Salmonella

Medical Author: Charles Davis, MD, PhD
Medical Editor: William C. Shiel Jr., MD, FACP, FACR

• What is Salmonella? What are its characteristics?
• Who discovered Salmonella?
• What kinds of diseases does Salmonella cause? What are symptoms of Salmonella infection?
• How is Salmonella transmitted to humans?
• How do Salmonella spp cause disease in people?
• How do you diagnose Salmonella infections?
• How are Salmonella infections treated?
• How can Salmonella infections be prevented?

What is Salmonella? What are its characteristics?

Salmonella (S.) is the genus name for a large number (over 2,500) of types of bacteria. Each type is distinctly identifiable by its specific protein coating. The types are otherwise closely related. Salmonella bacteria are rod-shaped, flagellated, Gram stain-negative and are known to cause disease in humans, animals, and birds (especially poultry) worldwide.

The terminology that identifies the particular protein coats, or serovars, is not well settled, and what previously were thought to be various species of the genus Salmonella are now thought to be serovars of only two species, S. enterica and S. bongori. However, these designations are not always accepted in the scientific literature and so common serovars that have been named in the past are still used (for example, S. typhi, S. typhimurium, S. enteritidis, S. cholerasuis). The serovars are identified by the Kauffman-White classification that uses two major types of antigens (somatic O and flagellar H) to distinguish the over 2,500 types of Salmonella bacteria. Sometimes laboratories or other reporting agencies identify isolates simply as Salmonella spp (species) and do not identify the serovars.

Who discovered Salmonella?

The bacteria were first isolated by Theobald Smith in 1885 from pigs. The genus name "Salmonella" was derived from the last name of D. E. Salmon, who was Smith's director.

What kinds of diseases does Salmonella cause? What are symptoms of Salmonella infection?

Salmonellosis (gastroenteritis characterized by nausea, vomiting, and diarrhea) is the most common disease caused by the organisms. Over 1.4 million cases per year occur in the U.S., and the rest of industrialized countries have similar rates. Countries with poor sanitation have a much higher incidence of Salmonellosis.

Typhoid fever occurs when some of the Salmonella organisms are not killed by the normal human immune defenses (macrophage cells). Salmonella then survive and grow in the human spleen, liver, and other organs and may reach the blood (bacteremia). Salmonella can be shed from the liver to the gallbladder, where they can continue to survive and be secreted into the patient's feces for up to a year. Symptoms include high fevers up to 104 F, sweating, inflammation of the stomach and intestines, and diarrhea. Symptoms usually resolve but many patients become Salmonella carriers. Approximately half of patients develop slow heartbeat (bradycardia), and about 30% of patients get flat, slightly raised red or rose-colored spots on the chest and abdomen. Typhoid fever is also referred to as enteric fever.

Paratyphoid fever, also termed enteric fever, has symptoms like typhoid, but it's usually not as severe. Subtypes are A, B, and C and vary by having small changes in symptoms, such as more rose spots (A), in conjunction with Herpes labialis and gastroenteritis (B), rarely, with septicemia and abscesses (C).

From the Doctors at MedicineNet.com

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