Corynebacterium mucifaciensin an immunocompetent patient with cavitary pneumonia
© Djossou et al; licensee BioMed Central Ltd. 2010
Received: 8 July 2010
Accepted: 17 December 2010
Published: 17 December 2010
Corynebacterium mucifaciens has been mainly isolated from skin, blood and from other normally-sterile body fluids. It has rarely been described as a human pathogen since its description.
We herein report the first case of cavitary pneumonia due to C. mucifaciens in an immunocompetent man returning from Maghreb.
C. mucifaciens should be considered as important human pathogen in patients with severe illness and compatible history of exposure even in individuals with no clearly identified immunosuppression.
Pathogenic manifestations of infection by Corynebacterium species have been mainly described to occur during C. diphtheriae infection, both among children or adult individuals . Indeed, other strains belonging to the Corynebacterium group remain rarely recognized as human pathogens, mainly in immunocompromised patients [1–3]. To the best of our knowledge, we herein report the first case of a cavitary pneumonia associated with C. mucifaciens isolation from blood cultures made from an adult immunocompetent male patient.
Besides, the antimicrobial susceptibility pattern showed the strain was susceptible for β-lactams, amino-glycosides and glycopeptides. Treatment was initiated with rifampicin-spiramycin combination and was not changed even when the coryneform bacterium identification was later moved to C. mucifaciens. The patient rapidly improved in the general condition with clinical cure after four weeks but the treatment was continued for three additional weeks. Consistently, chest radiography after four weeks showed a minimal residual homolateral pleuritis involvement. At the end of the treatment, thoracic computerized tomography showed complete radiological recovery. The patient was followed during five years after the episode without relapse.
Many new species of coryneform bacteria have been recently discovered and old species renamed, especially after molecular biology techniques were introduced. For many years, these organisms were disregarded as skin contaminants . However, they have been recognized as important human pathogens, often acting as opportunistic pathogens in immunocompromised or severely-ill patients with symptoms compatible with bacteremia and without presence of other pathogenic organism [1–3, 8]. Thus, eight strains of one of these new species had previously been isolated from human relevant clinical material. Concurrently, electron microscopy and comparative 16 S rRNA gene sequence analysis revealed that those formerly unknown coryneform bacteria belonged to a new subline within the genus corynebacterium and the name C. mucifaciens sp. was proposed . Concerning the origin of the eight strains studied, they were isolated between 1992 and 1996. Of these, seven were from Switzerland and one from Germany. The clinical sources were six from blood, one from joint fluid and another one from wound swab. Clinical patterns associated with isolation were respectively intestinal bleeding, cardiac surgery, HIV infection, arthritis or cat bite, and for the three remaining, fever of unknown origin. No information was noticed concerning therapeutic regimen, outcome or risk factors for exposure to C. mucifaciens . Concerning reports from human clinical specimens in non-European geographic areas, the evaluation of rare Corynebacterium species recovered in Canada have identified 23 strains of C. mucifaciens between 1985 and 2001. Of note, many of the clinical sources had been reported previously , with 10 from blood, three from abscesses or wound, although with the exception of recovery from dialysis and peritoneal fluid . Detailed clinical information for underlying diseases of the patients was generally not available. More recently in the 2003-2005 period, five strains were identified in Japan from specimens of middle ear effusion cultures conducted in patients with otitis media with effusion, and four other strains were isolated from the nasal polyps and nasal discharge of patients with chronic sinusitis .
Although coryneform bacteria are commonly part of the normal flora of skin, their potential pathogenicity still remains to be assessed [1, 2, 7]. Indeed, these organisms have been increasingly implicated in serious infections and a fatal case of bacteremia due to an atypical strain of C. mucifaciens has been recently reported in an elderly Brazilian severely-ill woman . Thereby, potential critical issue is stressing the importance for rapid and accurate laboratory identification and susceptibility testing of such unusual pathogens that might improve treatment and outcome of associated infection. In the case reported herein, the investigation was supported by a reference laboratory to confirm identification and provide molecular typing analysis of patient isolate.
With few exceptions, all Corynebacterium show good response to penicillin or vancomycin. In case of C. mucifaciens, beta-lactam antibiotics and aminoglycosides appear to have good activity .
From the sparse case series of patients infected with C. mucifaciens, no clear environmental exposure patterns have been recorded or evidenced. On the contrary, our patient had a recent history of contact with horses and horse sheds. Of interest, a study aiming to characterize the microbial exposure on farms using environmental dust has been previously conducted. This survey concluded that farms were highly exposed to different bacteria species including C. mucifaciens. Moreover, methods using single-strand conformation polymorphism were modified and validated for characterizing bacterial communities in environmental dusts. Results confirmed the transfer of microorganisms from animal-sheds (cow, chicken, and horse) to human environment .
In summary, the strain isolated in our case showed the most morphological and biochemical characters for C. mucifaciens identification: Gram staining revealing Gram-positive bacilli, circular, glistening mucoid and yellow colonies, consistent physiologic characters and molecular results, such as analysis of 16 S rRNA gene sequences. The strain identified was linked to a unique presentation of cavitary pneumonia that occurred in an immunocompetent man returning from Maghreb with horse contact and equine premises exposure, although the source of contamination and the transmission could not be formerly established.
The authors are grateful to Drs Khaled Ezzedine and Adam Doble and for their generous help in copyediting the manuscript. The patient has provided written consent to the use of his clinical history and images for publication.
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