Print version ISSN 1413-8670
Braz J Infect Dis vol.16 no.2 Salvador May/Apr. 2012
Seung Bok HongI; Kyudong HanII; Bo Ra SonIII; Kyeong Seob ShinIII,*; Byeong Cheol RimIV
IDepartment of Clinical Laboratory Science, Juseong University, South Korea
IIDepartment of Microbiology and Institute of Basic Science, Dankook University, South Korea
IIIDepartment of Laboratory Medicine, College of Medicine, Chungbuk National University, South Korea
IVDepartment of Neurosurgery, College of Medicine, Chungbuk National University, South Korea
Nocardia are a group of aerobic actinomycetes that are filamentous gram-positive, weakly acid-fast, and cause opportunistic infection in immunocompromised patients. Primary Nocardia infection mostly involves lung, skin and less commonly, the central nervous system (CNS). Among Nocardia CNS infections, spinal infection is extremely rare. We describe the first case of a spinal abscess caused by Nocardia nova in an immunocompetent patient who experienced a penetrating facial injury six months earlier. Nocardia species were isolated from intradural spinal abscesses and identified by 16S rRNA, hsp65 and secA1 sequence analyses. Surgical excision and treatment with amikacin, cefotaxime, and oral erythromycin was successful.
Keywords: Nocardia, Abscess, Spine, RNA, ribosomal, 16S
Nocardia species are a group of aerobic actinomycetes that are characteristically filamentous, branching, Gram-positive and modified acid-fast bacillus.1 Although Nocardia normally exist as soil saprophytes, increasing numbers of infections have been observed in immunocompromised individuals. Tsukamura first described N. nova in 1982 as a separate species with distinct features from the N. asteroides complex and N. farcinica.2 In 1990, Yano et al. reported that N. nova had different DNA homology with N. asteroides (39% homology) and N. farcinica (20% homology).3
It is an unusual pathogen that commonly causes pneumonia4 or cutaneous abscess,5 and rarely, osteomyelitis6 or sinusitis.7 The involvement of the central nervous system (CNS) by Nocardia occurs in up to 20% of the patients, but solitary spinal abscess due to Nocardia is extremely rare.8-10 Nocardia spinal abscesses are typically present as intra-medullary or epidural lesions, usually caused by N. asteroides.8-10
We were able to find only three cases of N. nova CNS infection in the English language literature search (PubMed), including two cases of brain abscess and one of spondylodiscitis.11-13 All three patients were immunocompromised, as a result of either steroid administration, renal transplantation, or human immunodeficiency virus (HIV) infection. To our knowledge, however, no case of spinal abscess caused by N. nova has ever been reported. Additionally, this was a case of primary nocardiosis without a pulmonary infection or cutaneous lesions, and it lacked predisposing factors, including immunosuppressive therapy, hematologic malignancy, and transplantation.
A 54-year-old female visited the emergency department because of progressive bilateral leg weakness and uncontrollable bowel movements. Upon arrival, she had complete paraplegia in both legs without fever. Six months earlier, she had experienced a penetrating injury in the left orbital area with continuous cerebrospinal fluid (CSF) rhinorrhea. At that time, she was treated with antimicrobials for three months following surgical intervention.
At this visit a laboratory evaluation showed a slightly elevated C-reactive protein level of 14.5 mg/L. The patient's white blood cell (WBC) count was 7,200/mm3 with 65% polymorphs. Her CSF examination contained 4,046 mg/dL protein, 70 mg/dL glucose, and 80 WBC/mm3. A CSF smear was negative on both Gram and acid-fast bacillus (AFB) staining. Bacterial cultures of the CSF were also negative. Magnetic resonance imaging with gadobutrol contrast revealed a diffusely increased intra-medullary signal intensity from T7 to the cauda equina, which suggested arachnoiditis, and multifocal expansion with rim enhancement of the spinal cord at T11-L1 and L3, suggesting multiple abscesses (Fig. 1).
The patient underwent a T11-L1 laminectomy, and spinal intradural and extra-medullary abscesses were removed from the T11-L1 level and cultured. The pus contained long filamentous organisms, as revealed by Gram staining. After three days of culture, small, wrinkled white colonies composed of Gram-positive cells arranged in branching filaments were observed. The microorganism was negative for AFB, but positive for modified AFB, suggesting a Nocardia species.
Accurate identification was made by 16s rRNA, hsp65, and secA1 sequencing14 (Table 1). The 16S rRNA gene sequence (921 bp) from the isolate CBU 09/875 showed 100% similarity with those of several N. nova strains including EU74135, DSM40806 and IFM0261. However, the strain showed similarity values of 99.56% with N. pseudosporangifera Z37136 and, 99.02% with N. jiangxiensis DQ840027, which are non-pathogenic to humans. The hsp65 sequence (409 bp) from the CBU 09/875 isolate showed the greatest similarity (99.51%) to three Nocardia species (N. nova AY75766527, N. veterana AY7576538 and N. africana AY756512). The secA1 sequence (438 bp) showed the greatest similarity (99.54%) to N. nova GU179114 and N. aobensis EU178744.
