Bacteriological and molecular characterization of B. melitensis isolated from aborted sheep and Malta fever patients.

Background: Zoonotic diseases are a major global health concern, particularly those with high prevalence or widespread impact. Brucella melitensis, the causative agent of human brucellosis or undulant fever, is a highly virulent pathogen that is transmitted mainly through contact with infected animals or consumption of unpasteurized dairy products. The significance lies in its public health impact and economic burden in endemic regions. Aim: This study aimed to isolate and identify B. melitensis from human patients and sheep using conventional and molecular techniques, with the goal of tracking its presence and genetic variations across both hosts. Methods: A total of 50 samples were collected from Al-Qadisiyah Province, Iraq, including 25 blood samples obtained via venipuncture from sheep owners clinically suspected of having Malta fever and 25 placenta samples aseptically collected from recently aborted ewes during field visits to local farms. We cultivated the collected samples on blood agar media and performed biochemical analysis using VITEK® 2 Compact 15 (V2C15). We also examined the samples using PCR and partial sequencing (PS) techniques, which used the 16S rRNA gene as the bacterial DNA target. Results: Classical bacteriological methods identified B. melitensis in 15 out of 25 (60%) human blood samples and 13 (52%) sheep placental samples. In V2C15, 13 (86.66%) and 11 (84%) human and sheep placental samples were positive for B. melitensis. PCR identified B. melitensis in 10 (76.9%) and 10 (90%) human and ewe placental samples, respectively. The partial gene sequencing (PGS) of two samples from humans and two samples from ewe placentas demonstrated isolates closely aligned with global isolates from China and India, respectively. Conclusion: The present study revealed continuous circulation of B. melitensis infection from sheep to humans in Al-Diwaniyah City, Iraq, and that the sequenced bacteria might have faced genetic evolution after they were descended from China or India isolates.