Symptoms of salmonellosis are indistinguishable from those caused by other gastrointestinal pathogens, therefore Salmonella must be identified with further studies. Stool culture in appropriate culture media, such as blood and MacConkey agars, is the most common study to identify the bacteria. When there is not enough bacteria on the sample, enrichment broths may be used to grown more salmonella. Serologic tests with polyvalent and specific antisera may be used to identify the serotype of Salmonella. Blood results from patients with salmonellosis may show unspecific findings, such as: leukocytosis and elevated LFTs on the CBC; hypokalemia and hyper or hyponatremia; elevated inflammatory markers; and bacterial growth on blood cultures. Urinalysis may show hypercalciuria, hypocitraturia and increased ammonium excretion. The bacteria may also be identified in stool by microscopic examination, and lactoferrin tests, however, due to the high dependence on the experience of the operator, in microscopic examination, and high cost and rate of false-positives, of the lactoferrin test, these are not commonly used.

The table below displays nonspecific laboratory abnormalities associated with Salmonellosis, including:^{[1][2][3][4][5]}

Stool cultures in adequate culture media, allow the correct identification of the pathogen responsible for infectious diarrhea. The organism should be isolated from fresh stool. The sample should be planted in different selective and nonselective culture agar media, such as:^[6]

• Blood
• MacConkey
• Bismuth sulfite
• Eosin-methylene blue
• Salmonella-Shigella

In cases where there is reduced number of pathogens, enrichment broths, such as tetrathionate or selenite, may be used prior to culture of bacteria.^[6]

Fecal leukocytes may also be identified in the specimen.^[7]

The identification of the organism allows specific treatment of the disease, as well as appropriate follow-up recommendations.^[8][9]

This test is not routinely performed due to its elevated cost, when compared with the accuracy of the results. Results from fecal cultures are often delayed and show an elevated rate of false-negatives.^[10]

Stool culture may remain positive during 4 to 5 weeks, and in rare cases (chronic) for more than 1 year.^[11]

After identification of Salmonella in stool cultures, the identification of the serologic type of the pathogen is given by serologic testing. Polyvalent and specific antisera should be used.^[6]

For this classification the following bacterial structures are considered:^[12]

• Capsular antigen
• Polysaccharide O antigens
• Flagellar antigens

The examination of stool samples, after staining with methylene blue, helps in the diagnosis of acute diarrhea. This test allows the identification of leukocytes in feces, suggesting an inflammatory etiology for the diarrhea. When the results indicate a serious form of the disease, further studies, such as stool cultures are indicated.^[10] Limitations of this test include:

• Smear must be obtained from a fresh specimen, preferably collected in a cup (sensitivity 95%) ^[13]
• The result is dependent on the experience of the operator

Some studies advocate the importance to test for fecal lactoferrin. This test is considered more sensitive than simple microscopic examination of PMN. The Lactoferrin Latex Agglutination (LFLA) is an in vitro test able to detect a highly sensitive leukocyte marker, indicative of the presence of PMN.^[10]

Its cost and high rate of false-positives in breast-fed children, limit its application.^{[8][14][10][15]}

• 
  Salmonella bacteria in tetrathionate enrichment broth stained using direct FA staining technique. From Public Health Image Library (PHIL). ^[16]
• 
  Salmonella bacteria in tetrathionate enrichment broth stained using direct FA staining technique. From Public Health Image Library (PHIL). ^[16]
• 
  Triple sugar iron agar (TSI) tested for Salmonella (H2S+) and (H2S-); Citrobacter sp. and S. arizonae. From Public Health Image Library (PHIL). ^[16]
• 
  Salmonella sp. bacteria. From Public Health Image Library (PHIL). ^[16]
• 
  SEM depicts a number of red-colored Salmonella sp. bacteria invading a mustard-colored ruffled immune cell. From Public Health Image Library (PHIL). ^[16]
• 
  Salmonella typhimurium bacteria isolated from a pure culture (8000x mag). From Public Health Image Library (PHIL). ^[16]
• 
  Salmonella typhimurium bacteria isolated from a pure culture (20000X mag). From Public Health Image Library (PHIL). ^[16]
• 
  Salmonella typhimurium bacteria isolated from a pure culture (25000X mag). From Public Health Image Library (PHIL). ^[16]

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