Detection of Pneumocystis carinii by in situ hybridization in the lungs of immunosuppressed rats

Detection of Pneumocystis infections by in situ hybridization in lung samples of Austrian pigs with interstitial pneumonia

Pneumocystis carinii f. sp. suis is a fungus multiplying in the respiratory tract of pigs which occasionally is associated with interstitial pneumonia. Identification of Pneumocystis in tissue samples is considered difficult and there are only scarce data on its occurrence in European pigs. This investigation presents an in situ hybridization (ISH) procedure for identification of Pneumocystis spp. in paraffin wax embedded tissue samples and its application for labeling the agent in lung samples of pigs with interstitial pneumonia. Thirty-two out of 100 lung samples from pigs on Austrian farms were identified as positive, five of them with multiple, 12 with moderate and 15 with few organisms but Grocott’s methenamine silver staining demonstrated that only 20 cases were unequivocally positive for Pneumocystis carinii. In addition to interstitial pneumonia Pneumocystis-positive pigs were more frequently affected with granulomatous pneumonia than Pneumocystis-negative pigs. Frequently concurrent infections with different viral or bacterial lung pathogens were noted but there was no positive correlation between Pneumocystis- and PCV-2-infections. With other infections, no clear-cut differences between Pneumocystis-positive and Pneumocystis-negative animals were found. This study shows that Pneumocystis infections occur frequently in Austrian pigs with interstitial pneumonia. It remains to be shown which are the factors triggering severe multiplication and whether infection with Pneumocystis alone is able to induce lung disease in pigs.

In situ hybridization for the differentiation of Actinomyces and Nocardia in tissue sections

The specific identification of filamentous bacteria in tissue sections can be difficult. The filamentous bacteria Actinomyces and Nocardia often produce similar host responses and single bacterial organisms seem morphologically similar; however, their differentiation may be clinically significant. In situ hybridization (ISH) may assist in the rapid and accurate identification of these microorganisms. In this study, DNA probes were directed against the variable regions of 16S ribosomal RNA genes of multiple Actinomyces and Nocardia spp. Probes were tested on 26 formalin-fixed, paraffin-embedded tissue specimens, each of which contained diagnostic foci of filamentous bacteria confirmed by both Gram and Grocott methenamine silver stains. On the basis of histology and clinical features, cases were classified as Actinomyces-related, n = 13 with 6 culture-proven cases and Nocardia-related, n = 13 with 11 culture-proven cases. Using this classification, all cases were assessed for cross-reactivity using other species-specific probes and probe specificity was determined. Overall, Gram and Grocott methenamine silver histochemical stains (100% sensitivity) were more sensitive than ISH (77% sensitivity for both Actinomyces and Nocardia probes). The slender caliber of filamentous bacteria was a limitation for ISH interpretation and necessitated careful examination of some slides. Probes demonstrated 100% specificity for identifying both species, 100% positive predictive value and 81% negative predictive value. No mixed infections were observed. This study demonstrates that ISH is highly specific for distinguishing between Actinomyces and Nocardia spp. in tissue sections. Although histochemical stains demonstrate greater sensitivity for organism detection, ISH is a rapid and specific technique that is especially useful for evaluating culture-negative or clinically unsuspected cases of filamentous bacterial infection.

Predictors of the response to gefitinib in refractory non-small cell lung cancer

Gefitinib, an epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor, has a response rate of 10% to 20% in refractory non-small cell lung carcinoma. Although female gender, adenocarcinoma, and never having smoked are possible markers of a favorable response, mutations of the EGFR gene have also been reported to be highly significant predictors of response. Seventy patients with relapsed non-small cell lung carcinoma were enrolled in the Expanded Access Program. After the drug became available commercially, 28 more patients were treated with gefitinib. Response evaluations were feasible in 80 patients. Twenty-seven tumor specimens (8 responders and 19 nonresponders) were available for the sequence analysis of the EGFR gene. The response rate was 25% (20/80) and the disease control rate (remission + stable disease) was 47.5% (38/80). The response rate was significantly higher for adenocarcinoma (41.0%) versus non-adenocarcinoma (9.8%, P = 0.001), in those who never smoked (58.8%) versus smokers (15.9%, P < 0.001), and in females (42.1%) versus males (19.7%, P = 0.049). A deletion or mutation of the EGFR gene was found in six of eight responders. Remission was noted in all patients with a mutation, whereas the response rate was 9.5% (2/21) in patients without a mutation (P < 0.001). The predictors of response showed significant correlations with survival and time to progression. In a multivariate logistic analysis, the independent predictors of response were smoking history and adenocarcinoma. Given that 9.5% of smokers and 6.7% of those with non-adenocarcinoma showed a mutation of the EGFR gene, the genetic profile may replace those variables as an independent predictor of a response.

