Microsporum canis pseudomycetoma and disseminated Mycobacterium genavense infection in an HIV/AIDS patient, an unusual combination.

Pseudomycetomas are rare fungal subcutaneous infections caused by dermatophytes, which are mainly observed in immunocompromised patients. Mycobacterium genavense is considered an opportunistic pathogen in people living with HIV/AIDS (PLWHA), clinically resembling the presentation of Mycobacterium avium complex (MAC). Here, we describe the case of a 26-year-old PLWHA with a 3-month history of a 4cm tumoral, duroelastic and painful lesion located on the back. Histopathology of the tumoral lesion revealed chronic granulomatous inflammation with grains composed of PAS-positive and Grocott-positive septate hyphae, as well as acid-fast bacilli (AFB). Culture on Sabouraud and lactrimel agar developed colonies that were later identified as Microsporum canis. In successive samples, the AFB were identified as M. genavense by restriction analysis of PCR products. Immunocompromised PLWHA not only suffer increased susceptibility to diseases due to unusual pathogens but also atypical clinical presentation of frequently encountered pathogens.

Un desafío terapéutico: la heterorresistencia en Mycobacterium tuberculosis / An emerging problem: heteroresistance in Mycobacterium tuberculosis

Resumen Se considera infección mixta por Mycobacterium tuberculosis (Mtb) a la coexistencia en forma simul tánea y en un mismo paciente de 2 cepas diferentes de Mtb o 2 variantes distintas de la misma cepa. Cuando una de las variantes selecciona mutaciones de resistencia, se denomina heterorresistencia (HTR) monoclonal; en caso de que sean 2 cepas diferentes, una sensible y una resistente (o cepas con diferentes patrones de resistencia), se denomina HTR policlo nal. Se presentan 3 pacientes, HIV/sida, todos con reiterados problemas de adherencia al tratamiento, en los cuales a través de la secuenciación genómica completa de Mtb se diagnosticó HTR monoclonal con coexistencia de 2 variantes de la misma cepa aisladas de muestras de pulmón y ganglios linfáticos, con diferentes perfiles de resistencia en cada uno de los casos. Es importante pensar en la posibilidad de HTR, principalmente en pacientes con múltiples intentos terapéuticos previos y altas poblaciones bacilares, como en el sida avanzado, dado que esta situación compromete potencialmente los resultados del tratamiento al coexistir cepas o variantes de ce pas sensibles y resistentes.

Abstract Mixed infection by Mycobacterium tuberculosis (Mtb) consists in the simultaneous coexistence in the same patient of two different strains of Mtb or 2 different variants of the same strain. When one of the variants selects for resistance mutations, it is called monoclonal heteroresistance (HTR); if there are 2 different strains, one sensitive and one resistant (or with different resis tance patterns), it is called polyclonal HTR. Three cases of HIV/AIDS patients are presented, all with repeated treatment adherence problems, in whom monoclonal HTR was diagnosed through Mtb complete genomic sequentiation with the coexistence of two variants of the same strain isolated from samples from lung and lymph nodes, with different resistance profiles in each case. It is important to consider the possibility of HTR, especially in patients with multiple previous therapeu tic attempts and high bacillary populations, such as in advanced AIDS, since this situation potentially com promises treatment results by coexisting sensitive and resistant variants of a strain (or strains).

[An emerging problem: heteroresistance in Mycobacterium tuberculosis]. / Un desafío terapéutico: la heterorresistencia en Mycobacterium tuberculosis.

Mixed infection by Mycobacterium tuberculosis (Mtb) consists in the simultaneous coexistence in the same patient of two different strains of Mtb or 2 different variants of the same strain. When one of the variants selects for resistance mutations, it is called monoclonal heteroresistance (HTR); if there are 2 different strains, one sensitive and one resistant (or with different resistance patterns), it is called polyclonal HTR. Three cases of HIV/AIDS patients are presented, all with repeated treatment adherence problems, in whom monoclonal HTR was diagnosed through Mtb complete genomic sequentiation with the coexistence of two variants of the same strain isolated from samples from lung and lymph nodes, with different resistance profiles in each case. It is important to consider the possibility of HTR, especially in patients with multiple previous therapeutic attempts and high bacillary populations, such as in advanced AIDS, since this situation potentially compromises treatment results by coexisting sensitive and resistant variants of a strain (or strains).

