In 2015, a germ called Salmonella heidelberg caused illness in 56 people across 15 different states. Over a third of these people needed to be hospitalized, and a relatively high proportion of these cases were in children less than 5 years old. At the same time, S. heidelberg was being implicated in severe illness and death losses in young dairy bull calves. It quickly became apparent that the majority of human cases originated from contact with infected dairy calves. Calf cases were tracked as far back as an auction market in Wisconsin.
How could this germ – usually associated with poultry – apparently come out of nowhere to cause such severe illness in calves and people? An SDSU research team led by the ADRDL’s Dr. Joy Scaria, along with personnel from the Wisconsin Veterinary Diagnostic Lab, was able to dive into the genomics of these and many other strains of S. heidelberg. Their analysis of over 600 different bacterial isolates found that these outbreak strains actually were likely present in the Midwest well before the 2015 outbreak, and were part of a genetic cluster that developed the ability to infect species other than birds. The acquisition of a gene type that helped the bacteria adhere to the gut of different species likely was the culprit. The investigators were also able to document an increased level of antibiotic resistance in these more recent S. heidelberg isolates compared to ones found years ago.
This work is an example of the ability of Dr. Scaria’s lab and the ADRDL to use genomic sequencing techniques to better understand the emergence of new strains of germs such as S. heidelberg. The group’s work on this issue is now published in the journal Gut Pathogens.
