Besides, David had been vaguely aware there were so-called good bacteria that helped to make things like cheese and yogurt. So when he had entered Angels Orthopedic Hospital early one Monday morning in 2007 to have his anterior cruciate ligament repaired with a cadaver graft, bacteria weren't one of his concerns. What he had worried about was the anesthesia and not waking up after the operation was over. He had also worried about the possibility he'd go through the whole ordeal, which a buddy had confided was painful, and it wouldn't work, meaning he wouldn't be able to get back to the tennis he loved.

As a computer programmer for a high-flying Manhattan-based software company, David had spent, as he put it, a lot of hours on his butt, shackled to his monitor. Being an athletically inclined individual from as early as he could remember, he needed competitive exercise, and tennis was his thing. Up until his injury a month prior to his surgery, he'd played at least four times a week. He'd even vainly tried to interest his two preteen sons in the game.

As for his injury he had no idea how it had happened. He'd always kept himself in good shape. All he had remembered about the event was charging the net after making what he thought had been a good lead shot. Unfortunately his shot had not been as good as he had hoped, and his opponent had followed up with a well-placed return to David's left. On the run, David had planted his leading foot and twisted left to try to get to the ball. But he never got near it. Instead, he had found himself on the ground, clutching a painful knee that had immediately begun to swell dramatically.

Considering David's fulminant postoperative course, one certainly could say that he should have been more respectful of bacteria. Within hours of his surgery, relatively small numbers of staphylococci, which had found their way into David's knee and the distal bronchioles of his lungs, began their molecular magic.