Se considera infección mixta por Mycobacterium tuberculosis (Mtb) a la coexistencia en forma simultánea y en un mismo paciente de 2 cepas diferentes de Mtb o 2 variantes distintas de la misma cepa. Cuando una de las variantes selecciona mutaciones de resistencia, se denomina heterorresistencia (HTR) monoclonal; en caso de que sean 2 cepas diferentes, una sensible y una resistente (o cepas con diferentes patrones de resistencia), se denomina HTR policlonal. Se presentan 3 pacientes, HIV/sida, todos con reiterados problemas de adherencia al tratamiento, en los cuales a través de la secuenciación genómica completa de Mtb se diagnosticó HTR monoclonal con coexistencia de 2 variantes de la misma cepa aisladas de muestras de pulmón y ganglios linfáticos, con diferentes perfiles de resistencia en cada uno de los casos. Es importante pensar en la posibilidad de HTR, principalmente en pacientes con múltiples intentos terapéuticos previos y altas poblaciones bacilares, como en el sida avanzado, dado que esta situación compromete potencialmente los resultados del tratamiento al coexistir cepas o variantes de cepas sensibles y resistentes.

Recurrences of multidrug-resistant tuberculosis: Strains involved, within-host diversity, and fine-tuned allocation of reinfections.

Recurrent tuberculosis occurs due to exogenous reinfection or reactivation/persistence. We analysed 90 sequential MDR Mtb isolates obtained in Argentina from 27 patients with previously diagnosed MDR-TB that recurred in 2018 (1-10 years, 2-10 isolates per patient). Three long-term predominant strains were responsible for 63% of all MDR-TB recurrences. Most of the remaining patients were infected by strains different from each other. Reactivation/persistence of the same strain caused all but one recurrence, which was due to a reinfection with a predominant strain. One of the prevalent strains showed marked stability in the recurrences, while in another strain higher SNP-based diversity was observed. Comparisons of intra- versus inter-patient SNP distances identified two possible reinfections with closely related variants circulating in the community. Our results show a complex scenario of MDR-TB infections in settings with predominant MDR Mtb strains.

Five-year microevolution of a multidrug-resistant Mycobacterium tuberculosis strain within a patient with inadequate compliance to treatment.

BACKGROUND: Whole-genome sequencing has shown that the Mycobacterium tuberculosis infection process can be more heterogeneous than previously thought. Compartmentalized infections, exogenous reinfections, and microevolution are manifestations of this clonal complexity. The analysis of the mechanisms causing the microevolution -the genetic variability of M. tuberculosis at short time scales- of a parental strain into clonal variants with a patient is a relevant issue that has not been yet completely addressed. To our knowledge, a whole genome sequence microevolution analysis in a single patient with inadequate adherence to treatment has not been previously reported. CASE PRESENTATION: In this work, we applied whole genome sequencing analysis for a more in-depth analysis of the microevolution of a parental Mycobacterium tuberculosis strain into clonal variants within a patient with poor treatment compliance in Argentina. We analyzed the whole-genome sequence of 8 consecutive Mycobacterium tuberculosis isolates obtained from a patient within 57-months of intermittent therapy. Nineteen mutations (9 short-term, 10 fixed variants) emerged, most of them associated with drug resistance. The first isolate was already resistant to isoniazid, rifampicin, and streptomycin, thereafter the strain developed resistance to fluoroquinolones and pyrazinamide. Surprisingly, isolates remained susceptible to the pro-drug ethionamide after acquiring a frameshift mutation in ethA, a gene required for its activation. We also found a novel variant, (T-54G), in the 5' untranslated region of whiB7 (T-54G), a region allegedly related to kanamycin resistance. Notably, discrepancies between canonical and phage-based susceptibility testing to kanamycin were previously found for the isolate harboring this mutation. In our patient, microevolution was mainly driven by drug selective pressure. Rare short-term mutations fixed together with resistance-conferring mutations during therapy. CONCLUSIONS: This report highlights the relevance of whole-genome sequencing analysis in the clinic for characterization of pre-XDR and MDR resistance profile, particularly in patients with incomplete and/or intermittent treatment.

