Salmonellosis (also called "a disease of civilization") is widespread across the globe, including the Russian Federation. Hence, measures to lower the morbidity of human beings, animals, and to limit propagation of infectious causative agents are needed. We studied colonization resistance and Salmonella typhimurium No5715 dissemination into chickens' tissues and organs. The duration of the experiment was 30 days. We identified microorganisms to study colonization resistance of bowels and salmonella dissemination into chickens' tissues and organs. We used the microscope "H604T Trinocular Unico" for morphological studies. We noticed acute and subacute course of salmonellosis, extensive vessel hemorrhages, cyanosis, hyperemia, numerous dotted and spotted hemorrhages in chickens' tissues and organs. Pathological signs developed were accidental transformation of thymus, bursa of Fabricius' atrophy, hyperplasia of the spleen, catarrhal-hemorrhagic pericarditis, air sacculusis, enteritis, perihepatitis, stagnant hemorrhagic infarct of kidneys. Common symptoms of infection were observed, such as exudation and infiltration, increase of plasma clumps, macrophage reactions, perivascular edema, and disseminated thrombosis. The study confirms that salmonellosis is a dangerous disease that can affect many organs and requires etiologic and pathogenetic treatment.