Serotype and genotype diversity of infectious bronchitis viruses isolated during 1985-2008 in Guangxi, China.

The genetic diversity of the hypervariable region I of S1 gene (HVR I) of infectious bronchitis (IB) vaccine strains H120, Ma5 and 4/91 was compared to that of 26 infectious bronchitis virus (IBV) strains isolated from the field in Guangxi province of China during the years 1985-2008, and the field isolates were classified into five major genotypes. Monovalent antisera against three vaccine strains and seven field isolates of different genotypes were prepared by immunizing rabbits with mineral oil adjuvant preparations containing viruses propagated in chicken embryos. Virus neutralization (VN) tests were performed in tracheal organ cultures (TOCs) using these 10 strains with the antisera, and a one-way VN test was then used to compare the relationship of 10 monovalent antisera to the other 19 field isolates. As a result, seven different serotypes were classified based on the results of VN tests with the 26 isolates plus the three vaccine strains. We found that different serotypes were prevalent during different time periods, that more new serotypes have been prevalent in more recent years, and the prevalence of the original dominant serotype has been in constant decline since 2004. In addition, the concordance rate of the 26 field isolates between the S1 genotypes and serotypes was 57.7%.

Persistence of Mycoplasma gallisepticum in chickens after treatment with enrofloxacin without development of resistance.

The ability of the avian pathogen Mycoplasma gallisepticum to persist despite fluoroquinolone treatment was investigated in chickens. Groups of specific pathogen free chickens were experimentally infected with M. gallisepticum and treated with enrofloxacin at increasing concentrations up to the therapeutic dose. When M. gallisepticum could no longer be re-isolated from chickens, birds were stressed by inoculation of infectious bronchitis virus or avian pneumovirus. Although M. gallisepticum could not be cultured from tracheal swabs collected on several consecutive sampling days after the end of the enrofloxacin treatments, the infection was not eradicated. Viral infections reactivated the mycoplasma infection. Mycoplasmas were isolated from tracheal rings cultured for several days, suggesting that M. gallisepticum persisted in the trachea despite the enrofloxacin treatment. The minimal inhibitory concentration (MIC) of enrofloxacin for most of the re-isolated mycoplasmas was the same as that of the strain with which the birds were inoculated. Furthermore, no mutation could be detected in the fluoroquinolone target genes. These results suggest that M. gallisepticum can persist in chickens without development of resistance despite several treatments with enrofloxacin.

The polypeptide composition of avian infectious bronchitis virus.

Avian infectious bronchitis virus grown in ovo was purified by differential centrifugation and isopycnic sedimentation in density gradients. The purified virus was analysed by SDS polyacrylamide gel electrophoresis and found to comprise up to sixteen polypeptides, four of which were glycopeptides. Bromelain treatment of the particles removed three polypeptides and two glycopeptides.