Rapid detection of mycobacteria in inflammatory necrotizing granulomas from formalin-fixed, paraffin-embedded tissue by PCR in clinically high-risk patients with acid-fast stain and culture-negative tissue biopsies

Canine pyoderma gangrenosum with recurring skin lesions of unknown origin and splenic involvement

BACKGROUND

Reports of canine pyoderma gangrenosum (PG) are uncommon in the veterinary literature. Rarer still are cases describing dogs with both skin lesions and internal organ involvement.

OBJECTIVE

To describe a case of canine PG with skin and internal organ involvement.

ANIMALS

A client-owned dog.

METHODS AND MATERIALS

Complete blood count, serum chemistry, C-reactive protein and SNAP cPL tests, and abdominal ultrasonography and fine-needle aspiration of the spleen were performed.

RESULTS

The dog was treated with oral prednisolone and ciclosporin. After three months of therapy, ultrasonography revealed normalization of the spleen and resolution of skin lesions.

CONCLUSION AND CLINICAL IMPORTANCE

Dogs with skin lesions compatible with PG should be screened carefully for internal organ involvement. Ciclosporin may be a useful treatment for the immediate and long-term management of canine PG.

Lung Infections

A review of pulmonary infections of all types with diagnostic and morphological features.

Polymerase chain reaction for Mycobacterium tuberculosis DNA detection from ocular fluids in patients with various types of choroiditis in a referral eye center in India

Aims:

The aim of this study was to detect Mycobacterium tuberculosis (MTB) DNA with polymerase chain reaction (PCR) in aqueous or vitreous samples of patients suffering from choroiditis presumed to be infectious origin.

Settings and Design:

Hospital-based, retrospective case–control study.

Subjects and Methods:

In all, forty eyes of forty patients with choroiditis divided into two groups – Group A (serpiginous-like choroiditis, ampiginous choroiditis, multifocal choroiditis) and Group B (choroidal abscess, miliary tuberculosis (TB), choroidal tubercle) were analyzed retrospectively. In 27 controls (patients without uveitis undergoing phacoemulsification), anterior chamber aspirate was done and sample subjected to real-time PCR. Patients underwent nested PCR for MTB using IS6110 and MPB64 primers from aqueous (n = 39) or vitreous (n = 1). All patients underwent detailed ophthalmological examination by slit-lamp biomicroscopy, fundus examination by indirect ophthalmoscopy, and fundus photograph and fundus fluorescein angiography if required.

Statistical Analysis:

Positive results of PCR for MTB within the group and between two groups were statistically analyzed using Chi-square test.

Results:

There were 25 males and 15 females. Mean age at presentation was 34.66 years (range, 14–62). PCR positivity rates were 41.3% (n = 12/29) and 81.82% (n = 9/11) in Groups A and B, respectively. No controls had PCR-positive result. Comparison of PCR positivity rates showed statistically significant difference between Groups A and B (P = 0.028). Systemic TB was detected in 57.14% (n = 12/21) of all PCR-positive cases (Group A - 33.3%, n = 4/12; Group B - 88.9%, n = 8/9). Systemic antitubercular treatment (ATT) for 9 months and oral steroids were successful in resolution of choroiditis in all PCR-positive patients (n = 21) without disease recurrence.

Conclusions:

Eyes with choroiditis of suspected/presumed tubercular origin should be subjected to PCR for diagnosis of TB and subjected to ATT for prevention of recurrences.

Pathology of pulmonary tuberculosis and non-tuberculous mycobacterial lung disease: Facts, misconceptions, and practical tips for pathologists

Most pathologists are familiar with the microscopic features of tuberculosis and the need to examine special stains for acid-fast bacteria (AFB) in cases of granulomatous lung disease. However, misconceptions do exist, including the concept that finding AFB in "caseating granulomas" confirms the diagnosis of tuberculosis. This dogma is attributable to the high prevalence of tuberculosis in many countries, as well as unfamiliarity with the microscopic spectrum of non-tuberculous mycobacterial lung disease. This review aims to provide surgical pathologists with practical tips to identify AFB, illustrate the histologic overlap between pulmonary tuberculosis and non-tuberculous mycobacterial lung disease, and highlight the importance of cultures in this setting. M. tuberculosis and non-tuberculous mycobacteria cannot be reliably differentiated either on the basis of the tissue reaction or by bacterial morphology on acid-fast stains. Although a presumptive clinical diagnosis of tuberculosis can be made without culture-confirmation, the only definitive means to determine the true identity of AFB is by cultures or molecular methods. Making this distinction is most critical when AFB are found in incidentally detected lung nodules in geographic locations where the incidence of tuberculosis is low, because in such settings AFB in necrotizing granulomas of the lung are more likely to be non-tuberculous mycobacteria than M. tuberculosis.

