Introduction

The genus Brucella belongs to the class alpha-proteobacterial, this genus is integrated by 29 validated species. Recently, a new member was recategorized in this genus and came from another known as Ochrobactrum. Ochrobactrum antrophi, now Brucella antrophi is a gram-negative, rod-like, non-fermenting bacterium found in a wide variety of environments such as water, soil, plants, and animals. They are considered low-virulence pathogens and have recently been associated with opportunistic infection¹. As they can be found not only in natural environments, but also in water sources, including normal saline, antiseptic solutions, and dialysis, with a robust survival ability, they are mainly associated with hospitalacquired infections, affecting mainly immunocompromised hosts with medical invasive devices^2,3. Management is complicated by its reported resistance profile to the most commonly used beta-lactams, such as cephalosporins and penicillin⁴.

Case report

A 28-year-old patient presented to the emergency department of a burn center with a scald burn injury. At the time of admission, the patient had a 20% burned body surface area, affecting both wrists and hands with third-degree burns, both thighs, and legs with second-degree burns, similar to the penis and scrotum. The patient underwent seven surgical wound toilets and debridement.

On the 29^th day after the burn injury, he was transferred to our center. Upon admission, the patient had a 12% burned body surface area without clinical signs of infection and a subclavian right central line. In the first hours of hospitalization, the patient presented 2 hours fever, central and peripheral blood cultures and urine cultures were taken, and the central line and urinary catheter were removed.

On the day after admission, the patient underwent tangential excision and grafting in the burned areas. On the first day after taking, blood cultures from central line were reported positive, with Gram stain showing gram-negative bacilli (figure 1-a). After 48 hours of inoculation, a Gram negative, non-lactose fermenter bacillus was reported in both blood cultures taken from central line and catheter tip culture (figure 1-b) and empirical meropenem was administered.

Figure 1 a) blood central line cultures in gram stain light microscopic examination showing clusters of gram-negative bacilli. b) Brucella anthropi in blood agar after 48 hours of incubation. 

Brucella anthropi was identified in the central line and catheter tip cultures using Vitek MS. The reported susceptibilities of the bacteria were cephalosporin, carbapenem, and colistin resistance, and the rest of the antibiogram was susceptible; therefore, meropenem was suspended, and the patient was treated with levofloxacin.

Six days after removal of the central line, the patient had no new events of fever, no clinical signs of bacteremia, no other clinical signs of infection, serum inflammatory markers normalized, and wounds showed no signs of infection. Therefore, the patient continued medical treatment at home for two weeks.

Discussion

Immune dysfunction is a hallmark of critical illness. Severe burn injuries are associated with proinflammatory and antiinflammatory responses, leading to immunosuppression⁵. In severe burn injuries, there is a prolonged and strong immune response, leading to multiple systemic effects such as multiple organ failure due to systemic inflammatory response syndrome (SIRS)⁶. Immunosuppression and prolonged inflammatory response lead to infectious complications⁷.

Pathogens affecting burn patients change over time; the first days of hospitalization are those of the skin flora and occasionally those of the digestive system. During prolonged hospitalization, these pathogens are replaced by colonization by hospital bacteria, mainly gram-negative bacilli, such as Pseudomonas aeruginosa and other Enterobacterales⁸. One of the main infections in burn patients is bloodstream infections. Most patients with severe burn injuries have invasive devices such as central bloodline catheters, which are the optimal port of entrance to the bloodstream⁹. Moreover, severe burn injuries are associated with prolonged hospital stay, and most patients undergo multiple surgical procedures, which increase the risk of bloodstream infections¹⁰.

Pathogens associated with these infections are mainly Gramnegative rods, like Pseudomonas aeruginosa, Klebsiella pneumoniae, Acinetobacter baumannii and yeast like Candida spp.¹¹. With the worldwide increase in antibiotic resistance, burn patients are at high risk of acquiring infections by multidrug-resistant (MDR) organisms¹².

Brucella anthropi has been recognized as an opportunistic emerging infection associated with a long hospital stay, invasive medical devices, and immunocompromised hosts. The Brucella genus consists of non - fermentative, strictly aerobic, oxidase-positive, and indole rapid-negative gram-negative rods¹³.

Brucella anthropi has been reported as an etiological agent associated with infection. In their literature review, Ryan et al. Brucella anthropi was associated with 46 bloodstream infections that were usually associated with catheters, 14 septicemia, two biliary sepsis, nine endophthalmitis, eight peritonitis, four pneumonia and two endocarditis¹⁴.

Treatment with Brucella anthropi represents a therapeutic challenge because of its increased association with resistance, and most isolates have been reported to be resistant to ß-lactams due to a chromosomal, induced AmpC ß-lactamase, which is resistant to clavulanic acid inhibition. It is generally considered to be susceptible to quinolones, trimethoprim/sulfamethoxazole, and colistin¹⁵.

In this clinical case, we present a bloodstream-related infection caused by Brucella anthropi in a previously healthy patient with a severe burn injury. The main associated risk factors were prolonged hospital stay, use of intravenous devices, multiple surgical events within the course of hospitalization, and use of broad-spectrum antibiotics. Microbiologic identification was performed using biochemical tests and confirmed with Vitek MS; however, reports of antibiotic susceptibilities were challenging because initial resistance to quinolones was discordant between isolations. Therefore, manual susceptibility tests were performed to confirm the susceptibility patterns. Genus Brucella are facultative intracellular parasites. Recently, Brucellae merged with Ochrobactrum spp. in the genus Brucella, based only on global genomic analysis. Some microbiologists believe this is incorrect because it was performed without a thorough phylogenetic analysis and poses a risk to those working with brucellosis. They suggested that the terms Ochrobactrum and Brucella remain valid separately¹⁶.

In conclusion, Brucella anthropi is a gram-negative bacillus recently associated with opportunistic infections in immuno-compromised hosts. Infections related to these bacteria are primarily bloodstream infections. Patients with severe burn injuries are at an increased risk of developing complicated infections due to immune dysfunction.

The diagnosis and treatment of Brucella anthropi infections are challenging because of low clinical suspicion, different methods of identification, and resistance patterns. In this clinical case, the patient had multiple risk factors that increased the risk of acquiring opportunistic infections, and identification was performed in the microbiology laboratory.

To our knowledge, this is the first report of a Brucella anthropi bloodstream infection in a patient with severe burns. We conclude that knowledge of the prevalence of infections associated with this microbiological agent, methods of identification, and resistance patterns must be increased to raise awareness of the capability of infection and complications of this agent and to provide better and more effective treatment strategies in high-risk populations.