Editorial: Bartonella species: Important cause of culture-negative endocarditis

Bartonella species, small Gram-negative rods, have emerged as an important cause of blood culture-negative endocarditis (BCNIE) mainly by the progress in serological and molecular techniques for the diagnosis of infection [1], [2], [3], [4], [5], [6]. Since the initial reports of Bartonella endocarditis in 1993 [7], [8], [9], seven types of Bartonella species (spp.) have been found as causative microorganisms of human infective endocarditis. Among these organisms, B. quintana and B. henselae are the most common as the causative species [1], [2], [3]. B. henselae often affects patients with previous valve diseases and contact with cats, whereas B. quintana primarily infects homeless patients with body lice. Identification of pathogen has been a diagnostic challenge as standard microbiologic culture and Gram stain are not useful for Bartonella spp.

The manuscript by Ghashghaei et al. [10] shows us the difficulty in the management of BCNIE. Most infections are caused by previous antibiotic use or fastidious microorganisms which need prolonged incubation time such as HACEK group bacteria (Haemophilus spp., Actinobacillus actinomycetemcomitans, Cardiobacterium hominis, Eikenella corrodens, and Kingella spp.) and Candida spp. Sometimes the intracellular bacteria such as Bartonella spp., Coxiella burnetti, and Tropheryma whippelei cause the ‘true’ culture-negative endocarditis that cannot be routinely cultured in blood. They are often diagnosed by ad hoc serologic test and/or polymerase chain reaction (PCR) on excised cardiac valve tissue [3], [4], [5], [6]. The current guideline of the European Society of Cardiology introduced the systematic serological test for Coxiella burnetii, Bartonella spp., Aspergillus spp., Mycoplasma pneumonia, Brucella spp. and Legionella pneumophila followed by PCR assays for Tropheryma whipplei, Bartonella spp. and fungi (Candida spp., Aspergillus spp.) [4].

The rigorous clinical approach is mandatory for the etiological diagnosis of BCNIE including a detailed, careful interview to screen the potential contact with animals and a complete examination to detect any accessible infectious focus. For Bartonella endocarditis, the history of contact with cats and signs of infection in other organs (lymphadenopathy, angiomatosis, hepatitis, and splenitis) are sometimes the reference for the diagnosis although they are not always accompanied.

In patients with BCNIE with risk factors for Bartonella (contact with cats, homeless and/or immunocompromised patients with alcohol abuse), serological test using immune-fluorescence assay (increased IgG and/or IgM titer for B. quintana and B. henselae) is recommended as a standard screening test. To confirm the positive serological results or when the serology is negative, western blotting is used as a more specific method for various Bartonella spp. Molecular analysis of valve tissues using real time PCR is also a contributive test for confirmation when early valve surgery is carried out [1], [2], [3], [4], [5], [6].

The standard treatment of Bartonella spp. endocarditis is oral doxycycline (100 mg/12 h) for 4 weeks in combination with intravenous gentamicin (3 g/24 h) for the first 2 weeks with expected treatment success rate over 90% [4]. Valvular surgery is required in more than 90% of cases [1]. Delayed treatment often leads to serious results especially in immunocompromised patients. Till date, most cases of Bartonella spp. endocarditis have been reported from Europe, North, and South America [1], [2], [3], [4], [11], although this genus might emerge as the causative microorganism of BCNIE in Asian countries in the near future [12], [13].

Disclosure

None.