Salmonella
Introduction
Salmonella is a genus of rod-shaped Gram-negative bacteria that belongs to the family Enterobacteriaceae. The bacteria are named after Daniel Elmer Salmon, an American veterinary surgeon who first identified them in 1885. Salmonella species are non-spore-forming, predominantly motile enterobacteria with cell diameters between about 0.7 and 1.5 µm, lengths from 2 to 5 µm, and flagella that grade in all directions (i.e., peritrichous).
Classification
The Salmonella genus has two species, S. enterica and S. bongori. S. enterica is the type species and is further divided into six subspecies that include over 2,600 serotypes. Salmonella serotypes are distinguished by a number of serological and biochemical characteristics. They can be classified into two broad categories: typhoidal and non-typhoidal Salmonellae.
Pathogenesis
Salmonella infections can be broadly divided into two types: gastroenteritis and typhoid fever, both of which are acute diseases. Salmonella species can also cause systemic diseases and chronic carrier states. The pathogenesis of Salmonella is a complex process that involves several stages: the entry into the host organism, the invasion of host tissues, the evasion of the host immune response, and the replication and spread within the host.
Epidemiology
Salmonella is one of the most common causes of foodborne illness worldwide. In the United States, the Centers for Disease Control and Prevention (CDC) estimates that there are about 1.35 million infections, 26,500 hospitalizations, and 420 deaths caused by Salmonella each year. Most people infected with Salmonella develop diarrhea, fever, and abdominal cramps between 12 and 72 hours after infection.
Diagnosis
The diagnosis of Salmonella infection involves isolating the organism from the infected individual. This is typically done by culturing the bacteria from a sample of the patient's stool. Other methods of diagnosis include serological tests and molecular methods such as polymerase chain reaction (PCR).
Treatment
Treatment of Salmonella infection depends on the severity and type of the disease. Most people with Salmonella gastroenteritis recover without specific treatment. However, in severe or systemic infections, antibiotics are often required. The choice of antibiotics is guided by the susceptibility pattern of the particular strain of Salmonella that caused the infection.
Prevention
Prevention of Salmonella infection involves proper food handling and preparation practices, such as cooking food to the right temperature and avoiding cross-contamination. Vaccines are also available for certain types of Salmonella.