Application of RLEP real-time PCR for detection of M. leprae DNA in paraffin-embedded skin biopsy specimens for diagnosis of paucibacillary leprosy

The TaqMan real-time polymerase chain reaction (PCR) assay was evaluated systematically with respect to the standard curve, linear range, and used for detecting Mycobacterium leprae DNA in paraffin-embedded skin biopsy specimens from 60 confirmed leprosy patients and three healthy individuals and 29 other dermatoses and bacterial DNA from 21 different species. The test was further evaluated with 51 paucibacillary (PB) patients. The results showed that the test had good sensitivity (8 fg) and good specificity with no cross-reactivity with 21 other bacterial species and the control specimens, except one with Xanthomatosis. The real-time PCR detection rate for the 51 PB specimens was 74.5% (38 of 51). We conclude that the real-time PCR test is a useful adjunct test for diagnosing early stage or PB leprosy cases.

Comparison of fixatives and fixation time for PCR detection of Mycobacterium in zebrafish Danio rerio

Mycobacteriosis is a common disease of laboratory zebrafish Danio rerio. Different infection patterns occur in zebrafish depending on mycobacterial species. Mycobacterium marinum and M. haemophilum produce virulent infections associated with high mortality, whereas M. chelonae is more widespread and is not associated with high mortality. Identification of mycobacterial infections to the species level provides important information for making management decisions. Observation of acid-fast bacilli in histological sections or tissue imprints is the most common diagnostic method for mycobacteriosis in fish, but only allows for diagnosis to the genus level. Mycobacterial culture followed by molecular or biochemical identification is the traditional approach, but DNA of diagnostic value can also be retrieved from paraffin blocks. Here we investigated the type of fixative, time in fixative before processing, species of mycobacteria, and severity of infection as parameters to determine whether the hsp gene PCR assay (primer set HS5F/hsp667R) could detect and amplify mycobacterial DNA from paraffin-embedded zebrafish. Whole zebrafish were experimentally infected with either M. chelonae or M. marinum, and then preserved in 10% neutral buffered formalin or Dietrich's fixative for 3, 7, 21, and 45 d. Subsequently, fish were evaluated by hematoxylin and eosin and Fite's acid-fast stains to detect mycobacteria within granulomatous lesions. The PCR assay was quite effective and obtained PCR product from 75 and 88% of the M. chelonae- and M. marinum-infected fish, respectively. Fixative type, time in fixative, and mycobacterial species showed no statistical relationship with the efficacy of the PCR test.

Frontal bone tuberculosis presenting with blindness in a 14-year-old girl: a case report

Introduction

The occurrence of tuberculosis in the flat bones of the skull is very rare. Only eight cases of tuberculosis of the frontal bone have been reported in the literature.

Case presentation

A 14-year-old girl of Asian ethnicity presented with gradual loss of vision. A computed tomography scan of her head showed a diffuse, homogeneously ill-defined hyperdense lesion of size 2.9 × 5.3 cm (anteroposterior × thickness) involving the right orbit. Biopsy of the lesion confirmed the presence of epithelioid cells and Langerhans giant cells with caseous material. After surgical debridement with antitubercular treatment, the patient had an uneventful recovery.

Conclusion

Although rare, tuberculosis can affect the flat bones of the skull. Tuberculosis of the frontal bone can be included in the differential diagnosis of blindness.

Effects of tissue handling and processing steps on PCR for detection of Mycobacterium tuberculosis in formalin-fixed paraffin-embedded samples

Development and standardization of reliable methods for detection of Mycobacterium tuberculosis in clinical samples is an important goal in laboratories throughout the world. In this work, lung and spleen fragments from a patient who died with the diagnosis of miliary tuberculosis were used to evaluate the influence of the type of fixative as well as the fixation and paraffin inclusion protocols on PCR performance in paraffin embedded specimens. Tissue fragments were fixed for four h to 48 h, using either 10% non-buffered or 10% buffered formalin, and embedded in pure paraffin or paraffin mixed with bee wax. Specimens were submitted to PCR for amplification of the human beta-actin gene and separately for amplification of the insertion sequence IS6110, specific from the M. tuberculosis complex. Amplification of the beta-actin gene was positive in all samples. No amplicons were generated by PCR-IS6110 when lung tissue fragments were fixed using 10% non-buffered formalin and were embedded in paraffin containing bee wax. In conclusion, combined inhibitory factors interfere in the detection of M. tuberculosis in stored material. It is important to control these inhibitory factors in order to implement molecular diagnosis in pathology laboratories.

