Botulism is a severe neuroparalytic disease caused by exposure to botulinum neurotoxins (BoNTs), which are produced by anaerobic, spore-forming, ubiquitous microorganisms belonging to the genus Clostridium, referred to as BoNT-producing clostridia (BPC). BoNTs are classified into seven serotypes, A through G, based on their antigenic properties 1.
66 strains of C. botulinum isolated in the last 4 years from 39 Italian animal botulism outbreaks and 7 reference strains of BPC were included in the study. The field strains were isolated from bovines (beef and dairy cattle), poultry (chicken, turkey, pheasant, domestic duck and goose), wild birds (mallard, swan and seagull), companion animals (cat and dog) and environmental samples collected in poultry outbreaks. All strains were analyzed by Matrix-Assisted Laser Desorption Ionization Time of Flight Mass Spectrometry (MALDI-TOF MS, Bruker Daltonics) and the spectra were compared using BioNumerics 7.1 software. Field strains were moreover tested for the mosaic forms C/D and D/C by a previously published PCR protocol 2. In the studied outbreaks only type C, C/D and D/C C. botulinum strains were isolated. Non-chimeric Type C strains were isolated only form bovines and from a carcass of cat connected with a bovine type C outbreak. All other bovine strains belonged to serotype D/C whereas strains isolated from birds belonged to serotype C/D. At the spectra analysis reference strains serotype A, B, E and F grouped separately from type C, D/C and C/D and moreover non-chimeric type C BPC were clustered separately from type D/C and C/D.
Data suggest that BPC strains isolated from animal botulism outbreaks belong to different unclassified Clostridia species than the C. botulinum serotypes usually involved in human cases.
MALDI-TOF MS could prove as a useful tool in epidemiological investigations since the strains isolated from different animals of the same outbreak were grouped in the same cluster.