NASA has already begun the countdown for the space shuttle Atlantis' blastoff Friday, which will be its last trip to the International Space Station and one of the final three space shuttle missions ever, according to The Associated Press . Three instruments built at University of Colorado-based nonprofit BioServe Space Technologies will accompany astronauts on the final flight, used to study cell-to-cell interactions on "biofilms" and why astronauts' immune systems weaken in space, according to Boulder's Daily Camera . The instruments, which could fit inside a suitcase, are used to study how microorganisms and cells interact in space, helping scientists understand, for instance, why bacteria seem to become more virulent and more resistant to antibiotics in low gravity. One experiment using BioServe's hardware will analyze changes in virulence of two particularly nasty strains of bacteria in the low gravity of space: salmonella, which can cause illness and death to humans by tainting food or water, and staphylococcus, which can cause a variety of infections, including methicillin-resistant staphylococcus aureus or MRSA. "Water quality, food safety, and disease are age-old problems on Earth," BioServe director Louis Stodieck says in a CU news release . "Not only do these experiments have applications for keeping crew members safe by helping scientists better understand gene and protein changes in pathogens, they also could help researchers find new ways to prevent and control infectious disease."