Ribosomal RNA Sequence Analysis of Brucella Infection Misidentified as Ochrobactrum anthropi Infection

Abstract

A Brucella isolate was identified from purulent material collected during a hip surgery. Two previous blood cultures from the same patient yielded Ochrobactrum anthropi. After rRNA sequencing, all the isolates were identified as Brucella species and subsequently serotyped as Brucella suis. Misidentification of Brucella species remains a problem with bacterial identification systems. CASE REPORTA 62-year-old female presented to the emergency department with left hip pain and was unable to bear weight on that hip. The day before presentation she had fallen while standing up from a sitting position. On presentation the patient was febrile (38.7°C) with a low white blood cell count of 4,300 cells/l. One set of blood cultures was obtained, but no antibiotics were given.The patient was admitted to the hospital for surgery to stabilize the impacted fracture with a pin. She continued to have a high temperature, and a second set of blood cultures was collected. The first blood culture became positive after 3 days of incubation, with a short, Gram-negative bacillus in the aerobic bottle only. This bacterium was identified as Ochrobactrum anthropi by the RapID NF Plus system (Remel, Lenexa, KS). The second blood culture remained negative after 7 days of incubation. Antibiotics were administered to the patient, and she was released from the hospital after a successful surgery that stabilized the femoral neck fracture. The patient was given 2 weeks of antibiotics as an outpatient.One month later, the patient was readmitted for severe abdominal pain. Despite the absence of subjective fever, chills, or sweats, her temperature was 38.6°C. Her white blood cell count was 3,100 cells/ml with 66% neutrophils. Two sets of blood cultures were obtained, and antibiotics were started. The fever resolved after 2 days. Four days after blood cultures were collected, a short, Gram-negative bacillus was detected in a single aerobic bottle and was also identified as Ochrobactrum anthropi by the RapID NF Plus system. Three other sets of blood cultures remained negative.Seven months later, the patient was again admitted to the hospital for a permanent repair of the femoral neck fracture.During surgery, purulent material was collected from inflammatory tissue around the screws and within the hip socket. Fluid analysis revealed chronic inflammation with 44,000 white blood cells/l. The Gram stain showed few neutrophils with no organisms. The bacterial culture was positive, with growth of small colonies on the sheep blood agar plate after 3 days of incubation. The Gram stain of the colonies was initially reported as corynebacterium-like bacteria with Gram-variable properties.The organism was not identified by the Vitek2 Gram-positive identification (GPI) card, and after review it was evaluated with the Vitek2 Gram-negative identification (GNI) card. The Vitek2 GNI card identified the isolate as Brucella melitensis with a 97% probability. After this identification, the two earlier blood culture isolates were reevaluated. The isolates that were ident...

A Literature Review of Laboratory-Acquired Brucellosis

“…Despite the publication of laboratory safety measures (15,16) and postexposure recommendations (17), laboratory exposures and laboratory-acquired brucellosis (LAB) cases continue to occur (18,19). In the United States, roughly 120 cases of brucellosis are reported annually.…”

Mistaken Identity of Brucella Infection

“…e read with interest the paper "Ribosomal RNA Sequence Analysis of Brucella Infection Misidentified as Ochrobactrum anthropi Infection" by Horvat and colleagues (1). The paper reported that a Brucella isolate was misidentified as Ochrobactrum anthropi.…”

Blood Cultures for the Diagnosis of Human Brucellosis

“…Sequencing of the 16S rRNA gene, which is in widespread use for bacterial identification, can be misleading and Brucella organisms cannot be accurately distinguished from the closely related α-protobacterial Ochrobacterium species [72]. A novel recA gene-based, multi-primer, single-target PCR assay has been recently developed and succeeded in differentiating between brucellae and Ochrobacterium anthropi and O. intermedium [73], although the test has a more prolonged turnaround time and is more expensive than the FISH test.…”