Rapid Protection of Gnotobiotic Pigs against Experimental Salmonellosis following Induction of Polymorphonuclear Leukocytes by AvirulentSalmonella enterica

Abstract

Oral inoculation of 5-day-old gnotobiotic pigs with Salmonella enterica serovar Typhimurium strain F98 resulted in severe enteritis and invasive disease. Preinoculation 24 h earlier with an avirulent mutant of Salmonella enterica serovar Infantis (1326/28) completely prevented disease for up to 14 days (when the experiment was terminated). S. enterica serovar Infantis colonized the alimentary tract well, with high bacterial counts in the intestinal lumen but with almost no invasion into the tissues. Unprotected pigs had high S. enterica serovar Typhimurium counts in the intestines, blood, and major nonintestinal organs. Recovery of this strain from the blood and major organs in S. enterica serovar Infantis-protected pigs was substantially reduced despite the fact that intestinal counts were also very high. Protection against disease thus did not involve a colonization exclusion phenomenon. Significant (P < 0.05) infiltration of monocytes/macrophages was observed in the submucosal regions of the intestines of both S. enterica serovar Infantis-protected S. enterica serovar Typhimurium-challenged pigs and unprotected S. enterica serovar Typhimurium-challenged pigs. However, only polymorphonuclear neutrophils (PMNs) were observed throughout the villus, where significant (P < 0.05) numbers infiltrated the lamina propria and the subnuclear and supranuclear regions of the epithelia, indicating that PMN induction and positioning following S. enterica serovar Infantis inoculation was consistent with rapid protection against the challenge strain. Similarly, in vitro experiments using a human fetal intestinal epithelial cell line (INT 407) demonstrated that, although significantly (P < 0.05) fewer S. enterica serovar Infantis than S. enterica serovar Typhimurium organisms invaded the monolayers, S. enterica serovar Infantis induced an NF-B response and significantly (P < 0.05) raised interleukin 8 levels and transmigration of porcine PMN. The results of this study suggest that attenuated Salmonella strains can protect the immature intestine against clinical salmonellosis by PMN induction. They also demonstrate that PMN induction is not necessarily associated with clinical symptoms and/or intestinal pathology.

Campylobacter jejuni-Induced Cytokine Responses in Avian Cells

“…However, this does not rule out IL-10 production in vivo by other cell types. Recent evidence from Salmonella enterica serovar Infantis infections of gnotobitic pigs shows that polymorphonuclear leukocyte influx can be uncoupled from the disease process and preempt a virulent infection, thus protecting against challenge with virulent Salmonella (13). Obviously, therefore, factors other than the signals that attract polymorphonuclear leukocytes are required for inflammatory disease.…”

Oral vaccination with a rough attenuated mutant of S. Infantis increases post-wean weight gain and prevents clinical signs of salmonellosis in S. Typhimurium challenged pigs

“…r (Serogroup C1) protected highly susceptible gnotobiotic piglets against lethal oral challenge with virulent S. Typhimurium F98 (Serogroup B) (Foster et al 2003;Foster et al 2005) when this strain was administered just 24 h after vaccination. In this case it was considered that the presence of the vaccine strain in the tissues generated a high level of nonspecific immunity which clearly acted against heterologous serogroups.…”

Stimulation of gp91 Phagocytic Oxidase and Reactive Oxygen Species in Neutrophils by an AvirulentSalmonella entericaSerovar Infantis Strain Protects Gnotobiotic Piglets from Lethal Challenge with Serovar Typhimurium Strain F98 without Inducing Intestinal Pathology

“…In Europe, Salmonella serovar Typhimurium is the serovar that is most frequently isolated from humans or pigs (25), while in the United States it is estimated that up to 4 million cases of salmonellosis occur annually, of which about 500 are fatal (19). Although vaccination of piglets against Salmonella is a desirable target, gnotobiotic piglets have previously been shown to be a useful model of enteric disease in humans (16,20,41). Recently, we showed that oral inoculation of 5-day-old gnotobiotic piglets with a rough lipopolysaccharide (LPS) mutant of S. enterica serovar Infantis 1326/28 (1326/28⌽ r ) protects against a subsequent, normally lethal challenge with Salmonella serovar Typhimurium strain F98 (16).…”

“…Although vaccination of piglets against Salmonella is a desirable target, gnotobiotic piglets have previously been shown to be a useful model of enteric disease in humans (16,20,41). Recently, we showed that oral inoculation of 5-day-old gnotobiotic piglets with a rough lipopolysaccharide (LPS) mutant of S. enterica serovar Infantis 1326/28 (1326/28⌽ r ) protects against a subsequent, normally lethal challenge with Salmonella serovar Typhimurium strain F98 (16). Furthermore, our results indicated that there is an immunological basis for this protection and that the protection is most likely due to the significant infiltration of neutrophils in the intestinal villi prior to challenge with Salmonella serovar Typhimurium strain F98.…”

“…To determine the extent of pathology due to Salmonella serovar Typhimurium strain F98 infection or the reductions in pathological changes due to protection by Salmonella serovar Infantis strain 1326/28⌽ r , a scoring system was used as described previously (11,16). Briefly, scores of 0 to 3 were used to describe the extent of flattening of the plica circularis and whether epithelial cell exfoliation had occurred at the tips or sides of the villi, as follows: 0, no flattening of plica and long slender villi with no exfoliation at the tips or sides; 1, flattened plica with stunted villi and no exfoliation; 2, flattened plica with stunted villi and exfoliation of the villus tips; and 3, flattened plica with stunted villi and exfoliation of both villus sides and tips.…”