[...]... bacilli are susceptible, but some rare bacilli are resistant to the different anti -tuberculosis drugs: these are resistant mutants These bacilli appear in a susceptible strain, without having been in contact with an antituberculosis drug, because of chromosomal mutation as soon as the bacillary 19 TUBERCULOSIS A MANUAL FOR MEDICAL STUDENTS CHAPTER I population is very large The pulmonary cavities are... tap water until the excess stain is washed away Replace all of the slides on the slide-rack and cover each slide with the sulfuric acid Leave for 3 minutes Rinse in running water Cover in 70° alcohol Leave for 5 minutes Rinse again in running water Destain again with the acid until almost all of the stain has disappeared Rinse each slide again under running water Counter-staining - Replace the destained... a number of bacilli may remain latent in the secondary foci for months or even years Different factors that can reduce the organism’s system of defence can lead to reactivation of the bacilli and their multiplication in one or more of these foci This 5 TUBERCULOSIS A MANUAL FOR MEDICAL STUDENTS CHAPTER I reactivation is the cause of clinical disease at extrapulmonary sites and of a proportion of cases... this method are not very encouraging 22 TUBERCULOSIS A MANUAL FOR MEDICAL STUDENTS CHAPTER I Appendix 3: Preparation of smears and Ziehl-Neelsen staining • Labelling the slides - - • Preparation of smears - - • Let the smear dry in the air for at least 15 minutes (15–30 minutes) Do not use the burner to dry the smear Fixation - • Take each slide by the end where the number is engraved, and place it on... (positive at 22 °C, destroyed by heat at 68 °C), and a nitrate reductase activity, and they accumulate nicotinic acid or niacin, which can be demonstrated by the niacin test In other cases another mycobacterium must be identified (M bovis, BCG or atypical mycobacteria) Criteria for identification of mycobacteria MYCOBACTERIA ASPECT OF NIACIN NITRATE CATALASE COLONIES 22° CATALASE 68° Tuberculous R + + + - Bovis... microscopy after Ziehl-Neelsen staining Photograph of cultures of Mycobacterium tuberculosis 25 TUBERCULOSIS A MANUAL FOR MEDICAL STUDENTS CHAPTER I TUBERCULOSIS HISTOLOGY Multiplication of tubercle bacilli in any site of the human body causes a specific type of inflammation, with formation of a characteristic granuloma Anatomic pathology involves examining tissue for suspect TB Tissue samples may be obtained... TUBERCULOSIS A MANUAL FOR MEDICAL STUDENTS CHAPTER I • Aspirated material The serous fluid or material obtained by aspiration of a lymph node can also benefit from culture in a mycobacteriology laboratory ❏ Histological techniques Whatever type of specimen is available, the following steps should be followed to prepare it for histological examination: • Fix the specimen: As soon as it has been obtained, the... fragment should be placed, in a quantity of fixing agent equal to at least 10 times the volume of the fragment (formol diluted to 10% or Bouin’s fluid) • Prepare the sample for examination: The sample is dehydrated, then placed in paraffin and cut with a microtome Slants are then treated with haematoxylin and eosin stains for histological examination Other slants are stained using Ziehl-Neelsen or auramine,... greyish and chalky When caseating material is obtained (from aspiration of an abscess or fistulation of a lymph node), tuberculosis is the first diagnosis that comes to mind Sometimes the granuloma softens, liquefies and drains away, leaving a cavity Various types of macroscopic lesions are symptomatic of tuberculosis Certain lesions can be observed on clinical examination of a patient: • Ulcerations on... TUBERCULOSIS A MANUAL FOR MEDICAL STUDENTS CHAPTER I The same evolution occurs in the lymph node, leading to the formation of caseating lymph nodes that resolve spontaneously in the majority of cases towards fibrosis, followed by calcification Animal experiments have shown that 2 to 3 weeks on average after experimental infection, humoral and cell-mediated immunity (delayed-type hypersensitivity) occur simultaneously . class="bi x0 y0 w1 h0" alt="" WHO/CDS/TB/99.272 TUBERCULOSIS A Manual for Medical Students By NADIA AIT-KHALED and DONALD A. ENARSON World Health Organization. publication. FOREWORD This manual aims to inform medical students and medical practitioners about the best practices for managing tuberculosis patients, taking