A 59 year old woman with systemic sclerosis and history of lung transplant with chronic allograft rejection presented to the hospital for progressive dysphagia and acute kidney injury necessitating dialysis. She continued her home drug regimen: immunosuppressives such as prednisone, tacrolimus, and mycophenolate as well as antibiotic prophylaxis consisting of itraconazole, trimethoprim-sulfamethoxazole, and azithromycin. Six days later she began to experience increased sputum production with a cough and shortness of breath. Repeat chest x-ray showed persistent bilateral pleural effusions and lower lobe opacities consistent with a chronic inflammatory process but could also represent infection. A sputum culture was obtained and she was started on a course of levofloxacin.
Gram stain of the sputum revealed moderate PMNS with abundant gram positive bacilli that appeared coryneform. The organism grew well on blood and chocolate agar, presenting as non-hemolytic white-gray moist smooth colonies.
MALDI-TOF revealed Corynebacterium striatum.
Until the past fifteen to twenty years it was believed that Corynebacterium striatum and many other non-toxigenic species of the Corynebacterium genus were almost always avirulent. C. striatum is typical of human skin and nasopharyngeal flora and most coryneform species were largely ignored with the exceptions of the toxigenic strains such as C. diphtheriae, C. ulcerans and C. pseudotuberculosis. However, the incidence of serious C. striatum infections has been rising and is attributed to the prolonged survival of patients in immunocompromised states, patients with chronic lung disease such as COPD and cystic fibrosis, and the increasing use of indwelling medical devices such as infusion ports, dialysis catheters, and joint prostheses. More and more cases of endocarditis and respiratory infections have been attributed to C. striatum and with repeated and prolonged hospital stays; frequent patient exposure to broad-spectrum antibiotics create ample opportunity for C. striatum to cause outbreaks of nosocomial infections.
However, there is still little evidence to suggest how C. striatum is actually transmitted and how it can adapt. It is left to the microbiology lab to decide whether its presence in culture represents an actual infection and coryneform bacteria are difficult to speciate on the basis of biochemical testing alone. Most importantly, a culture from a true C. striatum infection should grow out pure or predominant colonies. They are aerobic Gram positive bacilli related to Mycobacteria and Nocardia with a characteristic appearance on Gram stain: often pleomorphic, slightly curved with clubbed or tapered ends, and cells may occur singly or in pairs in what is often dubbed “Chinese letter” formation. Toxigenic forms of Corynebacterium are catalase positive (as is C. striatum) but many species are catalase negative. Unlike the toxigenic species, C. striatum is pyrazinamidase positive. Urease and nitrate are also useful but many species overlap in their biochemical testing characteristics and in order to truly name the species it is recommended that MALDI-TOF mass spectrometry be used which has been shown in several studies to be an accurate test for coryneform species identification.
-Dwight Parker is a 4th year medical student at the University of Vermont College of Medicine.
-Christi Wojewoda, MD, is the Director of Clinical Microbiology at the University of Vermont Medical Center and an Assistant Professor at the University of Vermont.