Microbiology
Summary
Salmonella bacteria are gram-negative, flagellated pathogens that are capable of causing various infections in humans and animals. The two main types of Salmonella are typhoidal salmonella (TS) and non-typhoidal salmonella (NTS). Salmonella is protected by a polysaccharide capsule known as the O-antigen, and can live and replicate inside macrophages, making it a facultative intracellular organism.
Non-typhoidal salmonella infections are common in industrialized countries and are typically zoonotic, with poultry being the primary reservoir. These infections can lead to diseases like gastroenteritis, characterized by fever, nausea, vomiting, diarrhea, and abdominal cramping. Salmonella can also cross the intestinal barrier and spread throughout the body, causing dangerous complications like bacteremia, meningitis, and osteomyelitis. In cases of severe gastrointestinal salmonella or invasive salmonella infections, antibiotics may be necessary for treatment, with fluoroquinolones being the preferred choice and third-generation cephalosporins, such as ceftriaxone, being a viable alternative.
Lesson Outline
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FAQs
Typhoidal salmonella refers to Salmonella serotypes Typhi and Paratyphi, which cause typhoid fever and paratyphoid fever, respectively. These serotypes are more focused on human hosts and are transmitted mainly through contaminated food and water. Non-typhoidal salmonella (NTS), on the other hand, refers to Salmonella serotypes such as Enteritidis and Typhimurium, which cause gastroenteritis. NTS infections are zoonotic, meaning that they can be transmitted from animals to humans, usually through the consumption of contaminated food.
Hydrogen sulfide gas is a byproduct of the metabolism of certain Salmonella species, including Salmonella enterica. In the laboratory, Hektoen agar is used for selective isolation of these species, as this medium contains compounds that allow the detection of hydrogen sulfide gas production as black colonies. The agar also often contains antibiotics and dyes that inhibit the growth of other organisms, making it easier to isolate and identify Salmonella based on its characteristic black color on the agar.
Salmonella enterica is a gram-negative rod-shaped bacterium that is a facultative intracellular organism. Being gram-negative, it has an outer membrane containing lipopolysaccharides, which make it more resistant to certain antibiotics. As a facultative intracellular organism, it can survive and reproduce both inside and outside host cells. This ability allows the bacterium to evade the host immune system and establish infections, which may lead to diseases like gastroenteritis or typhoid fever, depending on the specific serotype.
The most common serotypes of Salmonella associated with gastroenteritis, a type of non-typhoidal salmonella infection, are Salmonella enterica serotype Enteritidis and serotype Typhimurium. These serotypes are zoonotic and can be transmitted to humans through the consumption of contaminated food, particularly from animal products like poultry, eggs, and raw meat.
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