Salmonella typhi

Typhoid is a moderate to severe bacterial infection caused by Salmonella typhi. Headaches, diarrhea, constipation, abdominal pain, weakness, and vomiting are just a few of the signs and symptoms. Confusion arises from severe symptoms. Typhoid infections are caused by a lack of sanitation and a lack of hygiene. Culturing the blood and stool is a method of therapy. Antibiotics like fluoroquinolones, azithromycin, or third-generation cephalosporins are used to treat typhoid. The biochemical test for Salmonella typhi is xylose lysine deoxycholate agar (XLD) or triple sugar iron agar (TSI). The Widal test is still in widespread use, even though it can produce false-positive results. The testing of the salmonella typhi is through the biochemical test: xylose lysine deoxycholate agar (XLD) or Tripple sugar iron (TSI). Currently, the Widal test is widely on use even though it can give wrong positive results. The rapid test consists of the sensitivity of an immunochromatographic test. The sensitivity of IgM is 85% and 99% within 15 minutes.


Salmonella typhi is a bacteria causing typhoid fever which is an acute illness. Salmonella typhi is a gram negative bacteria containing outer and inner membrane. Due to the complex regulatory system of Salmonella typhi, it can respond to the external environment. Sigma factors alter the specificity of the RNA polymerase which produces the stress proteins, hence adapting to any environmental changes (Gal-Mor et al. 391). RNA polymerase regulates the 50 other proteins expression. It also responds to the variations in the PH, temperature, and starvation (Humphries 1108). Salmonella can grow in both aerobic and anaerobic environment. Bacteria can survive in food chain due to the ability to change the genotype and phenotype in response to change in the environment. Therefore, Salmonella bacteria are hard to control in the food due to the pathogenic nature.

Signs and symptoms

The first week: temperature of the body rises, headache, cough, and fluctuations on fever. Epistaxis: bloody nose and the possibility of the abdominal pain. Numbers of the white blood cells decrease with relative lymphocytosis and eosinopenia (Khan 851). If the patient undergoes Widal test by culturing the blood, the test will give negative results against salmonella typhi.

The second week: high fever of 1040F with dicrotic pulse wave. There is an appearance of the rose spot on the abdomen and lower chest. The fever rises at afternoon with the possibility of frequent constipation, and the pain extends to the bottom quadrant of the abdomen. Stool with smelly characteristics and diarrhea can also happen. Liver and spleen will also enlarge (Khan 851). Blood culture is positive at this stage. The Widal test is positive with antiH and antiO antibodies.

The third week: complication develops including respiratory diseases and acute bronchitis. The risk of the bleeding increases: due to platelet level going down. Intestinal haemorrhages as a result of the bleeding and metastatic abscesses. There is dehydration and patients are in typhoid states while a third of patients develop a macular rash (Khan 851).

Causes of the salmonella typhi

Contamination of vegetables and fruits

Raw egg

Lack of hygiene: in food preparation.

Eating uncooked food

Most amphibians and reptiles have salmonella in their guts .when they shed dropping, can come into contact with the skin, furniture, toys or clothing.


Salmonella bacteria invades the small intestines if the one consumer’s food or water under contamination. Usually, the salmonella bacteria flow with blood cells in liver, spleen and bone marrow place where multiplication takes place. The bacteria can multiply in a significant number of bacteria attacking lymphatic tissue and gallbladder (Khan 851). When the bacteria pass through the intestinal tract, the diagnosis can be in the form of stool.

Diagnosis is through stool, bone marrow, and blood culture through a Widal test (Salmonella antigens H-flagellar and O-somatic against antibodies).The Widal test is prone to the false positive results and more time-consuming (Panchalingam 301). The therapeutically trial time is given in an epidemic countries together with the chloramphenicol pending culture of the stool and blood in widal test. ELISA test detects the IgG and IgM antibodies against Salmonella typhi’s outer membrane protein (OMP).IgM means the remote infection while the IgM shows the recent infection (Humphries 1111). The ELISA test in one of the Typhidot medical test: shows positive results within two to three days. The Typhidot medical test saturates the nitrocellulose to confirm the specificity of the presence of the IgG and IgM antibodies. Three diagnostic test are; Typhidot test that shows in one hour the presence of IgG and IgM (sensitivity 95% and sensitivity is greater than95% respectively). Typhidot-M: (sensitivity 90% and sensitivity 93%) which detects only IgM. Typhidot rapid is very fast in 15 minutes in IgM in an immunochromatographic test with a sensitivity of 85% and 99% (Humphries 1112).


Hygiene and sanitation are important in the prevention of the salmonella typhi. Washing of hands after going to the toilets prevents the contamination of the bacteria. Proper washing of the vegetables and fruits before eating is important for preventive measures.

Biochemical test

Tripple sugar iron (TSI)

TSI (lactose, sucrose, and glucose and iron) is similar to Kligler’s iron agar except that KIA contains 1% lactose and 0.1% glucose (Panchalingam 295). Sucrose helps in identification of the gram negative bacteria while sucrose aids in the detection of the bacteria coliforms.


Streaking method: involves sterile needle over the surface of the media. Then inoculation: inoculum in ambient air of 350c in 18-24 hours (Panchalingam 297). If the results show production of the black color, it means the production hydrogen sulfide gas which forms ferrous sulfide.

XLD (xylose lysine deoxycholate agar)

XLD is a selective growth media for the shigella and salmonella species isolation in medical samples. The agar has a PH of 7 with red or bright red due to the coloration of the phenol red indicator. The phenol red indicates the color change to yellow due to lowering of PH as a result of sugar fermentation (Panchalingam 299). Acid production occurs when Salmonella bacteria ferment the xylose sugar. Shigella is unable to ferment the sugar due to decarboxylation of the lysine by salmonella, PH will increase. Differentiation occurs where salmonellae metabolize thiosulfate to form black center as a result of hydrogen sulfide.


In a case of the untreated cases, 10%-30% can lead to the death. However, the fatality rate can increase up to the 47%.bacteria can cause intestinal perforation (Humphries 1110). Treatment in the area where there is a low-level resistance of the bacteria, ciprofloxacin gives the best results. In a case of the oral administration, the Cefixime is effective (Humphries 1112). The event of the active resistance of the bacteria to the drug, cephalosporins like cefotaxime and ceftriaxone is the first drug to give to the patients.

Works cited

Gal-Mor, Ohad, Erin C. Boyle, and Guntram A. Grassl. “Same species, different diseases: how and why typhoidal and non-typhoidal Salmonella enterica serovars differ.” Frontiers in microbiology 5 (2014): 391.

Humphries, Romney M., et al. “In vitro susceptibility testing of fluoroquinolone activity against Salmonella: recent changes to CLSI standards.” Clinical infectious diseases 55.8 (2012): 1107-1113.

Khan, S., et al. “Early diagnosis of typhoid fever by nested PCR for flagellin gene of Salmonella enterica serotype Typhi.” Indian Journal of Medical Research 136.5 (2012): 850.

Panchalingam, Sandra, et al. “Diagnostic microbiologic methods in the GEMS-1 case/control study.” Clinical infectious diseases 55.suppl 4 (2012): S294-S302..

Waddington, Claire S., et al. “An outpatient, ambulant-design, controlled human infection model using escalating doses of Salmonella Typhi challenge delivered in sodium bicarbonate solution.” Clinical Infectious Diseases 58.9 (2014): 1230-1240.

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