We report here the first case of dual infection due Mycobacterium avium and Mycobacterium tuberculosis causing meningitis. This patients' HIV status was negative, however, he was a known case of pulmonary tuberculosis on treatment for the past four months, representing an immunosuppressed state. Clarithromycin was added to his but was lost on follow up as he left the institute against medical advice. This paper highlights the importance of multiplex PCRs in such conditions and raises an important question of whether molecular diagnostics should be a routine rather than exception in cases of suspected tubercular meningitis.
A 54 year old male patient previously diagnosed of Pott's spine on anti tuberculosis therapy (ATT) for the past two months presented to the emergency outpatient medical department with a history of fever for ten days which was high grade, along with headache for ten days duration, vomiting and altered sensorium for the past seven days accompanied with irrelevant talk. There was no history of contact, no history of diabetes mellitus or hypertension. His general physical was unremarkable. The systemic examination revealed decreased breath sounds in the left basal region. On chest roentgenogram the patient had right sided pheumothorax with left empyema. There was presence of neck rigidity and his central nervous system status was E4M4V2. A CT-scan of the skull showed basal exudates suggestive of tubercular meningitis. He also had left facial nerve palsy. His Hb count was 12.2g/dl, total leukocyte count: 7000/mm3, erythrocyte sedimentation rate: 40mm/1st hour. His differential leukocyte count per mm3 was neutrophils:40, lymphocytes:11, monocytes:2 and eosinophils:1. The Cerebrospinal fluid (CSF) examination showed a lymphocyte count of 30/ mm3. The CSF protein content was 256mg/dl and sugar content 60mg/dl. The patients' adenosine deaminase (ADA) level was 12U/L. The routine bacterial and tubercular CSF cultures were sterile.
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A CSF aliquot (200 µl) was processed for DNA extraction with QIAamp DNA Mini Kit (QIAGEN Inc., Chatsworth, Calif) as per the protocol provided by the manufacturer. The eluted DNA was stored at -20°C. A multiplex PCR was performed by a single step method to detect the presence of IS6110 (insertion sequence 6110) and RpoB gene specific for bacteria belonging to the M. tuberculosis complex. In addition a third gene specific for M. avium was also looked into. In all, 10u1 of the extract from the previous step was added to 40µl of the mix to give a final volume of 50µl. For reaction, final concentration included 5µ1 of l0x buffer (1,5mM MgC12,10mM Tris-HCl, 50mM KCL and Triton X-100), lµl of dNTPs of 10 pmols each, lul of all six primers (Table. 1) with_pmols of each, ___µl of Taq polymerase and ____µl of millipore water. Taq polymerase __ U/µl Amplification was done in a thermal cycler (Eppendorf). The reaction cycles consisted of _minutes at __° C followed by _ cycles of _minute at_°C and _ minute at _°C and final holding step of _ minutes at _°C. Water blanks were also used in the amplification step to monitor any carryover of amplicons. Amplified DNA was detected by electrophoresis of 20µl of the amplified product on 2.5% agarose gel with 0.1% ethidium bromide. The electrophoresis was done in submarine gel electrophoresis equipment. The amplified products (Table. 1) were detected with the help of ethidium bromide in agarose gel electrophoresis. GEL DOC (Bio-Rad) was used for documenting the gel picture. Nucleotide sequences of the suspected M.avium were performed with the Big Dye Terminator Cycle Sequencing kit, Version 3.1 (Applied Biosystems, CA, USA) for both the strands. All the sequencing reactions were purified and analyzed on ABI 3130 Genetic Analyzer (Applied Biosystems). The sequence obtained was compared with that in the GenBank DNA database. The sequences of our isolate gave ??% identity with the ex-type strain of Mycobacterium avium (????). Sequence data were submitted to the GenBank (Accession No.?????????). After the diagnosis of a dual infection was made, in addition to his ATT regimen, he was prescribed clarythromycin to cover for the M. avium infection. The patient was lost on follow up as he was from a very poor background and could not afford the treatment anymore. He left the institute against medical advice.
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The genus Mycobacteria contains a number of important human pathogens; the most significant of these pathogens in the world are Mycobacterium tuberculosis and Mycobacterium avium complex (MAC). The MAC is comprised of two species, Mycobacterium avium and Mycobacterium intracellulare. In addition, there are approximately 30 serotypes of MAC organisms; serotypes 1, 4, and 8 are the most common in AIDS patients in the United States. Though M. avium was originally identified as a pathogen of birds, it is important for clinicians to note that both M. avium and M. intracellulare are environmental saprophytes and survive well in soil, water, and food, in addition to the carriage of these pathogens by animals.(1)
MAC are opportunistic pathogens which cause disease primarily in compromised patients. Following an AIDS-defining illness and in the absence of an effective HAART regimen, the incidence of MAC is approximately 20% per year, and approximately 40% of patients with AIDS will develop MAC infection without preventive treatment.(2) Curiously, disseminated MAC is essentially unique to patients' immunosuppressed by HIV. Pulmonary MAC disease generally afflicts patients with underlying lung disease. Among the specific risk factors for this much less common form of MAC is previous or active tuberculosis, chronic obstructive pulmonary disease (COPD), bronchiectasis, chronic bronchitis, recurrent aspiration or one of the pneumoconiosis syndromes. The present case was a known case of pulmonary TB who had been on ATT for the past four months representing a immunosuppressed state, with the cell mediated arm of immunity being more affected. Had a multiplex PCR not been performed, the diagnosis could never have been clinched.
This case report adds a new dimension to the diagnosis of suspected tubercular meningitis in immunosuppressed individuals. Considering the meningitis to be only tubercular, there would have been no modification to his treatment. The non-responsiveness under such circumstances is taken as a clinical case of drug resistant tubercular meningitis. There may be a shift in therapy from the first line drugs to second line. Overuse has its known disadvantages of increase in drug resistance. In addition, in resource poor developing countries, like India, that also means additional financial burden on the patient and his kin.