Abstract
Streptococcus suis is a zoonotic pathogen of swine involved in arthritis, polyserositis, and meningitis. Colonization of piglets by S. suis is very common and occurs early in life. The clinical outcome of infection is influenced by the virulence of the S. suis strains and the immunity of the animals. Here, the role of innate immunity was studied in cesarean-derived colostrum-deprived piglets inoculated intranasally with either virulent S. suis strain 10 (S10) or non-virulent S. suis strain T15. Colonization of the inoculated piglets was confirmed at the end of the study by PCR and immunohistochemistry. Fever (≥40.5 °C) was more prevalent in piglets inoculated with S10 compared to T15 at 4 h after inoculation. During the 3 days of monitoring, no other major clinical signs were detected. Accordingly, only small changes in transcription of genes associated with the antibacterial innate immune response were observed at systemic sites, with S10 inducing an earlier response than T15 in blood. Local inflammatory response to the inoculation, evaluated by transcriptional analysis of selected genes in nasal swabs, was more sustained in piglets inoculated with the virulent S10, as demonstrated by transcription of inflammation-related genes, such as IL1B, IL1A, and IRF7. In contrast, most of the gene expression changes in trachea, lungs, and associated lymph nodes were observed in response to the non-virulent T15 strain. Thus, S. suis colonization in the absence of systemic infection induces an innate immune response in piglets that appears to be related to the virulence potential of the colonizing strain.
Highlights
Streptococcus suis is a major bacterial pathogen of swine, involved in meningitis, arthritis, septicemia, and acute death, among other clinical syndromes
Differences among the groups were observed in rectal temperature after the inoculation of the two strains. Both groups of S. suis inoculated piglets had higher temperature than the control group (PBS inoculated) at 4 h after the challenge, this difference was statistically significant only in the piglets inoculated with strain 10 (S10) (ANOVA Tukey’s Honest Significant Difference (HSD), P = 0.044; Figure 1)
The number of piglets with rectal temperature higher than 40.5 °C at 4 h post-inoculation was greater in the group inoculated with S10 (5 out of 8) than in the T15 group (1 out of 8); no statistical difference was found between the two S. suis-inoculated groups
Summary
Streptococcus suis is a major bacterial pathogen of swine, involved in meningitis, arthritis, septicemia, and acute death, among other clinical syndromes. S. suis is a zoonotic agent that is receiving increased scientific interest due to Chinese outbreaks in humans in 1998 and 2005 [2]. Streptococcus suis is an early colonizer of the swine upper respiratory tract, mainly found in tonsil and nasal cavity [3]. Newborn piglets experience the first contact with the bacterium in the birth canal during parturition, as S. suis colonizes the sow’s vaginal tract [4]. Animals housed in the same pen are exposed to horizontal colonization by direct contact or aerosol, especially during outbreaks when animals may shed bacteria in high numbers [5]
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