Pathological diagnosis of granulomatous lung disease: a review

Granulomas in the lung are common diagnostic problems encountered by pathologists. They occur in a wide range of pulmonary conditions, ranging from common entities to uncommon ones and including both infections and non-infectious diseases. This review summarizes the main histological features that help distinguish various granulomatous lung diseases. It concentrates on the most important and common entities that may be encountered and emphasizes helpful features in the differential diagnosis.

Detection of Mycobacterium leprae in Ocular Tissues by Histopathology and Real-Time Polymerase Chain Reaction

AIM

To report detection of leprosy in ocular tissue by histopathology and its confirmation by genetic analysis.

METHODS

Excised tissue from a clinically-suspected ocular leprosy patient was processed and analyzed histopathologically. The DNA from the paraffin-embedded tissue was extracted, an 85 A-C intergenic region of Mycobacterium leprae was amplified using specific primers and analyzed by conventional as well as real-time polymerase chain reaction (RT-PCR).

RESULTS

With periodic acid-Schiff-hematoxylin (PAS-H) staining the specimen showed presence of a thin fibrinous layer of inflammatory cells. The majority of the tissue was fibrovascular with extensive infiltration by histiocytes having reticulated cytoplasm. Modified PAS-H and acid-fast staining (AFS) showed the presence of several acid-fast organisms within the cytoplasm of histiocytes and mast cells. Conventional PCR showed a 250-bp DNA from excised conjunctival tissue, which was in agreement with the positive controls for M. leprae. Through RT-PCR, it was calculated that the suspected tissue had 44.68 pg of M. leprae DNA, which is 8937.06 genome copies of M. leprae.

CONCLUSIONS

Presence of inflammatory cells and AFS bacilli in tissue presented a typical picture of leprosy. M. leprae DNA can be detected using RT-PCR in ocular tissues when acid-fast bacteria are seen in histopathological sections. And when the diagnosis of leprosy is inconclusive and acid-fast bacteria are seen, RT-PCR for M. leprae DNA could be used as a rapid confirmatory test to identify the presence of M. leprae and, therefore, the diagnosis of leprosy.

Sarcoid-like lesions associated with the immune restoration inflammatory syndrome in AIDS: absence of polymerase chain reaction detection of Mycobacterium tuberculosis in granulomas isolated by laser capture microdissection

Highly active antiretroviral therapy (HAART)-treated human immunodeficiency virus (HIV)-positive patients can develop granulomatous lesions within the first few weeks of initiating therapy. This immune syndrome, called immune restoration inflammatory syndrome (IRIS), can induce sarcoid-like lesions in tissues. The pathogenesis of these granulomas is currently unknown because no pathogen has been identified to date in the lesions using morphological and/or microbiological approaches. However, the role of certain microbes, such as Mycobacterium tuberculosis, is still debated. The aim of this study was to look for the presence of M. tuberculosis in sarcoid-like lesions occurring in 14 AIDS patients treated with HAART. We used the PCR DNA amplification method in granulomas microdissected from sections stained by hematoxylin-eosin from formalin-fixed, paraffin-embedded specimens. Results were compared to those obtained from microdissected tuberculosis (TB) granulomas (15 patients) and from microdissected sarcoidosis granulomas (12 patients). M. tuberculosis DNA was undetectable from the microdissected sarcoid-like granulomas, whereas DNA from M. tuberculosis was isolated in all the microdissected TB granulomas and was absent in the microdissected sarcoidosis granulomas. Taken together, these data showed that M. tuberculosis DNA is not associated with the presence of sarcoid-like lesions occurring in HIV-positive patients treated with HAART.

Application of the polymerase chain reaction on formalin-fixed, paraffin-embedded tissue in the recognition of tuberculous osteomyelitis

A retrospective series of 45 cases of chronic osteomyelitis collected over a period of 14 years was histologically classified into tuberculous osteomyelitis (25) and chronic non-granulomatous osteomyelitis (20). The tuberculous osteomyelitis group was divided into three subgroups: a) typical granulomas (13 cases); b) ill-defined granulomas (seven cases), and c) suspected granulomas (five cases). An in-house polymerase chain reaction amplifying the 245 bp nucleotide sequence, and capable of detecting 10 fg of DNA of Mycobacterium tuberculosis, was used on the DNA extracted from the paraffin blocks. The polymerase chain reaction was positive in 72% of cases (18) of tuberculous osteomyelitis, but when typical cases of tuberculous osteomyelitis with confirmed granulomas were considered (13), this increased to 84.6% (11). The chronic non-granulomatous osteomyelitis group gave positive polymerase chain reaction results in 20% of the cases (4).

