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Salmonella

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Salmonella is a genus of rod-shaped bacteria known as bacilli. These organisms belong to the family Enterobacteriaceae. They are classified as Gram-negative, which describes their cell structure. Salmonella is a significant subject in microbiology because it includes many different types. Some of these types cause illness in humans and animals. Understanding these bacteria helps scientists prevent foodborne diseases and manage public health.

FDA Lab 3000 (4494152579)
FDA Lab 3000 (4494152579)

These bacteria have unique ways of moving and surviving. They possess peritrichous flagella, which are hair-like structures located all around the cell body. These flagella allow the bacteria to swim through different environments. Salmonella are also chemotrophs, meaning they get energy from oxidation and reduction reactions. They use organic sources to fuel these processes. Additionally, they are facultative anaerobes. This means they can produce adenosine triphosphate (ATP) using oxygen when it is available. If oxygen is missing, they use fermentation or other electron acceptors to generate energy.

FDA Lab 3000 (4494152579)
FDA Lab 3000 (4494152579)

The genus is divided into two primary species: Salmonella enterica and Salmonella bongori. Salmonella enterica is the type species and is highly diverse. It contains six subspecies, which include S. e. enterica, S. e. salamae, S. e. arizonae, S. e. diarizonae, S. e. houtenae, and S. e. indica. These subspecies are further divided into over 2,650 serotypes. Serotypes are specific varieties defined by their somatic O and flagellar H antigens. Scientists use the Kauffmann–White classification to organize these many different types.

FDA Lab 3000 (4494152579)
FDA Lab 3000 (4494152579)

History shows how our understanding of these bacteria grew over time. Karl Eberth first visualized Salmonella in 1880 within the spleens of typhoid patients. Four years later, Georg Theodor Gaffky successfully grew the pathogen in a pure culture. In 1885, Theobald Smith discovered Salmonella enterica while working for the United States Department of Agriculture. At that time, he worked under Daniel Elmer Salmon, a veterinary pathologist. The name Salmonella was proposed in 1900 by Joseph Leon Lignières to honor Salmon. Later, in the 1930s, Australian bacteriologist Nancy Atkinson established a specialized typing laboratory.

FDA Lab 3000 (4494152579)
FDA Lab 3000 (4494152579)

Salmonella causes different types of illness depending on the serotype. Nontyphoidal Salmonella are zoonotic, meaning they can move between animals and humans. They usually invade the gastrointestinal tract and cause salmonellosis. While these symptoms often resolve without antibiotics, they can be invasive in sub-Saharan Africa. Typhoidal Salmonella serotypes are different because they only transfer between humans. These can cause typhoid and paratyphoid fever by invading the bloodstream and organs. This can lead to serious conditions like septic shock or hypovolemic shock. Such cases require intensive care and antibiotics to treat.

FDA Lab 3000 (4494152579)
FDA Lab 3000 (4494152579)

These bacteria are remarkably resilient in many environments. They can survive desiccation, which is the process of drying out. This allows them to persist in dry foods and environments for years. Salmonella are not destroyed by freezing temperatures. However, they can be killed by heat or UV light. Most die after being heated to 165°F for 12 minutes. If they are in high-fat foods like peanut butter, they can survive up to 165°F for 30 minutes. To stay safe, it is recommended to heat food to an internal temperature of 165°F.

FDA Lab 3000 (4494152579)
FDA Lab 3000 (4494152579)

Modern science uses advanced tools to study and identify these bacteria. Scientists perform serotyping by mixing cells with antibodies for specific antigens. They also use molecular biology techniques like whole genome sequencing. Other methods include pulsed-field gel electrophoresis and real-time PCR. These DNA-based methods can be faster than traditional antibody reactions. Identifying the exact serotype helps investigators find the source of contamination. It also helps doctors choose the right antibiotics based on known resistance. This connection between genetics and medicine is vital for controlling outbreaks.

FDA Lab 3000 (4494152579)
FDA Lab 3000 (4494152579)
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