Sterigenics International LLC, a global provider of contract sterilization, gamma technologies and medical isotopes, has acquired Nelson Laboratories, Inc., a large U.S. provider of life-cycle microbiology testing services for the medical devices, pharmaceutical and tissue industries. Financial terms were not disclosed.   Nelson Labs has 570 employees, including more than 300 scientists and 60 registered and specialist microbiologists, and runs 85 labs out of five corporate buildings in Salt L...