Our preliminary study on tuberculous osteomyelitis shows that the polymerase chain reaction can be a very useful diagnostic tool, since a good correlation was seen between typical granulomas and polymerase chain reaction with a sensitivity of 84.6% and a specificity of 80%. In addition, our study shows that tuberculous osteomyelitis can be diagnosed in formalin-fixed paraffin-embedded tissues in the absence of typical granulomas.

Detection of Mycobacterium tuberculosis complex in formalin-fixed, paraffin-embedded tissue specimens with necrotizing granulomatous inflammation by strand displacement amplification

Rapid, reliable diagnosis of tuberculosis is essential to initiate correct treatment, avoid severe complications, and prevent transmission. Conventional microbiological methods may not be an option if samples are formalin-fixed and paraffin-embedded (FFPE) for histopathological examination. With the demonstration of necrotizing granulomatous inflammation, tuberculosis becomes an important differential diagnosis, although it was not initially suspected. Following paraffin extraction, BDProbeTec ET strand displacement amplification for detection of Mycobacterium tuberculosis complex (MTC) was applied to 47 prospectively and 19 retrospectively collected FFPE samples from various sources with granulomatous inflammation and results were compared to tuberculosis notification. Of the prospective samples, 20 were from patients who were notified as having tuberculosis and the assay was positive in 18 (90%). Specificity was 100%. For 27 of the patients with prospectively collected FFPE specimens, culture was performed on a specimen collected at a later date from the same location. Culture revealed MTC in 14 and nontuberculous mycobacteria in four. BDProbeTec ET was positive in 13 (92.8%) of the patients with positive MTC culture and negative in the remaining. The sensitivity and specificity in 19 archival samples was 40% and 100%, respectively, compared to notification data. The assay provided rapid, correct diagnosis on different sources of FFPE samples collected prospectively and therefore offers an important supplementary method for patients where tuberculosis was not initially suspected.

The value of polymerase chain reaction detection of Mycobacterium tuberculosis in granulomas isolated by laser capture microdissection

AIMS

The aim of this study was to investigate the usefulness of polymerase chain reaction (PCR) detection of Mycobacterium tuberculosis in granulomas isolated by laser capture microdissection (LCM).

METHODS

The PCR DNA amplification method was used to detect M. tuberculosis in granulomas microdissected from one section stained by haematoxylin and eosin (H&E) from a formalin-fixed paraffin-embedded specimen. The results were compared to those obtained from PCR performed from 10 whole paraffin sections of 5 micro m each, and with the histology, culture and the patient's clinical findings.

RESULTS

Forty-nine formalin-fixed and paraffin-embedded samples from 49 patients with a histological suspicion of a mycobacterial infection were investigated. Using culture as the reference method, the sensitivity for the detection of M. tuberculosis was 92% and the specificity was 100% using PCR from microdissected granulomas and were similar to those obtained by using PCR from 10 whole sections.

CONCLUSIONS

The PCR method of examination of microdissected granulomas from deparaffinised sections is a sensitive, specific and rapid method for the detection of M. tuberculosis in formalin-fixed and paraffin-embedded samples. The method is as sensitive as that using PCR on 10 whole tissue sections, thus making it suitable for small biopsies. However, although these methods reduce the delay in diagnosis, culture remains the gold standard for identification of mycobacteria in tissue. Culture also allows for the testing of antibiotic sensitivity of any isolated species, in this way determining appropriate treatment.

