On the evolution of Avian infectious bronchitis virus in VERO cells

Abstract

Avian infectious bronchitis virus (IBV) (Nidovirales: Coronaviridae) is a chicken Gammacoronavirus with the highestevolution rate in the genus and, despite the recently reported proofreading activity of its polymerase, intra and interhost diversity is a well-documented phenomenon. This study aimed to assess the genetic variation of serial passages of a variant genotype IBV strain in vitro. Strain CRG-BETA, propagated in chicken embryos, was inoculated in VERO cells monolayers up to the 4th passage and each passage was monitored with an RT-PCR targeted to the S1 gene (nt 705to 1094) and an RT-PCR to the protein 5a mRNA. All passages were positive to RT-PCRs to S1 and passages 1 to 3 to5a mRNA; S1 sequences showed no polymorphism. The finding of IBV mRNA in the cell cultures demonstrates that the CRG-BETA IBV strain is replicating in the VERO cells and regarding S1 sequence analysis, the lack of nucleotide mutations shows that CRG-BETA might have reached a fixed status. As a conclusion, different genotypes of IBV present different evolutionary patterns not only in vivo as previously known, but also in vitro, as described herein.