Le Infezioni in Medicina, n. 1, 124-128, 2022

doi: 10.53854/liim-3001-15

CASE REPORT

Trueperella bernardiae bloodstream infection following onco-gynaecologic surgery and literature review

Roberto Casale1,2, Gabriele Bianco1, Stefano Cosma3, Leonardo Micheletti3, Sara Comini1,2, Marco Iannaccone1, Matteo Boattini1,2, Rossana Cavallo1,2, Chiara Benedetto3, Cristina Costa1,2

1Microbiology and Virology Unit, University Hospital Città della Salute e della Scienza di Torino, Turin, Italy;
2Department of Public Health and Paediatrics, University of Torino, Turin, Italy;
3Gynecology and Obstetrics 1, Department of Surgical Sciences, City of Health and Science, University of Torino, Turin, Italy

Article received 24 December 2021, accepted 7 February 2022

Corresponding author

Roberto Casale

E-mail: roberto.casale.cr@gmail.com

SummaRY

Trueperella bernardiae is a Gram-positive commensal bacillus of the human skin and oropharynx. It is known as an opportunistic human pathogen causing surgical wound, skin, and soft tissue, osteoarticular, and bloodstream infections (BSIs) with severe complications. We report a case of surgical wound related T. bernardiae BSI following onco-gynaecologic surgery together with a comprehensive literature review of T. bernardiae infections to alert clinicians about this emerging pathogen.

Keywords: Trueperella bernardiae, sepsis, onco-gynaecologic surgery, surgical wound infection, Gram-positive bacillus, MALDI-TOF MS.

INTRODUCTION

Surgical wound infection is the most common health care–associated infection following surgery and may impact on morbidity and mortality, length of stay, and hospital costs [1, 2]. Staphylococcus aureus, coagulase-negative staphylococci, Streptococcus spp, Enterococcus spp, as well as Gram-negatives and anaerobic organisms, in the case of grossly contaminated wounds, are the most common pathogens isolated from infected surgical sites [3]. Trueperella bernardiae is a commensal of the human skin and oropharynx, coryneform, facultative anaerobic, catalase and oxidase negative, Gram-positive bacillus [4]. Despite human infections with Trueperella spp having a low prevalence, the addition to the Matrix-assisted laser desorption ionization–time of flight (MALDI-TOF) mass spectrometry database of the main spectrum for T. bernardiae made its pathogenicity increasingly documented in literature [5-23]. We report a case of T. bernardiae bloodstream infection (BSI) following onco-gynaecologic surgery together with a comprehensive literature review of T. bernardiae infections to help clinicians be aware about epidemiological, clinical, and microbiologic features of this emerging pathogen.

CASE REPORT

In May 2021, a 78-year-old woman with a history of hysterectomy for uterine myomas at the age of 38 and breast cancer treated with QUART six years earlier was admitted to the hospital for fever and abdominopelvic pain. Symptoms had started five days before the admission and had gradually become more severe. Two months before the admission she had been surgically treated undergoing total vulvectomy with bilateral inguinofemoral lymphadenectomy due to the presence of a keratinizing squamous infiltrating carcinoma (pT1b) with no additional therapy. On physical examination the patient showed diastasis and purulent drainage from the inguinal surgical wound. Her body temperature was 37.4°C, pulse rate was 97 bpm, respiratory rate was 24/min, and blood pressure was 113/39 mmHg. Blood analysis showed neutrophilic leukocytosis (white blood cell count 13,000 per mm3 [4,500-11,000]; neutrophils 85%) and increased inflammatory markers (C-reactive protein 276 mg/L [<0.5]; procalcitonin: 1.14 ng/mL [<0.5]). Abdominal-pelvic computer tomography revealed no alterations suggestive of infectious foci. Urine culture was negative. Polymicrobial flora was reported from the subculture of swab performed on the surgical wound. Four pairs of aerobic and anaerobic blood cultures (BCs) were drawn peripherally. Piperacillin/tazobactam (4.5 g every 8 h, i.v.) and metronidazole (500 mg every 8 h, i.v.) were started. Four BC vials became positive between 26 and 74 hours of incubation on the BACT/ALERT Virtuo (bioMérieux, Marcy l’Ètoile, France). Gram staining showed Gram-positive rods and non-hemolytic, whitish, rounded colonies grew on overnight subcultures on blood agar plates. MALDI-TOF mass spectrometry (Bruker DALTONIK GmbH, Bremen, Germany) provided identification of T. bernardiae (identification score of 2.20). Identification of the T. bernardiae isolate was confirmed by 16S rRNA gene sequencing. Three other BC vials became positive between 12 h and 20 h, and Gram-positive cocci and Gram-negative bacilli were observed at Gram staining. MALDI-TOF analysis identified Enterococcus avium and Bacteroides fragilis on overnight subcultures. In vitro susceptibility of T. bernardiae, B. fragilis, and E. avium was assessed with E-test® (bioMérieux, Marcy l’Étoile, France) and interpreted using the current EUCAST breakpoints (v.11 2021), specifically PK/PD (Non-species related), Gram-negative anaerobes, and Enterococcus spp. clinical breakpoints, respectively. T. bernardiae was susceptible to penicillin (MIC 0.064 µg/mL), amoxicillin-clavulanic acid (MIC 0.38 µg/mL), piperacillin/tazobactam (MIC 0.5 µg/mL), ertapenem (MIC 0.094 µg/mL), imipenem (MIC 0.094 µg/mL), meropenem (MIC 0.25 µg/mL), and non-interpretable due to insufficient evidence (IE) for clindamycin (MIC 0.047 µg/mL) and vancomycin (MIC 0.125 µg/mL). Both B. fragilis and E. avium were multi-susceptible. Following the results of susceptibility testing, piperacillin/tazobactam was stopped and clindamycin together with metronidazole was continued for 14 days. The surgical wound was cleaned and disinfected daily, kept without wound dressing, showing progressive improvement until purulent drainage stopped. Patient was discharged in good clinical condition, and she is still being followed up in the onco-gynecologic outpatient clinic of our center.

