Conversion of RpoS Attenuated Serovar Typhi Vaccine Strains to RpoS Improves Their Resistance to Host Defense Barriers.

The vast majority of live attenuated typhoid vaccines are constructed from the serovar Typhi strain Ty2, which is devoid of a functioning alternative sigma factor, RpoS, due to the presence of a frameshift mutation. RpoS is a specialized sigma factor that plays an important role in the general stress response of a number of Gram-negative organisms, including . Previous studies have demonstrated that this sigma factor is necessary for survival following exposure to acid, hydrogen peroxide, nutrient-limiting conditions, and starvation.

Use of Ensure® nutrition shakes as an alternative formulation method for live recombinant Attenuated Salmonella Typhi vaccines.

Background: To be effective, orally administered live Salmonella vaccines must first survive their encounter with the low pH environment of the stomach. To enhance survival, an antacid is often given to neutralize the acidic environment of the stomach just prior to or concomitant with administration of the vaccine. One drawback of this approach, from the perspective of the clinical trial volunteer, is that the taste of a bicarbonate-based acid neutralization system can be unpleasant.

A low gastric pH mouse model to evaluate live attenuated bacterial vaccines.

The low pH of the stomach serves as a barrier to ingested microbes and must be overcome or bypassed when delivering live bacteria for vaccine or probiotic applications. Typically, the impact of stomach acidity on bacterial survival is evaluated in vitro, as there are no small animal models to evaluate these effects in vivo. To better understand the effect of this low pH barrier to live attenuated Salmonella vaccines, which are often very sensitive to low pH, we investigated the value of the histamine mouse model for this application.

Salmonella as a vaccine delivery vehicle.

Attenuated Salmonella vaccines can be administered orally to deliver recombinant antigens to mucosal surfaces inducing a protective immune response against a variety of targeted pathogens. A number of exciting new approaches and technologies for attenuated Salmonella vaccines have been developed recently. However, a disconnect remains between results obtained with mice in preclinical studies and results obtained in human clinical trials.

A Phase I, dose-escalation trial in adults of three recombinant attenuated Salmonella Typhi vaccine vectors producing Streptococcus pneumoniae surface protein antigen PspA.

Background: Live, attenuated, orally-administered Salmonella strains are excellent vectors for vaccine antigens and are attractive as vaccines based on previous use of S. Typhimurium in animals. A Phase I dose escalation trial was conducted to evaluate the safety and immunogenicity of three newly constructed recombinant attenuated Salmonella enterica serovar Typhi vaccine (RASV) vectors synthesizing Streptococcus pneumoniae surface protein A (PspA).

Rapid, sensitive recovery of recombinant attenuated Salmonella enterica serovar Typhi vaccine strains from human blood.

Prior to initiating a phase 1 dose escalation trial of the safety and immunogenicity of live, oral, recombinant, attenuated Salmonella enterica serovar Typhi vaccine strains in human subjects, the suitability of conventional blood culture procedures to rapidly and reliably detect the organisms in human blood was investigated. Blood culture specimens, with and without added growth supplements, were inoculated with study organism concentrations ranging from approximately 300 to as few as 1 to 2 CFU/10 ml culture and processed in a Bactec 9240 fluorescent series aerobic blood culture system. All cultures seeded with >6 CFU and 93% of cultures seeded with ∼1 to 2 CFU were identified as positive for microbial growth within 44 h of incubation.

Low-pH rescue of acid-sensitive Salmonella enterica Serovar Typhi Strains by a Rhamnose-regulated arginine decarboxylase system.

For Salmonella, transient exposure to gastric pH prepares invading bacteria for the stresses of host-cell interactions. To resist the effects of low pH, wild-type Salmonella enterica uses the acid tolerance response and the arginine decarboxylase acid resistance system. However, arginine decarboxylase is typically repressed under routine culture conditions, and for many live attenuated Salmonella vaccine strains, the acid tolerance response is unable to provide the necessary protection.

Use of RapidChek® SELECT™ Salmonella to detect shedding of live attenuated Salmonella enterica serovar Typhi vaccine strains.

Identification of individuals shedding Salmonella enterica serovar Typhi in stool is imperative during clinical trial safety evaluations. Recovery of live attenuated S. Typhi vaccine strains can be difficult because the mutations necessary for safety in humans often compromise survival in stringent selective enrichment media.

The early humoral immune response to Bacillus anthracis toxins in patients infected with cutaneous anthrax.

Bacillus anthracis, the causative agent of anthrax, produces a tripartite toxin composed of two enzymatically active subunits, lethal factor (LF) and edema factor (EF), which, when associated with a cell-binding component, protective antigen (PA), form lethal toxin and edema toxin, respectively. In this preliminary study, we characterized the toxin-specific antibody responses observed in 17 individuals infected with cutaneous anthrax. The majority of the toxin-specific antibody responses observed following infection were directed against LF, with immunoglobulin G (IgG) detected as early as 4 days after the onset of symptoms in contrast to the later and lower EF- and PA-specific IgG responses.

Live recombinant Salmonella Typhi vaccines constructed to investigate the role of rpoS in eliciting immunity to a heterologous antigen.

We hypothesized that the immunogenicity of live Salmonella enterica serovar Typhi vaccines expressing heterologous antigens depends, at least in part, on its rpoS status. As part of our project to develop a recombinant attenuated S. Typhi vaccine (RASTyV) to prevent pneumococcal diseases in infants and children, we constructed three RASTyV strains synthesizing the Streptococcus pneumoniae surface protein PspA to test this hypothesis.

Immune response to two different dosing schedules of the anthrax vaccine precipitated (AVP) vaccine.

A pilot study compared the immune response of regular (0, 3, 6, 32 weeks) and extended (0, 10, 13, 32 weeks) schedules of the UK anthrax vaccine (anthrax vaccine precipitated, AVP). Concentrations of antibodies to protective antigen (PA) were higher (p<0.05) among recipients of the extended (n=7) versus regular schedule (n=6) at week 32, and 2 weeks after the second and third vaccinations.