Is Salmonella Evolving Into A Stronger, More Dangerous Infection?

EAST LANSING, Mich. — Salmonella cases in the state of Michigan are becoming increasingly severe and harder to treat, causing researchers to take notice. The food-borne bacterial infection is usually treatable through proper hydration and the use of antibiotics if caught early enough. However, researchers from Michigan State University have found a significant increase in antibiotic-resistant salmonella strains, and consequently, longer hospital stays for infected patients.

While this set of research focused on Michigan, the study’s authors believe their findings could act as a model of sorts for salmonella behavior patterns in other areas of the country.

“If you get a salmonella infection that is resistant to antibiotics today, you are more likely to be hospitalized longer, and it will take you longer to recover,” comments senior study author Shannon Manning, MSU Foundation professor in the Department of Microbiology and Molecular Genetics, in a release. “We need better detection methods at the clinical level to identify resistant pathogens earlier so we can treat them with the right drugs the first time.”

Now more than ever, researchers say it is important to identify and treat salmonella infections as soon as possible. Just one or two extra days without treatment could result in a much more rapid development of symptoms than in the past. Furthermore, in antibiotic-resistant strains, doctors may be able to get rid of a portion of the bacterial subpopulation, but especially resistant areas actually appear to be growing stronger in many cases.

For reference, typical salmonella infection symptoms include abdominal pain, nausea, and diarrhea, but more serious infections can become life threatening.

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The margin for error is also shrinking for Michigan doctors. There are various strains of salmonella, and each one reacts differently, and defends against, antibiotic treatments in its own way. So, correctly identifying salmonella strains in an efficient manner can make all the difference.

More specifically, doctors in Michigan are seeing an increasingly large number of strains that are resistant to ampicillin, one of the most commonly prescribed salmonella-fighting antibiotics. Making matters worse, there has also been an influx of multi-drug resistant salmonella strains, or strains capable of fighting off more than three antibiotic classes

“We’re still uncertain as to why this is happening; it could be that these antibiotics have been overprescribed in human and veterinary medicine and that possessing genes for resistance has allowed these bacteria to grow and thrive in the presence of antibiotics,” Manning continues. “Each state has its own antibiotic-resistance issues. It’s important that the medical profession remains vigilant to ever-changing patterns of resistance in salmonella and other foodborne pathogens, rather than look for a blanket national solution.”

Salmonella most commonly affects young children and the elderly, but Michigan has also seen adult diagnoses steadily increase in recent years. According to the study’s authors, this suggests that the very epidemiology of the infection appears to be evolving, at least in Michigan.

As far as individual strains, researchers noted that patients with Typhimurium were very likely to have antibiotic-resistant infections, as well patients who were infected during the winter, fall, or spring. Also, salmonella patients from more rural areas were more likely to experience intestinal inflammation and diarrhea. The study’s author theorize this is due to rural residents’ more frequent exposure to farm animals and dirty water.

Salmonella populations in different areas actually behave differently, so the research team made it a priority to advise that each state devise their own unique protocols and methods for dealing with salmonella.

“Our results show the importance of surveillance, monitoring resistance frequencies and identifying risk factors specific to each state and region,” Manning concludes. “The trends that are revealed can lead to new prevention strategies.”

The study is published in the scientific journal Frontiers in Medicine.

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