One way of classifying bacteria is by their colour after applying a chemical stain (called the Gram stain). Some bacteria stain blue (Gram-positive), while others stain pink (Gram-negative). Gram-positive and Gram-negative bacteria produce different kinds of infections. Worldwide, more than half of infections treated in hospital involve Gram-positive bacteria. These include Staph infections caused by Gram-positive Staphylococcus aureus bacteria, as well as Strep throat and toxic shock syndrome caused by Streptococcus bacteria. Many Gram-positive bacteria, such as methicillin-resistant Staphylococcus aureus (MRSA), are becoming resistant to antibiotics. The cell wall of all Gram-positive bacteria contains about 50 percent of teichoic acids, a diverse group of polymers (long-chain molecules). Dr. Leo Lin is investigating whether two common teichoic acids help these bacteria adhere to host cells in humans or even to the synthetic coatings of transplanted medical devices, such as pacemakers. For many bacteria, the ability to attach to the surface of a host cell is an essential first step in the infection process. Dr. Lin will determine the three-dimensional structure of the enzymes that synthesize these teichoic acid polymers using x-ray crystallography, a technique that can deduce the atomic structure of molecules. A lack of teichoic acid significantly destabilizes the bacterial cell wall. Dr. Lin is looking for ways in which this information can be used to develop ways of interfering with the ability of bacteria to attach to host cell surfaces as a first line of defense in protecting against the establishment of bacterial infections.