Abstract
Otago BMLSc student research project abstract.
Objectives: Histological stains are routinely used for identifying cellular architecture and microorganisms. Research suggests that bacteria can colonise tumours and have a role in carcinogenesis and tumorigenesis of primary cancers. It is not known whether bacteria are able to metastasise with cancerous cells to the brain. We aimed to evaluate histological stains for detecting bacteria in formalin-fixed paraffin embedded (FFPE) positive controls known to contain bacteria and apply the most effective technique to identify intratumoral bacteria in primary tumours and brain metastases.
Methods: The Gram Twort, DAB, BacLight™ red, and Brown and Hopps stain were assessed using FFPE positive controls, consisting of rat lungs incubated with Staphylococcus aureus (Gram positive coccus) and Escherichia coli (Gram negative rod) prior to fixation. Stains were evaluated and examined for bacteria by light and fluorescent microscopy.
Results: In the FFPE positive control, the Gram Twort, DAB, and BacLight™ red stains failed to clearly distinguish bacterial morphology. In contrast, the Brown and Hopps stain successfully demonstrated rods and cocci, but rods appeared purple rather than the expected pink. This method was applied to FFPE samples from prostate, melanoma, and metastatic brain tumours. Cocci and rod-shaped bacteria were observed in the prostate and melanoma samples, but identification in brain metastases was challenging due to necrosis and debris.
Conclusion: The Brown and Hopps stain offers a possible histological approach for detecting intratumoral bacteria. Despite limitations in sensitivity and specificity, it provides a foundation for future studies involving complementary molecular techniques to further explore the tumour associated microbiota in brain metastasis.