Effectiveness of tilmicosin against Paenibacillus larvae, the causal agent of American Foulbrood disease of honeybees.
American Foulbrood (AFB) of honeybees (Apis mellifera L.), caused by the Gram-positive bacterium Paenibacillus larvae is one of the most serious diseases affecting the larval and pupal stages of honeybees (A. mellifera L.). The aim of the present work was to asses the response of 23 strains of P. larvae from diverse geographical origins to tilmicosin, a macrolide antibiotic developed for exclusive use in veterinary medicine, by means of the minimal inhibitory concentration (MIC) and the agar diffusion test (ADT). All the strains tested were highly susceptible to tilmicosin with MIC values ranging between 0.0625 and 0.5 microg ml(-1), and with MIC(50) and MIC(90) values of 0.250 microg ml(-1). The ADT tests results for 23 P. larvae strains tested showed that all were susceptible to tilmicosin with inhibition zones around 15 microg tilmicosin disks ranging between 21 and 50mm in diameter. Oral acute toxicity of tilmicosin was evaluated and the LD(50) values obtained demonstrated that it was virtually non-toxic for adult bees and also resulted non-toxic for larvae when compared with the normal brood mortality. Dosage of 1000 mg a.i. of tilmicosin applied in a 55 g candy resulted in a total suppression of AFB clinical signs in honeybee colonies 60 days after initial treatment. To our knowledge, this is the first report of the effectiveness of tilmicosin against P. larvae both in vitro and in vivo.
Centro de Investigaciones de Fitopatología (CIDEFI), Facultad de Ciencias Agrarias y Forestales, Universidad Nacional de La Plata, calles 60 y 118, c.c. 31, 1900 La Plata, Argentina.
Francisco J
FJ
Reynaldi
Graciela N
GN
Albo
Adriana M
AM
Alippi
D000818:Animals; D000900:Anti-Bacterial Agents / Q000009:adverse effects / Q000627:therapeutic use*; D001516:Bees / Q000187:drug effects / Q000382:microbiology*; D024881:Drug Resistance, Bacterial; D006094:Gram-Positive Bacteria / Q000187:drug effects*; D007814:Larva / Q000382:microbiology; D008826:Microbial Sensitivity Tests; D011679:Pupa / Q000382:microbiology; D015645:Tylosin / Q000009:adverse effects / Q000031:analogs & derivatives* / Q000627:therapeutic use
D000900:Anti-Bacterial Agents; C052319:tilmicosin; D015645:Tylosin