Aspects related to the activity of the hexanic extract of Achyrocline satureioides on Paenibacillus larvae, a bacterial honey bee pathogen

PIMENTEL BETANCURT, DIANA; HEREDIA, ROMINA; PALETTI ROVEY MF; HUALLPA, C; OLIVA, MA DE LAS M

Congreso; APIMONDIA; 2023

Paenibacillus larvae is a spore-forming, Gram-positive bacterium that causes the devastating disease American foulbrood. This disease spreads rapidly, affecting the well-being of the hive and the apiary generating the considerable loss of this essential pollinating insect and contributing to the Colony collapse disorder (CCD). Currently, there is no cure for American foulbrood and beekeepers immediately act by burning contaminated hives.Plant extracts are proposed as an ecological, viable and acceptable alternative for the treatment of the disease in hives. Achyrocline satureioides is a plant native to southeastern part of South America. It is widely used for its pharmacological and antibacterial properties. Our previous findings show that the hexanic extract (HE) of this plant inhibits the growth of P. larvae at relatively low concentrations.This study investigates several hypotheses about how the HE of A. satureioides could act on P. larvae, by studying the effect of HE on bacterial growth, changes in P. larvae membrane by analysis of phospholipids, and fatty acids by GC-FID as well as the fluidity of P. larvae membrane and the changes in their morphology by electron transmission microscopy. HE had an inhibitory effect on the growth of the microorganism. P. larvae presented a high percentage of saturated acids compared to unsaturated ones. HE did not generate very visible changes in the membrane of P. larvae during the time cells were exposed to the extract under the assessed conditions neither did it have a negative effect on membrane fluidity. Bacterial cells treated with HE, exhibited multiple damages such as cell wall degradation, alteration of the membrane and loss of cytoplasmic content. Other effects such as deformed cells, polarization of the cytoplasmic content and more lysed cells were observed compared to the control at 72 h.The results suggested that HE from A. satureioides causes structural damage