Vaccination with attenuated Salmonella enterica Dublin expressing E coli O157:H7 outer membrane protein Intimin induces transient reduction of fecal shedding of E coli O157:H7 in cattle

Abstract

BackgroundEscherichia coli serogroup O157:H7 has emerged as an important zoonotic bacterial pathogen, causing a range of symptoms from self-limiting bloody diarrhea to severe hemorrhagic colitis and hemolytic-uremic syndrome in humans. Beef and dairy cattle are considered the most important animal reservoirs for this pathogen. One of the important virulence characteristics of E. coli O157:H7 is the eaeA gene encoding the 97 kDa surface protein intimin. Intimin is required for attachment and effacement during the interaction of enterohemorrhagic E. coli with human and bovine neonatal enterocytes. The present study was undertaken to test the hypothesis that an adaptive mucosal immune response directed against intimin will reduce or prevent enteric colonization and fecal shedding of E. coli O157:H7 in cattle.ResultsCattle were orally inoculated with either milk (control), milk with live attenuated Salmonella enterica serovar Dublin (vector), or milk with live attenuated recombinant S. Dublin expressing intimin (vaccinated) on days 0, 14 and 28. On day 98, all calves were challenged orally with E. coli O157:H7 to evaluate whether vaccination with the recombinant S. Dublin expressing intimin would reduce the level of E. coli O157:H7 fecal shedding.During the first 28 days, vaccinated calves shed both the vector strain and the intimin-expressing S. Dublin strain at a similar level. The vector strain was shed for a significantly longer period as compared to the level of recombinant vaccine strain. Calves that received the intimin-expressed vaccine ceased shedding S. Dublin from day 28 to day 63. All calves were challenged with E. coli O157:H7 on day 98 to determine the effect on fecal shedding of E. coli O157:H7. The amount of E. coli O157:H7 in feces was measured for 30 days post-challenge. We observed a transient clearance of E. coli O157:H7 from the feces in the vaccinated calves. The magnitude of fecal E. coli O157:H7 shedding did not correlate with the presence of intimin-specific fecal IgA.ConclusionOral vaccination with live attenuated recombinant S. Dublin expressing intimin reduced enteric colonization and fecal shedding of E. coli O157:H7. However, the transient clearance of E. coli O157:H7 was not associated with an enhanced IgA-mediated mucosal immune response.

Immune Responses to New Vaccine Candidates Constructed by a Live Attenuated Salmonella Typhimurium Delivery System Expressing Escherichia coli F4, F5, F6, F41 and Intimin Adhesin Antigens in a Murine Model

“…In order to examine whether our vaccine constructs were excreted into feces, we attempted to detect the strains in fecal samples taken from randomly selected mice in each immunization group (n=5 per group). The vaccine strain was not detected in any of the fecal samples, suggesting that it may not be excreted in feces and therefore may not contaminate the environment unlike the previous studied candidate [21]. Adverse reactions such as diarrhea and weight loss were not observed in any of the groups during the experimental period.…”

“…Khare et al [21] also reported that intimin-expressing S. Dublin strain was shed in feces of vaccinated calves till 28 days post prime oral immunization. In order to examine whether our vaccine constructs were excreted into feces, we attempted to detect the strains in fecal samples taken from randomly selected mice in each immunization group (n=5 per group).…”

“…Translocation of such highly immunogenic antigens into the cell envelope or secretion from the cell should increase the strength of the immune response elicited by vaccine strains expressing foreign antigens. Several previous studies reported that the recombinant antigens, such as ETEC fimbriae [1,6] or outer membrane protein intimin, an important virulence factor of E. coli serogroup O157 [21], expressed on the membrane surface of live-attenuated Salmonella vectors, were delivered and were examined as vaccine candidates. However, the antigens expressed and embedded in membrane surface of the bacteria are less effective as vaccine candidates than the secreted type antigens to host environments from the live Salmonella-based systems [9,10,20].…”

Improving microbial safety in the beef production chain

“…Both induced humoral immunity in calves but did not protect against colonisation by E. coli O157 upon subsequent challenge (van Diemen et al, 2007). A recent study showed that inoculation with a recombinant S. Dublin strain expressing E. coli O157 intimin reduced enteric colonisation and faecal shedding of E. coli O157 in calves, although it did not correspond with the presence of intiminspecific IgA in faeces (Khare et al, 2010). Another study examined vaccines containing E. coli O157 type III secreted proteins and it was found that faecal shedding and duration of shedding was reduced (Potter et al, 2004) but a subsequent field trial in feedlot cattle showed no significant association between pen prevalence of faecal E. coli O157 and vaccination (Van Donkersgoed et al, 2005).…”

OMV-based vaccine formulations against Shiga toxin producingEscherichia colistrains are both protective in mice and immunogenic in calves

“…These models include formulations based on recombinant expression of virulence factors, 22–26 culture supernatants from virulent strains grown under conditions promoting virulence factor secretion, 27 , 28 subunits or components directly extracted from STEC strains, 29–31 and heterologous expression of STEC virulence factors in both attenuated and unrelated bacteria. 32 Due to the complex mechanism responsible for colonization, it is not surprising that protection has only been observed for multi-antigenic formulations. Noteworthy, as anti-STEC vaccination in domestic cattle will not bring any economic benefit to cattle breeders, keeping the cost per dose of candidates as low as possible is mandatory.…”