Gram-negative organisms

Please note: This is for information only.

Refer to local guidelines for treatment recommendations.


  • Includes the Coliform bacilli eg E. Coli, Klebsiella sp, Enterobacter sp, Salmonella sp and the Pseudomonas, Acinetobacters, Neisseria sp. and Bacteroides.

Main clinical infections:

  • Abdominal and urinary tract infections.
  • Coliforms and Pseudomonas can be responsible for hospital-acquired pneumonia particularly ventilator-associated.

Usually sensitive to:

  • Quinolones (ciprofloxacin, levofloxacin) (except Bacteroides)
  • Aminoglycosides (gentamicin, tobramycin, amikacin) (except Neisseria sp).
  • The 2nd and 3rd generation cephalosporins (Pseudomonas and Acinetobacter only sensitive to the 3rd generation cephalosporin ceftazidime.)
  • Piptazobactam (tazocin)
  • Carbapenems (imipenem, meropenem)

Usually resistant to:

  • Vancomycin,
  • Teicoplanin
  • Metronidazole.
  • Over 50% of coliform bacilli are now resistant to amoxicillin, therefore only indicated for treatment if known sensitive strain.
  • Pseudomonas and Acinetobacters are resistant to amoxicillin, trimethoprim and co-amoxiclav.