First Human Infection of Nocardia Crassostreae in an Immunocompetent Patient.

To the Editor: Nocardia species are Gram-positive partially acid-fast Bacilli that are found in soil and water. Nocardial brain abscess is rare but carries a high fatality rate, and there is controversy in literature whether these lesions should be routinely excised or simply aspirated.[1] The first case of Nocardia crassostreae brain abscess in a 31-year-old immunocompetent male is reported here to highlight this emerging pathogen and the antimicrobial sensitivity. He presented with a 1-week history of progressive right hemiparesis. He regularly swam in the open sea and had a cut on his right big toe while swimming. His temperature was 36.2°C. He was alert and orientated with grade 4 Medical Research Council weakness in the right upper limb and grade 2 in the right lower limb, with brisk (3+) reflexes. The magnetic resonance imaging (MRI) of the brain showed an abscess [Figure 1a]. His white blood count including lymphocytes with differentials was normal, and blood cultures were negative. He had a normal chest radiograph.

Figure 1

Axial T1-weighted postcontrast magnetic resonance imaging scan ring enhancing lesion at presentation (a) and 4 weeks after treatment (b).

A computed tomography-guided stereotactic aspiration yielded creamy nonoffensive pus. Laboratory examination of the pus showed Gram-positive Bacilli, and a modified Ziehl–Neelsen stain showed partially acid-fast Bacilli without true branching. Rough white colonies grew in blood agar aerobically within 48 h. The antimicrobial susceptibility of the isolate (Etest, AB Biodisc, Solna, Sweden) was shown in Table 1. It was identified by polymerase chain reaction and 16S ribosomal DNA sequence analysis as N. crassostreae. The patient was treated with oral clarithromycin and ciprofloxacin. He regained full power in 4 weeks with excellent radiological resolution on MRI [Figure 1b]. He was discharged from outpatient follow-up after 1-year and did not show any evidence of immunocompromise.

Table 1

Drug susceptibility of Nocardia crassostreae isolated from the patient (Etest, AB Biodisc, Solna, Sweden)

Antimicrobial agent	Susceptibility
Penicillin G	S
Amoxicillin	S
Co-amoxiclav	S
Mezlocillin	S
Piperacillin	S
Cefaclor	S
Cefuroxime	S
Cefuroxime axetil	S
Imipenem	S
Meropenem	S
Gentamicin	I
Tobramycin	I
Netilmicin	I
Amikacin	I
Ciprofloxacin	S
Ofloxacin	S
Levofloxacin	S
Tetracycline	S
Doxycycline	S
Erythromycin	S
Clindamycin	R
Vancomycin	R
Teicoplanin	R

S: Susceptible; I: Intermediate; R: Resistant.

The portal of entry for the organism is likely to be the cut, he sustained while swimming. Therefore, it is postulated that antigen-specific T-cells and macrophages of the immunocompetent host cleared the peripheral foci, whereas any organism that successfully invades the brain is relatively protected from these activated cells (an immune sanctuary).[2]

This organism was most susceptible to β-lactam antibiotics, and the tetracyclines but resistant to vancomycin and teicoplanin [Table 1] and in this respect did not fit any of the patterns identified by Wallace et al. for Nocardia asteroides which caused the majority of human Nocardia infections.[3] It also differs from the only other case reported in humans while this manuscript was in preparation.[4] In conclusion, this unique case is presented to allow other clinicians to learn from the outcome of this case, and the antimicrobial sensitivity which maybe variable.

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Conflicts of interest

There are no conflicts of interest.