Proteus vulgaris complex

• P. hauseri
• P. penneri
• P. vulgaris

Gram Stain

• Gram negative bacilli - fermenter

Clinical Significance

These organisms are found in a variety of environmental sources and may be part of commensal gastrointestinal flora.

P. penneri and P. vulgaris cause healthcare associated infections, especially of the urinary tract and skin/soft tissues (wounds).

They have been associated with bacteremia and abscesses in immunocompromised patients who have received prolonged antibiotic therapy.

Usual Susceptibility Pattern

These organisms produce an inducible chromosomal cephalosporinase (cefuroximase) and are resistant to ampicillin and 1st/2nd generation cephalosporins.

Hyperproduction of this enzyme can result in 3rd generation cephalosporin resistance.

They are typically susceptible to beta-lactamase inhibitor combinations, aminoglycosides, TMP/SMX, quinolones, and carbapenems.

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

Most strains resistant to nitrofurantoin, tetracycline, and colistin.

Fosfomycin susceptibility is variable.