Beneficial Bacteria and Plant Extracts Promote Honey Bee Health and Reduce Nosema ceranae Infection

The research aims to give new insights on the effect of administering selected bacterial strains, isolated from honey bee gut, and/or a commercial plant extract blend (HiveAlive®) on Nosema ceranae. Analyses were first performed under laboratory conditions such as different infective doses of N. ceranae, the effect of single strains and their mixture and the influence of pollen administration. Daily survival and feed consumption rate were recorded and pathogen development was analysed using qPCR and microscope counts. Biomarkers of immunity and physiological status were also evaluated for the different treatments tested using one bacterial strain, a mixture of all the bacteria and/or a plant extract blend as treatments. The results showed an increase of abaecin transcript levels in the midgut of the honey bees treated with the bacterial mixture and an increased expression of the protein vitellogenin in the haemolymph of honey bees treated with two separate bacterial strains (Bifidobacterium coryneforme and Apilactobacillus kunkeei). A significant effectiveness in reducing N. ceranae was shown by the bacterial mixture and the plant extract blend regardless of the composition of the diet. This bioactivity was seasonally linked. Quantitative PCR and microscope counts showed the reduction of N. ceranae under different experimental conditions. The antiparasitic efficacy of the treatments at field conditions was studied using a semi-field approach which was adapted from research on insecticides for the first time, to analyse antiparasitic activity against N. ceranae. The approach proved to be reliable and effective in validating data obtained in the laboratory. Both the mixture of beneficial bacteria and its association with Hive Alive® are effective in controlling the natural infection of N. ceranae in honey bee colonies.

Pathogens Detection in the Small Hive Beetle (Aethina tumida (Coleoptera: Nitidulidae))

Aethina tumida Murray is currently a worldwide emergent pest of Apis mellifera L. hives. Although the damaging effect on the colony stores and brood is well known, the possible role of these beetles as a disease carrier is not clear. This is the first report of DNA presence of the trypanosome honeybee parasite Lotmaria passim and Crithidia bombi, and the Apis mellifera filamentous virus (AmFV) in A. tumida. Further studies will be needed to determine if A. tumida is indeed a mechanical or biological vector of these pathogens.

Heat shock proteins in Varroa destructor exposed to heat stress and in-hive acaricides

Varroa destructor is one of the major pests that affect honeybees around the world. Chemical treatments are common to control varroosis, but mites possess biochemical adaptive mechanisms to resist these treatments, enabling them to survive. So far, no information is available regarding whether these pesticides can induce the expression of heat shock protein (Hsp) as a common protective mechanism against tissue damage. The aims of this study were to determine differences in heat shock tolerance between mites collected from brood combs and phoretic ones, and to examine patterns of protein expression of Hsp70 that occur in various populations of V. destructor after exposure to acaricides commonly employed in beekeeping, such as flumethrin, tau-fluvalinate and coumaphos. Curiously, mites obtained from brood cells were alive at 40 °C, unlike phoretic mites that reached 100% mortality, demonstrating differential thermo-tolerance. Heat treatment induced Hsp70 in mites 4 × more than in control mites and no differences in response were observed in phoretic versus cell-brood-obtained mites. Dose-response assays were carried out at increasing acaricide concentrations. Each population showed a different stress response to acaricides despite belonging to the same geographic region. In one of them, coumaphos acted as a hormetic stressor. Pyrethroids also induced Hsp70, but mite population seemed sensitive to this treatment. We concluded that Hsp70 could represent a robust biomarker for measuring exposure of V. destructor to thermal and chemical stress, depending on the acaricide class and interpopulation variability. This is relevant because it is the first time that stress response is analyzed in this biological model, providing new insight in host-parasite-xenobiotic interaction.

