Trueperella Bernardiae: Infections, Symptoms, and Treatment

Trueperella bernardiae is a slow-growing, Gram-positive bacterium that lives quietly on human skin and mucous membranes but can cause serious infections when it gets the opportunity, particularly in people with weakened immune systems, chronic wounds, or implanted medical devices.¹ For years it was dismissed as a harmless contaminant when it showed up in lab cultures, which means its true role in human disease is still catching up with clinical reality. Better identification technology has changed that picture considerably, and the bacterium is now recognized in a widening range of infections from skin abscesses to bloodstream sepsis and bone disease.

A Bacterium That Was Easy to Overlook

T. bernardiae belongs to a group of bacteria sometimes called coryneform bacilli, which are small, irregularly shaped rods. It was originally classified within the genus Arcanobacterium and later moved to the newly created genus Trueperella based on genetic and chemical comparisons.² That taxonomic reshuffling matters because it helps explain why the organism has historically been hard to pin down. Coryneform bacteria are notoriously tricky to identify using traditional culture methods, and T. bernardiae grows slowly enough that faster-growing bacteria in a mixed culture can easily overshadow it.³ When a lab did isolate it, the default assumption for decades was contamination rather than true infection.⁴

The result is an organism whose clinical significance was likely underestimated for a long time. Case reports have accumulated steadily since the mid-2010s, and the consensus in infectious disease literature now treats T. bernardiae as a genuine opportunistic pathogen rather than an innocent bystander.⁵

Who Is at Risk

Most documented T. bernardiae infections occur in people who have some form of immune compromise or chronic illness. The published case literature highlights several recurring risk factors:¹

• Diabetes: chronic foot ulcers and poorly healing wounds provide a gateway for bacteria that normally stay on the skin surface.
• Injection drug use: repeated, non-sterile skin punctures create direct access to deeper tissues and the bloodstream.
• Immobility: bedridden patients develop pressure sores and skin breakdown that invite opportunistic colonization.
• Implanted devices: prosthetic joints, surgical hardware, and other foreign materials can serve as surfaces for bacterial attachment.
• Cancer and immunosuppressive therapy: malignancy itself and treatments like long-term corticosteroids reduce the body’s ability to clear colonizing bacteria.

That said, a handful of case reports have documented T. bernardiae infections in otherwise healthy individuals, so immune compromise is not an absolute prerequisite.¹ Environmental exposure may play a role in some of those cases. One report of olecranon bursitis (an infection of the fluid-filled sac at the elbow) in a patient without major underlying illness emphasized the importance of considering environmental and occupational contact as a route of infection.⁶

The Range of Infections and Their Symptoms

T. bernardiae does not cause a single signature illness. Instead, it shows up across a surprisingly broad spectrum of infection sites. Published reports have documented it in urinary tract infections, bloodstream infections, brain abscesses, breast abscesses, skin and soft tissue infections, post-surgical wound infections, bone infections, prosthetic joint infections, and septic thrombophlebitis (infected blood clots in deep veins).⁷ The most commonly reported sites of isolation are blood, urine, and abscesses.⁸

Symptoms depend entirely on where the infection takes hold. Skin and soft tissue infections tend to produce redness, swelling, warmth, and pus, the same signs you would see with any bacterial skin infection. Bone infections (osteomyelitis) develop more insidiously. In one case report, a patient initially had a foot ulcer that progressed over weeks to purulent drainage, foul smell, and a positive probe-to-bone test, meaning the bone was exposed through the wound, before osteomyelitis was confirmed.⁹ Bloodstream infections can present with fever, chills, and the systemic signs of sepsis. In a case involving an injection drug user, the organism contributed to septic thrombophlebitis that led to infected blood clots traveling to the lungs, causing cavitary lesions, along with deep soft tissue abscesses.¹⁰

Prosthetic joint infections deserve special mention because they are notoriously difficult to treat regardless of the organism involved. T. bernardiae has been identified as the cause of prosthetic hip infection with abscess formation, adding it to the growing list of uncommon bacteria that can colonize artificial joint surfaces.¹¹ Patients with prosthetic joints who develop persistent pain, swelling, or drainage months or years after surgery should be evaluated for infection even if the organism recovered is unfamiliar to their clinical team.

