This book contains ten chapters which cover current trends on antibiotic resistance in different parts of the world. Some of the chapters are dedicated to specific type of bacteria like marine and cholera associated microorganisms. Whereas rest of the chapters are mainly focused on the mechanism of drug resistance with special reference to beta lactamases. Since most of the antibiotics used to treat infections belong to β lactam group which is lactam ring (β lactam) or penam is a lactam with a heteroatomic ring structure, consisting of three carbon atoms and one nitrogen atom. A lactam is a cyclic amide. The main focus of this book is to understand the different molecular markers responsible for developing resistance against this group of antibiotics. CTX-M family of enzyme which hydrolyzes third generation of cephalosporins preferably, cefotaxime, belongs to the category of Extended-spectrum β lactamases (ESBLs). These types of enzymes are emerging among Gram-negative bacteria; predominantly Klebsiella pneumoniae, Escherichia coli and other species in different parts of the world. In the current scenario, the CTX-M family includes almost 40 variants. The blaTEM, and blaSHV are another important class of β lactamases, most prevalent among enterobacteriacae which are also discussed in this book.