Salmonella 2025 Outbreak? Be Ready with abinScience Tools

Public Health Impact of Salmonella

Salmonella, a genus of Gram-negative rod-shaped bacteria within the Enterobacteriaceae family, is a leading cause of foodborne illness worldwide. Found in the digestive tracts of humans and animals, it is responsible for approximately 93 million cases of gastrointestinal infections and over 150,000 deaths annually, according to the World Health Organization (WHO).

On June 11, 2025, a multi-state egg contamination outbreak in the U.S., caused by Salmonella enterica serovar Enteritidis, infected 79 individuals, with 21 hospitalizations. This incident underscores the high transmission risk of Salmonella in poultry supply chains and highlights the need for rapid detection and robust control measures.

Structure and Classification of Salmonella

The Salmonella genus comprises two species: S. enterica and S. bongori. S. enterica, the primary pathogenic species, is divided into six subspecies with over 2,650 serotypes, classified using the Kauffman–White serotyping system based on O (somatic lipopolysaccharide) and H (flagellar) antigens. S. enterica predominantly infects humans and warm-blooded animals, accounting for over 99% of human infections, while S. bongori primarily affects cold-blooded animals like reptiles and is less pathogenic.

Fig. 1. Schematic illustration of the structure of Salmonella. (doi.org/10.3390/foods12091756)

Key biological characteristics include:

Pathogenic Factors and Secretion Systems: From SPI to T3SS

Salmonella employs virulence factors encoded by Salmonella Pathogenicity Islands (SPIs) to breach epithelial barriers and survive intracellularly. SPI-1 encodes the Type III Secretion System (T3SS-1) for invasion, SPI-2 encodes T3SS-2 for intracellular survival, SPI-7 contains the Vi capsular antigen, SPI-11 encodes toxins like CdtB, and SPI-19 carries T6SS. These systems collectively enable cross-species infection in diverse hosts.

Fig. 2. Schematic diagram of Salmonella structure and secretion system. (doi.org/10.3390/foods12091756)

PhoPQ System and Host Adaptation

A seminal study published in Cell (Bader et al., 2005) identified the PhoPQ system as a critical two-component signal transduction system enabling Salmonella to counter host antimicrobial peptides (e.g., LL-37). PhoQ, a transmembrane sensor kinase, detects cationic antimicrobial peptides and low Mg²⁺ levels, undergoing conformational changes and autophosphorylation to activate the PhoP response regulator. PhoP induces downstream gene expression, including lipopolysaccharide (LPS) modification, outer membrane protein regulation, and polymyxin resistance proteins (e.g., PmrAB system). These adaptations reduce bacterial surface charge to evade TLR4 recognition, enhance membrane stability, and increase resistance, bolstering survival in macrophages and other immune environments.

Fig. 3. Schematic diagram of PhoPQ activation mechanism. (Bader et al., 2005)

Infection Process and Intracellular Survival Strategies

Salmonella crosses the intestinal epithelium via effector-mediated invasion, forming Salmonella-containing vacuoles (SCVs). The SPI-2-encoded T3SS-2 prevents SCV-lysosome fusion and modifies vacuolar membranes to facilitate nutrient acquisition and replication, establishing a stable intracellular niche.

Fig. 4. Schematic diagram of SCV formation and effector transport pathway.(doi.org/10.3390/foods12091756)

Drug Resistance Mechanisms and Epidemiological Trends

Salmonella’s resistance mechanisms include plasmid-encoded resistance genes, efflux pump activation, enzyme modification (e.g., β-lactamases), and chromosomal mutations (e.g., gyrA). Multidrug resistance is increasingly prevalent, particularly in livestock products. S. Typhimurium and S. Enteritidis are the most common serotypes causing human infections, transmitted through eggs, meat, water, and produce. Clinical manifestations include gastroenteritis, bacteremia, and organ complications, with elderly, children, and immunocompromised individuals most vulnerable.

Current Status and Challenges in Vaccine Development

Vaccines for S. Typhi include live attenuated vaccines (e.g., Ty21a, Crucell Switzerland LTD), purified Vi polysaccharide vaccines (Sanofi), and conjugate vaccines (e.g., Typbar-TCV), widely used in high-prevalence regions. However, no broadly effective vaccine exists for non-typhoidal Salmonella (NTS) due to challenges like diverse serotypes (>2,500), heterogeneous virulence and immune profiles, frequent antigenic drift, and difficulties in eliciting mucosal immunity. Future research focuses on:

• Multi-antigen subunit vaccines (integrating O antigens, outer membrane proteins, T3SS effectors)
• Nanodelivery systems to enhance mucosal immunogenicity of oral vaccines
• Attenuated Salmonella strains as vaccine carriers
• Adjuvant designs targeting immune modulation

The goal is to develop safe, broad-spectrum vaccines suitable for vulnerable populations.

Recommended Research Products: abinScience Salmonella Tools

abinScience offers recombinant proteins and antibodies to support Salmonella molecular mechanism and vaccine target research. Targeting key pathogenic factors like cell wall synthesis (murE, murD, murG) and immune evasion (porin OmpC), these products aid in dissecting virulence pathways and identifying vaccine candidates:

About abinScience

abinScience is a global leader in high-quality research reagents, offering recombinant proteins, antibodies, and bulk customization services tailored for life sciences. We collaborate with researchers worldwide to advance studies in pathogenesis, vaccine development, and molecular biology. Our Salmonella research tools are built on scientific precision, accelerating infectious disease research and control.