Salmonella

According to the "Quality Control of Laboratory Animals for Biopharmaceutical Production and Testing" section within the third volume of the 2020 Pharmacopoeia, which covers "Specific Biological Raw Materials/Animals and Excipients," Salmonella is identified as a mandatory pathogen to be excluded from clean-grade and SPF-grade mice used for identification purposes, as well as from production-use mice. This article will provide a brief introduction to Salmonella.

Laboratory animal personnel are no strangers to this bacterium. Salmonella is a common zoonotic pathogen that poses significant threats to both human and animal health. Globally, salmonella-related foodborne illnesses rank highest among all food poisoning cases. In developed countries such as the United States and Japan, 40% to 60% of foodborne outbreaks are caused by poultry-associated Salmonella strains, with Enteritidis being the primary pathogen. Meanwhile, in China, 70% to 80% of bacterial foodborne illnesses are attributed to Salmonella.

Salmonella, discovered over a century ago by Salmon, is a group of important pathogenic bacteria that pose significant health risks to both humans and animals. This genus encompasses a wide variety of serotypes and exhibits complex antigenic structures. Since its first isolation in 1885 by Salmon and Smith from swine cholera, more than 67 serogroups, along with over 2,000 serotypes and variants, have been identified in both humans and animals. Among these, the most common include Salmonella enterica, Salmonella Typhimurium, and Salmonella Choleraesuis. Salmonella demonstrates a certain level of resilience against external environmental conditions—surviving for weeks to months in water, milk, meat, and egg products; persisting for 1 to 10 months in feces; and maintaining viability for several months even in frozen environments. However, it lacks strong resistance to heat.

Salmonella is considered one of the most significant foodborne pathogens worldwide today. Foodborne transmission is the primary route through which humans become infected with Salmonella, and many foods—including meat (especially poultry), eggs and egg products, unpasteurized milk and dairy products, and seafood—are commonly associated with salmonellosis. Human salmonellosis typically manifests as nausea, vomiting, diarrhea, abdominal pain or cramping, fever, and headache. The incubation period ranges from 8 to 72 hours, with symptoms usually appearing 12 to 36 hours after consuming contaminated food. In some cases, symptoms may persist for up to a week.

Intestinal infections are the most common manifestation of Salmonella infection, causing digestive symptoms such as diarrhea, nausea, vomiting, and abdominal pain. Pathologically, these infections primarily result in inflammation and damage to the intestinal mucosa, including redness and swelling of the gut, ulcer formation, and bacterial invasion. Typhoid fever and paratyphoid fever, on the other hand, are systemic infections mainly caused by Salmonella, with symptoms including high fever, weakness, fatigue, headache, loss of appetite, and abdominal pain. At the pathological level, these conditions typically involve hyperplasia and inflammation of lymphoid tissues and the spleen, and may also lead to lesions in the liver and other internal organs. Salmonella can spread via the bloodstream to the skeletal system, triggering osteomyelitis, which manifests as persistent bone pain, joint inflammation, localized redness and swelling, and restricted mobility. The primary pathological changes here include inflammation and destruction of the bone marrow, as well as involvement of the surrounding bone tissue. Additionally, Salmonella can cause pulmonary infections, particularly in individuals with compromised immune systems, leading to symptoms such as fever, cough, shortness of breath, and chest pain. Pathologically, this often results in inflammation and damage to lung tissues, including alveolitis and interstitial pneumonia.

The interaction between Salmonella infection and the host immune system is a complex process, which can be better understood by investigating Salmonella's infection mechanisms and the host's immune responses—insights that deepen our knowledge of immunology fundamentals. For instance, studying how Salmonella evades the host immune response or triggers inflammatory reactions sheds light on the mechanisms by which the host immune system detects and regulates bacterial infections.

Salmonella is an important pathogen, and studying its pathogenic mechanisms helps uncover the biological characteristics and disease-causing strategies of this bacterium, thereby providing a theoretical foundation for developing new preventive and therapeutic approaches. By investigating Salmonella's virulence factors and the molecular mechanisms underlying bacterial-host interactions, researchers can identify innovative ideas and methods for disease prevention and control.

Salmonella infections have a high incidence rate worldwide, and traditional antibiotics are increasingly facing growing resistance from Salmonella. Therefore, it is crucial to investigate drug-based strategies for preventing and treating Salmonella infections, as well as to identify novel drug targets and antimicrobial agents. By simulating Salmonella infections in the laboratory and evaluating the inhibitory effects of antibacterial drugs, researchers can uncover promising new antibiotics and antimicrobial therapies.

Salmonella is a common foodborne pathogen capable of contaminating food and causing food poisoning incidents. Therefore, studying the spatiotemporal distribution, epidemiological trends, and transmission routes of Salmonella infections can help inform the development and refinement of public health policies, ultimately enhancing food safety standards.

Salmonella is primarily transmitted through food, making food safety crucial for preventing infection. This involves implementing proper food-handling practices—such as thoroughly cooking meals, meticulously washing fruits and vegetables, and avoiding the consumption of raw or undercooked foods. Additionally, it’s important to monitor and maintain appropriate storage temperatures to prevent contamination from moisture or high-heat environments. Individuals infected with Salmonella should avoid close contact with others, especially during periods of fever. Furthermore, infected individuals should follow their doctor’s guidance in selecting the right antibiotic treatment and complete the full course of therapy to minimize the risk of spreading the infection. Finally, to address contamination sources in environments affected by Salmonella, ensure thorough cleaning and disinfection using chlorine-based disinfectants, alcohol, or other effective sanitizers on surfaces. At the same time, maintaining good indoor ventilation is essential to curb bacterial growth and proliferation.

The key to preventing and eliminating Salmonella infections lies in food safety, personal hygiene, controlling animal contact, avoiding cross-contamination, and ensuring proper disinfection. By implementing these measures effectively, you can significantly reduce the risk of infection and eradicate the presence of Salmonella.

In the context of widespread Salmonella infections, laboratory animal facilities and personnel should pay close attention to this issue. Readers are encouraged to share your valuable experiences and suggestions.  

References

1. Chinese Pharmacopoeia 2020 Edition

2. Food Microbiology Testing – Salmonella Testing GB4789.4-2010

3. Research Progress on Methods for Detecting Foodborne Salmonella Huang Wenyu, Liu Chenjian

4. Classification, Nomenclature, and Distribution of Salmonella Serovars in China: A Review by Zhang Hezhan, with Editorial Review by Shi Qingwu

5. Risk Assessment of Salmonella in Animal-Derived Foods Wang Jun, Zheng Zengren, Wang Jingyu

6. 2005 Detection of Salmonella in Meat Using PCR and Culture Methods

7. 2007 Comparison of Culture, ELISA & PCR for Salmonella Detection in Fecal Samples from Cattle, Pigs, and Poultry