It was two days after the young Yemeni man was released from surgery that the doctors first noticed the smell. The bullet that wounded the leg of the 22-year-old college student had shattered bone and torn a hole in the soft tissue. Now, the wound was emitting a distinct smell, described in the medical literature as “offensive.” It strongly suggested infection, perhaps life-threatening, and the wound was not getting better.

Realizing that normal antibiotics were not working, the doctors at a trauma center run by Doctors Without Borders sent a blood culture for analysis to their new microbiology lab, the only one of its kind in the region. The tests found a bacterium, Acinetobacter baumannii, resistant to most standard antibiotics. Nobody knows how the student — who was identified using his initials, A. S., to preserve his privacy — acquired the drug-resistant infection, but it is so common in Yemen that it could have come from the bullet itself or the sand on the ground when he fell, said Dr. Nagwan Mansoor, the chief physician in Doctors Without Borders’s antibiotic stewardship program.

Doctors started the gunshot victim on a program of specialized antibiotics, medicines rarely used because of their potentially dangerous side effects. He required numerous surgeries, seven in all. What would normally have been a five-day stay became three weeks, during which the man was put into isolation to prevent him from infecting other patients. When his family came to visit, they could not touch him without wearing protective clothing.

A. S. survived. “We captured the patient from the mouth of death,” said Dr. Mansoor. But A. S. was lucky: Most hospitals in Yemen do not have the capacity or protocols in place to detect and treat drug-resistant infections; if he had been anywhere else, he would have lost his leg, or died.