The room went quiet. “Staphylococcus aureus,” Horton said. “One of the most ubiquitous bacteria in existence.” She directed her laser point at the purplish-blue blotches. She circled one of the purple blobs. “There isn’t a person in this room who doesn’t have millions of these organisms growing on their skin as I speak.”

With the lights dimmed and her slides behind her, she felt herself begin to relax. A polished speaker from years of lecturing undergrads, Horton instinctively tailored the level of her talk to the nonscientific audience around her. “Normally, staph aureus is a commensal. In other words, it lives on the skin without causing infection.” She clicked a button and an arm appeared on the screen. It was fire-engine red from the elbow down. In the center of the forearm, the skin rose into a huge whitehead that looked as if a golf ball had erupted through the skin. “But with any break in the skin it can become invasive. Staph aureus is responsible for most boils and abscesses.” She ran the laser pointer over the fiery skin. “Along with group-A streptococcus, or G.A.S., it also causes the vast majority of the type of skin infection known as cellulitis.”

She clicked the remote and the infected arm gave way to the picture of a man whose identity was protected by the black bar running across his eyes and mid-face. His complexion was ashen. A tube led from his mouth to the life-support system by his bed. Other tubes, lines, and wires crisscrossed his body, as if he lay under a power grid.

Horton deliberately paused to allow the deathly image to sink in. “Not uncommonly, staph aureus is responsible for more invasive forms of infection such as bone infections, meningitis, or pneumonia, as we see in this patient. And it can be rapidly fatal.” She paused. “The man on the screen died within hours of this photo being taken.”

She advanced the slide. A steadily climbing line graph popped up on the screen. “In the 1950s, the first penicillin-resistant strains of staph aureus emerged. In the seventies and eighties, resistance to another common antibiotic, methicillin, was first noted. This led to the genesis of the very first of the superbugs, methicillin-resistant Staphylococcus Aureus or MRSA.” She pronounced the latter mer-sa.

Ice tumbled into a water glass and then the room fell into absolute silence. “Superbugs are forms of multiresistant bacteria that live, breed, and spread within hospitals.” Horton stressed the final word. “They are resistant to most classes of common antibiotics. And because of the intrahospital spread, they pose an enormous threat to health care delivery.”