Utility of Histologic and Histochemical Screening for 16S Ribosomal RNA Gene Sequencing of Formalin-Fixed, Paraffin-Embedded Tissue for Bacterial Endocarditis

OBJECTIVES

16S ribosomal RNA (rRNA) sequencing is a powerful but expensive tool for the identification of bacteria in culture-negative endocarditis. Histologic criteria to screen formalin-fixed, paraffin-embedded (FFPE) specimens for testing are evaluated.

METHODS

Sixty-eight cases of infective endocarditis and controls were histologically reviewed and analyzed by 16S rRNA gene sequencing.

RESULTS

Sequencing identified a specific pathogenic organism in 33 (49%) of 68 cases with acute inflammation and in 0 of 10 controls (P = .004). Visualization of organisms by Gram or Grocott methenamine silver stains had the strongest association with positive sequencing, while antibiotic treatment effect and acid decalcification decreased sensitivity. Molecular identifications were concordant with blood culture results in 90% of the cases, and a positive sequencing result was obtained in approximately half of the cases with negative valve cultures.

CONCLUSIONS

Histologic screening criteria are extremely helpful for identifying cases likely to be positive by molecular testing and can provide significant cost savings in filtering out low-yield specimens.

Secondary syphilis in HIV positive individuals: correlation with histopathologic findings, CD4 counts, and quantity of treponemes in microscopic sections

BACKGROUND

Although syphilis is uncommon, infection rates are much higher in HIV-infected individuals than the general population. A proposed explanation is impaired cellular immunity with HIV infection.

METHODS

A search of one institution yielded 10 patients with a diagnosis of secondary syphilis on skin biopsy, positive syphilis serology and available CD4 counts. We evaluated 11 biopsies from the 10 patients. We correlated the patients' CD4 counts with the histologic findings and with the number of treponemes on skin biopsies, highlighted by immunohistochemistry (IHC). We also compared the detection of spirochetes in silver stained sections (e.g. Warthin-Starry) with T. pallidum IHC. All biopsies were assessed for various histologic features.

RESULTS

The sensitivity of IHC to detect treponemes was 64% and of silver stain was 9% (p-value 0.04). The number of treponemes on the biopsies was determined by IHC. High numbers of spirochetes (i.e. >100 per 10 hpf) were only seen in patients with CD4 counts less than 250 cells/ml.

CONCLUSION

The most consistent histologic finding was a moderate to severe lymphoplasmacytic infiltrate. Although the study is small, it appears that a higher number of spirochetes is associated with CD4 counts less than 250 cell/ml. The T. pallidum IHC stain was vastly superior to the Warthin-Starry stain.

Fusobacterium liver abscess

Fusobacterium is well characterized as an oropharyngeal pathogen that may induce a septic thrombophlebitis by direct extension of abscess into an adjacent neck vessel (Lemierre's syndrome); its potential for visceral abscess formation, however, remains under-recognized. A 65-year-old man with a recent history of multiple rim-enhancing liver lesions presented to the emergency room with fever and abdominal pain. Based on interval increase in the size of the lesions, abscess was suspected. A liver biopsy was performed, and although no organism could be identified on routine microscopy, Warthin-Starry stain revealed Gram-negative bacilli consistent with an anaerobic Fusobacterium species as the underlying etiology of liver abscess formation. Subsequent anaerobic culture results confirmed the diagnosis. This case highlights the importance of consideration for Fusobacterium infection in the setting of liver abscess if anaerobic organisms have not yet been excluded on initial culture evaluation.