Rhinosporidium seeberi; a preliminary study of the morphology and life cycle

Revisiting the Utility of Histopathological Examination of Biopsy: A Necessity in Microbiology

INTRODUCTION

Culture is the gold standard, while potassium hydroxide mount is simplest technique used for diagnosis of fungal pathogens. Histopathological examination is the only definitive means to identify certain uncultivable fungi.

AIM

To analyse role of histopathological examination and potassium hydroxide (KOH) mount for diagnosing fungal infections by correlating them with culture.

MATERIALS AND METHODS

In this nine year retrospective study, all biopsy specimens submitted for microbiological examination were included. Histopathological examination of biopsies of cases with positive microbiological findings on either KOH mount or culture was carried out. Any discrepancy between histopathology interpretation and microbiology KOH or culture results, taking culture as the gold standard, were noted.

STATISTICAL ANALYSIS

Open Epi software was used for statistical analysis. Comparisons between groups were made by using the chi-square test. A p-value < 0.05 was considered statistically significant. Cohen's Kappa coefficient (κ) was calculated as a measure of agreement between different variables.

RESULTS

Concurrent pathology specimen could be obtained in 70 samples positive for fungal elements in either KOH or culture. Thirty-two cases were positive for fungi in culture, of which 16 were correctly identified by histopathological examination. Histopathological examination was strongly associated with culture result. KOH mount was in good agreement with positive culture result for yeast. Eleven culture negative but KOH and histopathology positive cases included seven samples with hyphae suggestive of zygomycosis, and two cases of rhinosporidiosis. Allergic mucin was strongly associated with Aspergillus species. KOH mount and detection of allergic mucin on histopathological examination were found to be excellent complementary tools for diagnosing Aspergillus species. Necrosis was highly specific for fungal growth in culture and had good positive predictive value.

CONCLUSION

We advocate using histopathology, culture and KOH examination in an integral manner to avoid potential lapses in patient management.

The assessment of the viability of the endospores of Rhinosporidium seeberi with MTT (3-[4, 5-dimethyl-2-thiazolyl]-2, 5-diphenyl-2H-tetrazolium bromide)

This report describes tests with Evan's Blue and MTT (3-[4, 5-dimethyl-2-thiazolyl]-2, 5-diphenyl-2H-tetrazolium bromide) for the assessment of the viability of rhinosporidial endospores. MTT stained a proportion of the spherical bodies that we regard as the Electron Dense Bodies (EDBs), and the cytoplasm of freshly prepared endospores or ones that were stored at 4 degrees. Slow-freezing at -20 degrees C, exposure to 10% formalin, or 0.1% sodium azide of the endospores abolished MTT-staining in both sites. Evan's Blue stained the EDBs and cytoplasm of fresh endospores or those stored at 4 degrees, and of sodium azide-treated or frozen (-20 degrees)-thawed endospores. TMRE (tetramethyl-rhodamine ethyl ester) specifically labelled the spherical bodies, supporting the conclusion that these spherical bodies have a mitochondrial-like structure. TMRE-staining was however retained in endospores after their treatment with formalin, sodium azide and slow-freezing while MTT-staining was abolished in all these treated endospores. These results indicate that EvB and TMRE were capable of revealing the morphological integrity of endospores but failed to identify the metabolic inactivation of the endospores after treatment with formalin, sodium azide or slow-freezing. Only MTT was capable of identifying metabolically active endospores and hence their viability and could prove to be of value in standardizing models of infection.

In vitro studies on the mechanisms of endospore release by Rhinosporidium seeberi

Studies of Rhinosporidium seeberi have demonstrated that this organism has a complex life cycle in infected tissues. Its in vivo life cycle is initiated with the release of endospores into a host's tissues from its spherical sporangia. However, little is known about the mechanisms of sporangium formation and endospore release since this pathogen is intractable to culture. We have studied the in vitro mechanisms of endospore release from viable R. seeberi's sporangia. It was found that watery substances visibly stimulates the mature sporangia of R. seeberi to the point of endospore discharge. The internal rearrangement of the endospores within the mature sporangia, the opening of an apical pore in R. seeberi's cell wall, and the active release of the endospores were the main features of this process. Only one pore per sporangium was observed. The finding of early stages of pore development in juvenile and intermediate sporangia suggested that its formation is genetically programmed and that it is not a random process. The stimulation of R. seeberi's sporangia by water supports the epidemiological studies that had linked this pathogen with wet environments. It also explains, in part, its affinities for mucous membranes in infected hosts. The microscopic features of endospore discharge suggest a connection with organisms classified in the Kingdom Protoctista. This study strongly supports a recent finding that placed R. seeberi with organisms in the protoctistan Mesomycetozoa clade.

