Abstract
To construct a novel live vaccine against Salmonella enterica serovar Montevideo (SM) infection in chickens, two important bacterial regulatory genes, lon and cpxR, which are associated with invasion and virulence, were deleted from the wild type SM genome. Attenuated strains, JOL1625 (Δlon), JOL1597 (ΔcpxR), and JOL1599 (ΔlonΔcpxR) were thereby generated. Observations with scanning electron microscopy suggested that JOL1625 and JOL1599 cells showed increased ruffled surface which may be related to abundant extracellular polysaccharide (EPS) production. JOL1597 depicted milder ruffled surface but showed increased surface corrugation. ConA affinity-based fluorometric quantification and fluorescence microscopy revealed significant increases in EPS production in JOL1625 and JOL1599. Four weeks old chickens were used for safety and immunological studies. The mutants were not observed in feces beyond day 3 nor in spleen and cecum beyond day 7, whereas wild type SM was detected for at least 2 weeks in spleen and cecum. JOL1599 was further evaluated as a vaccine candidate. Chickens immunized with JOL1599 showed strong humoral responses, as indicated by systemic IgG and secretory IgA levels, as well as strong cell-mediated immune response, as indicated by increased lymphocyte proliferation. JOL1599-immunized groups also showed significant degree of protection against wild type challenge. Our results indicate that Δlon- and/or ΔcpxR-deleted SM exhibited EPS-enhanced immunogenicity and attenuation via reduced bacterial cell intracellular replication, conferred increased protection, and possess safety qualities favorable for effective vaccine development against virulent SM infections.
Highlights
Salmonella infection remains a major global public and veterinary health problem (Todd, 1997)
scanning electron microscopic (SEM) images revealed that both JOL1625 and JOL1599 were more ruffled on their cell surface
Fluorescence microscopy images revealed the differences in extracellular polysaccharide (EPS) abundance and morphological changes (Figure 2)
Summary
Salmonella infection remains a major global public and veterinary health problem (Todd, 1997). SM has gained attention in recent years due to several SM-related cases and Avirulent Salmonella Montevideo Confers Protection outbreaks reported in humans (Threlfall et al, 1999; Dominguez et al, 2009). Centers for Disease Control and Prevention (CDC) reported several multistate SM outbreaks in human in the United States since 2009 till recently on May 20161,2 (CDC, 2010). The sources of infection in most cases were linked to live poultry system, meat, and agricultural products. The sources of infection in most cases were linked to live poultry system, meat, and agricultural products4 According to these CDC reports, since 2009 till 2016 there were 378 SM-cases in human, with approximately 23% of them requiring hospital care. Salmonella may proceed to systemic infection resulting in death. It has been reported that eggs and egg products, and meat and meat products are the most common vehicles of transmission of Salmonella infections (Humphrey, 2004)
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