No abstract

American Foulbrood (AFB) is a contagious and severe brood disease of honey bees caused by the spore-forming bacterium Paenibacillus larvae. The identification of honey bee colonies infected by P. larvae is crucial for the effective control of AFB. We studied the possibility of identifying the infection levels by P. larvae in honey bee colonies through the examination of powdered sugar samples collected in the hives. The powdered sugar was dusted on the top bars of honeycombs and collected from a sheet paper placed at the bottom of the hive. Three groups of honey bee colonies were examined: Group A1- colonies with clinical symptoms of AFB (n = 11); Group A2 – asymptomatic colonies located in apiaries with colonies showing symptoms of AFB (n = 59); Group B – asymptomatic colonies located in apiaries without cases of the disease (n = 49). The results showed that there was a significant difference in spore counting between Groups and that the spore load in sugar samples was always consistent with the clinical conditions of the colonies and with their belonging to AFB-affected apiaries or not. Based on the obtained results the cultural examination of powdered sugar samples collected from hives could be an effective tool for the quantitative non-destructive assessment of P. larvae infections in honey bee colonies.

Paenibacillus larvae (P. larvae) is responsible for American foulbrood (AFB), the most severe bacterial disease of honeybees. The enumeration of P. larvae spores in substrates taken from hives allows for the identification of the contamination levels of the colonies, mostly in those with atypical symptoms or with asymptomatic infections; in these cases, it is essential for the effective control of American foulbrood (AFB). In this work we described a new quantitative TaqMan® probe-based real-time PCR (qPCR) assay, targeting the 16S rRNA gene of P. larvae, used for the quantification of P. larvae spores in powdered sugar samples collected from hives, in comparison to the culture. A total of 105 colonies were selected, belonging to 10 apiaries with different levels of infection, located in northern Italy. The proportions of positive colonies was 54% (57/105) with the culture and 66% (69/105) with qPCR. A significant difference between the two methods was found with McNemar’s test (p = 0.02). Out of the 51 positive samples by both methods, 45 showed higher infection by qPCR compared to the culture. A close concordance with the clinical–epidemiological status of the hives was observed by both methods, with higher infection levels found by qPCR.