What is Salmonella?

One of the symbiotic bacteria living in our intestinal tract is Salmonella. This is a Gram-negative rod-shaped bacterium with different species and subspecies. It causes infection when it enters our digestive system through contaminated food. The species that live in our GI system are different from those causing the infections. In this section, we will study Salmonella, its different species, its cytology, cell structure, shape, and its nature.

Salmonella is a very common bacteria that can be found in our food. It can be present in processed food and can make us sick. In fact, two of the species of this bacterium are also present in our intestinal tract and of other animals.

As per the Salmonella typhi diagram, this is a rod-shaped Gram-negative bacterium that can cause food poisoning as pathogens. It is anaerobic in nature and falls in the family of Enterobacteriaceae. The two prime species are Salmonella bongori and Salmonella enterica. The enterica species have six subspecies and continued to have 2600 serotypes. It was first identified by an American vet named Daniel Elmer Salmon and was named after him.

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This is a non-sporophytic motile enterobacterium that has flagella spread across the body. It uses the flagella to move around in its ecosystem. as mentioned earlier, it is an anaerobic bacterium that lives in the absence of oxygen. All the species are facultative anaerobes which means they can produce ATP when in contact with oxygen or do not produce this energy unit in absence of oxygen. The Salmonella Gram stain is negative.

What is Salmonella Typhi?

Salmonella typhi is the salmonella species that causes typhoid. When it enters the system through contaminated water or food, it starts to reproduce vigorously causing the symptoms of typhoid. The infection caused by Salmonella bacteria is called salmonellosis. On the other hand, paratyphoid fever is caused by Salmonella paratyphi. The other species causing paratyphoid fever are S. hirschfeldii and S. schottmuelleri. All these are the different variants of S. enteridis.

The Salmonella typhi structure suggests its rod-shaped cytology with the presence of flagella around its body. The movement of these bacteria is controlled by these flagella. The diameter of the cell varies from 0.7 μm to 1.5 μm. This species does not need oxygen to build its food and energy. It depends on the chemotropic reactions (oxidation and reduction of organic sources) inside the hosts.

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The Salmonella typhi gram stain is negative. This pathogen enters the system of a human being via the gastrointestinal tract via contaminated water and food. It then passes through the intestinal lymphatic system and enters the circulatory system. Once it enters the blood, it can then reach the major organs such as the liver, spleen, and kidneys and take the secondary foci form. The endotoxins released due to the reproduction and the disruption of the cell envelopes cause different symptoms such as abnormal thermal regulation, nausea, vomiting, diarrhea, etc. They also act on the nervous and vascular apparatus of the infected person’s physiology at first and increase the permeability of the vessels. The Salmonella typhi shape and structure aid them to pass the lymphatic barrier in the small intestines and to enter.

What Happens Due to Salmonella Invasion?

In the severe form of typhoid fever, the infected person loses electrolytic balance due to the loss of water. The water-salt metabolism is extremely affected causing a significant decrease in the circulatory fluid volume. Eventually, the arterial pressure drops, and the patient may reach hypovolemic shock. In many cases, patients can also suffer from a septic shock. Most cases of salmonellosis significantly show the symptoms of both shocks. Renal involvement can make the cases worst. It happens due to toxemia and hypoxia.

Its invasion can also cause gastroenteritis, an infection in the gastric region. The pathogens enter the host’s body via food or water and then start multiplying. Colonizing occurs due to the heavy reproduction of these species. S. choleraesius can also cause heavy blood poisoning. There are different species causing different kinds of diseases in humans. A proper culture of the samples collected reveals the strain. Significant treatment is planned accordingly. It has also been found that most of the infection cases go undetected.

Causes of Salmonella Infection

The prime cause of salmonella bacteria contamination is eating undercooked raw meat such as chicken, beef, duck, turkey, pork, etc. Eating raw vegetables and fruits can also cause the same infection. Undercooked raw eggs and unpasteurized milk can also contain this bacterium species. Proper hygiene should be maintained to avoid contamination. Washing hands properly and keeping pets clean is mandatory in a household.

Symptoms of Salmonella Infection

  • Stomach cramps

  • Blood in stool

  • Cold chills

  • Diarrhea

  • Fever

  • Headache

  • Vomiting

  • Upset stomach

These symptoms should be brought under medical supervision to get the underlying problem detected. Treatment should be started according to the diagnosis or it can take time to cure a patient properly. As we know Salmonella Gram positive or negative, the specific set of antibiotics is started under medical supervision.  


After reading about this bacterium species, you can easily answer whether Salmonella is Gram positive or negative. Learn more about this rod-shaped bacterium and how it causes such diseases.

FAQs (Frequently Asked Questions)

1. What is the Salmonella SPP Gram Stain?

Ans: As per the cytology of this bacterium, the Salmonella SPP Gram stain is negative. This species has flagella all over its body for swift movements within the host tissues. It belongs to the Family Enterobacteriaceae.

2. How Does Salmonella Gram Stain Negative Enter a Host?

Ans: Salmonella is generally found in undercooked food and contaminated water. It reaches the host’s gastrointestinal tract and crosses the lymphatic barrier. After crossing the barrier, it enters the circulatory system and reaches the major organs and tissues.

3. How Endotoxins are Produced Causing the Symptoms of Salmonellosis?

Ans: Salmonella Gram stain-negative bacteria enter the host cells, use their organic resources by chemotrophic means, reproduce, and disrupt the cells to come out. During this disruption, the endotoxins or the waste products are released into the blood circulatory system. These endotoxins cause the symptoms in a host.