What is the fine-grained topic of the following text: When the scientists gave oral antibiotics to mice infected with Salmonella typhimurium, a small minority -- so called "superspreaders" that had been shedding high numbers of salmonella in their feces for weeks -- remained healthy; they were unaffected by either the disease or the antibiotic. Only return the topic.
Effect of antibiotics on "superspreaders" mice infected with Salmonella typhimurium