American foulbrood is a disease that produces effects at colony level, but does not affect the physiological parameters on nurses? bees (Apis mellifera).

GENDE LB; GARRIDO PM; DAMIANI N; FERNANDEZ NJ; PORRINI M; MOLINE M.P; ALVAREZ BS; BUFFA F; FLORIS I.; CHURIO MS; EGUARAS M

Barcelona

Congreso; VI International Conference on Environmental, Industrial and Applied Microbiology - BioMicroWorld2015; 2015

Paenibacillus larvae is a Gram-positive spore-forming bacterium, and the causative agent of American foulbrood (AFB), one of the most serious and destructive brood diseases of honeybees Apis mellifera. Only spores represent the infectious stage when the larvae have ingested them. A colony is known to be diseased when larvae are observed with the clinical symptoms; meanwhile, adult honeybees are not affected by P. larvae becoming asymptomatic carriers. At colony level, behavioral mechanisms are involved in disease resistance. The defense system used by eusocial insects against pathogens includes changes on individual physiological parameters as well as group defenses. The aim of this work was to study the spread of P. larvae spores in experimental mini-hives and evaluate the impact of higher microbial loads on different physiological parameters of individual worker bees and colony development. After the artificial infection, the experimental design allowed to follow the development of the disease via the visual inspection. The spores load in the inoculated group was greater than in the uninoculated one, proving the effectiveness of the inoculation method. In the colonies that showed all clinical symptoms of AFB, the average number of spores per bee was significantly higher than 2,855.9 units. Bees that emerged from one healthy colony were marked and introduced in colonies with severe clinical symptoms of AFB, as well as on control group. No changes were observed in physiological and immunological defense mechanisms at individual level on marked bees recaptured at 10 days-old when comparing uninoculated and inoculated hives groups. The high sporulate load did not change the total proteins content in hemolymph, the degree of development of their hypopharyngeal glands and their abdominal fat body by comparison with bees introduced into uninfected colonies within each analyzed time interval. Nurse bees from the same cohort were not able to indicate the progressive bacterial infection by altering physiological and immunological parameters studied. This work constitutes the first study linking the effects of AFB disease with a possible disruption of normal development of adult bees under field conditions.