Historically, infections have been thought of as being caused by a single microbial agent, and while this is true for some instances of disease, in reality it is often more complicated. There is mounting evidence that polymicrobial infections are much more common than once thought and can lead to increased virulence of the infecting partners. Despite this, polymicrobial interactions remain an understudied area, particularly for the deadly pathogens Acinetobacter baumannii (Ab) and Klebsiella pneumoniae (Kp). Polymicrobial infections of Ab and Kp have been reported at rates of up to 40% of infections involving either species and generally lead to worse outcomes for patients including increased mortality rates and increased resistance to antibiotics. Furthermore, co-transmission of Ab and Kp between patients has been demonstrated in an Australian hospital setting.
Utilising a strain pair of Ab (AB6870155) and Kp (KP6870155) co-isolated from a single lung infection, we investigated the co-culture dynamics and potential for cross-feeding between these species. In planktonic culture Kp was initially more abundant, however, both strains were able to persist in the population and relative abundances approached 1:1 over time. In biofilms, Ab was more abundant. The KP6870155 strain had a broader range of carbon source utilisation than AB6870155 and it was found that Kp could cross-feed excreted metabolites of sugar fermentation, ethanol and lactate, to Ab. Furthermore, cross-feeding extended to other strain pairs of Ab and Kp that were not co-isolates, albeit to varying extents.
These findings have implications for their co-persistence in infection and environmental settings. Developing a greater understanding of the conditions under which Ab and Kp may be dependent upon one another could allow the development of strategies that target and destabilise this interaction, potentially decreasing persistence and allowing eradication of both strains.