AUTHOR=Niggli Selina , Wechsler Tobias , Kümmerli Rolf 

TITLE=Single-Cell Imaging Reveals That Staphylococcus aureus Is Highly Competitive Against Pseudomonas aeruginosa on Surfaces

JOURNAL=Frontiers in Cellular and Infection Microbiology

VOLUME=11

YEAR=2021

URL=https://www.frontiersin.org/journals/cellular-and-infection-microbiology/articles/10.3389/fcimb.2021.733991

DOI=10.3389/fcimb.2021.733991

ISSN=2235-2988

ABSTRACT=<p><italic>Pseudomonas aeruginosa</italic> and <italic>Staphylococcus aureus</italic> frequently occur together in polymicrobial infections, and their interactions can complicate disease progression and treatment options. While interactions between <italic>P. aeruginosa</italic> and <italic>S. aureus</italic> have been extensively described using planktonic batch cultures, little is known about whether and how individual cells interact with each other on solid substrates. This is important because both species frequently colonize surfaces to form aggregates and biofilms in infections. Here, we performed single-cell time-lapse fluorescence microscopy, combined with automated image analysis, to describe interactions between <italic>P. aeruginosa</italic> PAO1 with three different <italic>S. aureus</italic> strains (Cowan I, 6850, JE2) during microcolony growth on agarose surfaces. While <italic>P. aeruginosa</italic> is usually considered the dominant species, we found that the competitive balance tips in favor of <italic>S. aureus</italic> on surfaces. We observed that all <italic>S. aureus</italic> strains accelerated the onset of microcolony growth in competition with <italic>P. aeruginosa</italic> and significantly compromised <italic>P. aeruginosa</italic> growth prior to physical contact. Upon direct contact, JE2 was the most competitive <italic>S. aureus</italic> strain, simply usurping <italic>P. aeruginosa</italic> microcolonies, while 6850 was the weakest competitor itself suppressed by <italic>P. aeruginosa</italic>. Moreover, <italic>P. aeruginosa</italic> reacted to the assault of <italic>S. aureus</italic> by showing increased directional growth and expedited expression of quorum sensing regulators controlling the synthesis of competitive traits. Altogether, our results reveal that quantitative single-cell live imaging has the potential to uncover microbial behaviors that cannot be predicted from batch culture studies, and thereby contribute to our understanding of interactions between pathogens that co-colonize host-associated surfaces during polymicrobial infections.</p>