Evaluating the effects of virulence genotype, swarming motility, and multi-locus sequence types of Escherichia coli on layer chicken embryos.

AIMS: To determine the effects of swarming motility (SM) and multi-locus sequence types (MLST) on the main effect of virulence genotype of Escherichia coli through an embryos lethality assay between the 12th and 18th days of incubation. METHODS AND RESULTS: We collected 58 E. coli isolates from asymptomatic commercial hens (n = 42) and lesions of colibacillosis cases (n = 16), then classified their virulence genotype as avirulent, moderately virulent, virulent-healthy, and virulent-colibacillosis categories by the presence of five virulence-associated genes (iroN, ompT, hlyF, iutA, and iss). These isolates were further classified as non-motile, motile, or hyper-motile by SM assay. From the 58 isolates, we selected 29 for ELA and determined their MLST. Each isolate was inoculated into 15 embryonated eggs through the allantoic cavity. We found the avirulent isolates reduced the relative embryo weight compared to virulent-colibacillosis and moderately virulent isolates (37.49 vs. 41.51 and 40.34%, P = 0.03). Among the moderately virulent and virulent-colibacillosis categories, embryo lethality was lower when isolates were non-motile. Yolk retention was unaffected by virulence categories, motility, or MLST. CONCLUSION: Interaction between virulence genotype and SM substantially influenced the embryo lethality assay of E. coli isolates.

Genetic comparison of the Mycoplasma gallisepticum 6/85 vaccine strain and 6/85-like field isolates.

Mycoplasma gallisepticum infection in poultry leads to disease and pathology that can reduce producer profits. Live attenuated vaccines are available that can limit or completely prevent the effects of infection. Field isolates that are genetically related to the attenuated vaccine strains have been isolated, raising the question of whether the attenuation of the vaccine strains is limited and can lead the strains to revert to more virulent forms. The 6/85 live attenuated vaccine is derived from a field isolate collected in the United States. Analysis of the genome of sequenced M. gallisepticum strains revealed a cluster of 10 6/85-like strains that group with the 6/85 vaccine strain. Four genomic regions were identified that allowed for strain differentiation. The genetic differences between strains points toward nine of the ten strains most likely being sister strains to the 6/85 vaccine strain. Insufficient differences are present in the tenth strain to make a definitive conclusion. These results suggest that most if not all strains similar to the live attenuated vaccine strain are field isolates of the parent strain used to derive the live attenuated vaccine.