In vitro inhibition of Paenibacillus larvae by different extracts and pure compounds from Flourensia spp

Abstract

Paenibacillus larvae, a sporulating Gram-positive bacterium, is the etiological agent of American foulbrood disease in Apis mellifera L. Plant extracts could be a natural alternative to control this pathology. The current study assessed the anti-. P. larvae effect of extracts and pure principal products from the Flourensia genus: F. riparia, F. fiebrigii and F. tortuosa. Their inhibitory effect was assayed against different P. larvae strains according to the disk diffusion technique and subsequently, the minimal inhibitory concentrations (MIC) of extracts by the agar dilution method was determined. Furthermore, toxicity of the most effective extracts against P. larvae was tested in bees. All extracts inhibited growth of the different P. larvae strains assayed. However, the magnitude of the antagonistic effect depended on the chemical nature of the extract and the P. larvae strain. Chloroform extracts (CE) and ethyl ether extracts (ETE) from F. riparia and ETE from F. fiebrigii were most active against P. larvae Azul, the most sensitive indicator strain with MIC values of 250. ppm (CE) and 2000. ppm (ETE) for F. riparia, and 2500. ppm (ETE) for F. fiebrigii. Hexane extracts from the three species did not present any significant inhibitory effect. These results would indicate that one or some of the more polar compounds would cause inhibition of this pathogen. Toxicity assays demonstrated that even the highest concentrations assayed (125,000. ppm) did not show lethal effects on exposed bees during in vitro conditions. © 2013 Elsevier B.V.