Trends of Two Epidemic Multidrug-Resistant Strains of Mycobacterium tuberculosis in Argentina Disclosed by Tailored Molecular Strategy.

Two Mycobacterium tuberculosis strains-M (sublineage 4.1) and Ra (sublineage 4.3)-have long prevailed in Argentina among patients with multidrug-resistant tuberculosis (MDR-TB). Recently, budget constraints have hampered the surveillance of MDR-TB transmission. Based on whole-genome sequence analysis, we used M- and Ra-specific single nucleotide polymorphisms to tailor two multiplex allele-specific polymerase chain reactions (PCRs), which we applied to 252 stored isolates (95% of all newly diagnosed MDR-TB cases countrywide, 2015-2017). Compared with the latest data available (2007-2009), the M strain has receded (80/324 to 20/252, P < 0.0001), particularly among cross-border migrants (12/58 to 0/53, P = 0.0003) and HIV-infected people (30/97 to 7/74, P = 0.0007), but it still accounts for 4/12 new cases of extensively drug-resistant TB. Differently, the Ra strain remained stable in frequency (39/324 to 33/252) and contributed marginally to the extensive drug-resistance load (1/12). Our novel strategy disclosed recent trends of the two major MDR-TB strains, providing meaningful data to allocate control interventions more efficiently.

Survival of an epidemic MDR strain of Mycobacterium tuberculosis and its non-prosperous variant within activated macrophages.

The fitness of a pathogen results from the interaction of multiple factors favoring either epidemiological success or failure. Herein, we studied the performance of the M strain, a highly successful multidrug resistant Mycobacterium tuberculosis genotype, and its non-prosperous variant, the 410 strain, in activated human monocyte-derived macrophages. Both strains showed comparable ability to induce necrotic cell death and to survive in apoptotic macrophages. Of the various macrophage activation conditions tested, none led to an enhanced control of the outbreak strain. The combination of 1,25(OH)2 vitaminD3 and IFN-γ favored significantly the control of the non-prosperous 410 strain. These observations indicate that the ability of the M strain to survive within the hostile intracellular milieu is conserved, and the overall fitness cost paid by this genotype would be low. Our results provide additional evidence on bacterial traits that may have contributed to the epidemiological success of the M strain.

Endocarditis infecciosa por Mycobacterium mageritense asociada a dispositivo cardíaco electrónico / Electronic cardiovascular device-associated to infective endocarditis caused by Mycobacterium mageritense

Las micobacterias de crecimiento rápido son una rara causa de endocarditis bacteriana. Durante las últimas décadas han aumentado las infecciones debido a este tipo de micobacterias, en especial las postraumáticas y las posquirúrgicas. Estas infecciones pueden ser localizadas o diseminadas, y también pueden producir brotes nosocomiales debido a la contaminación del equipamiento médico. Por lo general, las tinciones para bacterias ácido-alcohol resistentes no se emplean de rutina en el procesamiento de hemocultivos positivos. Sin embargo, el microbiólogo debe estar atento al ver un bacilo gram positivo, ya que podría tratarse de una micobacteria de crecimiento rápido. Describimos un caso de endocarditis por de Mycobacterium mageritense en una paciente con parche pericárdico autógeno y un catéter para medir la presión en la aurícula izquierda. La bacteria fue identificada por espectrometría de masas (MALDI-TOF MS), score 2,3, y luego confirmada por secuenciación y análisis del gen ARNr 16s con las bases de datos del NCBI y EzTaxon, con una concordancia del 99,8 y el 100%, respectivamente.