Is Pneumocystis carinii vertically transmitted to neonatal rats?

Pneumocystis carinii is a pulmonary pathogen of immunocompromised humans or other mammals. Its infection results from activation of organisms involved in latent infection or from new infection through the air. Almost all children are known to be infected within 2 to 4 years of birth, though prenatal transplacental transmission has not yet been demonstrated. In this study we observed experimental P. carinii infection in neonatal rats, thus investigating the possibility of transplacental vertical transmission by Diff-Quik staining of the lung impression smears and in-situ hybridization for lung sections. The positive rate of P. carinii infection in immunosuppressed maternal rats was 100%, but that in normal maternal rats was 0%. Cystic forms of P. carinii were observed in three of six 1-week old neonatal rats born of heavily infected mothers, but none of them was positive by in-situ hybridization. Five weeks after birth, cystic forms were detected in four neonatal rats. In the lobes of the lungs, no predilection site of P. carinii was recognized. Counts of cystic forms on smears and the reactivity of in-situ hybridization in the lungs of neonatal rats were significantly lower than in maternal rats. The present findings suggest that P. carinii is rarely transmitted through the placenta and proliferates less successfully in the lungs of neonatal rats than in mothers.

Detection of Aspergillus ribosomal RNA using biotinylated oligonucleotide probes

Aspergillosis continues to be a devastating disease entity that results in significant mortality in immunosuppressed patients. Rapid diagnosis is often required to initiate appropriate therapy. Although the histopathologist may be able to visualize fungal organisms in tissue specimens, the histology of Aspergillus species may overlap with a variety of fungi, so diagnosis often relies on fungal cultures that can take weeks to complete. Recently, an in situ hybridization assay targeting Aspergillus 5S ribosomal RNA (rRNA) was reported. This assay proved to be useful when fungal cultures were negative or not performed but when fungi compatible with Aspergillus species were identified in tissue sections. That study was performed to compare the probe described in the previous study (5S-1 probe) with two other probes specific for Aspergillus. Two customly designed 21- and 23-base oligonucleotide probes complementary to 5S (5S-2 probe) and 18S (18S-1 probe) rRNA of Aspergillus were synthesized and labeled with multiple biotin moieties at the 3' termini. By GenBank analysis, the sequence of the 18S-1 probe was shown to have 90% to 100% homology to Aspergillus fumigatus group, Aspergillus flavus, Aspergillus niger, Aspergillus terreus, Aspergillus parasiticus, Aspergillus tamarii, and Aspergillus glaucus group; the 5S-2 probe was homologous to Aspergillus flavus, Aspergillus niger, Aspergillus nidulans, Aspergillus awamori, and Aspergillus wentii. In situ hybridization was performed on 43 cases of Aspergillus infection including 41 localized aspergillomas in the lung, brain, sinonasal tract, and ear, and 2 cases of invasive aspergillosis involving pleura and soft tissue of the scapular region. The results were compared with those obtained using a previously reported 5S-1 probe. In situ hybridization was positive in 38, 38, and 40 cases with the 5S-1, 5S-2, and 18S-1 probes, respectively. The 18S-1 probe was most useful because of a wider detection spectrum. In situ hybridization for Aspergillus rRNA provides a useful means for rapidly and accurately identifying Aspergillus in tissues and may be useful if fungal organisms suggestive of Aspergillus species are present but if cultures are negative or have not been performed.