[The informative value of various methods for identifying acid-fast bacilli in relation to the degree of tuberculosis process activity]

[Pathological anatomy of tuberculosis in the presence of human immunodeficiency virus infection]

Tuberculosis occupies a leading position among secondary infections in the structure of mortality in HIV-positive patients. Moreover, the concurrence of these diseases frequently makes a morphological diagnosis most difficult due to the atypical course of tuberculosis (TB) in the presence of immunosuppression.

AIM

to assess the clinical and morphological characteristics of concurrent TB/HIV infection.

MATERIAL AND METHODS

An autopsy material obtained from the S.P. Botkin Clinical Infectious Diseases Hospital (CIDH) in 2018 was analyzed. Eight samples stained with hematoxylin and eosin, Ziehl-Neelsen carbol-fuchsin, auramine-rhodamine were thoroughly examined, followed by fluorescent microscopy; an immunohistochemical (IHC) study was performed.

RESULTS AND DISCUSSION

736 autopsies made at the S.P. Botkin CIDH in 2018 revealed 357 deaths from HIV infection; 86 (24%) cases of which were caused by concurrent HIV/TB infection. All the cases showed an extremely diverse and heterogeneous pattern that considerably differed from that of classical granulomatous inflammation in tuberculosis. Ziehl-Neelsen staining could demonstrate single clusters of acid-resistant bacteria with a total of not more than 1000 in the specimen of predominantly rod-shaped bacteria. Auramine-rhodamine staining revealed focal clusters of mycobacteria with a total of 1000 to 2000 in the specimen of predominantly rod-shaped and coccoid bacteria. An IHC study identified clusters of mycobacteria with a total of more than 2000 in the sample, which were characterized by a moderate variety of shapes: rods, cocci, granules, clavate, and branched ones. Mycobacteria were present extracellularly in all the studied cases.

CONCLUSION

Tuberculosis holds the most important place in the pattern of causes of death in HIV infection, accounting for 24%. The lifetime diagnosis of tuberculosis remains not entirely satisfactory. The alterative component of inflammation more often predominates, although without completely losing the ability to form granulomas. The concurrence of different morphological forms of tuberculosis makes it highly desirable to clarify and/or supplement the existing classifications. None of the methods used to detect Mycobacterium tuberculosis in the tissues could reveal the intracellular localization of the pathogen. Most mycobacteria had a typical rod-shaped morphology.

Principios físicoquímicos de los colorantes utilizados en microbiología Principios físicoquímicos de los colorantes

La utilización de los colorantes en los procesos de identificación en microbiología se fundamenta en las propiedades fisicoquímicas de estas sustancias. En el campo de la física, la óptica explica cómo todos los objetos son observables dependiendo de las longitudes de onda que se absorben y se transmiten dentro del denominado “espectro visible”. Dichas transiciones se deben, a su vez, a los compuestos químicos y a los movimientos electrónicos dentro de los átomos. Así mismo, cuando interacciona un colorante con una célula o un tejido, ocurren reacciones que dependen de grupos químicos  funcionales denominados cromóforos y auxocromos. Dependiendo de los compuestos químicos que los constituyen, los colorantes pueden ser ácidos, básicos o neutros y esta connotación se debe a la parte activa del colorante y a la reacción que ocasiona sobre las células microbianas. De otra parte, las tinciones en microbiología pueden ser simples o diferenciales, dependiendo si toda la muestra se tiñe de uno o más colorantes. En el primer caso se encuentra el ejemplo de la coloración con azul de lactofenol y en el segundo, la coloración de Gram. En el presente artículo se reseñan las principales coloraciones utilizadas en microbiología y se explican los fundamentos físicos y químicos de dichos procesos.

Application of Laser Scanning Confocal Microscopy for the Visualization of M. tuberculosis in Lung Tissue Samples with Weak Ziehl-Neelsen Staining

One of the key requirements for the diagnosis of pulmonary tuberculosis is the identification of M. tuberculosis in tissue. In this paper, we present the advantages of specific fluorescent antibody labelling, combined with laser scanning confocal microscopy (LSCM), for the detection of M. tuberculosis in histological specimens of lung tissues. We demonstrate that the application of LSCM allows: (i) The automatic acquisition of images of the whole slice and, hence, the determination of regions for subsequent analysis; (ii) the acquisition of images of thick (20–40 μm) slices at high resolution; (iii) single bacteria identification; and (iv) 3D reconstruction, in order to obtain additional information about the distribution, size, and morphology of solitary M. tuberculosis; as well as their aggregates and colonies, in various regions of tuberculosis inflammation. LSCM allows for the discrimination of the non-specific fluorescence of bacteria-like particles and their aggregates presented in histological lung samples, from the specific fluorescence of labelled M. tuberculosis, using spectrum emission analysis. The applied method was effective in the identification of M. tuberculosis in lung histological samples with weak Ziehl–Neelsen staining. Altogether, combining immunofluorescent labelling with the application of LSCM visualization significantly increases the effectiveness of M. tuberculosis detection.