Contents lists available at ScienceDirect Veterinary Microbiology journal homepage: www.elsevier.com/locate/vetmic Gram-negative multi-drug resistant bacteria influence survival to discharge for horses with septic synovial structures: 206 Cases (2010–2015) Jessica M. Gilbertie a,c , Lauren V. Schnabel c , Darko Stefanovski a , Donna J. Kelly b , Megan E. Jacob c , Thomas P. Schaer a, ⁎ a Department of Clinical Studies, New Bolton Center, School of Veterinary Medicine, 382 West Street Rd., Kennett Square, PA 19348, United States b Department of Pathobiology, New Bolton Center, School of Veterinary Medicine, 382 West Street Rd., Kennett Square, PA 19348, United States c North Carolina State University, College of Veterinary Medicine, North Carolina State University, 1060 William Moore Drive, 27607 Raleigh, NC, United States ARTICLE INFO Keywords: Septic synovitis Infectious arthritis Equine Multi-drug resistance (MDR) Fluoroquinolones Gram-negative bacteria ABSTRACT Bacterial colonization of synovial structures can cause infections that are difficult to treat. Systemic and local antimicrobials and repeated joint lavages are the mainstays of therapy. However, despite aggressive treatments, infection may persist, leading to significant tissue damage or death of the patient. In order to investigate the impact of bacterial culture and antimicrobial resistance on survival to discharge, we reviewed medical records of horses admitted to the University of Pennsylvania’s large animal teaching hospital from 2010–2015. Two- hundred and six cases with a definitive diagnosis of septic synovitis and a synovial fluid sample submitted for microbiological culture were included in the study. Of these horses, 48% were culture negative and 52% were positive for any bacterial growth, of which 66% were gram-positive and 28% were gram-negative aerobic or- ganisms with 4% anaerobic and 2% fungal organisms. Overall survival to discharge from hospital was 86%. Horses that had negative growth on culture were more likely to survive until discharge (p < 0.02). Multivariable analyses revealed that the likelihood of euthanasia was significantly associated with identification of coagulase positive Staphylococcus spp. (OR 7.66, 5.46–10.74, p < 0.0001), β-hemolytic Streptococcus spp. (OR 5.18, 3.56–7.55, p < 0.0001), Enterococcus spp. (OR 18.38, 11.45–29.52, p = 0.002), Enterobacteriaceae (OR 31.37, 22.28–44.17, p < 0.0001), Pseudomonas aeruginosa (OR 9.31, 5.30–16.34, p = 0.0004) or other gram-negative species (OR 3.51, 2.07–5.94, p = 0.001). Multi-drug resistance and gram-negative bacteria spe- cies were associated with significantly decreased survival rates (OR 119.24, 70.57–201.46, p < 0.0001). In conclusion, prognosis for survival to discharge was poor for horses that were infected with gram-negative or- ganisms, particularly those with MDR phenotypes. 1. Introduction Infectious or septic synovitis in horses is a medicalemergency and treatment of this condition can be prolonged and unrewarding (Morton, 2005; Carstanjen et al., 2010). Bacterial colonization of synovial structures, such as a joint, tendon sheath or bursa, can cause infections that are difficult and costly to treat (Meijer et al., 2000; Morton, 2005). There are two main routes of bacterial infection: hematogenous or exogenous spread. Hematogenous spread is more common in foals secondary to a bacteremia (Meijer et al., 2000; Morton, 2005). Exo- genous spread can be either of traumatic origin such as from a pene- trating wound or iatrogenic in nature following delivery of intra-ar- ticular medication or a surgical procedure (Seror et al., 1999; Richardson, 2008; Ahern et al., 2010; Steel et al., 2013). Staphylococcus aureus is the most commonly isolated bacterial species from equine wounds and in cases of septic arthritis due to the high prevalence of this organism on the skin (Schneider et al., 1992b; Lugo and Gaughan, 2006; Robinson et al., 2016). Similarly, in human medicine, S. aureus is the most commonly isolated bacterial species from septic arthritis and infected orthopedic implants (Shirtliff and Mader, 2002; Vincze et al., 2014). Once infection is established within a synovial structure, ther- apeutic intervention is required to attempt to eradicate the etiological agent, restore the normal synovial environment, and preserve function. Standing joint flush or surgical lavage under general anesthesia is es- sential to establish drainage and promote the clearance of bacteria, inflammatory cells, and metalloproteinases that lead to degenerative changes, especially within joints (Steel et al., 1999; Meijer et al., 2000; https://doi.org/10.1016/j.vetmic.2018.10.009 Received 8 July 2018; Received in revised form 26 September 2018; Accepted 10 October 2018 ⁎ Corresponding author. E-mail address: tpschaer@vet.upenn.edu (T.P. Schaer). Veterinary Microbiology 226 (2018) 64–73 0378-1135/ © 2018 Elsevier B.V. All rights reserved. T