Environmental detection of Penicillium marneffei and growth in soil microcosms in competition with Talaromyces stipitatus

Penicillium marneffei is an endemic mycosis of humans in southeast Asia. Epidemiological data have shown that exposure to soil and season increase the risk of infection, and it is assumed that the main environmental reservoir is in soil. We sampled soils from a P. marneffei - endemic region of Thailand and confirmed by quantitative PCR and sequencing that P. marneffei DNA can be detected, a finding that we replicated over three sampling seasons. P. marneffei-positive and -negative sampling locations can be viewed using a dynamic browser located at www.spatialepidemiology.net/pmarneffei. We subsequently examined the hypothesis that P. marneffei isolates representing the two major phylogeographic clades of this species can grow in: (i) soil and (ii) competition against the closely related species, Talaromyces stipitatus, in a model soil environment. P. marneffei was not detected in non-sterile soil microcosms 14 d post inoculation, showing that the pathogen is unable to compete against complete soil fauna under our laboratory conditions. However, both isolates of P. marneffei persisted and increased in biomass when inoculated into sterile soil. P. marneffei stably co-existed with T. stipitatus, and that the main competitive interaction was the inhibition of T. stipitatus growth at low spore application by the ‘Eastern’ isolate of P. marneffei. We conclude that P. marneffei is present in soils within endemic regions, and is able to grow in soil under certain conditions. More research is required to ascertain the specific conditions that regulate the growth of P. marneffei in soils in natural environments.