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Case Report |
1 Infectious Diseases Unit, Carmel Medical Center, Haifa, Israel
2 Microbiology Laboratory, Rambam Medical Center, Haifa, Israel
Correspondence
Yoav Keynan
keynany{at}yahoo.com
Received 31 July 2006
Accepted 29 November 2006
Present address: Department of Medical Microbiology, University of Manitoba, Winnipeg, Canada. 
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Case report |
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Urine and blood cultures failed to grow any organism and no source of infection was noted on repeated examinations or imaging of the chest and abdomen. On the tenth day, a fever of 38.4 °C accompanied by tachycardia and leukocyturia appeared. Urine and blood cultures were obtained and antimicrobial therapy was changed to ertapenem after urinary culture grew Klebsiella pneumoniae harbouring an extended-spectrum ß-lactamase, with rapid resolution of fever.
She remained afebrile for 4 days, after which fever re-emerged with a temperature reaching 38.6 °C. Three sets of blood samples were inoculated in aerobic and anaerobic blood culture vials (BacT/Alert 3D; bioMérieux), a peripherally placed intravenous line was removed and antibiotic treatment was withheld awaiting culture results in a haemodynamically stable patient. Two aerobic bottles from two sets of blood cultures obtained through separate needle puncture sites were positive. Orange colonies of a Gram-positive bacillus that fermented glucose and sucrose and was oxidase- and catalase-positive were grown. Reactions for indole, raffinose, citrate, maltose, urea and aesculin were negative.
The organism was sensitive to penicillins, cephalosporins, aminoglycosides and quinolones. The patient was given cefuroxime according to the antimicrobial susceptibility of the isolate, and by the next day she was afebrile and remained so throughout the duration of her hospital stay.
The bacterium could not be identified using API Coryne (bioMérieux) and was submitted for identification based on the nucleic acid sequence of the 16S rRNA gene. DNA was extracted from the bacterium using the QIAamp DNA Blood Mini kit (QIAGEN). After amplification with universal bacterial primers (Harmsen et al., 2002), amplicons were purified and directly sequenced. Public databases were then scrutinized for sequences with homology to the resulting nucleotide sequences using BLAST analysis (http://www.ncbi.nlm.nih.gov/blast/). The nucleotide sequence of the amplified fragment identified the organism as Exiguobacterium acetylicum (99 % identity of 506 nucleotides).
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Discussion |
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Case reports attributing disease states to coryneform bacteria are sometimes incorrect for several reasons including: (i) the inability to rely entirely on the databases of commercial identification systems, due to the limited number of taxa that they cover; (ii) significant changes in the taxonomy of coryneform bacteria; and (iii) the distinction between colonization and infection has not been made in many cases (Coyle & Lipsky, 1990). Gavin et al. (1992) observed that the API Coryne system identified about 84 % of 177 strains tested to the correct species with no additional tests.
Identification of coryneform bacteria to the species level should be attempted whenever they grow in pure culture from clinical specimens or when they represent the predominant organisms in normally sterile samples, in order to identify new species and to ascribe a pathogenic role to species previously regarded as saprophytes (von Graevenitz et al., 1994).
The analysis of cellular fatty acid (CFA) patterns is an extremely useful method for identification of coryneform bacteria. However, it is time-consuming, depends on incubation conditions and is not available to many laboratories (von Graevenitz et al., 1991; Bernard et al., 1991). Molecular genetic techniques for species identification of Corynebacterium strains greatly increased the ability to identify coryneform bacteria to a species level and allowed the identification of new potentially pathogenic members (Loubinoux et al., 2005).
The genus Exiguobacterium originally described in 1983 contained Exiguobacterium aurantiacum as its only species. In 1994, Farrow et al. (1994) included the former species Brevibacterium acetylicum in the genus Exiguobacterium. There are significant differences between the two genera, namely: colonies of E. acetylicum exhibit a golden-yellow pigment and the organism is oxidase-positive and facultatively anaerobic with a fermentative carbohydrate metabolism, fermenting D-mannose and cellobiose; Brevibacterium colonies are whitish-grey later turning yellow, and it is obligately aerobic with variable oxidative carbohydrate metabolism. Both Exiguobacterium species are motile by virtue of peritrichous flagella and have a unique CFA pattern. Several other members have been reported and can be differentiated by fatty acid composition (Hollis & Weaver, 1981; López-Cortés et al., 2006).
The Centers for Disease Control has reported a number of Exiguobacterium strains from various clinical sources (e.g. skin, wounds, cerebrospinal fluid) (Funke et al., 1997), but case reports are few, and to our knowledge bacteraemia has not been documented. The source of bacteraemia in this case was not documented but urinary or respiratory sources were ruled out in the presence of normal urinalysis and lung imaging. The bacteraemia followed a hospital stay that included several antibiotic courses to which the organism was susceptible, suggesting nosocomial acquisition. The most likely source is catheter-related, supported by the rapid response to removal of the intravenous line and treatment.
This case report documents the role of Exiguobacterium in causing hospital-acquired infection. The availability of sequence-based methods facilitates rapid, less cumbersome identification and has expanded the spectrum of diseases attributed to coryneform bacteria.
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