The phase of the infection, from invasion to replication to escape, determines when the bacteria secretes a particular virulence factor and where they go in the host. Virulence factors are small molecules and proteins which perform a variety of functions during infection. When the bacteria Listeria monocytogenes infect a human cell, they overcome cell defenses using a set of virulence factors. In order to fight these infections, researchers at the University of Colorado have developed a new technique to find out how bacteria are picking our security system locks. Unfortunately, though, bacteria have developed clever tricks for getting around the cell’s security system and causing infections. On a scale ranging from the loose deadbolt on your apartment door to the fingerprint scanners, motion detectors, and laser fields that I am led to believe are used in all casinos, bank vaults, and fancy museums, the human cell ranks right near the top. A human cell’s set of defenses against infection can be seen as a type of custom security system.