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Alterations in the pathogenicity of one Paracoccidioides brasiliensis isolate do not correlative with its in vitro
S S Kashino1, L M Singer-Vermes, V L Calich
1Depto. Imunologia, Universidade de São Paulo, Brasil.
Abstract:
The in vitro subcultivation of some microorganisms for long periods causes measurable loss of their pathogenicity, which can be reverted by reisolation from infected hosts. We compared the pathogenicity and the in vitro growth pattern of one P. brasiliensis isolate (Pb 18) in its yeast phase, using the following samples: 1) The original pathogenic Pb 18 (OP). 2) Pb 18 attenuated by continuous in vitro subcultivation (AT). 3) Pb 18 (AT) reisolated from susceptible B10.A mice (RS). 4) Pb 18 (AT) reisolated from resistant A/SN mice (RR). Pathogenicity was evaluated by anatomopathology and mortality of mice infected i.p. with 5 x 10(6) fungi. Median survival times of mice infected with OP ranged from 74 to 117 days during the first 51 months of subculturing; with more cycles of subculturing the median survival time increased, reaching 250 days at the 64th month. This indicated decreasing virulence of OP during this period of subculturing. Survival of mice infected with RS and RR was respectively 112 and 123 days, which is similar to the behavior of the OP variant. The in vitro growth curve profile of RR showed significantly higher numbers of total and viable yeasts than the other studied variant. These results show that: 1) Pb 18 isolate loses its pathogenicity by continuous subcultivation. This phenomenon is reverted by reisolation from mice, independently from their susceptibility to the fungus; 2) the in vitro growth patterns of Pb 18 do not correlate with alterations in pathogenicity but are influenced by the host's environment.
Insights
Continuous in vitro cultivation of Paracoccidioides brasiliensis (Pb 18) reduces its pathogenicity, but reisolation from mice restores virulence. In vitro growth patterns did not correlate with pathogenicity changes.
Area of Science:
- Medical Mycology
- Infectious Diseases
- Microbial Pathogenesis
Background:
- Long-term in vitro subcultivation of microorganisms can lead to attenuation of pathogenicity.
- Reisolation from a host organism can potentially restore virulence in attenuated microbial strains.
Purpose of the Study:
- To compare the pathogenicity and in vitro growth patterns of Paracoccidioides brasiliensis (Pb 18) isolate.
- To investigate the effects of continuous in vitro subcultivation and subsequent reisolation from mice on Pb 18 virulence.
Main Methods:
- Comparison of original pathogenic (OP), in vitro attenuated (AT), and reisolated (RS, RR) Pb 18 yeast phase isolates.
- Pathogenicity assessment via mouse mortality and median survival times after intraperitoneal infection.
- In vitro growth curve analysis to determine total and viable yeast counts.
Main Results:
- Continuous in vitro subcultivation of Pb 18 led to decreased pathogenicity, indicated by increased median survival times in infected mice.
- Reisolation of Pb 18 from both susceptible (RS) and resistant (RR) mice restored pathogenicity, with survival times similar to the original strain.
- The reisolated (RR) variant exhibited significantly higher in vitro yeast counts compared to other variants, but this did not correlate with pathogenicity.
Conclusions:
- Paracoccidioides brasiliensis isolate Pb 18 loses pathogenicity with prolonged in vitro subcultivation, which is reversible upon reisolation from infected mice.
- In vitro growth characteristics of Pb 18 are influenced by the host environment but do not directly correlate with observed changes in pathogenicity.