Haemophilus parainfluenzae

Gram Stain

•  Gram negative coccobacilli small pleomorphic (facultative anaerobic)

Clinical Significance

This organism is part of the commensal flora of the human upper respiratory tract.

It can cause infections similar to H. influenzae, including bacteremia, endocarditis, meningitis, epiglottitis, septicemia, brain abscesses, septic arthritis, osteomyelitis, pneumonia, peritonitis, wound and genitourinary infections.

Usual Susceptibility Pattern

This organism is susceptible to 2nd/3rd generation cephalosporins, quinolones, and aminoglycosides.

Susceptibility to amoxicillin, tetracycline, TMP/SMX, and newer macrolides is variable.  Note routine susceptibility testing may not detect all mechanisms of resistance to TMP/SMX.

Amoxicillin-clavulanate and cefuroxime resistance may be increasing and will not be detected if testing only for presence of beta-lactamase. 

It is always resistant to 1st generation cephalosporins.