Title : A mysterious tale of two joints and two bacteria
Abstract:
Introduction
Acinetobacter radioresistens (AR), as resistant as the name sounds, is a Gram-negative, aerobic bacillus that survives desiccation, hydrogen peroxide, and UV irradiation and thrives in the hospital environment. It evades detection in the laboratory, adding vile to its name. To date, only 9 cases of AR bacteremia have been described worldwide.1 Here we describe a case of bacteremia caused by this rare organism which kept us guessing its source.
Case presentation?
A 68-year-old man with obstructive sleep apnea, asthma, hypertension, atrial fibrillation, benign prostatic hyperplasia, and severe osteoarthritis of both knees presented to the emergency department with chills for 10 days and diarrhea for 3 days. Clinically, he was in septic shock requiring vasopressors. His initial work up revealed leukocytosis, acute kidney injury, metabolic acidosis, pyuria, and prostatitis on CT abdomen.
Due to increasing encephalopathy and vasopressor requirements, he was placed on mechanical ventilation. He was started on broad spectrum antibiotics vancomycin and piperacillin-tazobactam. Examination of knee joints revealed warmth and effusion without obvious erythema. Upon further questioning his wife, the patient received corticosteroid injections into both knees 2 weeks ago for longstanding severe osteoarthritis. Arthrocentesis of both knees revealed frank pus. Synovial fluid culture from both knees and blood cultures grew heavy colonies of methicillin-sensitive staphylococcus aureus (MSSA).
While the patient was treated for high-grade MSSA bacteremia with cefazolin, one subsequent blood culture from an aerobic bottle demonstrated Acinetobacter radioresistens. Antibiotic coverage was broadened to meropenem, ampicillin-sulbactam, and minocycline in view of persistent fevers and elevated white cell counts. The patient was placed on strict contact isolation. Source control was achieved by arthroscopic lavage of both knees. The patient’s clinical condition progressively improved and he was discharged home.
Discussion?
Staphylococcus aureus septic arthritis and secondary bacteremia are well-reported in the literature. However, a thorough evaluation failed to reveal the source of Acinetobacter bacteremia. AR is a normal inhabitant of human skin mostly in moist areas, still a rare agent for human disease. In our case, even though the portal of entry was possible via joint injection, AR was not cultured in synovial fluid.
Additionally, its detection only in the subsequent blood cultures makes a nosocomial origin likely. Identification of AR is quite challenging due to its ability to retain crystal violet, and resist decolorization misleading it as Gram-positive cocci, which may underestimate the true prevalence of AR bacteremia.
Conclusion?
Identification of Acinetobacter radioresistens has important implications. AR has been reported to cause profound bacteremia leading to death.2,3 It has been reported to be a source of class D OXA-23 carbapenemase which confers carbapenem resistance. Prompt identification of this organism and starting appropriate antibiotics can improve patient outcomes as well as potentially prevent the spread of the organism in the hospital and prevent carbapenem resistance.
Audience Take Away:
- Our case highlights important facts about Acinetobacter radioresistens that could prove useful for physicians treating infectious diseases.
- When Acinetobacter radioresistens infection is proven, it is important to treat it to prevent carbapenem resistance in Acinetobacter baumani. Also implementing strict contact prevention can help prevent the spread of this highly resistant organism.
- Since this is a rarely reported organism, with unknown true incidence or prevalence due to the challenges in identification, more vigilant identification and reporting in different settings can improve our understanding of this organism to better control it.
