It is the causative organism of typhoid fever. People exposed to contaminated meat, eggs, or poultry, or those in close contact with animals such as turtles, snakes, lizards, iguanas, and dogs, are at risk of salmonellosis. Salmonellosis is a reportable disease.
Vi antigen is a heat-labile surface antigen that acts as a virulence factor for Salmonella by protecting the bacteria from opsonization. Salmonella can cause enteric (typhoid/paratyphoid) fever, enterocolitis, septicaemia, and osteomyelitis.
Once Salmonella enter the gastrointestinal tract through contaminated food or water, they grow and multiply in the intestinal Peyer’s patches. From there, they enter the bloodstream and spread throughout the body, with a predilection for the gallbladder and the reticuloendothelial system. Persistent infection of the gallbladder can lead to a chronic carrier state. In fulminant infections, Peyer’s patches may ulcerate, which can cause intestinal perforation.
Classically, a “step ladder” pattern of fever is seen. Patients may present with diffuse abdominal pain, constipation, delirium, splenomegaly, and bradycardia in later stages. Without treatment, symptoms become progressively worse.
Rose spots may be seen on the trunk. These are salmon-colored, blanching, maculopapular rashes, typically fewer than 5 in number. They are caused by bacterial embolisation to the dermis.
Patients with sickle cell anemia are predisposed to Salmonella osteomyelitis. Salmonella enterocolitis presents with abdominal pain and diarrhea, usually with blood in the stools.
Samples include stool and blood for culture, as well as bone marrow and bile. Culture shows non-lactose-fermenting colonies with a characteristic jet black color and metallic sheen on Wilson and Blair medium. Blood cultures should be examined by subculture for 10 days before issuing a negative report.
Biochemically, all strains ferment glucose with acid and gas production, except for S.typhi, which forms acid only. H2S is produced by all except S.paratyphi A and S.cholerae-suis. Slide agglutination tests can be done for epidemiological purposes.
Antibody detection can be done by Widal test (not used that much these days), indirect haemagglutination, counter immunoelectrophoresis (CIEP), ELISA, or radioimmunoassay. Demonstration of a rise in titre of antibodies is diagnostic. Antibody tests may be negative during the first 10 days of infection.
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