The study was conducted to assess 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 Salmonella enterica serovar Typhimurium, determine the role of LPS-liposome conjugate as a potential vaccine against Salmonella enterica serovar Typhimurium in albino male mice, and finally evaluate humoral and cellular immune responses (total and absolute counts of leukocytes, phagocytosis, Arthus reaction; AR and delayed type hypersensitivity reaction; DTHR) of vaccinated mice, in addition to histopathological changes in liver and spleen. Ninety five patient were admitted to the Central Pediatric Hospital and AlKadhiymiah 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%) Salmonella enterica serovar Typhimurium isolates (S1 and S2). Antibiotic sensitivity test demonstrated that S1 isolate was more resistance than S2 isolate; therefore it was considered morevirulent and subjected for further manipulations, which included extraction of LPS from the bacterial outer membrane. 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 extracted LPS by using gel-filtration chromatography (sephacryl 200 S) showed three peaks, and after determination of protein and carbohydrate concentrations for each peak, the second peak 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).
