Rhodococcus Equi Infection in a Surgical Wound
Total Page：16
File Type：pdf, Size：1020Kb
CLINICAL PRACTICE Rhodococcus equi Infection in a Surgical Wound STUART R. PAASCHE ABBREVIATIONS: ED= Emergency Department; WBC= A 35-year-old diabetic male received routine day surgery to White Blood Cell Count; BAP= Sheep’s Blood Agar Plate repair a ventral hernia. The surgical wound, upon follow-up visits, appeared to be healing properly. One month later, INDEX TERMS: Rhodococcus equi, surgical wound infections however, the patient presented to the ED with complaints of abdominal pain, after the patient had received an undisclosed Downloaded from Clin Lab Sci 2009;22(3):141 minor trauma to the wound, while working outdoors for the local school department. The patient began having occasional ABSTRACT: A 35-year-old male presented with abdominal feverish episodes along with erythema and the drainage of pain one month after receiving a routine ventral hernia repair. purulent material from the wound thereafter. There was no Over the course of two months, repeated wound cultures evidence of a pathogenic infection in the wound, as cultures were ordered and eventually produced growth of Rhodococ- yielded only ‘normal skin flora’, which included coagulase http://hwmaint.clsjournal.ascls.org/ cus equi. Appropriate antibacterial therapy was initiated to negative Staphylococcus and diphtheroids. Cephalexin was resolve the infection. prescribed and the patient returned home. OBJECTIVES: Review the history, pathogenesis, diagnosis, One week later, the patient returned to the ED with what was and treatment of non-pulmonary R. equi infections; inform described as a “non-healing surgical wound”. The wound was laboratory professionals of the possibility and severity of R. cleansed and packed with gauze. With both wound and blood equi infections, and what can be done to facilitate prompt cultures appearing negative for significant bacterial growth, diagnosis and recovery. anti-fungal treatment was initiated due to the patient’s con- tinued failure to heal under the antibiotic treatment. ACKNOWLEDGEMENTS: The author wishes to thank on September 30 2021 Dr. Susan Leclair and the department of Medical Laboratory Due to the persistent infection, the wound was surgically re- Science at the University of Massachusetts, Dartmouth along opened two weeks later, and the infected periumbilical patch with the laboratory staff of Jordan Hospital for helping make was removed by an open approach. A gram stain from a sterile this case study possible. swab of the wound yielded no organisms. Two days later, the patient returned to the ED with severe abdominal pain. Stuart R. Paasche, CLS (NCA), is a Clinical Laboratory Sci- Additional microbiological workup was ordered on wound entist at Lee Memorial Hospital, Fort Myers, FL 33901 specimens collected using sterile swabs and anaerobic cul- turettes for both aerobic and anaerobic cultures, along with Address for Correspondence: Stuart Paasche, 1826 Beach acid fast stains and cultures. Table 1 outlines the numerous Parkway, Cape Coral FL 33904, 774-244-1834 (Cell), tests ordered along with their corresponding findings. [email protected] LABORATORY RESULTS The area surrounding the surgical wound was largely inflamed The peer-reviewed Clinical Practice Section seeks to publish case stud- and erythemic with purulent discharge coming from the ies, reports, and articles that are immediately useful, are of a practical wound site. The patient’s WBC count was slightly elevated nature, or contain information that could lead to improvement in the at 13.7 x103/uL (3.9-10.0 x103/uL), though he was afebrile. quality of the clinical laboratory’s contribution to patient care, includ- Swabs taken from the wound, now over a month after the ing brief reviews of books, computer programs, audiovisual materials, infection began, grew small, mucoid colonies on BAP, which or other materials of interest to readers. Direct all inquiries to Berna- at nearly 4 days after planting, developed a distinctive pink dette Rodak MS CLS(NCA), Clin Lab Sci Clinical Practice Editor, Clinical Laboratory Science Program, Indiana University, Clarian pigmentation. The colonies were gram-stained and showed Pathology Laboratory, 350 West 11th Street, 6002F, Indianapolis IN long, gram-positive bacilli. An acid-fast stain was performed 46202. [email protected] on the colonies, and the organisms were variably positive. VOL 22, NO 3 SUMMER 2009 CLINICAL LABORATORY SCIENCE 141 CLINICAL PRACTICE The organisms were catalase positive, oxidase negative, and composition and biochemical reactions were found to be urea positive. A CAMP test on BAP was performed using a more closely related to Nocardia and Mycobacterium than streak of Staphylococcus aureus with a perpendicular streak of Corynebacterium, that the genus was changed to Rhodococcus the organism in question. A striking zone of beta-hemolysis (“red-pigmented coccus). 