Final answer:
(D) Bartonella henselae is the most likely organism causing the patient's infection. Cat-scratch disease (CSD) is a bacterial infection caused by this organism when a human is bitten or scratched by a cat. Diagnosis can be challenging, but immunofluorescence, serological tests, PCR, and gene sequencing can help identify the bacterium.
Step-by-step explanation:
The organism most likely to be the cause of this patient's infection is Bartonella henselae. Cat-scratch disease (CSD), also known as cat-scratch fever, is a bacterial infection caused by B. henselae, a facultative intracellular gram-negative bacterium. The infection occurs when a human is bitten or scratched by a cat, introducing the bacteria into the lymph nodes.
Common signs and symptoms of CSD include painful cutaneous papules and pustules near the bite site, tender unilateral axillary lymphadenopathy, occasional low-grade fever, and other systemic symptoms like fatigue. Diagnosis of CSD can be challenging as the bacterium does not grow readily in the laboratory, but various diagnostic tests such as immunofluorescence, serological tests, PCR, and gene sequencing can be performed to identify the bacterial species.
In most cases, cat-scratch disease is self-limiting and antibiotics are not normally prescribed. However, immunocompromised patients may develop more severe complications such as bacillary angiomatosis or bacillary peliosis, which may require treatment with antibiotics like rifampin, azithromycin, ciprofloxacin, gentamicin, or TMP-SMZ.