Rapidly growing non-tuberculosis mycobacteria are a rare cause of bacterial endocarditis. During the last decades, there has been an increase in infections due to rapidly growing mycobacteria, mainly after trauma and post-surgical procedures, both localized and disseminated, as well as nosocomial outbreaks due to contamination of medical equipment. Routine acid-fast staining for blood culture bottles is not always performed; however, the microbiologist should be aware of potential RGM infections especially when gram positive bacilli are observed. We describe a case of endocarditis caused by Mycobacterium mageritense in a patient with an autologous pericardial patch and a pressure catheter in the left auricle. The bacterial species was identified as Mycobacterium mageritense by mass spectrometry (MALDI-TOF MS), score 2.3, and confirmed by 16S rRNA analysis with 99.8 and 100% agreement, respectively.

[Electronic cardiovascular device-associated to infective endocarditis caused by Mycobacterium mageritense]. / Endocarditis infecciosa por Mycobacterium mageritense asociada a dispositivo cardíaco electrónico.

Rapidly growing non-tuberculosis mycobacteria are a rare cause of bacterial endocarditis. During the last decades, there has been an increase in infections due to rapidly growing mycobacteria, mainly after trauma and post-surgical procedures, both localized and disseminated, as well as nosocomial outbreaks due to contamination of medical equipment. Routine acid-fast staining for blood culture bottles is not always performed; however, the microbiologist should be aware of potential RGM infections especially when gram positive bacilli are observed. We describe a case of endocarditis caused by Mycobacterium mageritense in a patient with an autologous pericardial patch and a pressure catheter in the left auricle. The bacterial species was identified as Mycobacterium mageritense by mass spectrometry (MALDI-TOF MS), score 2.3, and confirmed by 16S rRNA analysis with 99.8 and 100% agreement, respectively.

Genotypic diversity of Mycobacterium tuberculosis in Buenos Aires, Argentina.

Buenos Aires is an overpopulated port city historically inhabited by people of European descent. Together with its broader metropolitan area, the city exhibits medium tuberculosis rates, and receives migrants, mainly from tuberculosis highly endemic areas of Argentina and neighboring countries. This work was aimed to gain insight into the Mycobacterium tuberculosis population structure in two suburban districts of Buenos Aires which are illustrative of the overall situation of tuberculosis in Argentina. The Lineage 4 Euro-American accounted for >99% of the 816 isolates analyzed (one per patient). Frequencies of spoligotype families were T 35.9%, LAM 33.2%, Haarlem 19.5%, S 3.2%, X 1.5%, Ural 0.7%, BOV 0.2%, Beijing 0.2%, and Cameroon 0.2%. Unknown signatures accounted for 5.3% isolates. Of 55 spoligotypes not matching any extant shared international type (SIT) in SITVIT database, 22 fitted into 15 newly-issued SITs. Certain autochthonous South American genotypes were found to be actively evolving. LAM3, which is wild type for RDrio, was the predominant LAM subfamily in both districts and the RDrio signature was rare among autochthonous, newly created, SITs and orphan patterns. Two genotypes that are rarely observed in neighboring countries ̶ SIT2/H2 and SIT159/T1 Tuscany ̶ were conspicuously represented in Argentina. The infrequent Beijing patterns belonged to Peruvian patients. We conclude that the genotype diversity observed reflects the influence of the Hispanic colonization and more recent immigration waves from Mediterranean and neighboring countries. Unlike in Brazil, the RDrio type does not play a major role in the tuberculosis epidemic in Buenos Aires.

Performance of a highly successful outbreak strain of Mycobacterium tuberculosis in a multifaceted approach to bacterial fitness assessment.