Why Infections Are Often Polymicrobial

One of the more interesting patterns in T. bernardiae case reports is how frequently it shows up alongside other bacteria rather than alone. In the osteomyelitis case mentioned above, cultures grew five different organisms simultaneously, including Pseudomonas aeruginosa and Streptococcus agalactiae alongside T. bernardiae.⁹ The septic thrombophlebitis case involved T. bernardiae mixed with a group of anaerobic organisms.¹⁰ Cases of polymicrobial infection with necrotizing fasciitis and chronic bone infections have also been reported.³

This tendency toward polymicrobial infection has practical consequences. Whether T. bernardiae and its companion organisms are working together synergistically or merely occupying the same damaged tissue at the same time is still an open question.³ Either way, the polymicrobial context makes treatment more complicated. Clinicians have to decide whether every organism in a mixed culture is contributing to the disease or just along for the ride. And because T. bernardiae grows slowly, faster-growing bacteria in the same sample can mask it entirely, potentially leading to incomplete treatment if the slower organism is the one driving persistent symptoms.

Patients with chronic wounds who have already been through multiple rounds of antibiotics seem especially prone to these mixed infections. Repeated antibiotic exposure can shift the microbial landscape of a wound, suppressing some species while allowing hardier or more resistant organisms, including T. bernardiae, to persist.⁹

How It Gets Identified

For a long time, the main reason T. bernardiae was dismissed as a contaminant was that the conventional methods available to identify it were unreliable. Traditional biochemical tests could classify it to the general group of coryneform bacteria but often could not pin it to the species level with confidence. That ambiguity fed the assumption that it was not clinically meaningful.

The game changer has been a technology called MALDI-TOF mass spectrometry, which identifies bacteria by analyzing their protein profiles. The technique is fast, accurate, and does not depend on how quickly the organism grows. Case reports have credited it directly with enabling reliable identification of T. bernardiae in clinical samples.¹⁰ Laboratory studies have confirmed that it can match clinical isolates to the T. bernardiae reference strain with high confidence.¹²

Gene sequencing provides another route to identification. Sequencing of the 16S ribosomal RNA gene and certain housekeeping genes can confirm a T. bernardiae isolate to the species level, and these molecular methods have been validated alongside MALDI-TOF in both human clinical and veterinary contexts.¹³ However, sequencing takes longer and costs more than MALDI-TOF, so in practice MALDI-TOF is the first-line identification tool in hospitals that have the equipment. The broader adoption of this technology across microbiology labs is likely a major reason why T. bernardiae is showing up in case reports more frequently now than it did twenty years ago. The organism was probably always there; we just could not name it reliably.

Treatment Approaches

There are no formal clinical guidelines for treating T. bernardiae infections, which is unsurprising for an organism known mainly from scattered case reports. Treatment decisions have been made case by case, guided by antimicrobial susceptibility testing of each individual isolate.

The good news is that T. bernardiae tends to be susceptible to a wide range of common antibiotics. In one well-documented case, susceptibility testing showed very low resistance levels to penicillin, co-amoxiclav, cefuroxime, cotrimoxazole, linezolid, doxycycline, imipenem, and amikacin. The notable exception was erythromycin, to which the isolate was highly resistant.¹⁰ That erythromycin resistance is worth watching because macrolide antibiotics are widely used, and if a clinician treated empirically with a macrolide before susceptibility results came back, the infection could worsen.