DISCUSSION

Identification of Gram-positive rods in blood cultures should always alert about the possibility of blood sample contamination, as they are mostly skin commensal bacteria with low pathogenic potential. In this report, we presented a microbiologically well documented case of T. bernardiae BSI in which the surgical wound was the plausible route of infection and we also highlighted how the introduction of MALDI-TOF mass spectrometry analysis provided both rapid bacterial identification and clinical contextualization of this emerging organism.

The rising and pathogenic role in immunocompromised patients of microorganisms previously considered to be contaminants is supported, in our case, by the fact that T. bernardiae isolates were identified from several blood culture vials drawn from different sites, the plausible route of infection, and patient’s clinical history. However, since T. bernardiae is often reported to be identified, as in our case, in polymicrobial infections, it is difficult to establish its real pathogenicity and contribution to the clinical setting, especially when patient improvement following broad-spectrum antimicrobial treatment is observed.

Since the virulence of T. bernardiae is still unclear, and its occurrence is overall rare, a comprehensive literature review of T. bernardiae infections was performed. We conducted a literature search in Pubmed, with the keywords “Trueperella bernardiae” OR “Arcanobacterium bernardiae”, which resulted in 27 articles. The more relevant articles were analyzed and epidemiological and clinical features of all recently diagnosed cases of T. bernardiae were provided in the Table 1 [6-23]. We highlight that T. bernardiae infection has been mostly identified in immunocompromised hosts, with no apparent age or gender predilection, often diagnosed in polymicrobial cultures, and presenting a good prognosis. T. bernardiae was deemed to cause skin and soft tissue including two cases of breast abscess, osteoarticular, BSIs with severe complications, and two cases of brain abscess following otitis media are also reported [6-23]. Of note, among soft tissue and osteoarticular infections, there are various cases related with arthroplasty and, as in our case, surgical wound.

Identification of Gram-positive bacilli is quite difficult using conventional laboratory methods, while implementation of MALDI-TOF mass spectrometry has greatly assisted in the final diagnosis. Concerning T. bernardiae, MALDI-TOF mass spectrometry analysis showed to provide rapid and reliable identification at species level helping to elucidate the pathogenic role of this rarely isolated microorganism [5]. A treatment of choice for T. bernardiae infection has not been established yet, because of the small amount of data available and the lack of clinical breakpoints for this bacterium. Drug resistance in T. bernardiae still seems not to represent a relevant clinical issue, since T. bernardiae has been reported to be multi-susceptible to the antibiotics tested with few exceptions regarding ciprofloxacin, gentamicin, and penicillin [6, 7, 17, 22].

In conclusion, we report a case of T. bernardiae BSI following onco-gynaecologic surgery with the surgical wound as the bacteraemia’s port of entry. Rapid bacterial identification with MALDI-TOF mass spectrometry analysis and envisaging possible routes of infection could help clinicians to set the clinical value of Gram-positive rods observed in blood cultures obtained from patients suffering surgical wound infections.

Ethical approval

This study was conducted in accordance with the Declaration of Helsinki. Written informed consent was obtained from the patient.

Disclosure statement

No competing interests exist.

Funding information

No funding was received for this study.

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