2,3 was noted near the intersection of the two streaks. A Re- mel™ Rapid CB Plus strip was inoculated yielding a 99.9% Rhodococcus equi can be found in all continents of the world identification of Rhodococcus equi. The culture was sent to except Antarctica, and can flourish in both fresh and saltwater the State Laboratory for confirmation, and a preliminary environments, and also within the intestines of bloodsucking identification of R. equi was reported. The State Laboratory arthropods.4 R. equi, however, is more commonly associated later verified the identification. with zoonotic infections mostly from horses, but also sporadi- cally from cattle, sheep, pigs, goats, deer, dogs, wild birds and BACKGROUND even cats.3,4,5 R. equi colonizes the gastrointestinal tract of Downloaded from The genus Rhodococcus is in the family Nocardiaceae in the grazing mammals, and can be isolated from the manure and suborder Corynebacterineae of the Actinomycetales order.1 R. soil.4 Exposure to R. equi can be via the oral route by ingest- equi was originally termed Corynebacterium equi due to its ing products contaminated with soil or manure, inhalation morphological characteristics representing diphtheroids.1 of airborne organisms in dust, or direct inoculation due to 5 It wasn’t until 1980, however, that the organism’s cell wall trauma with soil or manure containing the organism. http://hwmaint.clsjournal.ascls.org/ Table 1: Wound Cultures and Tests Ordered. There were no issues associated with the surgery, performed on 9/10, and for a month thereafter. However, after the patient received trauma to the wound, perhaps contaminating the wound with dirt, an infection began that persisted for nearly two months. This table outlines the course taken, involving repetitive wound cultures and gram stains, until the final, confirmed ID of Rhodococcus equi was reported, and the patient was properly treated allowing for full recovery. Date Test Ordered Result on September 30 2021 10/5 Wound Gram Stain Few WBC No organisms seen Wound Culture Light growth “Skin Flora” (Coagulase negative Staphylococcus & diphtheroids) 10/12 Wound Gram Stain Few WBC No organisms seen Wound Culture Light growth “Skin Flora” Blood Culture No Growth @ 5 days 10/29 Wound Gram Stain Few WBC No organisms seen Wound Culture Light growth “Skin Flora” 10/30 Wound Gram Stain Few WBC No organisms seen Anaerobic Wound No Anaerobes Isolated Culture Blood Culture No Growth @ 5 days Wound Culture Positive growth with Rhodococcus equi (Preliminary ID reported 11/6) 11/6 Wound Culture Rhodococcus equi (Confirmatory ID reported on (reference laboratory) 11/25 142 VOL 22, NO 3 SUMMER 2009 CLINICAL LABORATORY SCIENCE CLINICAL PRACTICE About 80-90% of patients with R. equi infections are immu- fast bacterium such as M. tuberculosis, which often causes nocompromised.6 Causes for immunosuppression can range more trouble for the patient’s recovery. More often, however, from the most commonly seen AIDS/HIV, to malignancy, R. equi is overlooked or ignored due to its diphtheroid-like transplantation, chronic renal disease, alcoholism, immu- morphology and the slow development of its characteristic nosuppressive therapy (including prednisone, azothiopine pigmentation, often leading to the misdiagnosis as a con- and corticosteroid therapies) or, as in this case, diabetes taminant.6 R. equi can also be confused with Nocardia spp. mellitus.5,6,7 On rare occasions, however, an infection with because of its acid-fast nature, and fungal characteristics, R. equi may be acquired in the immunocompetent. About such as the formation of aerial hyphae.7 A misidentification 50% of the cases in the immunocompetent patient are due of R. equi could lead to inappropriate antibiotic treatment, to trauma.7 and if left untreated, death. Rhodococcus equi infections have ranged from necrotizing R. equi grows well on nonselective media when incubated Downloaded from pneumonia, to “wound infections, subcutaneous abscess, aerobically at 37o C. On blood agar plates, large, smooth, thyroid abscess, retroperitoneal abscess, peritonitis, osteomy- irregular, mucoid colonies can appear within 48 hours, how- elitis, endophthalmitis, lymphadenitis, lymphangitis, septic arthritis, osteitis, bloody diarrhea, and fever of unknown 7 origin among others.” http://hwmaint.clsjournal.ascls.org/ Table 2: Reactions of Rhodococcus equi Rhodococcus equi is a facultative intracellular pathogen.5 The pathogenicity of R. equi is based upon its ability to infect and Test Reaction live within macrophages, inhibiting their phagocytic capa- bilities, and eventually destroying them.5,6 R. equi will cause Gram Stain Gram positive bacilli inflammation, cell destruction and