP and CRAB, selected from 85 isolates using rep-PCR genotyping. MDR status was confirmed through standard susceptibility testing.

Results and conclusions. All RJ samples showed strong antioxidant activity and high levels of bioactive compounds, with RJ1 consistently exhibiting the highest content of ABTS, polyphenols, flavonoids, and proteins. FTIR analysis revealed variation in carbohydrate and lipid composition among samples, while protein content remained relatively uniform, and indicated the highest concentrations of sugars, lipids, and proteins in RJ1. GC-MS identified octanoic acid (48.09–83.07 %) as the predominant volatile compound, particularly abundant in RJ1 and RJ4. Despite some variability in chemical profiles, both chemical composition and antibacterial activity were comparable between samples from Mediterranean and continental regions. All RJ samples inhibited MDR bacteria, suggesting a potential synergistic effect of crude RJs, with inhibition zones ranging from 11.8 mm (CRKP) to 16.8 mm (MRSA). A. baumannii was most susceptible (MIC/MBC=27.2 µg/mL), while E. faecium was the most resistant (MIC=96.6 µg/mL, MBC=126.4 µg/mL). Beyond interspecies differences, pronounced strain-level variability in antibacterial response was also observed.

Novelty and scientific contribution. This is the first study to simultaneously evaluate RJ’s antibacterial activity against multiple strains of clinically relevant MDR pathogens alongside comprehensive chemical profiling. Importantly, it reveals for the first time that RJ’s efficacy varies not only between species but also among strains within the same species, emphasizing the need to consider strain-level differences in future assessments.