Morganella morganii

Gram Stain

• Gram negative bacilli - fermenter

Clinical Significance

This organism is widespread in the environment and part of the commensal gastrointestinal tract flora.

 
M. morganii infections are rare in healthy individuals.

This organism is associated with urinary tract infections typically in patients with recurrent urinary infections or in patients who have received multiple previous antibiotics.

It is a common cause of asymptomatic bacteriuria in institutionalized and/or catheterized elderly patients.

It has been associated with bacteremia, skin/soft tissue infections (especially wound infections), pneumonia, peritonitis, bone/joint infections, and meningitis. It has also been implicated in gastroenteritis.

Usual Susceptibility Pattern

This organism produces an inducible cephalosporinase and is resistant to ampicillin and 1st/2nd generation cephalosporins. Therapy with 3rd generation cephalosporins is not recommended as clinical failures occur despite in vitro susceptibility.

Note: Piperacillin-tazobactam is effective as the cephalosporinase of M. morganii is inhibited by tazobactam, but not clavulanate.

It is resistant to fosfomycin, nitrofurantoin, tetracycline, and colistin while typically susceptible to aminoglycosides, quinolones, TMP/SMX, and carbapenems.

Exception: Imipenem (not meropenem or ertapenem) resistance is common due to a decreased affinity of imipenem to penicillin binding proteins (PBP2).