Evaluation of some essential oils for the control and prevention of American Foulbrood disease in honey bees

American foulbrood is a dangerous world-wide spread disease of honey bees caused by the Paenibacillus larvae bacterium. Antibiotic treatments are less effective and leave residues in bee products. It is therefore necessary to find an alternative, especially using natural ingredients such as plant essential oils, probiotics, fatty or organic acids. Two strains of P. larvae were used for this study: CCM 4488, a strain from the Czech collection of micro-organisms and a Slovak field strain which was isolated from infected bee combs and characterized on the basis of biochemical properties. Plant essential oils of sage (Salvia officinalis), anise (Pimpinella anisum), oregano (Origanum vulgare), caraway (Carum carvi), thyme (Thymus vulgaris), rosemary (Rosmarinum officinalis), clove (Syzygium aromaticum), camomile (Chamomilla recutita) and fennel (Foeniculum vulgare) were used for the testing of the inhibitory activity against P. larvae. Essential oils at amounts of 5 µl and 10 µl were applied to sterile discs on MYPGP agar; inhibition zone diameters were measured after 24-h incubation at 37 °C. The strongest inhibitory activity against both P. larvae strains was noted in case of the essential oils from oregano, thyme and clove; essential oils from camomile, rosemary and fennel showed no or weak antibacterial activity. Medium strong inhibition activity was recorded in case of previously untested essential oil from Carum carvi. There was a difference in sensitivity of both tested strains to essential oils. Our study confirmed that some essential oils can be used in the prevention of American foulbrood but further experiments aimed at their influence on physiological intestinal microflora of honey bees must be performed.

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Inhibitory action of essential oils against proteases activity of Paenibacillus larvae, the etiological agent of American Foulbrood disease

Spanish Journal of Agricultural Research ◽

10.5424/sjar/2017154-10785 ◽

2018 ◽

Vol 15 (4) ◽

pp. e0504 ◽

Cited By ~ 2

Author(s):

María C. Pellegrini ◽

Lucía Zalazar ◽

Sandra R. Fuselli ◽

Alejandra G. Ponce

Keyword(s):

Essential Oils ◽

Protease Activity ◽

Growth Curves ◽

Sublethal Concentration ◽

Etiological Agent ◽

Paenibacillus Larvae ◽

American Foulbrood ◽

Early Production ◽

American Foulbrood Disease ◽

Antiproteolytic Activity

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.

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