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Bartonella species are fastidious, facultative intracellular, slow-growing, gram-negative bacteria that cause a broad spectrum of diseases in humans. This genus includes more than 30 distinct species or subspecies, of which at least 16 have been recognized as confirmed or potential human pathogens; Bartonella bacilliformis, Bartonella quintana, and Bartonella henselae are most commonly identified (Table 69-1). Most Bartonella species have successfully adapted to survival in specific domestic or wild mammals. Prolonged intraerythrocytic infection in these animals creates a niche where the bacteria are protected from both innate and adaptive immunity and which serves as a reservoir for human infections. Bartonella characteristically evades the host immune system by modification of its virulence factors (e.g., lipopolysaccharides or flagella) and by attenuation of the immune response. B. bacilliformis and B. quintana, which are not zoonotic, are exceptions. Arthropod vectors are often involved. Isolation and characterization of Bartonella species are difficult and require special techniques. Clinical presentation generally depends on both the infecting Bartonella species and the immune status of the infected individual. Bartonella species are susceptible to many antibiotics in vitro; however, clinical responses to therapy and studies in animal models suggest that the minimal inhibitory concentrations of many antimicrobial agents correlate poorly with the drugs’ in vivo efficacies in patients with Bartonella infections.
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