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Infectious Disease
Published in John S. Axford, Chris A. O'Callaghan, Medicine for Finals and Beyond, 2023
Susanna J. Dunachie, Hanif Esmail, Ruth Corrigan, Maria Dudareva
CSF examination: a large volume sample is needed (8–10 mL). Cell count: white cell count is usually elevated (lymphocyte predominance). Protein and lactate concentration can be markedly raised and the CSF : serum glucose is usually <50%.Culture: rarely positive prior to 10 days incubation. Sensitivity is only 80% against a clinical diagnosis of TBM.Ziehl–Neelsen stain: this generally has a poor sensitivity (10–20%), which can be improved by concentration of a large volume, microscopist expertise and time spent looking at the slide.Xpert MTB/RIF assay: rapid, automated, NAAT, in comparison to CSF culture sensitivity is 80% and specificity is 99%.
Understanding Microbiology Culture Results
Published in Firza Alexander Gronthoud, Practical Clinical Microbiology and Infectious Diseases, 2020
Mycobacteria can be detected using a Ziehl–Neelsen stain or a fluorescent auramine stain. Mycobacteria have a waxy mycolic acid in their cell wall which resists a Gram stain. A Ziehl–Neelsen stain was developed whereby carbol fuchsin is used as the initial stain and heat is applied to fixate the carbol fuchsin into the cell wall. Because of mycolic acid in their cell wall, the acid alcohol used in the decolourization is not able to remove carbol fuchsin from the cell wall, and consequently, they appear bright red. This is why mycobacteria are also called acid-fast bacilli. A sputum sample needs to contain at least 104 mycobacteria per millilitre before they can be detected with microscopy.
Pulmonary Tuberculosis In Children
Published in Lourdes R. Laraya-Cuasay, Walter T. Hughes, Interstitial Lung Diseases in Children, 2019
The tubercle bacillus, Mycobacterium tuberculosis, discovered in 1882 by Robert Koch, is the etiologic agent of tuberculosis. It is a slender, straight or slightly curved rod, 1 to 4 μm in length. Its most distinctive property, as demonstrated with the Ziehl-Neelsen stain, is the absorption of the carbol-fuchsin dye by the chemically complex, largely lipid cell wall of the intact organism, which resists decoloration by acid-alcohol. Organisms from cultures and in clinical materials stand out as brilliant red against the blue background of the counterstain. Cultures from clinical material placed on enriched media at 37°C in the presence of ample oxygen grow very slowly. The small, dry, scaly colonies cannot be seen before 10 to 20 days of incubation. M. tuberculosis is distinguished from other acid-fast mycobacteria by its production of niacin.1
Tuberculous Scleritis and Multidrug Resistance
Published in Ocular Immunology and Inflammation, 2022
Mamta Agarwal, Gazal Patnaik, Shweta Agarwal, Geetha Iyer, A. R. Anand, Gayathri Ar, Jyotirmay Biswas, Manfred Zierhut
Meanwhile, BACTEC MicroMGIT culture showed a positive signal at the end of 10 days of incubation. Ziehl-Neelsen stain performed on the culture isolate showed the presence of many acid-fast bacilli with cording. nPCR targeting MPB64 and IS6110 region confirmed the isolate as M. tuberculosis. Phenotypic drug susceptibility testing (DST) for the first-line drug streptomycin (STR), isoniazid (INH), rifampicin (RIF), ethambutol (EMB), and pyrazinamide (PZA) was performed by the BACTEC MicroMGIT culture system. The M. tuberculosis isolate was resistant to all the five first-line drugs tested. The isolate was therefore labeled as multidrug-resistant M. tuberculosis (MDR-TB). Further, phenotypic DST for the second-line drug amikacin, kanamycin, capreomycin, ciprofloxacin, ofloxacin, levofloxacin, ethionamide, and para-aminosalicylic acid were performed. The organism was sensitive to all the tested second-line drugs, except ciprofloxacin. With these findings, the patient now was confirmed as a case of “Multi-drug-resistant (MDR)-tuberculous sclerokeratitis.”
Abdominal wall mycobacterial spindle cell pseudotumor lesion
Published in Baylor University Medical Center Proceedings, 2021
Douglas D. Lim, Abida Bushra, Haiying Zhang
A computed tomography scan of his abdomen revealed a 5.3 cm upper abdominal wall soft tissue mass with erosion of the xyphoid process extending into the omental fat; this was thought to be a neoplasm. A core needle biopsy of the mass revealed large areas of spindled to focally epithelioid cell aggregates with bland nuclei and abundant pale cytoplasm (Figure 1a). Occasional multinucleated histiocytes with lymphocytes, plasma cells, and focal neutrophils were also present. There were no atypical lymphoid cells or evidence of carcinoma. The spindled cells were diffusely positive for CD163 on immunohistochemical staining. S-100 immunostain focally highlighted the spindle cells and intracytoplasmic bacilli. CD34 immunostain was negative in the spindle cells. A Ziehl-Neelsen stain was positive for numerous acid-fast bacilli (Figure 1b). The histologic findings of spindle-shaped histiocytes containing acid-fast bacilli are compatible with the diagnosis of mycobacterial spindle cell pseudotumor.
Strategies for the diagnosis and management of meningitis in HIV-infected adults in resource limited settings
Published in Expert Opinion on Pharmacotherapy, 2021
Marise Bremer, Yakub E Kadernani, Sean Wasserman, Robert J Wilkinson, Angharad G Davis
The diagnosis of TBM is challenging due to a paucibacillary CSF and lack of rapid diagnostic tests with high sensitivity and specificity. Ziehl-Neelsen stain microscopy is the most commonly implemented method for rapid diagnosis of TBM through detection of acid-fast bacilli, despite a sensitivity of 10–20% [37]. The gold standard for diagnosis and drug susceptibility testing (DST) is CSF culture, with sensitivity just over 70% (higher when using liquid vs solid media) when compared to case definition of probable or definite TBM [38]; however, the long culture duration (6–8 weeks) means this test is seldom useful for initial treatment decisions.