Emerging Infectious Diseases • www.cdc.gov/eid • Vol. 25, No. 8, August 2019 1587 RESEARCH LETTERS Erwinia billingiae as Unusual Cause of Septic Arthritis, France, 2017 Isabelle Bonnet, Baptiste Bozzi, Eric Fourniols, Stéphane Mitrovic, Olivia Soulier-Escrihuela, Florence Brossier, 1 Wladimir Sougakof, Jérôme Robert, Stéphane Jauréguiberry, Alexandra Aubry, on behalf of the Pitié- Salpêtrière Infection Ostéo-articulaire group 2 Author afliations: Assistance Publique–Hôpitaux de Paris, Hôpitaux Universitaires Pitié Salpêtrière–Charles Foix, Paris, France (I. Bonnet, B. Bozzi, E. Fourniols, S. Mitrovic, O. Soulier-Escrihuela, F. Brossier, W. Sougakof, J. Robert, S. Jauréguiberry, A. Aubry); Sorbonne Université, Cimi-Paris, U1135, Paris (I. Bonnet, F. Brossier, W. Sougakof, J. Robert, A. Aubry) DOI: https://doi.org/10.3201/eid2508.181073 In 2017 in France, we treated a patient with knee septic arthritis caused by Erwinia billingiae after trauma involv- ing a palm tree. This rare pathogen could only be identifed through 16S rRNA gene sequencing. For bacterial infec- tions after injuries with plants, 16S rRNA gene sequencing might be required for species identifcation. T he prevalence of acute septic arthritis in Western Eu- rope is ≈4–10 cases/100,000 inhabitants (1). We report a case of posttraumatic knee septic arthritis in an immuno- competent patient in France that was caused by Erwinia billingiae, a gram-negative environmental bacterium of the family Enterobacteriaceae. We also review the characteris- tics of Erwinia species and infections. On April 9, 2017, a 65-year-old man with an unremark- able medical history was admitted to an emergency unit in Nice, southern France, for painful right knee swelling that occurred a few hours after a Phoenix palm tree needle pierced the area. The foreign body was partly removed, and the wound was sutured. The patient was discharged with- out any knee pain and given a prescription for amoxicillin/ clavulanic acid (1 g 3×/d for 6 d). On April 22, the patient was admitted to the emer- gency unit of our hospital in Paris because of sudden right knee pain and fever. Synovial fuid collected by knee puncture the day of his admission to the orthopedic unit (April 23) contained 118 × 10 9 leukocytes/L, consisting of 64% polymorphonuclear cells, 33% lymphocytes, and 3% other leukocytes; no microorganism could be identifed after Gram staining and cultures. A second knee puncture was performed 3 days after admission, and gram-negative rods grew within 2 days solely within the anaerobic blood culture vial (BacT/ALERT SN; bioMérieux, https://www. biomerieux.com). Subcultures of the blood culture vial were positive after 24 hours of incubation at 37°C on blood agar (Trypticase Soy agar + 5% horse blood and Mueller Hinton 2 agar + 5% sheep blood; bioMérieux) and Drigals- ki agar (BD, https://www.bd.com) under aerobic conditions and chocolate agar (BD) under microaerobic conditions. Matrix-assisted laser desorption/ionization time-of- fight (MALDI-TOF) mass spectrometry (Bruker Daltonik, https://www.bruker.com) was performed on colonies and failed to correctly identify the species. Therefore, we per- formed species identifcation by 16S rRNA amplifcation and sequencing with primers RNA-S (16S, 5′-AGAGTTT - GATCCTGGYTCAG-3′) and RNA-AS (16AS, 5′-CTT - TACGCCCARTAAWTCCG-3′) at a hybridization tempera- ture of 52°C. We amplifed a 521-bp sequence that matched the E. billingiae genome of 2 isolates with 99.4% similarity (GenBank accession nos. JQ929658 and JN175337). Other closely related species displayed lower similarities: Pantoea rwandensis (99.0%), Erwinia persicina (98.9%), Pantoea cofeiphila (98.7%), Erwinia tasmaniensis (98.5%), and Er- winia aphidicola (98.3%). Following guidelines of the Anti- biogram Committee of the French Society for Microbiology (https://www.sfm-microbiologie.org/2019/01/07/casfm-eu- cast-2019), we tested the E. billingiae isolate with the antimi- crobial drugs recommended for Enterobacteriaceae; the iso- late was susceptible to all these drugs, including ampicillin. Because of the lack of clinical improvement, the joint was washed on day 6 after admission. After this interven- tion, an empiric antimicrobial drug treatment was started with amoxicillin/clavulanic acid (2 g 3×/d intravenously). Once results of drug susceptibility testing became available (i.e., 10 days after admission), his treatment was switched to cefotaxime (2 g 3×/d intravenously) and ciprofoxacin (500 mg 2×/d orally for 8 d), followed by ciprofoxacin (500 mg 2×/d alone for 38 additional days). Total duration of treatment was 45 days. The clinical evolution of this pa- tient was favorable; he fully recovered and had no relapses up to 1 year after treatment completion. In the past, some members of the Erwinia genus were reassigned to the genera Enterobacter or Pantoea. Erwinia spp. are ubiquitous in the environment, especially in wa- ter ecosystems and soils. Plant-associated Erwinia species comprise epiphytic nonpathogenic (i.e., E. billingiae and E. tasmaniensis) and pathogenic (i.e., E. amylovora and E. pyrifoliae) species. The MALDI-TOF mass spectrom- etry system failed to identify the bacterium, even though E. billingiae is contained in the database for either method used (direct deposit or on-plate formic acid treatment). Future expansion of the database with more spectra will likely improve the performance of the MALDI-TOF mass 1 Deceased. 2 Group members are listed at the end of this article.