Development of traditional and plant virus-based Staphylococcus aureus and Escherichia coli recombinant enterotoxin vaccines

Each year, enteric diseases, such as those caused by Staphylococcus aureus and Escherichia coli, cause significant morbidity and/or mortality worldwide. Staphylococcal enterotoxin (SE) is the primary virulence factor produced by S. aureus and is intimately involved in the pathogenesis of staphylococcal food poisoning and toxic shock syndrome. Although E. coli is part of the normal intestinal flora, some strains have acquired enterotoxins that contribute to diarrheagenic and systemic diseases. Effective enterotoxin vaccines must be detoxified (toxoid) and contain protective antigenic epitopes. A novel vaccine delivery system utilizes enterotoxoid expression in genetically modified plants and mucosal immunization. This study, (i) demonstrated that an SE type C1 mutant (SEC1(-12C)), devoid of emetic, pyrogenic, and shock-enhancing activity, was an effective cross-protective parental or mucosal vaccine towards SEC1 or SE type B (SEB) but not SE type A (SEA) in a rabbit model, (ii) constructed SE chimeras with combinations of N- and C-terminal domains of SEC1 or SEC1(-12C) and SEA, tested their immunological characteristics, and showed that one chimera (referred to as the SEC/A chimera) elicited cross-protection towards SEC1 but not SEA after parental but not mucosal vaccination, (iii) constructed stable toxoids of the Shiga toxin type 1 (Stx1), a tetramer of the heat stable toxin (ST), and a fusion protein of ST and Stx (St/Stx), (iv) engineered recombinant Tobacco mosaic virus (TMV)-derivatives (p30B.TMV) that contain the structural genes for SEC1(-12C), the SEC/A chimera, ST, Stx, or ST/Stx and infected Nicotiana benthamiana, (v) tested toxoid expression in N. benthamiana and found that only SEC1(-12C) or the SEC/A chimera were expressed; (vi) used a recombinant p30B.TMV, containing a green fluorescent protein, as a reporter and identified Chenopodium quinoa as an edible plant host, (vii) expressed SEC1(-12C) and the SEC/A chimera in C. quinoa and characterized the coordination of viral infection symptomology and expression, and (viii) tested the stability of the recombinant TMVs in planta and showed that the viruses recombined and lost the toxin genes. Recombination of the p30B. TMV-derivatives allowed for controlled infections that expressed toxoid only after a specific inoculation was made.