BIOS Instant Notes in Microbiology, 4<SUP>th</SUP> edition, has been streamlined to concentrate on features that are unique to the microbial world, including viruses and prions. Information on pathogenesis has been placed within other sections. The text has been generally updated, and coverage of applied microbiology expaned, but retains the Instant Notes philosophy of focusing on clearly and concisely presenting only essential topics.