Natural compounds and extract for the control of American foulbrood

American foulbrood (AFB) is a serious spreading worldwide disease of honeybees caused by the spore-forming, Gram-positive bacterium Paenibacillus larvae. In most European countries, AFB-affected colonies are destroyed by burning the hives and treatment with antibiotics is legally banned. In many countries, where antibiotic treatment is a common practice to suppress the clinical outbreak, resistance becomes a concern. Antimicrobial natural products may provide a safe and acceptable alternative in prevention and combat of AFB.

In total, 27 natural compounds of various chemical classes and 22 extracts (methanol-dichlormethane, 1:1) were tested in vitro against three strains of P. larvae (ATCC 9545 and two isolates), using the broth microdilution method [1], medium MYPGP, concentration range starting from 64µg/ml. Their selection was based on previously reported antimicrobial properties, ethno-pharmacological use and commercial availability. Antimicrobial activity was expressed as minimum inhibitory concentration (MIC).

Sanguinarine showed highest activity (MIC 4µg/ml) against all strains, followed by thymoquinone and nordihydroguaiaretic acid (MIC 4–32µg/ml). Among the extracts, common hop (Humulus lupulus L.) and myrtle (Myrtus communis L.) are the most prospective (MIC 2–4µg/ml) and are considered for follow-up toxicological and in-vivo experiments.

Acknowledgements: This research was supported by grant NAZV 72144 and CIGA 20082012.

References: 1. Jorgensen J.H., Turnidge J.D. (1999) Manual of Clinical Microbiology. ASM Press. Washington, DC