Abstract
American foulbrood (AFB) is a disease affecting the larva of Apis mellifera. The etiological agent is Paenibacillus larvae, which releases metalloproteases involved in the degradation of larval tissues. Through quorum sensing (QS) mechanism, bacteria are able to activate specific genes such as virulence factors. The exoproteases regulation of P. larvae could be associated with QS. A promising mechanism of AFB control is to block QS mechanism with essential oils (EO). The aim of this study was to investigate the potential presence of QS signals in the regulation of P. larvae proteases and the effect of seven EOs on the exoproteases activity of P. larvae. From growth curves and evaluation of the presence of proteases by milk agar plates assay, it was observed protease activity during the late exponential phase of growth. Early production of protease activity (15 hours earlier than control) was observed when a low density culture was incubated with late exponential spent medium (SM) suggesting the presence of factor(s) inducing this activity. SM was obtained by the ultrafiltration of P. larvae cultures on late growth phase and was free of proteases. Proteolytic activity was quantified on P. larvae cultures in presence of sublethal concentration of EO by azocasein method. The EOs, except S. chilensis EO, reduced significantly protease activity (more than 50%). We report for the first time evidence on the possible role of QS on P. larvae and the antiproteolytic activity of EOs (except for S. chilensis) on exoproteases, an interesting therapeutic strategy to control AFB.
Highlights
American Foulbrood (AFB) is considered the most serious illness plaguing apiculture with a nearly cosmopolitan distribution
We report for the first time evidence on the possible role of quorum sensing (QS) on P. larvae and the antiproteolytic activity of essential oils (EO) on exoproteases, an interesting therapeutic strategy to control American foulbrood (AFB)
P. larvae low density cultures were suspended in fresh medium or in a cell-free culture medium obtained from a filtration of a culture of cells grown to late exponential phase (OD600 = 2.5) (SM) and the time course of extracellular protease activity was examined
Summary
American Foulbrood (AFB) is considered the most serious illness plaguing apiculture with a nearly cosmopolitan distribution It is a highly contagious disease affecting the larval stage in the development of honey bees (Apis mellifera L.). Antúnez et al (2009, 2010, 2011a,b) determined that P. larvae produces and secretes different proteins with proteolytic activity during vegetative replication, such as metalloproteases and enolase. These proteins are produced within the cell and secreted into the external medium, where they remain on the surface of the spores producing an immune response on A. mellifera and. It has been proposed that metalloproteases released by P. larvae are involved in the inhibition of the immune system through the degradation of antibacterial polypeptides and in the degradation of larval tissues
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