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Revista do Instituto de Medicina Tropical de São Paulo

On-line version ISSN 1678-9946

Rev. Inst. Med. trop. S. Paulo vol.41 n.5 São Paulo Sept./Oct. 1999

http://dx.doi.org/10.1590/S0036-46651999000500003 

Paracoccidioides brasilienses isolates obtained from patients with acute and chronic disease exhibit morphological differences after animal passage

 

Terezinha Inez Estivalet SVIDZINSKI(1,2), Marcílio Hubner MIRANDA NETO(1,3), Rosângela Getirana SANTANA(1,4), Olga FISCHMAN(5,6) & Arnaldo Lopes COLOMBO(5,7)

 

 

SUMMARY
The basis for virulence in Paracoccidioides brasiliensis is not completely understood. There is a consensus that the sequencial in vitro subcultivation of P. brasiliensis leads to loss of its pathogenicity, which can be reverted by reisolation from animal passage. Attention to morphological and biochemical properties that are regained or demonstrated after animal passage may provide new insights into factors related to the pathogenicity and virulence of P. brasiliensis. We evaluated morphological characters: the percentage of budding cells, number of buds by cell and the diameter of 100 mother cells of yeast-like cells of 30 P. brasiliensis isolates, before and after animal passage. The isolates were obtained from patients with different clinical forms of paracoccidioidomycosis (PCM): acute form (group A, n=15) and chronic form (group C, n=15). The measurement of the yeast cell sizes was carried out with the aid of an Olympus CBB microscope coupled with a micrometer disc. We measured the major transverse and longitudinal axes of 100 viable cells of each preparation. The percentage of budding cells as also the number of buds by cell was not influenced by animal passage, regardless of the source of the strain (acute or chronic groups). The size values of P. brasiliensis isolates from groups A and C, measured before the animal passage exhibited the same behavior. After animal passage, there was a statistically significant difference between the cell sizes of P. brasiliensis isolates recovered from testicles inoculated with strains from groups A and C. The maximum diameter of mother cells from group A isolates exhibited a size of 42.1mm in contrast with 32.9
mm exhibited by mother cells from group C (p<0.05). The diameter of 1500 mother cells from group A isolates exhibited a medium size of 16.0mm (SD ± 4.0), a value significantly higher than the 14.1mm (SD = ± 3.3) exhibited by 1500 mother cells from group C isolates (p<0.05). Our results reinforce the polymorphism exhibited by P. brasiliensis in biological material and the need for further investigations to elucidate the role of morphological parameters of the fungus in the natural history of the disease.
Keywords: Paracoccidioides brasiliensis; Morphology; Paracoccidioidomycosis.

 

 

INTRODUCTION

Paracoccidioidomycosis (PCM) is the most frequent endemic systemic mycosis in Latin America. It usually affects rural male workers aged 30 to 50 years20. Healthy subjects living in endemic areas may be infected by inhalation of infecting propagules of P. brasiliensis and develop one of two clinical forms: (i) acute or subacute form, with severe involvement of the mononuclear phagocyte system; or (ii) the chronic form, with insidious evolution and involvement of one or more organs6,10.

There is mounting evidence that different clinical forms of the disease may be related to host factors (e.g. age, cell-mediated immunity) as well as characteristics of the infecting agent. There are clear indications that P. brasiliensis strains exhibit great biological diversity in terms of morphology, growth rate13, biochemistry11, antigenicity and virulence9,21. Differences of size and budding cells among P. brasiliensis strains have also been reported1,3,4,5,13,15. However, the relationship between these morphological variations and clinical forms of the disease has not yet been studied.

We evaluated the morphometrical variability of P. brasiliensis strains isolated from the two clinical forms of the disease in samples of cultures obtained before and after hamster testicular infection.

 

MATERIAL AND METHODS

Microorganisms: We studied 30 clinical strains of P. brasiliensis previously obtained from different biological material of two groups of patients: 15 were isolated from patients with the acute form of the disease (group A) and the others from cases with the chronic form (group C). Cultures had been maintained in the mycelial phase on Sabouraud-dextrose agar at 25 ºC for variable period of times.

In vitro evaluation of fungal strains morphometrical characters: Before beginning the experiment, samples of cultures were sequentially plated 3 times on PYGA (peptone yeast extract glucose agar)18, and incubated at 35 ºC up to complete transformation from mycelial to yeast form of the fungus. After wards, every strain was cultured on PYGA and incubated at 35 ºC for four days. In order to evaluate the yeast morphology and viability of the strains, a inoculum suspension with turbidity adjusted to 50-60% ± 1% transmission (T), by spectrophotometry (530nm wavelength) was prepared on PBS (pH 7.2). Aliquots of 100mL of the mentioned suspension were stained with equal volume of Janus Green B 0.02% vital dye2 and placed on a glass slide. Using a Neubauer chamber, the elements not stained by vital dye were counted as viable cells. Under microscopic observation we recorded the following parameters: the percentage of budding cells, the number of buds exhibited by each cell and the diameter of the mother cells. The measurement of the yeast cell sizes was carried out with the aid of an Olympus CBB microscope coupled with a micrometer disc. We measured the major transverse and longitudinal axes of 100 viable cells of each preparation19.

