Gram negative bacteria appear pink/red when stained using the Gram stain. Common Gram negative bacteria include E. coli, Pseudomonas aeruginosa and Acinetobacter. Gram negative bacteria include the most common causes of urinary tract infection, traveler’s diarrhea and ventilator-associated pneumonia (VAP). Some antibiotics with activity against Gram positive bacteria (for example, vancomycin, linezolid or daptomycin) have absolutely no useful activity against Gram negative bacteria. Development of new antibiotics active against Gram negative bacteria has lagged behind development of antibiotics versus Gram positive bacteria. Increasingly, Gram negative bacteria are found with resistance to all commercially available antibiotics.