Research comparing bacteria in the microbiome – those colonizing our noses, skin and other areas of the body – with the bacteria that cause pneumonia, diarrhea, bloodstream infections and surgical site infections shows that the bacteria living innocuously on our own bodies when we’re healthy are most often responsible for these bad infections when we’re sick.

Our results revealed that while the species of bacteria living on the back skin of patients vary remarkably between people, there are some clear patterns. Bacteria colonizing the upper back around the neck and shoulders are more similar to those in the nose; those normally present on the lower back are more similar to those in the gut and stool. The relative frequency of their presence in these skin regions closely mirrors how often they show up in infections after surgery on those same specific regions of the spine.

In fact, 86% of the bacteria causing infections after spine surgery were genetically matched to bacteria a patient carried before surgery.