Strains of Salmonella bacteria cause foodborne illnesses and have tended to affect the young and elderly. But adult cases are increasing in Michigan, and researchers are concerned. It may be a precursor to worsening infections elsewhere. Scientists at Michigan State University (MSU) have documented the substantial rise in Salmonella infections that are resistant to antibiotics, and that last longer and require lengthier hospital stays; the pathogen is becoming increasingly virulent. The findings have been reported in Frontiers in Medicine.
"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," noted Shannon Manning, MSU Foundation Professor in the Department of Microbiology and Molecular Genetics and the senior author of the study. "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."
Salmonella infections can cause nausea, diarrhea, vomiting, and pain in the abdomen, and some of these illnesses are severe enough to be life-threatening. It's important to diagnose the problem quickly. If the proper treatment is not applied, symptoms worsen.
Every strain of the bacterium can have a different reaction to various antibiotics that doctors prescribe. It's crucial to use the right one. If the wrong one is selected, a subpopulation of the offending pathogens might get killed off, but resistant microbes can get stronger, added Manning.
Doctors in Michigan are finding that more Salmonella is gaining resistance to a common antibiotic used to treat the infection, ampicillin. There has also been a rise in microbes that are multidrug-resistant, meaning they are impervious to the effects of over three classes of antibiotics. This complicates the treatment.
"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 said. "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."
Researchers have found that patients infected with a strain of Salmonella called Typhimurium are more likely to harbor resistant infections when they are infected during the spring, fall or winter months.
They also learned that compared to urban populations, people in rural areas have higher rates of enteritis infections, which inflame the intestine. It may be that rural populations are exposed to untreated water or farm animals more often.
Every state harbors its own population of Salmonella, so different approaches may be needed to tackle the population in different places.
"Our results show the importance of surveillance, monitoring resistance frequencies and identifying risk factors specific to each state and region," Manning said. "The trends that are revealed can lead to new prevention strategies."