Based on our 16S rRNA, hsp65 and secA1 sequence analyses, we concluded that the CBU 09-875 isolate was N. nova. The 16S rRNA gene sequence of this isolate was assigned to the GenBank nucleotide sequence database under accession number HM584914. The phylogenic relationships of isolate CBU 09-875 with other related Nocardia strains based on 16S rRNA gene sequences are shown in Fig. 2.
The patient was treated empirically with amikacin, cefotaxime and vancomycin. After identification of the Nocardia species and antimicrobial susceptibility testing by disk diffusion, the regimen was changed to amikacin and cefotaxime for three months. The isolate was found to be sensitive to ampicillin, erythromycin, amikacin, imipenem, cefotaxime and trimethoprim-sulfamethoxazole (TMP-SXT) but resistant to penicillin, amoxicillin/clavulanic acid and tobramycin by E-test, which is compatible with the typical antibiotic susceptibility pattern of N. nova.15
The patient had a favorable clinical response. Treatment was continued on an outpatient basis with erythromycin; the patient completed a year of treatment. Five months postoperatively, the patient had recovered sufficiently to walk with an aid, and had better bowel control. After one year, she was able to walk without support.
Biochemical methods for identifying Nocardia species are limited in their ability to differentiate these organisms.
The application of molecular methods, including sequence analysis of the Nocardia 16S rRNA gene, has greatly expanded the knowledge of the spectrum of pathogenic Nocardia species.16 Meanwhile, because 16S rRNA gene sequencing alone is sometimes insufficient for the identification of Nocardia species, the sequencing of other conserved regions, such as hsp65 and secA1, can serve as adjuncts to 16S rRNA sequencing.17,18
In this case, the 16S rRNA gene sequence of CBU 09/875 showed complete identity with N. nova and strong similarity (> 99%) with two other Nocardia species, which have not yet been reported to be responsible for human infections. To improve the differentiation, hsp65 and secA1 were sequenced, and showed the greatest similarity with N. nova, N. veterana and N. africana among the species pathogenic to humans. Based on these data, CBU 09/875 was identified as N. nova; this was subsequently confirmed by biochemical testing, including a positive two-week arylsulfatase assay and an inability to degrade casein, xanthine, tyrosine and hypoxanthine (data not shown).
Nocardiosis is often difficult to treat; the choice of therapy should therefore be guided by susceptibility testing. Treatment with a combination of antibiotics is necessary to avoid both the recurrence of infection and drug resistance. Additionally, prolonged antibiotic therapy from six months to a year or longer is required, due to the slow replication rate of the organism.19 A three-drug regimen comprising TMP-SXT, amikacin, and either ceftriaxone or imipenem has been used successfully.19 Patients with abscesses may require surgical drainage to ensure the adequate penetration of antibiotics and clearance of the bacteria.
N. nova is characterized by susceptibility to erythromycin, clarithromycin, amoxicillin, and linezolid, and by resistance to amoxicillin/clavulanic acid. The case we describe here was successfully treated with a combination of amikacin and cefotaxime, following by oral erythromycin based on antibiotic susceptibility testing.
Human infections by Nocardia result from trauma-related introduction of the organism, as well as from inhalation, with the resulting establishment of a pulmonary focus.20 In the present case, the patient had a history of an orbital penetrating injury with CSF rhinorrhea six months prior, and since then she had undergone surgical intervention and antibiotic treatment for three months. Additionally, she lacked the predisposing factors for Nocardia infection, including immunosuppressive therapy, hematologic malignancy, transplantation, etc. Consequently, in this case, the spinal abscess by N. nova likely resulted from the previous orbital injury rather than the surgical intervention at that time.
This is the first reported case of a spinal abscess without extra-neural infection caused by N. nova in an immunocompetent host after a skull-penetrating injury. Rapid and accurate identification of the Nocardia species by various molecular methods including 16S rRNA, hsp65 and secA1 sequence analyses will assist in the provision of appropriate treatments to patients infected with Nocardia, because the antimicrobial susceptibility revealed the patterns that are typical among Nocardia species.
This work was supported by a research grant from the Chungbuk National University, 2011.
Conflict of interest
All authors declare to have no conflict of interest.
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Received 14 September 2011
Accepted 12 October 2011
* Corresponding author at: Department of Laboratory Medicine, College of Medicine Chungbuk National University, 52 Naesudong-ro, Heungduk-gu, Cheongju, Chungbuk 361-763, South Korea E-mail address: email@example.com (Kyeong Seob Shin)