Having bacteria growing inside you—other than in your digestive tract—is generally considered a bad deal. One example of such bad deals is bacterial endocarditis, an infection of the innermost lining of the heart or the heart valves. Researchers in France looked at infective endocarditis cases for patterns in the bacteria that were causing them.

What the researchers wanted to know: Do different pathogens infect different people's hearts?

What they did: The researchers looked at every patient who went to one of four university hospitals in Marseilles with infective endocarditis. For each patient, a doctor looked at the heart and took a blood sample to grow bacteria from it. They were able to identify some bacteria by species; others were put into categories like the evocatively named "group A beta-haemolytic streptococci."

What they found: There were a few patterns in which organisms appear where; for example, people with an infection of the mitral valves were more likely to be infected with Streptococcus bovis and less likely to have bacteria in the coagulase-negative staphylococci group. There were no significant differences by age or gender with respect to which bacteria were evolved, except that people aged 65 and up were more likely to have Enterococcus (which includes the common-as-dirt E. coli) and S. bovis.

What the study means to you: Bacterial endocarditis can cause serious damage to the heart. A physician might use this data to guess, based on the fact that she's looking at a 68-year-old man with a pacemaker, which bacteria are most likely to be growing in his heart, and use that information to decide how to treat the infection.

Caveats: This is only one city, and infections may vary depending on where you are. Also, bacteria are very difficult to grow, so the researchers almost certainly didn't identify everything that was there.

Find out more: The American Heart Association explains bacterial endocarditis and gives advice on prevention.

Read the article: Barrau, K., et al. "Causative Organisms of Infective Endocarditis According to Host Status." Clinical Microbiology and Infection. April 2004, Vol. 10, No. 4, pp. 302–308.

Abstract online: www.blackwell-synergy.com