Salmonella enterica

Salmonella enterica is a rod-shaped, Gram-negative bacterium. It is a member of the Salmonella genus. This microorganism is a facultative anaerobe, meaning it can grow with or without oxygen. It is also a flagellate, which means it uses whip-like structures to move. Salmonella enterica is a very resilient organism. It can survive for long periods in hot and dry environments. This toughness helps it survive in harsh places like farm settings. It also helps the bacteria survive the difficult environment of the gastrointestinal tract.

The bacterium is divided into six distinct subspecies. These are arizonae, diarizonae, houtenae, salamae, indica, and enterica. Most versions that cause human disease belong to the enterica subspecies. Each subspecies has many different serovars, which are variations based on antigenic specificity. There are over 2,500 known serovars. Some important serogroups include S. Typhi, which causes typhoid fever. Other notable serovars are S. Enteritidis, S. Paratyphi, S. Typhimurium, and S. Choleraesuis. The subspecies arizonae is named after the state of Arizona. It is commonly found in cold-blooded animals like snakes.

Salmonella enterica uses complex mechanisms to infect hosts. The bacteria produce secreted proteins that are vital to their pathogenesis, or the process of causing disease. They possess many adhesins, which are proteins that help the bacteria stick to host cells. These adhesins also help the bacteria form biofilms. Once they attach, secreted proteins help the bacteria invade host cells. They also help the bacteria multiply inside those cells. Regulatory proteins, such as IgaA, help the bacteria maintain their outer envelope. These proteins also help the bacteria respond to stress during an infection.

The bacteria also have advanced ways to repair their own DNA. When exposed to bile salts, the bacteria experience DNA damage. This exposure can cause specific types of mutations. To fix this, Salmonella enterica uses a process called base excision repair. It also uses an enzyme called RecBCD for recombinational repair. This ability to repair DNA makes the bacteria even more resistant to the environment. Additionally, small nonprotein-coding RNAs, or sRNAs, help regulate the bacteria. For example, an sRNA called AsdA helps regulate DNA replication. This helps the bacteria manage how they divide and grow.

History shows that this bacterium has been with humans for a very long time. Scientists have reconstructed genomes from human remains that are 6,500 years old. These remains were found across Western Eurasia. This suggests that the bacteria were widespread during prehistory. In the 16th century, Salmonella enterica may have caused an epidemic in New Spain, now Mexico. This epidemic was known as cocoliztli. In 1545, the outbreak spread very quickly. Over the next century, the disease killed up to 90% of the Indigenous population.

In the United States, Salmonella enterica is the leading foodborne pathogen. It causes the highest number of deaths and the greatest cost burden from foodborne illness. The primary reservoir, or home, for the bacteria is poultry. About 70% of human cases come from eating contaminated eggs, chicken, or turkey. Bacteria can live in animal intestinal tracts, soil, bedding, and fecal matter. In eggs, the bacteria often start in the egg whites. If an egg stays at room temperature, the yolk membrane can break. This allows the bacteria to spread into the yolk.

Preventing infection requires careful food handling. Refrigeration and freezing can slow the growth of bacteria, but they do not kill all of them. Commercial producers use pasteurizing or food irradiation to kill the bacteria in foods like ice cream. At home, foods made with raw eggs, like mayonnaise or cookies, must be cooked properly. Certain people are at higher risk for serious illness. This includes children under five, the elderly, and immunosuppressed adults. If the disease causes systemic dissemination, it can lead to anemia or septicaemia. Once these complications appear, the mortality rate is 15%. Doctors often treat these cases with antibiotics like fluoroquinolones and plenty of fluids.