The laboratory of Paul Keim, a geneticist at the Northern Arizona University (NAU) in Flagstaff, has taken an early lead in trying to identify the strains of the causative bacterium, Bacillus anthracis, involved in the mail attacks. More than 1,200 strains of B. anthracis have been identified around the world, and the NAU laboratory has used AFLP (amplified fragment length polymorphism) DNA analysis to examine all of them. Data derived from the AFLP technique are held in databases at the NAU and at the Los Alamos National Laboratory in New Mexico. Keim's laboratory has also adapted a more precise test called multi-locus VNTR (variable-number tandem repeat) analysis, or MLVA, for use with microorganisms. With MLVA, researchers use polymerase chain reaction (PCR) to amplify regions of the genome containing repeated sequences and so develop a genetic fingerprint for a strain or species. The genome of B. anthracis contains short sequences of DNA that, depending on the strain, are repeated a different number of times at certain loci. Keim's group has published findings on eight such markers.