**6. HACEK**

Per the US and European guidelines, microbiologic susceptibility testing might be difficult to perform on HACEK microorganisms, and they should be considered ampicillin resistant secondary to β-lactamase production. Penicillin and ampicillin should not be used for the treatment of patients with endocarditis. Ceftriaxone should be used unless the patient has a severe β-lactam allergy. The duration of therapy for HACEK native valve endocarditis is 4 weeks; for prosthetic valve infections, duration of therapy is 6 weeks or longer. Gentamicin is not recommended in the US guidelines because of its nephrotoxicity risks but is an option in the European guidelines. A fluoroquinolone (ciprofloxacin, levofloxacin, ormoxifloxacin) can be used in patients with a β-lactam allergy. Ampicillin-sulbactam is also a treatment option.


Treatment of the following unusual pathogens in CNE is best summarized in the European guidelines and in Broqui et al. [21].
