Gram-negative bacteria are a group of germs that can cause respiratory infections. Bronchiectasis patients are particularly susceptible to gram-negative infections, and many get infected with Pseudomonas aeruginosa. Other species of gram-negative bacteria that bronchiectasis patients are known to get are Klebsiella pneumoniae and Acinetobacter baumannii.
Sometimes patients are co-infected with more than one pathogen, such as nontuberculous mycobacteria and a gram-negative bacterium. In such cases, your doctor may decide to treat one infection and not the other, depending on which one seems to be causing most of your symptoms.