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Author affiliations: Spital Schwyz, Schwyz, Switzerland (R. Di Micco, M. Schneider, R. NÃ¼esch); University of Basel, Basel, Switzerland (R. NÃ¼esch)
Genre Paenibacillus includes an increasing number of species of motile rod-shaped bacteria with peritrichous flagella (1). Paenibacillus The species share 89.6% sequence similarity of the 16S rDNA gene and grow as unpigmented colonies on tryptic soy agar (1). Better known as an almost ubiquitous environmental bacteria, many Paenibacillus are potential opportunistic pathogens in humans (2). We report a case of isolated surgical site infection caused by P. thiaminolyticus in an otherwise healthy patient.
A 33-year-old woman presented to the emergency room with a fever and reported having a painful and fluctuating abdominal wall mass for 3 days. She had undergone lipoabdominoplasty at another hospital 7 days earlier. Laboratory tests showed anemia (hemoglobin 88 g / L, hematocrit 0.24 L / L) and an isolated increase in C reactive protein (117 mg / L). Computed tomography of the abdomen showed a collection of fluid in the abdominal wall measuring 22 Ã 9.5 Ã 5 cm. The patient was admitted for observation. Blood cultures performed at 38.5 Â° C showed no bacterial growth.
Empirical intravenous antimicrobial drug therapy for a suspected hematoma was initiated with amoxicillin / clavulanate (2.2 g 3 Ã / d), according to local hospital guidelines. While on antimicrobial medication, the patient’s fever resolved, but her abdominal pain persisted.
On day 3, we aspirated a sample of the fluid collection in the abdominal wall for microbiological examination. Aspirate was grown on blood agar incubated at 35 Â° C with 5% CO2 for 48 hours; on MacConkey agar incubated at 35 Â° C., aerobically, for 24 h; and on selective anaerobic agar at 35 Â° C, anaerobic, for 5 days. All 3 gave a pure culture of gram-variable rod-shaped bacteria. We used Biotyper Matrix Assisted Laser Desorption / Ionization Time-of-Flight Mass Spectrometry (MALDI-TOF) (Bruker Corporation, https://www.bruker.com) and the Bruker mass spectra database, which returned P. thiaminolyticus with a best match score of 2.07 (a >2 means identification at species level) (3,4).
On day 7, the patient bled at the operative site, and we performed surgical evacuation with drainage of the fluid collection. We took an intraoperative microbiological swab sample and performed another MALDI-TOF mass spectrometry analysis, which confirmed that the pathogen was P. thiaminolyticus with a best match score of 2.17.
After evacuation of the hematoma, the patient recovered quickly. Since no specific clinical threshold has been established for Paenibacillus spp., we used non-species clinical cutoffs from the European Committee on the Pharmacokinetics and Pharmacodynamics of Antimicrobial Susceptibility Testing (table). The intravenous antimicrobial treatment was continued for a total of 10 days. On day 14, the patient was discharged with oral amoxicillin / clavulanate (1 g 3 Ã / d) for an additional 2 weeks. We decided to carry out clinical and laboratory follow-up at 2, 4 and 8 weeks after discharge. At the end of 2 months, the surgical wound was healed, the patient was well and without sequelae.
Of the 49 species of Paenibacillus known to cause symptomatic infection in humans, the most commonly reported are P. alvei, P. phoenicis, P. macerans, P. lautus, P. timonensis, P. provencensis, and P. thiaminloyticus (2). The clinical manifestation in patients is heterogeneous, ranging from paucisymptomatic to severe sepsis. Bacteria are usually found in the blood with overt bacteremia (2). In that case, P. thiaminolyticus was found in aspirates from infected abdominal wall hematoma, but not in blood cultures or other body compartments.
Because Paenibacillus spp. are possible laboratory contaminants (5), organisms should be detected in multiple sets to rule out contamination. The lack of clear and discriminating phenotypic characteristics necessitates molecular biology methods to identify the bacteria, such as MALDI-TOF mass spectrometry or, if in doubt, sequencing of the 16S rRNA gene (4).
P. thiaminolyticus is reported to be potentially resistant to ampicillin alone (2), vancomycin (2) and clindamycin (6). In this case, the bacteria showed resistance to tetracycline. Therefore, antimicrobial susceptibility testing is necessary. According to the antibiograms reported in the literature, empiric treatment with trimethoprim / sulfamethoxazole or amoxicillin / clavulanate is recommended. Although this patient’s condition improved with intravenous antimicrobial drug therapy, clinical resolution did not occur until after surgical evacuation of the fluid collection from the abdominal wall. Due to reports of persistent infections (7), patients should be monitored after treatment.
P. thiaminolyticus was identified in human stool in 1951 (8). Anecdotally, its thiaminase activity can reduce the available thiamine necessary for energy metabolism in the central nervous system, causing poliencephalomalacia in ruminants (9). So far, no human disease syndrome has been explicitly linked to P. thiaminolyticus. In 2008, P. thiaminolyticus has been reported as the causative agent of bacteremia of unknown origin in a dialysis patient with multiple underlying conditions and a long-term catheter (6). Since then, 3 more isolates have been reported in the blood (2), vitreous humor (2) and cerebrospinal fluid (ten).
In summary, this case reminds us of the existence of a rare potential pathogen in our microbiota, although the causality can be debated because Paenibacillus spp. mostly environmental bacteria remain. Therefore, identification relies on MALDI-TOF mass spectrometry or sequencing of the 16S rRNA gene. Surgical debridement of the site of infection is also recommended. The microorganism exhibits a variable antimicrobial susceptibility profile, and trimethoprim / sulfamethoxazole and amoxicillin / clavulanate are empirical first-choice treatments available after successful identification.
Dr Di Micco is a general surgery resident at Spital Schwyz, Switzerland. His main research interests are translational medicine, abdominal surgery and the prevention of surgical wound infections.
Suggested citation for this article: Di Micco R, Schneider M, NÃ¼esch R. Postoperative Paenibacillus thiaminolyticus wound infection, Switzerland. Emerg Infect Dis. Jul 2021 [date cited]. https://doi.org/10.3201/eid2707.203348
The conclusions, findings, and opinions expressed by the authors contributing to this review do not necessarily reflect the official position of the United States Department of Health and Human Services, the Public Health Service, the Centers for Disease Control and Prevention, or institutions affiliated with the. authors. . Use of trade names is for identification purposes only and does not imply endorsement of any of the groups mentioned above.