Pharmaceutical pollution alters the cost of bacterial infection and its relationship to pathogen load
Lucinda C Aulsebrook1, Bob B M Wong1, Matthew D Hall1
1School of Biological Sciences, Monash University, Melbourne, Victoria 3800, Australia.
Abstract:
The relationship between pathogen proliferation and the cost of infection experienced by a host drives the ecology and evolution of host-pathogen dynamics. While environmental factors can shape this relationship, there is currently limited knowledge on the consequences of emerging contaminants, such as pharmaceutical pollutants, on the relationship between a pathogen's growth within the host and the damage it causes, termed its virulence. Here, we investigated how exposure to fluoxetine (Prozac), a commonly detected psychoactive pollutant, could alter this key relationship using the water flea Daphnia magna and its bacterial pathogen Pasteuria ramosa as a model system. Across a variety of fluoxetine concentrations, we found that fluoxetine shaped the damage a pathogen caused, such as the reduction in fecundity or intrinsic growth experienced by infected individuals, but with minimal change in average pathogen spore loads. Instead, fluoxetine modified the relationship between the degree of pathogen proliferation and its virulence, with both the strength of this trade-off and the component of host fitness most affected varying by fluoxetine concentration and host genotype. Our study underscores the potential for pharmaceutical pollution to modify the virulence of an invading pathogen, as well as the fundamental trade-off between host and pathogen fitness, even at the trace amounts increasingly found in natural waterways.
Insights
Pharmaceutical pollution, like fluoxetine, alters pathogen virulence and the host-pathogen trade-off. This study shows environmental contaminants can change how pathogens impact host fitness, even at low concentrations.
Area of Science:
- Ecology and Evolutionary Biology
- Environmental Toxicology
- Microbial Pathogenesis
Background:
- Host-pathogen dynamics are shaped by the balance between pathogen proliferation and host infection costs.
- Limited understanding exists on how emerging contaminants, such as pharmaceutical pollutants, affect this critical relationship.
- Fluoxetine (Prozac) is a common psychoactive pollutant found in natural waterways.
Purpose of the Study:
- To investigate the impact of fluoxetine exposure on the relationship between pathogen proliferation and virulence.
- To determine how fluoxetine alters the trade-off between pathogen growth and the damage it inflicts on the host.
- To assess these effects using the *Daphnia magna* and *Pasteuria ramosa* model system.
Main Methods:
- Exposed *Daphnia magna* to varying concentrations of fluoxetine.
- Infected exposed water fleas with the bacterial pathogen *Pasteuria ramosa*.
- Quantified pathogen spore loads and measured host fitness costs (fecundity, growth) across different fluoxetine levels and host genotypes.
Main Results:
- Fluoxetine significantly altered the virulence of *Pasteuria ramosa*, affecting host fitness metrics like fecundity and growth.
- Average pathogen spore loads showed minimal change, indicating fluoxetine primarily modified the *expression* of virulence, not pathogen replication.
- The trade-off between pathogen proliferation and virulence was reshaped by fluoxetine, with effects varying by contaminant concentration and host genotype.
Conclusions:
- Pharmaceutical pollution, even at trace amounts, can significantly modify pathogen virulence and the fundamental host-pathogen fitness trade-off.
- Environmental contaminants can alter the ecological and evolutionary dynamics of host-pathogen interactions.
- This study highlights the need to consider the impact of pharmaceutical pollutants on wildlife health and ecosystem function.
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