Proteus mirabilis

Gram Stain

• Gram negative bacilli - fermenter

Clinical Significance

This organism is found in a variety of environmental sources and can be part of commensal human gastrointestinal tract flora.

It is a cause of both community and healthcare associated urinary tract infections, usually in chronically catheterized patients.

Isolation of this organism is typically indicative of an upper and/or complicated urinary tract infection.

It has also been associated with bacteremia and skin/soft tissue infections (typically post-operative wounds).

Usual Susceptibility Pattern

Although generally susceptible to beta-lactams, non-beta-lactam antibiotics appear more efficacious in treatment of urinary tract infections.

The number of strains producing extended spectrum beta-lactamases (ESBL) or AmpC cephalosporinases is increasing.

This organism is usually susceptible to aminoglycosides, quinolones, TMP/SMX, and carbapenems.

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

P. mirabilis is resistant to nitrofurantoin, tetracyclines, and colistin.

Susceptibility to fosfomycin is variable.