Trueperella bernardiae is a Gram-positive, rod-shaped bacterium and an opportunistic human pathogen. While not typically aggressive, it can cause serious infection when a person’s natural defenses are compromised or when it enters normally sterile body sites. This bacterium was often overlooked or misidentified in laboratory settings, leading to a low reported prevalence in clinical literature. Advances in rapid identification technology have since revealed that T. bernardiae is clinically relevant.
Classification and Natural Reservoir
The taxonomic history of Trueperella bernardiae is complex, reflecting the difficulty in accurately classifying this organism before modern molecular techniques. It was first described in 1987 and later classified into the genus Actinomyces in 1995. In 1997, it was transferred to the genus Arcanobacterium as Arcanobacterium bernardiae. This former name is particularly relevant, as older medical records and literature may still use it. The final reclassification occurred in 2011, establishing its current place in the genus Trueperella.
T. bernardiae is a Gram-positive, rod-shaped bacillus. It is also categorized as a facultative anaerobe, which means it can grow in both the presence and absence of oxygen. The bacterium is considered part of the normal human flora, colonizing the skin and the upper respiratory tract. This presence establishes the organism as a commensal, explaining its role as an opportunistic pathogen. When the integrity of these barriers is broken, such as through trauma or surgery, the bacterium can enter deep tissues or the bloodstream. Identification has been significantly improved by the use of Matrix-Assisted Laser Desorption/Ionization-Time of Flight Mass Spectrometry (MALDI-TOF MS).
Spectrum of Clinical Infections
Infections caused by Trueperella bernardiae typically occur when the bacterium breaches the body’s natural defenses, often in association with trauma, foreign bodies, or surgical procedures. The clinical presentations are diverse and often involve sites where the organism has direct access to deeper tissues. The most commonly reported clinical syndromes include infections of the skin and soft tissues.
These soft tissue infections can manifest as abscesses, cellulitis, or surgical wound infections. The organism has also been linked to specific conditions, such as breast abscesses and diabetic foot ulcers. A frequent characteristic of T. bernardiae infections is their polymicrobial nature, meaning the organism is often isolated alongside other bacterial species.
The bacterium is also capable of causing serious invasive disease, including bloodstream infections (BSIs). These bacteremia cases can sometimes lead to severe complications, such as septic thrombophlebitis. Less common, but destructive, infections involve bone and joint structures, categorized as osteoarticular infections. Specific examples include septic arthritis, osteomyelitis, and infections of prosthetic joints. The organism has also been implicated in infections of the central nervous system, with cases of brain abscesses reported. Urinary tract infections have also been documented.
Patient Risk Factors and Treatment Strategies
Infections occur primarily in individuals with compromised health. Significant risk factors include an immunocompromised status, underlying chronic conditions such as diabetes mellitus or malignancy, and non-healing skin ulcers (such as pressure ulcers). Recent trauma, surgery, or the presence of foreign bodies like joint devices provide a route for the commensal organism to become invasive. Specific high-risk behaviors, such as intravenous drug use, have also been linked to severe infections.
The management of T. bernardiae infection often necessitates a dual approach involving surgical intervention and antimicrobial therapy. Surgical debridement—the removal of infected or necrotic tissue—is frequently necessary, especially for localized infections or infected joint hardware. This mechanical reduction of the bacterial load supports the effectiveness of subsequent antibiotic treatment.
T. bernardiae is generally susceptible to many common antibiotics, particularly beta-lactams like penicillin and amoxicillin/clavulanate. Susceptibility data frequently indicates effectiveness against:
- Cephalosporins
- Carbapenems
- Vancomycin
- Clindamycin
However, resistance patterns can vary, and resistance to erythromycin and clindamycin has been reported. Because of the variability in resistance and the lack of standardized clinical breakpoints from organizations like the Clinical and Laboratory Standards Institute (CLSI), antibiotic susceptibility testing (AST) is important. AST involves culturing the organism and performing sensitivity testing to guide the specific choice and duration of therapy. Treatment typically involves using susceptible antibiotics for a prolonged period, especially for deep-seated infections.