First Report of Septic Arthritis Caused by Bacillus megaterium in South America

Abstract

Bacillus megaterium is a Gram-positive, aerobic bacillus commonly used in soil fertilization in agriculture. This species, previously described as non-pathogenic, has recently been isolated as an opportunistic pathogen in individuals, typically with preexisting  conditions. This case report detailed the first documented case of septic arthritis related to this bacillus. A literature review conducted by the authors identified 9 clinical case reports associated with this bacterium from 1937 to 2024, spanning three continents: Asia, Europe, and the Americas. The patient in this report, a 28-year-old male with sickle cell trait, developed septic arthritis associated with pulmonary thromboembolism on the 5th postoperative day (POD) following posterior cruciate ligament (PCL) reconstruction of the left knee. After the onset of pulmonary thromboembolism, the patient reported increased pain intensity at the surgical site. Joint aspiration was performed, and Bacillus megaterium was identified through culture on NAC (nalidixic acid and colistin) Columbia agar and chocolate agar. Despite initial management with antibiotic therapy and surgical re intervention, the patient exhibited clinical deterioration. Following adjustment of the antimicrobial regimen, there was resolution of the infection, hospital discharge was achieved, and oral antibiotic therapy was continued on an outpatient basis for 28 days. Therefore, although Bacillus megaterium infections remain rare, early recognition and diagnosis were crucial for optimizing clinical therapy, understanding the disease's progression, and ultimately reducing the risk of complications and prolonged hospitalizations.