Purification of the endospores and sporangia of Rhinosporidium seeberi on Percoll columns

Human rhinosporidial tissue was used as the source of the various developmental stages of Rhinosporidium seeberi--endospores with electron dense bodies, juvenile, and immature sporangia. After homogenisation in phosphate buffered saline (PBS) and removal of tissue fragments by centrifugation, the rhinosporidial bodies were isolated on centrifuged Percoll columns with gradients of densities or on triple-layered columns of varying density. The separated bands, after repeated washing in PBS gave bodies free from human tissue as shown on Leishman and PAS staining and indirect immunofluorescence with rabbit and human patients' anti-rhinosporidial sera. Sonicates of these bodies were tested on agarose gel for precipitation with antisera, and on SDS-PAG electrophoresis and Coomassie Blue staining. Percoll columns were shown to be capable of isolating these stages of R. seeberi, free from human tissue and contaminating bacteria.

Infection of the conjunctiva by Rhinosporidium seeberi

Rhinosporidiosis is an unusual fungal disease that rarely affects the eye. It was first described as a pathogen in humans at the turn of the century. The etiologic agent, Rhinosporidium seeberi, commonly produces granulomatous inflammation of the upper respiratory mucosa. Most reported ocular infections have occurred in hot, dry climatic regions. We present a case of conjunctival rhinosporidiosis in an 11-year-old boy from western New York state, the first such report from the temperate zones of North America. The clinical characteristics, histopathologic features, and recommended therapeutic measures are discussed.

Scleral melting in a patient with conjunctival rhinosporidiosis

A remarkable case of a scleral melting reaction in association with conjunctival rhinosporidiosis is presented and its surgical treatment with a scleral graft described.

Culture of Rhinosporidium seeberi: preliminary report

Every year 400 to 450 cases of Rhinosporidium are reported from Trivandrum Medical College. Twenty-five swabs were collected from patients suffering from Rhinosporidiosis and cultured in standard media. Positive results were obtained in 23 cases. The conidia produced from the colony were compared with the structures obtained from the patient material. Light microscopy using histopathological techniques were used. The consistent appearance of the organism in patient material, the repeatability of growth in subcultures and the negative growth in controls indicated that the organism grown in culture is the causative agent of the disease. The effect of parameters like pH, temperatures, etc, were also studied.

Nasal rhinosporidiosis in the dog

Rhinosporidiosis was diagnosed in six dogs from the southeastern United States. All six dogs had unilateral nasal polyps with multiple small white sporangia visible beneath the surface. Microscopically, the polyps consisted of organisms and fibrovascular tissue with a surface of columnar or squamous epithelium. Juvenile sporangia were unilamellar, 15-75 microns in diameter, nucleated, and accounted for about 65% of sporangia seen. Approximately 5% of the sporangia were in intermediate stages of maturation, were bilamellar, 100-150 microns in diameter, and contained immature endospores. Mature sporangia comprised about 30% of the total, were usually unilamellar, 100-400 microns in diameter, and contained a mixture of immature and mature endospores. The inner layer of the wall of the intermediate sporangia and the single wall of the mature sporangia were argyrophilic and carminophilic. Ultrastructurally, the earliest stage contained a nucleus and many ribosomes, lipid droplets, and phagolysosomes. Maturing sporangia contained discrete membrane-bound, round clevage products. These structures subsequently matured to spores, each of which had a wall and contained a nucleus and many lipid droplets. The organism from one dog was cultured and grown in vitro for 7 months and is the first successful cultivation of Rhinosporidium seeberi.