Immunogenic Activity of Lipopolysaccharide Isolated from Salmonella enterica serovar Typhimurium and Conjugated with Liposome in Albino Male Mice.

This study was designed to evaluate the role of Salmonella enterica serovar Typhimurium as a causative pathogen in hospitalized diarrhoeal patients younger than five years old, extract and purify endotoxin (lipopolysaccharide; LPS) from isolated and identified S. Typhimurium, and determine the immunogenic activity (humoral and cellular immune responses) of LPS-liposome conjugate in albino male mice. The patients (95 cases) were admitted to the Central Pediatric Hospital and Al- Kadhiymiah Pediatric Hospital in Baghdad during the period 24/10/2010 - 30/11/2010, because of severe diarrhoea and fever. Bacterial evaluation of stool samples revealed the identification of two (2.1%) S. Typhimurium isolates (S1 and S2). Antibiotic sensitivity test demonstrated that S1 isolate was more resistance than S2 isolate; therefore it was considered more virulent and subjected for extraction and purification of LPS. Chemical characterization of the extracted LPS revealed that the carbohydrate content was 2.34 mg/ml, while the protein concentration was very low (0.52 μg/ml). Partial purification of extracted LPS by using gel-filtration chromatography (Sephacryl S200) showed three peaks, and after determination of protein and carbohydrate concentrations for each peak, peak two was observed to have the highest carbohydrate content (25%) and the lowest contaminated protein (0.001%). The LPS of this peak was immunologically evaluated in mice at a concentration of 100 μg/ml, alone or in conjugation with a commercially available liposome (LIP). These evaluations revealed that LPS-LIP conjugate was able to modulate the humoral and cellular immune responses against live S. Typhimurium.