In vivo evaluation of fungal strains morphometrical characters: Before beginning the experiment, an inoculum suspension of each strain containing 2.0 x 106 viable cells/mL of PBS was prepared with the aid of a hemocytometer. Thirty sixty-day old male hamsters with weights between 90 and 100g were challenged by inoculation of a 100mL of standard inoculum into the right testicle8,12. The animals were kept in individual cages and were given food and water ad libitum. Animals were observed daily for the presence of orchitis. In the presence of orchitis, hamsters were sacrificed and the right testicle was removed. Samples of fluids obtained by punction of each animal testicle were placed on a glass slide for further evaluation. All morphological parameters were studied according to the methodology previously described for in vitro evaluation of P. brasiliensis strains.

Statistical analysis: The morphometrical characters of fungal cells from P. brasiliensis strains were contrasted in two steps: (i) comparison of morphological parameters obtained with 30 isolates before and after animal infection, regardless of the origin of the strain; (ii) comparison of the morphological parameters exhibited by P. brasiliensis strains from the two groups (A and C) recorded after animal infection. These variables were analyzed by Student t-test, performed with the aid of the Statistica for Windows Microsoft Corporation version 6.0.

 

RESULTS

We were able to convert to the yeast phase all 30 P. brasiliensis isolates that had been maintained in the mycelial phase for variable periods of times. However, 2 isolates (A15 and C27) exhibited persistence of pseudo-hyphae and hyphae forms even after more than 10 sequential cultures on PYGA at 35 ºC. The high viability of all yeast cells, confirmed by using Janus Green B vital dye, ranged from 80 to 99% (mean=90%).

All animals were successfully challenged intratesticularly and the enlargement of the inoculated testis was observed after periods of 5 to 10 weeks (mean 60 days). During the 30 experiments performed in the present series, four (13%) animals exhibited progressive lost of vitality and weight, and death occurred before the documentation of orchitis. The animal passage was successfully repeated with those isolates and all challenged hamsters developed orchitis.

Yeast cells of P. brasiliensis were always recovered from the fluids of infected testicles. The variability of the morphological aspects of the yeast cells is shown in Figure 1. About 80% of the isolates presented spherical cells, seconded by oval and elongated ones. Of note, it was also possible to observe small pseudo-hyphae and hyphae forms among samples obtained from 2 isolates (A15 and C27). In contrast to the high incidence (>70%) of budding yeast cells observed with isolates maintained in cultures, samples of P. brasiliensis obtained after animal passage exhibited only 29% of the yeast cells as budding forms (Table 1). The mean of budding cells observed with all isolates was 2 buds/cell before animal passage and 0.6 buds/cell after animal passage. The percentage of budding cells as also the number of buds by cell was not influenced by animal passage, regardless of the source of the strain (acute or chronic groups).

 

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The estimated diameter size and the micromorphometrical aspects of P. brasiliensis in yeast-like form are depicted in figure 2. Table 2 shows the sizes of the P. brasiliensis isolates from groups A and C measured before and after animal passage. The size values of P. brasiliensis isolates from groups A and C, measured before the animal passage exhibited the same behavior. The diameter of all 30 isolates before animal passage, recorded by the analyses of 100 mother cells of each strain, exhibited a minimum size of 2.6mm, a maximum of 35.5mm and a medium of 12.3mm (SD = ± 4.7). The same parameters measured after animal passage were: minimum = 5.3mm, maximum 42.1mm, medium = 12.2mm (SD ± 4.4) (p=0.31).

 

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After animal passage, there was a statistically significant difference between the cell sizes of P. brasiliensis isolates recovered from testicles inoculated with strains from groups A and C. The maximum diameter of mother cells from group A isolates exhibited a size of 42.1mm in contrast with 32.9mm exhibited by mother cells from group C (p<0.05). The diameter of 1500 mother cells from group A isolates exhibited a medium size of 16.0mm (SD ± 4.0), a value significantly higher than the 14.1mm (SD = ± 3.3) exhibited by 1500 mother cells from group C isolates (p<0.05).

 

 DISCUSSION

The basis for virulence in P. brasiliensis is not completely understood6,16. There is a consensus that sequential in vitro passage of P. brasiliensis leads to loss of virulence. Furthermore, the animal passage of attenuated P. brasiliensis may restore some virulence factors7,14. Attention to morphological and biochemical properties that are regained or demonstrated after animal passage may provide new insights into factors related to the pathogenicity and virulence of P. brasiliensis.

In the present study we investigated the effect of animal passage on the morphometrical characteristics of 30 isolates of P. brasiliensis. The selection of hamsters for animal passage of P. brasiliensis strains was based on previous publications addressing the efficacy of the intratesticular route of infection as well as the success of recovering the fungus from inoculated testis8,12. In our series of experiments orchitis developed in all challenged hamsters after 5 to 10 weeks and the recovery rate of P. brasiliensis from infected testis was 100%.