Determining bacterial fitness represents a major challenge and no single parameter can accurately predict the ability of a certain pathogen to succeed. The M strain of Mycobacterium tuberculosis managed to spread and establish in the community and caused the largest multidrug-resistant tuberculosis outbreak in Latin America. We have previously shown that the M strain can manipulate the host immune response, but we still have no direct evidence, other than epidemiology, that can account for the enhanced fitness of the M strain. Our objective was to further characterize the performance of the outbreak strain M in different fitness assays. Two main aspects were evaluated: (1) molecular characterization of selected isolates from the M outbreak and related strains and (2) comparative fitness and in vivo performance of representative M strain isolates vs. the non-prosperous M strain variant 410. Our approach confirmed the multifaceted nature of fitness. Altogether, we conclude that the epidemiologically abortive strain 410 was vulnerable to drug-driven pressure, a weak competitor, and a stronger inductor of protective response in vivo. Conversely, the isolate 6548, representative of the M outbreak peak, had a growth disadvantage but performed very well in competition and induced lung damage at advanced stages in spite of reaching relatively low CFU counts. Integration of these observations supports the idea that the M strain managed to find a unique path to success.

Relation of Mycobacterium tuberculosis mutations at katG315 and inhA-15 with drug resistance profile, genetic background, and clustering in Argentina.

We analyzed 362 isoniazid-resistant clinical isolates of Mycobacterium tuberculosis obtained countrywide for the presence of mutation at katG315 and inhA-15 in relation to genotype, pattern of phenotypic resistance to other drugs, and ability to spread. We found the following mutation frequencies: katG315MUT/inhA-15wt 53.0%, katG315wt/inhA-15MUT 27.4%, katG315wt/inhA-15wt 19.3%, and katG315MUT/inhA-15MUT only 0.3%. Mutation at katG315 associated with the LAM superfamily; mutation at inhA-15 associated with the S family and the T1 Tuscany genotype; the combination katG315wt/inhA-15wt associated with the T1 Ghana genotype. Isolates harboring katG315MUT/inhA-15wt tended to accumulate resistance to other drugs and were more frequently found in cluster; isolates harboring katG315wt/inhA-15wt were more frequently found as orphan isolates. Although epidemiological and host factors could also be modulating the events observed, in Argentina, the systematic genotyping of drug resistant clinical isolates could help to predict an enhanced risk of transmission and a propensity to develop resistance to increasing numbers of drugs.

[Disease due to Mycobacterium simiae and "Mycobacterium sherrisii" in Argentina]. / Enfermedad por Mycobacterium simiae y "Mycobacterium sherrisii" en la Argentina.

A revision of mycobacterial disease due to M simiae (n = 4) and "M. sherrisii" (n = 6) identified during an eight-year period is presented. Cases occurred among patients with AIDS (n = 6), previous history of silicosis (n = 2) or tuberculosis (n = 2). One case was lost to follow-up and the remaining nine responded poorly to chemotherapy based on clarithromycin, ethambutol and fluoroquinolones. Five patients died of whom four were HIV-positive, three remained chronic and one was cured. These microorganisms originated 2.1% of mycobacterioses cases detected in an eight-year period. Timely identification of this group of uncommon mycobacteria by molecular methods seems to be clinically relevant in order to warn of difficulties inherent to the treatment. However, the distinction between both closely related microorganisms might not be crucial for case management as no distinctive characteristics were evident among patients affected by M. simiae or "M. sherrisii".

