Efeitos da inoculação in ovo de peptídeos bacterianos e CpG-ODN no controle da infecção de aves SPF por Salmonella enterica sorovar Heidelberg

Abstract

Salmonella enterica subspecies enterica serovar Heidelberg (SH) is relevant for both poultry production and public health. The increasing frequency of pathogenic and antimicrobial resistant isolates represents a worldwide concern. Therefore, new approaches for preventing and controlling infection by this bacterium are needed. The present study aimed at investigating the potencial protective effects of in ovo inoculation of a formulation based on bacterial peptides solely or added with CpG oligodeoxynucleotides (CpG-ODN) against SH infection in birds. For this, SH genomes sequences available in public databases were analyzed and the deduced amino acid compositions of structural protein sequences and/or those of greater relevance for intestinal colonization were selected. Such sequences were submitted to predictors of linear epitopes for the selection of peptides with greater immunogenicity. 180 embryonated eggs free of specific pathogens (SPF) were incubated and, at 18 days of incubation, they were separated into groups and received the formulations via amniotic fluid, as described below. Group A (embryos that received peptides + CpG-ODN), B (embryos that only received peptides), C (embryos that received only CpG-ODN), D (embryos that received PBS) and intact eggs. On the third post-hatching day, birds of groups A, B, C and D were orally challenged with 5.6 x 10³ colony forming units (CFU) of SH. At 7, 14, 21 and 28 days post-infection (dpi), five birds from each treatment were euthanized and had their livers, cecal contents and intestinal segments collected. Cecal colonization and systemic infection were assessed by serial plating counts of cecal and liver contents. Fecal SH excretion was monitored using cloacal swabs collected from all birds twice a week. In addition, histomorphometric analysis of the duodenum was performed. It was noted that, at 7 dpi, the birds in group A (peptides + CpG-ODN) had a lower counting of SH in cecal content when compared to those in group D (PBS) (P < 0.05). However, the formulations used in the embryos did not reduce the overall SH-fecal excretion over the study. SH counts remained zero in the livers of birds from all infected groups during the study. At 21 dpi, the birds of group C had a lower crypt depth when compared to those in group D (infected control) (P < 0.05). At 28 dpi, the birds of group C did also have a higher villus height when compared to birds from the other infected groups (P < 0.05). The results suggested that in ovo inoculation of peptides + CpG-ODN may help to reduce cecal colonization of SH in the first week post-infection, although did not reduce total fecal excretion. In addition, the CpG-ODN inoculation may have positively affected the intestinal health of the birds, which showed improvement in parameters such as crypt depth and villus height at the end of the study.