The bacteria, classified as Gram-negative because of their color on the Gram stain, can cause severe pneumonia and infections of the urinary tract, bloodstream, and other parts of the body. Their cell structures make them more difficult to attack with antibiotics than Gram-positive organisms like methicillin-resistant "Staphylococcus aureus". In some cases, antibiotic resistance is spreading to Gram-negative bacteria that can infect people outside the hospital. "For gram-positives we need better drugs; for gram-negatives we need any drugs," said Dr. Brad Spellberg, an infectious-disease specialist at Harbor-UCLA Medical Center, and the author of "Rising Plague", a book about drug-resistant pathogens.