Survival ofParacoccidioides brasiliensisyeast cells under microaerophilic conditions

Abstract

The ability of P. brasiliensis yeast cells to withstand microaerophilic-conditions was investigated in a liquid medium distributed in tall columns in screw-capped tubes. Young cells of three isolates were inoculated on top of the medium, and the tubes were incubated aerobically and anaerobically at 36 °C for 28 days. The viability of cells that had sedimented to the bottoms of the tubes was studied by fluorescent micro.~6opy and by their capacity to resume growth when transferred to fresh medium undercontinuous agitation. The proportion of viable cells in the sediments diminished with time of incubation. However, after 28 days, 27 % of the cells were still viable and fully capable of active growth when placed under adequate aeration. On the other hand, drastic reduction of oxygen access elicited an accelerated death rate, with no survival after 7 days of incubation.The yeast and the mycelial phase of Paracoccidioides brasiliensis both require a generous supply of oxygen for growth. This is particularly true when cultures are attempted in liquid media. Irrespective of the quality of the medium, no growth is obtained in stationary liquid cultures, while continuous agitation results in adequate development of the fungus I-4, 8, 9].This stringent oxygen requirement is difficult to reconcile with the long periods of latency known to occur in clinical paracoccidioidomycosis, as illustrated by cases diagnosed outside of the endemic areas, the majority of which have involved patients who developed paracoccidioidomycosis 15 or more years after their return from endemic countries to non-endemic zones [5]. This extreme latency of infection indicates that the fungus can persist dormant within closed lesions, in a manner similar to Mycobacterium tuberculosis [13,14]. Furthermore, the finding of residual nodular lesions containing the characteristic P. brasiliensis cells in the lung and the adrenals of apparently normal individuals [1], as well as the description of a healed primary pulmonary lymph node complex 1-12], point to the reticuloendothelial system as the most probable site of residence of the fungus during, the latency period.We investigated the survival of the yeast (tissue) phase of P. brasiliensis under conditions of oxygen deprivation in order to assess the possibility of accommodation to the environment operating in walled-off lesions. MATERIALS AND METHODSThree isolates of the fungus, recovered from patients with chronic progressive paracoccidioidomycosis were employed: C81, isolated in 1962, LA in 1970 and CG in 1980. They have been maintained in the mycelial phase by bi-monthly transfers on Sabouraud dextrose agar (BBL, Cockeysville, Maryland, U.S.A.) at 24-26 °C.

Paracoccidioidomycosis: an update.

“…The yeast and mycelial phases of P. brasiliensis both require a generous supply of oxygen for growth (258); however, young yeast cells can adapt gradually to reduced oxygen tension and enter a resting stage. Resting cells can regain metabolic activity when placed under adequate conditions of oxygenation (258). This capacity may well explain the prolonged latency of this mycosis (4).…”

Recovery ofParacoccidioides brasiliensisfrom a partially calcified lymph node lesion by microaerophilic incubation of liquid media

“…However, Pedroso found that the semianaerobic environment offered by liquid cultures in tall columns was advantageous for the primary isolation of the yeast phase [5]. The latter report, however, is not very detailed, thus hindering complete assessment of the finding.Recent experimental studies revealed that the yeast-like cells of this fungus can accommodate to the microaerophilic conditions present in stationary liquid cultures [9]. Long periods of latency are known to occur in human paracoccidioidomycosis [2] and we therefore wondered whether dormancy of P. brasiliensis, similar to that seen in vitro, might occur in vivo.…”

“…Recent experimental studies revealed that the yeast-like cells of this fungus can accommodate to the microaerophilic conditions present in stationary liquid cultures [9]. Long periods of latency are known to occur in human paracoccidioidomycosis [2] and we therefore wondered whether dormancy of P. brasiliensis, similar to that seen in vitro, might occur in vivo.…”