Enfermedad por Mycobacterium simiae y "Mycobacterium sherrisii" en la Argentina / Disease due to Mycobacterium simiae and "Mycobacterium sherrisii" in Argentina

Se presenta información reunida retrospectivamente sobre casos de micobacteriosis originados por Mycobacterium simiae (n = 4) y "M. sherrisii" (n = 6). Los casos ocurrieron entre pacientes con sida (n = 6), historia de silicosis (n = 2) o tuberculosis previa (n = 1). Un caso se perdió luego de diagnosticado y nueve fueron tratados con esquemas terapéuticos basados en claritromicina, etambutol y quinolonas. La respuesta fue muy pobre: cinco pacientes fallecieron (cuatro eran HIV positivos), tres permanecieron crónicos y sólo uno curó. Estas micobacterias originaron 2.1% de los casos de micobacteriosis registrados en un período de ocho años. La distinción de estas micobacterias raras de otras más frecuentes por métodos moleculares rápidos, parece ser clínicamente útil para advertir sobre la dificultad que puede presentar el tratamiento. Sin embargo, la diferenciación genotípica entre M. simiae y "M. sherrisii" parecería no ser clínicamente relevante, dado que no quedaron expuestas características que distingan a los pacientes afectados por los dos microorganismos tan estrechamente relacionados.

A revision of mycobacterial disease due to M simiae (n = 4) and "M. sherrisii" (n = 6) identified during an eight-year period is presented. Cases occurred among patients with AIDS (n = 6), previous history of silicosis (n = 2) or tuberculosis (n = 2). One case was lost to follow-up and the remaining nine responded poorly to chemotherapy based on clarithromycin, ethambutol and fluoroquinolones. Five patients died of whom four were HIV-positive, three remained chronic and one was cured. These microorganisms originated 2.1% of mycobacterioses cases detected in an eight-year period. Timely identification of this group of uncommon mycobacteria by molecular methods seems to be clinically relevant in order to warn of difficulties inherent to the treatment. However, the distinction between both closely related microorganisms might not be crucial for case management as no distinctive characteristics were evident among patients affected by M. simiae or "M. sherrisii".

[False diagnosis of tuberculosis by culture]. / Falso diagnostico de tuberculosis por cultivo.

A remarkable input to the epidemiology of tuberculosis was not the only benefit of the molecular tools developed in the early nineties for Mycobacterium tuberculosis intra-species differentiation. These genotyping methods served also to unveil specimen cross-contamination, which was until then overlooked in laboratories culturing mycobacteria. This error consists in the accidental carry-over of bacilli from a specimen with high bacterial load to that, or those, processed subsequently. The ensuing detection of falsely positive cultures can result in a wrong diagnosis of tuberculosis and the initiation of a long-lasting treatment with potentially toxic drugs. This series of errors implies the mismanagement of patients, the distraction of public health system resources, and the distortion of epidemiological data. M. tuberculosis laboratory cross-contamination was detected wherever investigated systematically, with a median rate of 3% of all positive cultures. The confirmation of this error requires a critical appraisal of bacteriological, clinical, epidemiological and genotyping results. We present here a review of national and international information on laboratory cross-contamination and describe measures recommended for minimizing the risk, surveying the occurrence, and avoiding clinical consequences of this laboratory error that raises a question on the reliability of a positive culture.

Falso diagnóstico de tuberculosis por cultivo / False diagnosis of tuberculosis by culture

Las herramientas de genotipificación intra-especie de Mycobacterium tuberculosis desarrolladas durante los años 90 no sólo dieron un impulso notable a la epidemiología de la tuberculosis, también pusieron de manifiesto un fenómeno hasta entonces soslayado en los laboratorios de tuberculosis: la contaminación cruzada de muestras. Este error consiste en la transferencia accidental de bacilos de una muestra con alta carga bacilar a la o las procesadas subsecuentemente. La consiguiente aparición de falsos cultivos positivos puede inducir al diagnóstico erróneo de tuberculosis y la instauración de tratamientos prolongados con drogas potencialmente tóxicas. Esa secuencia de errores conduce al mal manejo de los pacientes involucrados, la distracción de los recursos del sistema de salud y la distorsión de los resultados de análisis epidemiológicos. Se detectó contaminación cruzada en todos los laboratorios donde fue investigada sistemáticamente, con tasas de alrededor del 3% de los cultivos positivos. La confirmación requiere confrontar resultados bacteriológicos, clínicos, epidemiológicos y de genotipificación. Realizamos aquí una revisión de la información nacional e internacional sobre el tema y describimos las medidas recomendadas para minimizar el riesgo, vigilar la ocurrencia y evitar las consecuencias clínicas de este error de laboratorio que vulnera la certeza de un cultivo positivo.