Comparison of polymerase chain reaction with histopathologic features for diagnosis of tuberculosis in formalin-fixed, paraffin-embedded histologic specimens

Objective.-To investigate the relationship between various histopathologic features and the results of the tuberculosis (TB)-polymerase chain reaction (PCR) method in routinely submitted histologic specimens for the histopathologic diagnosis of TB. Design.-We used 95 formalin-fixed, paraffin-embedded tissue blocks from 81 patients who were clinically suspected of having TB. We assessed the presence of histopathologic features including well-formed granuloma, poorly formed granuloma, caseous necrosis, and Langhans-type giant cells. We performed nested PCR for IS6110 and Ziehl-Neelsen staining for acid-fast bacilli (AFB). Results.-Of the 81 patients studied, 53 patients had chronic granulomatous inflammation, whereas 28 patients had only chronic inflammation without definite granulomatous inflammation. Of the 53 cases with chronic granulomatous inflammation, 17 (32%) were AFB positive and 36 (68%) were TB-PCR positive. Among cases with chronic granulomatous inflammation, the percentage that were positive and negative by TB-PCR differed significantly with the presence of various histopathologic features. All of the 13 cases with well-formed granuloma, caseous necrosis, and Langhans-type giant cells were TB-PCR positive; however, 10 (36%) of the 28 cases with chronic inflammation without granulomatous lesions were also TB-PCR positive. Conclusions.-TB-PCR is a rapid, sensitive method for the diagnosis of TB in routinely processed formalin-fixed, paraffin-embedded histologic specimens and is readily available in histopathology laboratories. We recommend use of TB-PCR when TB is suspected clinically, especially in cases of chronic inflammation without definite evidence of granulomatous inflammation.

The early increase in intestinal permeability and systemic endotoxin exposure in patients with severe acute pancreatitis is not associated with systemic bacterial translocation: molecular investigation of microbial DNA in the blood

INTRODUCTION

Sepsis is the main cause of late mortality in patients with severe acute pancreatitis and is largely attributed to secondary infection of pancreatic necrosis with gram-negative enteric organisms. This is commonly preceded by a significant increase in intestinal colonization with such microbes and with early increases in intestinal permeability, thus suggesting a mechanism of bacterial translocation. Whilst cultures of blood specimens from these patients often remain sterile, it is conceivable that bacteria might translocate in small volumes with detrimental effects but elude detection by standard microbial culture techniques.

AIMS

To investigate the incidence and frequency with which bacterial DNA may exist in the systemic circulation of patients with acute pancreatitis and to relate that to disease severity, changes in intestinal permeability, and systemic endotoxin exposure.

METHODOLOGY

Blood samples were obtained at admission and on days 3 and 7 from 26 patients with acute pancreatitis (seven with severe cases) and from 10 healthy controls for DNA extraction and standard microbial cultures. Polymerase chain reaction techniques were used to amplify a gene region (16S ribosomal RNA) found in all bacteria. Levels of serum endotoxin and antibodies to endotoxin core (EndoCAb) were measured at admission, and intestinal permeability to the macromolecule polyethylene glycol 3350 was determined within 72 hours of the onset of symptoms.

RESULTS

Blood cultures yielded and enterococci for one patient with a severe attack and coagulase-negative staphylococci for another patient with a mild attack. No bacterial DNA was found in any of the samples. Endotoxemia was detected in 20 patients (five with severe cases), and levels of serum IgM EndoCAb were depleted in patients with severe attacks but remained relatively unchanged during mild attacks (p = 0.033). Intestinal permeability was significantly increased in patients with severe attacks of acute pancreatitis but remained unchanged during mild attacks (p < 0.05).

CONCLUSIONS

Whilst severe attacks of acute pancreatitis are associated with early derangement in gut barrier function and systemic endotoxin translocation, there is no molecular evidence for associated bacterial "translocation."

Sensitivity of acid-fast staining for Mycobacterium tuberculosis in formalin-fixed tissue

Microscopic examination of tissue sections of mycobacterial lesions frequently results in few or no bacilli seen, even if the lesions appear active histologically. This might be due to the effects of the fixative fluid and/or organic solvent, both of which are conventionally used to make tissue sections for histopathology, on the acid-fast staining of bacteria. The present study was performed to examine how formalin and xylene lower the sensitivity of acid-fast staining for Mycobacterium tuberculosis and to clarify the meaning of the staining result in tissue sections. Microscopic observation of mycobacteria smeared on glass slides revealed that both of these agents greatly reduced the sensitivity of acid-fast staining. Moreover, the number of bacilli was calculated in 30 samples of paraffin-embedded granulomatous lesions using acid-fast microscopy and real-time polymerase chain reaction. The numbers of bacilli present that were estimated by real-time polymerase chain reaction were considerably higher than those counted with a microscope. These results suggest that the bacilli are frequently missed or underestimated with acid-fast microscopy on formalin-fixed, paraffin-embedded tissue.