Lactobacillus kunkeei strains decreased the infection by honey bee pathogens Paenibacillus larvae and Nosema ceranae

Due to their social behaviour, honey bees can be infected by a wide range of pathogens including the microsporidia Nosema ceranae and the bacteria Paenibacillus larvae. The use of probiotics as food additives for the control or prevention of infectious diseases is a widely used approach to improve human and animal health. In this work, we generated a mixture of four Lactobacillus kunkeei strains isolated from the gut microbial community of bees, and evaluated its potential beneficial effect on larvae and adult bees. Its administration in controlled laboratory models was safe for larvae and bees; it did not affect the expression of immune-related genes and it was able to decrease the mortality associated to P. larvae infection in larvae and the counts of N. ceranae spores from adult honey bees. These promising results suggest that this beneficial microorganism's mixture may be an attractive strategy to improve bee health. Field studies are being carried out to evaluate its effect in naturally infected colonies.

Synergistic effect of surfactin from Bacillus subtilis C4 and Achyrocline satureioides extracts on the viability of Paenibacillus larvae

The aim of this work was to determine the in vitro effect of the mixture between the lipopeptide surfactin, synthesized by Bacillus subtilis C4 (strain isolated from honey) and the most active vegetal extract from Achyrocline satureioides, a traditional medicinal plant, on local strains of Paenibacillus larvae, the agent of American Foulbrood in honeybees. Five P. larvae strains isolated in Córdoba, Argentina, were phenotypically characterized. These and 12 other P. larvae strains from different regions of Argentina were analysed. The antimicrobial activities of the essential oil, hexane (HE) and benzene extracts from A. satureioides were assessed against P. larvae and the HE showed the highest anti-P. larvae activity. A combination of the biosurfactant surfactin, produced by B. subtilis C4, and the HE of A. satureioides revealed a synergistic action on P. larvae. The effective surfactin concentration in the mixture decreased from 32 to 1 μg ml(-1) and the HE concentration from 32 to 4 μg ml(-1), values similar or equal to minimal inhibitory concentrations observed for oxytetracycline. The fractional inhibitory concentration index confirmed synergism in 4 strains and partial synergism in one strain. The combination of surfactin synthesized by B. subtilis C4 and the HE from A. satureioides could be a natural alternative to help beekeepers to combat the American foulbrood agent P. larvae.

Evaluation of culture media for Paenibacillus larvae applied to studies of antimicrobial activity

This study was conducted to compare different liquid culture media for Paenibacillus larvae growth in order to find the best one to be used in studies on activity of antimicrobial substances, such as essential oils. P. larvae presented poor growth in usual broths such as Mueller-Hinton, commonly employed in antimicrobial activity assays. Growth in liquid media was evaluated using Paenibacillus larvae strains isolated from hives located in different geographical zones. The MYT medium (Mueller-Hinton broth, yeast extract and thiamine) was selected out of the eight liquid media analyzed, as it proved to be the most adequate due to its higher absorbance at 620 nm. The following mean values were obtained from the four P. larvae strains: 0.227 +/- 0.016 for the Cobo strain, 0.279 +/- 0.015 for La Plata strain, 0.758 +/- 0.020 for Mechongué strain and 0.244 +/- 0.0079 for Sierra de los Padres strain, respectively.

[Inhibition of Paenibacillus larvae employing a mixture of essential oils and thymol]

In vitro antimicrobial activity of a mixture of two essential oils and thymol against Paenibacillus larvae, causal agent of American Foulbrood (AFB), was evaluated. The essential oils were extracted from cinnamon (Cinnamomum zeylanicum) and thyme (Thymus vulgaris). The third component used, thymol, is the major component of the essential oil of thyme which contains 39.9% of thymol. Minimal inhibitory concentration (MIC) in Mueller-Hinton broth by the tube dilution method and minimal bactericide concentration (MBC) on MYPGP agar were evaluated. Thyme registered MIC values of 150-250 microg/ml and MBC values of 200-300 microg/ml, while the MIC and MBC values obtained for cinnamon were of 50-100 microg/ml and 100-125 microg/ml. Thymol showed similar MIC and MBC values of 100-150 microg/ml. No significant differences between the bacterial strains were detected, but significant differences between essential oils and thymol activity were registered (P<0,01). An inhibitory synergetic effect on AFB was observed reducing MIC and MBC values due to the use of a mixture of 62.5% of thyme, 12.5% of cinnamon and 25% of thymol.