What organism is responsible for cat scratch disease, which is characterized by painful swelling of lymph nodes after a cat bite or scratch?

Cat scratch disease is primarily caused by the organism Bartonella henselae. This zoonotic infection typically arises after an injury from a cat scratch or bite, leading to a notable immune response that manifests as painful lymphadenopathy, particularly in the regional lymph nodes nearest to the site of exposure.

Bartonella henselae is a gram-negative bacillus and is well recognized for its role in cat scratch disease, often resulting in symptoms such as fever, fatigue, and swollen lymph nodes, which can persist for several weeks to months. The association with domestic cats is particularly significant, as they can carry the organism asymptomatically and transmit it through scratches or bites.

The other organisms listed are linked to different infectious diseases. For example, Brucella melitensis is known for causing brucellosis, which is typically acquired through unpasteurized dairy products or contact with infected animals. Burkholderia mallei is associated with glanders, primarily in horses, and Francisella tularensis causes tularemia, usually transmitted through rabbits or ticks. Hence, the unique characteristics and transmission methods specifically tie Bartonella henselae to cat scratch disease, making it the correct choice for this question.