Amplified in situ hybridization with peptide nucleic acid probes for differentiation of Mycobacterium tuberculosis complex and nontuberculous Mycobacterium species on formalin-fixed, paraffin-embedded archival biopsy and autopsy samples

The aim of this study was to evaluate sensitivity and specificity of in situ hybridization (ISH) using peptide nucleic acid (PNA) probes and tyramide-based amplification for the differentiation between Mycobacterium tuberculosis (MTB) and mycobacteria other than tuberculosis (MOTT) on formalin-fixed, paraffin-embedded tissue samples. We performed ISH simultaneously with both probes on 86 specimens from different organs: 70 obtained at autopsy and 16 by biopsy, all with a histologic evidence of mycobacterial infection confirmed by Ziehl-Neelsen-positive staining. Taking culture as the "gold standard," the sensitivity and the specificity of the MTB probe were 100% (41/41) and 95% (38/40), respectively. In only 2 cases ISH failed to identify mycobacteria. Culture results were not available in 3 cases. We propose ISH as a relatively simple and rapid method to differentiate mycobacteria on formalin-fixed, paraffin-embedded specimens (it is more specific than usual histologic stains) and as an alternative to polymerase chain reaction, allowing the morphologic evaluation of positive bacilli.

Molecular detection of Mycobacterium tuberculosis in tissues showing granulomatous inflammation without demonstrable acid-fast bacilli

Early diagnosis of tuberculosis (TB) is important for early medical intervention and prevention of spread of the bacteria. It is not uncommon to observe granulomatous inflammation but without demonstrable acid-fast bacilli (AFB) on Ziehl-Neelsen (ZN) staining in tissues sent for histologic examination, and the definitive diagnosis of TB cannot be made because no concurrent tissue is sent for TB culture. In this study, the authors explored the feasibility of using polymerase chain reaction (PCR) for early detection of Mycobacterium tuberculosis (Mtb) in formalin-fixed, paraffin-embedded tissues where a definite diagnosis of TB cannot be made. One hundred fifteen patients (131 paraffin blocks of biopsy specimens) with granulomatous inflammation but ZN-negative for AFB were studied. DNA was extracted from paraffin sections and amplified by PCR with the IS6110 primers (specific for the Mtb complex) and the specific 122-base pairs (bp) PCR product was detected by agarose gel electrophoresis. Sixty-eight of the 115 (59%) patients were TB-PCR positive, thus enabling definite diagnosis of TB in significant numbers of these patients in 3 days. The authors conclude that molecular diagnosis by PCR is useful for early detection of TB in histologic material where morphologic features are suggestive but not confirmatory because of negative staining for AFB.

Choroidal tuberculosis diagnosed by polymerase chain reaction. A clinicopathologic case report

PURPOSE

To show the use of the polymerase chain reaction (PCR) in a granulomatous choroidal lesion to support a diagnosis of tuberculosis.

DESIGN

Observational case report.

TESTING

Nucleic acid target amplification of a choroidal specimen using PCR for detection of Mycobacterium tuberculosis was tested.

MAIN OUTCOME MEASURES

Positive nucleic acid target amplification for M. tuberculosis in the ocular sample was measured.

RESULTS

PCR was positive for M. tuberculosis with appropriate negative controls.

CONCLUSIONS

PCR was thought to be a useful supportive technique in the diagnosis of choroidal tuberculosis.

Detection of mycobacterial infections using the Dieterle stain

Retrospective review comparing the modified Dieterle stain with standard acid-fast stains was performed on seven surgical pathology cases that contained culture-positive mycobacteria infections. Tissues examined comprised cervical and submandibular lymph nodes and soft tissues of the face and chest. Modified Dieterle staining was performed on paraffin-embedded tissue sections, and the results were compared with those of hematoxylineosin stains and auramine-rhodamines and carbolfuchsin acid-fast stains. The acid-fast stain showed organisms in three of seven cases on initial review and five of seven cases on retrospective review; the auramine-rhodamine stain retrospectively revealed organisms in five cases. In contrast, the Dieterle stain showed organisms in all seven sections on retrospective examination. Dieterle stains revealed either beaded bacilli or nocardia-like filamentous organisms, sometimes with abundant granular debris possibly representing degenerative organisms. In three cases in which bacteria were readily apparent with the Dieterle stain, only rare organisms could be identified with the acid-fast stain. The modified Dieterle stain was more sensitive than the acid-fast stain in the identification of mycobacteria in pediatric specimens, and its use is recommended in cases with necrotizing granulomas. However, its specificity is limited by morphologic similarities of the organisms to those of nocardiosis and cat scratch disease.