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.

American foulbrood is a bacterial disease of worldwide distribution that affects larvae of the honeybee Apis mellifera. The causative agent is the Gram-positive, spore-forming bacterium Paenibacillus larvae. Several authors have proposed that P. larvae secretes metalloproteases that are involved in the larval degradation that occurs after infection. The aim of the present work was to evaluate the production of a metalloprotease by P. larvae during larval infection. First, the complete gene encoding a metalloprotease was identified in the P. larvae genome and its distribution was evaluated by PCR in a collection of P. larvae isolates from different geographical regions. Then, the complete gene was amplified, cloned and overexpressed, and the recombinant metalloprotease was purified and used to generate anti-metalloprotease antibodies. Metalloprotease production was evaluated by immunofluorescence and fluorescence in situ hybridization. The gene encoding a P. larvae metalloprotease was widely distributed in isolates from different geographical origins in Uruguay and Argentina. Metalloprotease was detected inside P. larvae vegetative cells, on the surface of P. larvae spores and secreted to the external growth medium. Its production was also confirmed in vivo, during the infection of honeybee larvae. This protein was able to hydrolyse milk proteins as described for P. larvae, suggesting that could be involved in larval degradation. This work contributes to the knowledge of the pathogenicity mechanisms of a bacterium of great economic significance and is one step in the characterization of potential P. larvae virulence factors.

For more than 60 years, sporadic cases of massive summer honey bee larvae mortality in colonies located near freshwater systems with abundant riparian vegetation have been reported in Uruguay. This odd phenomenon, known as “River disease” by beekeepers, can lead to colony death by depopulation. The aim of this study was to detect the causes of larvae death. Different experiments and analyses were performed using affected apiaries located between two important water courses. 1 day old larvae were the most susceptible and substances that killed the larvae were present in the nectar but not in the pollen. A palynological analysis of nectar samples showed that bees collect this resource from commonly pollinated floral species in the country. However, abundant fungi spores and conidia were found, which indicates that the bees also collected honeydews. In the riparian vegetation, bees were observed collecting the secretions of the planthopper Epormenis cestri on Sebastiania schottiana trees. It was found that the mortality period of larvae overlaps with the presence of E. cestri. Larvae maintained in the laboratory were fed (i) nectar from healthy colonies, (ii) nectar from affected colonies, and (iii) secretions of E. cestri. The mortality of the larvae that received nectar from colonies affected with River disease and secretions of E. cestri was higher than the mortality of those receiving nectar from healthy colonies. This represents the first report of planthopper honeydew causing mass larval mortality in honey bees.

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The western honeybee Apis mellifera exhibits a diverse set of adaptations in response to infestations by its most virulent disease-causing agent, the ectoparasitic mite Varroa destructor. In this study, we investigated the effect of honeybee pupae genotype on the expression of four host and parasite traits that are associated with the reproductive phase of the mite in the brood of its host. We first phenotyped cells containing bee pupae to assess their infestation status, their infestation level, the reproductive status of the mites, and the recapping of cells by adult workers. We then genotyped individual pupae with five microsatellites markers to compare these phenotypes across full sister groups. We found that the four phenotypes varied significantly in time but did not across the subfamilies within the colonies. These findings show that V. destructor mites do not differentially infest or reproduce on some particular honeybee patrilines, and that workers do not target preferentially specific pupae genotypes when performing recapping. These findings bring new insights that can help designing sustainable mite control strategies through breeding and provide new insights into the interactions between A. mellifera and V. destructor.

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For microbiologists, the importance of microorganisms in our daily lives and their impact on our well-being is evident. However, microbiology literacy in our society is far from being enough for individuals to make informed choices and to demand actions based on that information. The vaccine hesitation movement and the alarming increase in antimicrobial resistance due to overuse and misuse of antibiotics are just two examples of how much work is needed to make our society literate in topics related to microbiology. Considering the challenges of communicating a discipline surrounded by misconceptions, which studies the role of living organisms that cannot be seen in plain sight, we need to explore different strategies to effectively contribute to microbiology literacy in our society. Here, we will comment on the use of comics for such a task.