After animal passage, the yeast-like cells of P. brasiliensis exhibited a limited number of budding yeasts compared to the number observed before animal passage. The adversity of the environment caused by host defense mechanisms, pH modification of the infected tissue, as well as the high concentration of organisms found in the animal testis may have led to decrease in the reproduction of the fungus at the moment we obtained the sample for analysis.

The polymorphism of P. brasiliensis in clinical specimens has been well documented and includes variable sizes of isolated or multibudding yeasts and sometimes elongated distorted cells or chains of yeasts1,3,4,5,13,15,16,17. In the present series we were able to demonstrate a high variability of forms exhibited by P. brasiliensis in fluids obtained from testis of infected animals. As depicted in figure 1, the fungus revealed not only yeast forms with and without budding cells but also rare small hyphae and amorphous structures. Of note, the occurrence of filamentous forms of P. brasiliensis in clinical specimens has rarely been reported15,17.

Some isolates obtained from patients with acute form of PCM generated larger yeast cells after animal passage than those obtained from fluids of animals infected by isolates from patients with the chronic form of PCM. Apparently, yeast cells of P. brasiliensis maintained in vitro for long periods of time tend to become more homogeneous in size. Animal passage could be a stimulus for recovery of the original characteristics of the organism, including virulence factors. Consequently, the morphological differences we observed with P. brasiliensis isolates after animal passage suggest that the size of the yeast-like form of the fungus may play a role in the virulence of the organism as well as in the severity of the disease.

According to LACAZ et al.15, yeast like cells of P. brasiliensis isolated from fluids from enlarged lymph nodes of patients with PCM have large cells (up to 25mm) in contrast to the small cells (up to 5mm) seen in oral lesions. Our results reinforce the polymorphism exhibited by P. brasiliensis in clinical specimens and the need for further investigation to elucidate the role of morphological parameters in the natural history of this disease.

 

 

 RESUMO

Isolados de Paracoccidioides brasiliensis obtidos de pacientes com doença crônica e aguda exibem diferenças morfológicas após passagem animal

Os mecanismos de virulência em Paracoccidioides brasiliensis não estão totalmente esclarecidos. Há um consenso que subcultivos sucessivos de P. brasiliensis acarretam a perda de sua patogenicidade que pode ser revertida pelo reisolamento do agente após passagem animal. As propriedades morfológicas e bioquímicas que são recuperadas ou demonstradas após passagem animal podem fornecer novas informações quanto a fatores relacionados à patogenicidade e virulência de P. brasiliensis. Nós avaliamos características morfológicas: porcentagem de células brotantes, número de brotamentos por célula e determinação do diâmetro de 100 células-mãe em 30 isolados de P. brasiliensis, antes e após passagem animal. Os isolados foram obtidos de pacientes com diferentes formas clínicas de paracoccidioidomicose (PCM): forma aguda (grupo A n=15) e forma crônica (grupo C n=15). A mensuração do tamanho das células foi feita em microscópio óptico Olympus CBB acoplado com régua micrométrica. Nós medimos o maior eixo transversal e longitudinal de 100 células viáveis de cada preparação. A porcentagem de células brotantes bem como o número de brotamentos por célula não foram influenciados pela passagem animal independente da origem da amostra (grupo agudo ou crônico). Os valores dos tamanhos dos isolados de P. brasiliensis dos grupos A e C medidos antes e após passagem animal exibiram o mesmo comportamento. Após passagem animal, houve diferenças estatisticamente significativas entre o tamanho das células de P. brasiliensis isolados a partir de testículos inoculados com amostras dos grupos A e C. O diâmetro máximo das células mãe dos isolados do grupo A exibiram tamanho de 42.1mm, em contraste com 32.9mm exibidos pelas células mãe do grupo C (p<0.05). O diâmetro de 1500 células do grupo A exibiram tamanho médio de 16.0mm (SD ± 4.0), valor significativamente maior que 14.1mm (SD ± 3.3) exibidos pelas 1500 células do grupo C (p<0.05). Nossos resultados confirmam o polimorfismo exibido por P. brasiliensis em amostras biológicas e reforça a necessidade de mais investigações com o objetivo de elucidar o papel que parâmetros morfológicos do fungo possam assumir na história natural da doença.

 

 

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(1) State University of Maringá, Paraná, Brasil
(2) Department of Clinical Analyses/Division of Medical Mycology
(3) Department of Morphophysiological Science
(4) Department of Statistics
(5) Federal University of São Paulo, Paulista School of Medicine, São Paulo, SP, Brasil
(6) Division of Cellular Biology
(7) Division of Infectious Diseases.

Correspondence to: Prof. Dr. Arnaldo Lopes Colombo, Universidade Federal de São Paulo, Divisão de Doenças Infecciosas e Parasitárias, Rua Botucatu 740, 04023-062 São Paulo, SP, Brazil. Fax # 55 11 549 6585 - 576 4334. E-mail: lemidipa@ruralsp.com.br

Received: 19 March 1999
Accepted: 20 September 1999

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