Why Is Salmonella So Widespread?

Salmonella Typhimuriam DT104 is multidrug resistant, infects livestock


Most people know that raw chicken often carries Salmonella bacteria. However, fewer may know that there are different strains of the bacteria, some of which are better at surviving and spreading than others.

According to a press release issued by the American Society for Microbiology, a new study has discovered why one strain of Salmonella—Salmonella Typhimuriam DT104—has been so successful. Researchers hope that these will help combat other successful pathogens.

The study’s findings are especially significant when considering that Salmonella is responsible for approximately 1.2 million foodborne illnesses in the US each year, according to the Centers for Disease Control and Prevention (CDC).

To conduct the study, researchers performed whole-genome sequencing of DT104 samples that were collected from patients for over 40 years, between 1969 and 2012. The samples came from 21 countries and six continents. The researchers noted slight changes in the genome over time and were able to map the strain’s family tree.

Researchers were able to roughly estimate when the strain started to develop resistance to treatments. They found that a lot of DT104’s success was due its resistance to at least five antibiotics—ampicillin, chloramphenicol, streptomycin, sulphonamide and tetracycline.

The study also found that DT104, unlike other Salmonella strains, was able to infect several kinds of livestock, including cattle, poultry, pigs and sheep.

"Having multiple hosts increases the chances of dissemination,” corresponding author Pimlapas Leekitcharoenphon, PhD, said in the press release.

Dr. Leekitcharoenphon is a postdoctoral researcher at the Research Group for Genomic Epidemiology, National Food Institute, Technical University of Denmark.

The team used a program to determine the rate of mutations in DT104. They estimated that the strain emerged in 1948 and was initially susceptible to antibiotics. Though researchers are unsure when DT104 developed multi-drug resistance, they think it may have happened in 1972.

"If we know and understand the past, we might be able to solve the current resistance problems and prevent future ones," concludes Leekitcharoenphon in the press release.

The full study was published March 4 in Applied and Environmental Microbiology. It was funded by the Center for Genomic Epidemiology. The authors disclosed no conflicts of interest.