Development and evaluation of temperature-sensitive clones as vaccine candidates.

is economically the most important pathogenic species of waterfowl in Europe and Asia. The lack of commercially available vaccines against had prompted this study with the aim to produce temperature-sensitive (ts) clones as candidates for an attenuated live vaccine. The production of ts clones was performed by N-methyl-N'-nitro-N-nitrosoguanidine (NTG)-induced mutagenesis of Hungarian field isolates. The clones were administered via eye-drop and intracloacally to 33-day-old geese. Colonization ability was examined by PCR and isolation from the trachea and cloaca, while the serological response of the birds was tested by ELISA. Pathological and histopathological examinations were performed in the eighth week after inoculation. Whole-genome sequence (WGS) analysis of the selected clone and its parent strain was also performed. NTG-treatment provided three ts mutants (MA177/1/11, MA177/1/12, MA271). MA271 was detected at the highest rate from cloacal (86.25%) and tracheal (30%) samples, while MA177/1/12 and MA271 elicited remarkable serological responses with 90% of the birds showing seroconversion. Re-isolates of MA271 remained ts throughout the experiment. Based on these properties, clone MA271 was found to be the most promising vaccine candidate. WGS analysis revealed 59 mutations in the genome of MA271 when compared to its parent strain, affecting both polypeptides involved in different cellular processes and proteins previously linked to bacterial fitness and virulence. Although further studies are needed to prove that MA271 is in all aspects a suitable vaccine strain, it is expected that this ts clone will contribute to the control of infection. Three ts vaccine candidates were produced by NTG-mutagenesis.Clone MA271 was able to colonize geese and induce a serological response.MA271 re-isolates remained ts during the 8-week-long experiment.WGS analysis revealed 59 mutations in the genome of MA271.