A remarkable input to the epidemiology of tuberculosis was not the only benefit of the molecular tools developed in the early nineties for Mycobacterium tuberculosis intra-species differentiation. These genotyping methods served also to unveil specimen crosscontamination, which was until then overlooked in laboratories culturing mycobacteria. This error consists in the accidental carry-over of bacilli from a specimen with high bacterial load to that, or those, processed subsequently. The ensuing detection of falsely positive cultures can result in a wrong diagnosis of tuberculosis and the initiation of a long-lasting treatment with potentially toxic drugs. This series of errors implies the mismanagement of patients, the distraction of public health system resources, and the distortion of epidemiological data. M. tuberculosis laboratory cross-contamination was detected wherever investigated systematically, with a median rate of 3% of all positive cultures. The confirmation of this error requires a critical appraisal of bacteriological, clinical, epidemiological and genotyping results. We present here a review of national and international information on laboratory crosscontamination and describe measures recommended for minimizing the risk, surveying the occurrence, and avoiding clinical consequences of this laboratory error that raises a question on the reliability of a positive culture.

Falso diagnóstico de tuberculosis por cultivo / False diagnosis of tuberculosis by culture

Las herramientas de genotipificación intra-especie de Mycobacterium tuberculosis desarrolladas durante los años 90 no sólo dieron un impulso notable a la epidemiología de la tuberculosis, también pusieron de manifiesto un fenómeno hasta entonces soslayado en los laboratorios de tuberculosis: la contaminación cruzada de muestras. Este error consiste en la transferencia accidental de bacilos de una muestra con alta carga bacilar a la o las procesadas subsecuentemente. La consiguiente aparición de falsos cultivos positivos puede inducir al diagnóstico erróneo de tuberculosis y la instauración de tratamientos prolongados con drogas potencialmente tóxicas. Esa secuencia de errores conduce al mal manejo de los pacientes involucrados, la distracción de los recursos del sistema de salud y la distorsión de los resultados de análisis epidemiológicos. Se detectó contaminación cruzada en todos los laboratorios donde fue investigada sistemáticamente, con tasas de alrededor del 3% de los cultivos positivos. La confirmación requiere confrontar resultados bacteriológicos, clínicos, epidemiológicos y de genotipificación. Realizamos aquí una revisión de la información nacional e internacional sobre el tema y describimos las medidas recomendadas para minimizar el riesgo, vigilar la ocurrencia y evitar las consecuencias clínicas de este error de laboratorio que vulnera la certeza de un cultivo positivo.(AU)

A remarkable input to the epidemiology of tuberculosis was not the only benefit of the molecular tools developed in the early nineties for Mycobacterium tuberculosis intra-species differentiation. These genotyping methods served also to unveil specimen crosscontamination, which was until then overlooked in laboratories culturing mycobacteria. This error consists in the accidental carry-over of bacilli from a specimen with high bacterial load to that, or those, processed subsequently. The ensuing detection of falsely positive cultures can result in a wrong diagnosis of tuberculosis and the initiation of a long-lasting treatment with potentially toxic drugs. This series of errors implies the mismanagement of patients, the distraction of public health system resources, and the distortion of epidemiological data. M. tuberculosis laboratory cross-contamination was detected wherever investigated systematically, with a median rate of 3% of all positive cultures. The confirmation of this error requires a critical appraisal of bacteriological, clinical, epidemiological and genotyping results. We present here a review of national and international information on laboratory crosscontamination and describe measures recommended for minimizing the risk, surveying the occurrence, and avoiding clinical consequences of this laboratory error that raises a question on the reliability of a positive culture.(AU)