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Introduction: Polymicrobial infections contribute significantly to the burden of morbidity and mortality of infectious diseases. Because microbial interactions can be cooperative or competitive, this study sought to assess the in vitro interactions of Klebsiella pneumoniae, Pseudomonas aeruginosa and Staphylococcus aureus.
Materials and Methods: In vitro competition assays with K. pneumoniae (KP05), P. aeruginosa (ATCC27853) and S. aureus (ATCC25923) were performed in Luria Bertani (LB) broth at 37oC under aerobic conditions. Duplex (1:1 ratios) and triplex culture combinations (1:1:1 ratio) contained 1 x 103 cells/ml of each bacterium. Cell numbers were estimated at 1-, 2-, 4-, 8-, 12-, 24- and 48-hr timepoints and generation times were determined alone or in combination with other bacteria. Competitive PCR was used to assess the detectability of selected virulence-associated genes (one from each bacterium) at 8-, 24- and 48- hr timepoints.
Results: While the growth curve for monocultures followed normal growth patterns, duplex and triplex co-cultures saw marked evidence of competition and cooperation between and among the bacteria. Of note, S. aureus grew better with P. aeruginosa versus co-culture with K. pneumoniae. P. aeruginosa did not produce any measurable growth in the presence of S. aureus. K. pneumoniae grew better with S. aureus and least with P. aeruginosa. Competitive PCR for organism-specific genes were in the order: S. aureus > K. pneumoniae > P. aeruginosa which mirrored the growth parameters observed.
Conclusion: The findings revealed that of the three bacteria, S. aureus was the dominant species in both duplex and tripartite cultures.