Bartonella infection: a significant cause of native valve endocarditis necessitating surgical management

Contemporary drug treatment of infective endocarditis

Infective endocarditis (IE) occurs at a rate of approximately 0.9-6.2 per 100,000 people per year and is associated with a high morbidity and mortality despite advancements in antibiotic and surgical treatments. The general approach to the treatment of IE is initial clinical stabilization, early acquisition of blood cultures, and definitive medical and/or surgical treatment. Surgical consultation should be obtained early when indicated in order to determine the best treatment approach for each individual patient. Surgery is indicated in most cases of prosthetic valve endocarditis, Staphylococcus aureus endocarditis, fungal endocarditis, and endocarditis associated with large vegetations (≥10 mm). Initial antibiotic therapy for IE should be targeted to the culprit microorganism; however, in some cases, empiric therapy must be initiated prior to definitive culture diagnosis. Empiric antibiotics should be targeted toward the most likely pathogens, including staphylococci, streptococci, and enterococci species. Here we discuss the recommended antibiotic regimens for the most common causes of IE as indicated by the American Heart Association and European Society of Cardiology. In 2008, the ACC/AHA published guideline updates on the treatment of valvular heart disease, which included a focused update on endocarditis prophylaxis. According to the most recent guidelines, the number of patients who require antibiotic prophylaxis has decreased substantially. Treatment of IE should be targeted toward the causative microorganism and must be based on the type and location of valve involved (native, prosthetic, left or right sided), the clinical status of the patient, and the likelihood for clinical success. This requires a collaborative effort from multiple medical specialties including infectious disease specialists, cardiologists, and cardiothoracic surgeons.

Bartonella quintana-induced apoptosis inhibition of human endothelial cells is associated with p38 and SAPK/JNK modulation and with stimulation of mitosis

Previous studies demonstrated that live Bartonella quintana often induces angioproliferative lesions in humans. It modulates endothelial cell apoptotic and inflammatory patterns, thus inducing a very early overexpression of caspase 8 and Apaf-1 and increasing mRNA production of TNF-alpha, interleukin-8, and E-selectin. However, starting at 10 hours postinfection, the bacteria provoke antiapoptotic effects that induce an increase of bcl-2 gene transcription. To gain further insight into the cellular mechanisms that regulate apoptosis, survival and proliferation, we studied the modulation of mitogen-activated protein kinase (MAPK) and the activation state of cdc2 kinase, which regulates progression into mitosis. Confocal microscopy findings indicated a maximum rate of Bartonella entry into host cells between postinfection hours 6 and 10. Live bacteria caused substantially higher apoptosis of human umbilical vein endothelial cells-cryopreserved (HUVEC-C) than heat- and trypsin-inactivated microorganisms. During the first 6 hours postinfection, B. quintana triggered a peak of apoptosis, induced activation of p38 MAPK and stress-activated protein kinase/c-Jun N-terminal kinase (SAPK/JNK), with bacterial clusters appearing at the cellular surface of the HUVEC-C. However, at 8 to 24 hours postinfection, B. quintana was internalized and inhibited proapoptotic signals such as p38 MAPK and SAPK/JNK while inducing antiapoptotic signals. Indeed, expression of the bcl-2 gene and the increase of the bcl-2 kinase active form was concomitant to activation of mitosis, as shown by cdc2 protein activation. These data thus suggest that mechanisms that induce mitotic activity and inhibit apoptotic signals may contribute to the ability of B. quintana to cause vascular proliferation.

In vitro Bartonella quintana infection modulates the programmed cell death and inflammatory reaction of endothelial cells

Bartonella quintana is an epicellular bacterium, which in vivo as well as in vitro, invades endothelial cells and develops within them inducing proliferative effects that play a pivotal role in neovascular manifestation of this disease. We investigated the effect of live Bartonella quintana and its LPS on apoptosis and inflammatory response in HUVEC-C, an endothelial cell line. The kinetics of the programmed cell death of Bartonella quintana-infected HUVEC-C showed a peculiar course. Even if early during infection apoptosis reached a peak after 6 h, later on apoptosis was inhibited. Such apoptosis inhibition was not observed during Bartonella quintana lipopolysaccharide treatment because LPS-stimulated HUVEC-C did progress to cell death. Evaluation of multiple cell signal transduction pathways revealed an overexpression of Apaf 1 and caspase 8 in HUVEC-C after 2 h of infection, and of bcl-2 starting from 10 h post Bartonella quintana infection. Moreover, Bartonella quintana and its LPS showed a different effect on the activation of genes involved in inflammatory response as revealed by molecular analysis of host cells. Bartonella quintana appears to be able to inhibit programmed cell death, inducing intracellular signals leading to survival and proliferation through the bcl-2 gene, despite the early increase of inflammatory status induced in endothelial cells. This mechanism, together with a poor endotoxin ability to stimulate strong inflammatory response, could contribute to the capability of the bacteria to persist intracellularly, causing chronic disease and producing neovascular manifestations.