In practice, treatment regimens in published cases have varied based on the infection site and severity. A patient with diabetic foot ulcers and sepsis was treated with surgical debridement combined with piperacillin-tazobactam (a broad-spectrum intravenous antibiotic), followed by a course of oral amoxicillin, for a total of about a month.¹⁴ An osteomyelitis case was managed with a four-week course of ciprofloxacin and trimethoprim-sulfamethoxazole, which achieved complete symptom resolution.⁹ A case of olecranon bursitis resolved with appropriate antimicrobial therapy after the organism was properly identified.⁶

The common thread across these cases is that surgical drainage or debridement, when the infection involved an abscess or dead tissue, combined with targeted antibiotics based on susceptibility results, produced good outcomes. The challenge is not that the organism is hard to kill once you know what you are dealing with. The challenge is recognizing it in the first place and not dismissing it as irrelevant when it shows up in a mixed culture.

The Post-Surgical Wound Connection

Surgical wounds represent one of the more concerning infection sites for T. bernardiae because the organism can colonize incisions even after relatively routine procedures. The first documented case of T. bernardiae wound infection after laparoscopic surgery highlighted that even minimally invasive surgery with small incision sites can provide a portal of entry.¹⁵ A separate case involved bloodstream infection following gynecologic cancer surgery, suggesting that the organism can gain access during more extensive procedures as well.⁵

For patients recovering from surgery, the practical takeaway is straightforward: any wound that is not healing as expected, or that develops new redness, drainage, or odor, warrants evaluation. This is true for any surgical wound infection, of course, but the relevance to T. bernardiae is that if it does appear in a wound culture, it should not be automatically assumed to be a contaminant. A lab that identifies it using MALDI-TOF or molecular methods has likely made a correct call, and the clinical team should weigh whether it needs treatment.

T. Bernardiae in Animals

Although T. bernardiae is primarily recognized as a human pathogen, it is not exclusively one. The bacterium has been isolated from animals, including Peking ducks across multiple farms, confirmed by both mass spectrometry and gene sequencing.¹³ Two canine urogenital isolates closely related to T. bernardiae have also been reported, though genomic analysis placed them in a distinct lineage, raising the possibility that what looks like T. bernardiae in animals may sometimes be a closely related but separate species.¹⁶

The question of whether T. bernardiae is truly zoonotic, meaning whether it can jump from animals to humans or vice versa, remains unanswered. Its close relative Trueperella pyogenes is a well-known animal pathogen that causes abscesses and mastitis in livestock, so the genus as a whole has a foot in both worlds. For people with regular exposure to livestock, poultry, or animal environments, the finding of T. bernardiae in ducks is worth being aware of, although no confirmed case of animal-to-human transmission has been documented so far.

Why More Cases Are Showing Up Now

If you search the medical literature, T. bernardiae case reports have been appearing with increasing frequency over the past decade. This pattern almost certainly reflects better detection rather than a genuine increase in infections. Before MALDI-TOF mass spectrometry became standard in clinical microbiology labs, T. bernardiae isolates would have been classified vaguely as “coryneform bacteria” or dismissed as skin contaminants, and many labs would not have pursued further identification. The technology to reliably identify it at the species level simply did not exist in most hospitals until relatively recently.¹⁰

This detection-bias effect is common in clinical microbiology. A whole category of organisms that were previously too obscure to identify reliably are now being named and linked to clinical syndromes. For infectious disease specialists, T. bernardiae fits into a broader pattern of “emerging” pathogens that were always present but previously invisible. The emerging part is our ability to see them, not their appearance on the scene.

For lab personnel and clinicians who encounter an unfamiliar Gram-positive rod in a wound, blood, or urine culture, the broader lesson from the T. bernardiae literature is to take identification seriously before writing off any isolate. The organism grows slowly and can be overshadowed by faster organisms in mixed cultures, but when it is the real culprit, missing it can mean prolonged or inadequately treated infections, especially in patients with chronic wounds or implanted devices who are already at risk for poor outcomes.