MORE THAN LYME: NEW BARTONELLA STUDY
This new 2026 study from Tulane University researchers investigated the antibiotic susceptibility of Bartonella henselae (the primary cause of cat scratch disease) across its different growth states—extracellular, intracellular (in DH82 canine macrophage-like cells), and in pre-formed biofilms—to address the lack of standardized treatments and frequent treatment failures in bartonellosis.
They tested single antibiotics (doxycycline, gentamicin, azithromycin, azlocillin, rifampin, and clarithromycin) and combinations via minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) assays in relevant media. Monotherapies often inhibited extracellular growth but failed to eliminate intracellular bacteria or eradicate biofilms, highlighting the pathogen's evasion strategies via host cells and biofilm formation. However, combinations such as gentamicin with rifampin or gentamicin with azlocillin significantly reduced bacterial loads across multiple microenvironments, supporting the use of combination therapy for more effective clearance, especially in persistent or severe infections.
While over 45 Bartonella species have been identified overall, about 12 have documented links to human infections. The three primary ones responsible for the vast majority of clinical cases are B. henselae (cat scratch disease and related syndromes), B. quintana (trench fever, etc.), and B. bacilliformis (Carrion’s disease). Other species/subspecies implicated in rarer human cases include B. elizabethae, B. vinsonii (including subsp. berkhoffii and arupensis), B. grahamii, B. koehlerae, B. clarridgeiae, B. rochalimae, B. alsatica, B. washoensis, B. tamiae, and occasionally “Candidatus” species like B. melophagi or B. mayotimonensis.
Bartonella species, including B. henselae, are primarily transmitted via scratches or bites from infected cats (or other animals), as well as by fleas and potentially other arthropods such as sandflies. Ticks have also been found to harbor Bartonella DNA and experimental studies suggest they can transmit certain Bartonella spp. in animal models.
