Molecular characterization and comparison of Clostridium botulinum type C avian strains

Type C botulinum neurotoxin (BoNT/C)-producing Clostridium botulinum causes animal botulism worldwide and has become a serious problem in poultry flocks and waterfowl in Sweden. The objectives of the present study were to isolate, characterize and subtype C. botulinum type C avian isolates in order to increase the knowledge of the genetic diversity. Isolates from 13 birds were identified by 16S rRNA sequencing and BoNT/C gene detection by real-time polymerase chain reaction (PCR). Conventional PCR was used to distinguish a chimeric BoNTC/D gene, often associated with avian botulism, from the BoNT/C gene. The isolates analysed all contained the gene coding for a chimeric toxin type C/D. Two fingerprinting techniques, pulsed-field gel electrophoresis (PFGE) and randomly amplified polymorphic DNA analysis (RAPD), were optimized and used to investigate the epidemiological relatedness among the strains. The isolates were divided into three different pulsotypes based upon their restriction profiles for SmaI and SalI. The RAPD system proved to be as discriminative as PFGE. This study reveals a small genetic diversity among Swedish type C strains, with a high similarity between strains from broilers and herring gulls.