Acute lower respiratory infections are one of the most common diseases in worldwide. Sometimes they constitute the most usual cause of death in children aged less than five years, with pneumonia like the leading origin. In Chapter One, the epidemiology (community-acquired and hospital-acquired pneumonia), causes, risk factors and clinical basic aspects of bacterial pneumonia are presented. The genus Enterococcus coexists with several Gram-positive bacteria. Chapter Two discusses how new tools must be developed to track glycopeptide resistance dissemination by using ISs as markers in epidemiological investigations across the world. Chapter Three summarizes the different antibiotic resistances that are being found in enterococci isolates from food and clinical cases and also its possible relationship.