Mannheimia haemolytica

(previously Pasteurella haemolytica)

Gram Stain

• Gram negative bacilli small (facultative anaerobic)

Clinical Significance

This organism causes mastitis, pneumonia and septicemia in bovine animals and has rarely been associated with human infections such as septicemia, endocarditis with metastatic abscesses, cellulitis (following bite or scratch from infected animal), meningitis, hepatic abscesses,  pneumonia, peritonitis, and urinary tract infections.

Usual Susceptibility Pattern

This organism is typically resistant to 1st generation cephalosporins, erythromycin, clindamycin, and aminoglycosides. 

It is usually susceptible to quinolones, amoxicillin-clavulanate, tetracyclines, azithromycin, and TMP/SMX. 

Bovine/porcine strains may be more resistant.