Key Facts About Salmonella Every Biology Student Must Know
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.
Conclusion
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 on Salmonella: Causes, Symptoms, and Prevention
1. What is Salmonella and what types of illnesses does it cause?
Salmonella is a genus of rod-shaped, Gram-negative bacteria belonging to the Enterobacteriaceae family. It primarily causes two types of illnesses in humans:
- Salmonellosis: A common form of food poisoning (gastroenteritis) that affects the intestinal tract, typically caused by species like Salmonella Enteritidis and Salmonella Typhimurium.
- Typhoid Fever: A more severe, systemic illness that spreads throughout the body, caused specifically by the bacterium Salmonella enterica serovar Typhi.
2. What are the most common sources of a Salmonella infection?
The most common sources of Salmonella are contaminated food and water. Key sources include:
- Raw or undercooked poultry, meat, and eggs.
- Unpasteurised milk and dairy products.
- Contaminated raw fruits and vegetables.
- Infected food handlers who do not practice proper hygiene.
- Contact with infected animals, including pets like reptiles and birds.
3. How is Salmonella transmitted from a source to a human?
Salmonella is primarily transmitted through the faecal-oral route. This happens when a person ingests food or water that has been contaminated with the faeces of an infected person or animal. For example, if a food preparer does not wash their hands properly after using the toilet, they can transfer the bacteria to the food. Similarly, vegetables can get contaminated if irrigated with water containing sewage.
4. What are the primary symptoms of Salmonellosis (Salmonella food poisoning)?
The primary symptoms of Salmonellosis typically appear 6 to 72 hours after infection and include:
- Diarrhoea (which may be bloody)
- Fever
- Abdominal cramps
- Nausea and vomiting
- Headache
5. How does the Salmonella bacterium cause disease once it enters the body?
Once ingested, Salmonella bacteria survive the stomach acid and invade the cells lining the small intestine. Inside these cells, they multiply and produce endotoxins. This triggers a strong inflammatory response from the body's immune system, leading to the damage of intestinal tissue and causing symptoms like diarrhoea and cramps. The release of endotoxins into the bloodstream contributes to the fever.
6. What is the main difference between Typhoid fever and common Salmonellosis?
The main difference lies in the severity and location of the infection. Salmonellosis is typically a localised infection confined to the gastrointestinal tract. In contrast, Typhoid fever, caused by S. Typhi, is a systemic infection. The bacteria pass from the intestine into the bloodstream and then spread to other organs like the liver, spleen, and bone marrow, causing a high, sustained fever and more severe complications.
7. How is Typhoid fever, caused by Salmonella typhi, specifically diagnosed?
Typhoid fever is confirmed through a diagnostic blood test known as the Widal test. This test is designed to detect the presence of specific antibodies (agglutinins) that the body produces against the O (somatic) and H (flagellar) antigens of the Salmonella typhi bacterium. A rising titre of these antibodies in the patient's blood serum indicates an active infection.
8. What are the most effective ways to prevent Salmonella infections?
Prevention focuses on hygiene and safe food handling practices. Key measures include:
- Cooking food thoroughly: Ensure poultry, ground meat, and eggs are cooked to a safe internal temperature.
- Avoiding cross-contamination: Use separate cutting boards for raw meat and produce, and wash hands, knives, and surfaces after handling raw food.
- Practising good hygiene: Wash hands with soap and water frequently, especially after using the bathroom and before preparing food.
- Using safe water: Drink and cook with water from a safe, treated source.
9. Can a person who has recovered from Typhoid fever still spread the infection?
Yes, some individuals can become chronic asymptomatic carriers of Salmonella typhi after recovering from Typhoid fever. The bacteria can persist in their gallbladder for years without causing any symptoms. These carriers continue to shed the bacteria in their faeces and can unknowingly infect others, acting as a reservoir for the disease. The classic historical example is "Typhoid Mary".
10. How serious is a Salmonella infection, and what is the typical treatment?
For most cases of Salmonellosis, the illness is self-limiting and resolves within a week. The main treatment is supportive care, focusing on rehydration to replace fluids lost from diarrhoea and vomiting. However, for severe infections, or for all cases of Typhoid fever, doctors prescribe antibiotics to kill the bacteria. If left untreated, Typhoid can lead to serious complications, including intestinal perforation or sepsis, which can be fatal.
