Gentamicin is an aminoglycoside antibiotic , used to treat many types of bacterial infections, particularly those caused by Gram-negative bacteria. However, gentamicin is not used for Neisseria gonorrhoeae , Neisseria meningitidis or Legionella pneumophila bacterial infections (because of the risk of the patient going into shock from lipid a endotoxin found in certain gram negative organisms).