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Although most laboratory investigations have been performed using pure cultures of single microorganisms, bacteria generally grow in a polymicrobial environment. Noting that in cystic fibrosis patients, colonization with Pseudomonas aeruginosa often follows colonization with Staphylococcus aureus, and that P. aeruginosa produces a factor (4-hydroxy-2-heptylquinoline-N-oxide [HQNO]) that suppresses the growth of many gram-positive organisms, researchers in Canada and the U.S. investigated whether these two pathogens might interact.
When P. aeruginosa and S. aureus were co-cultured, P. aeruginosa strains suppressed S. aureus growth. However, in the presence of aminoglycoside antibiotics at concentrations inhibitory for S. aureus, S. aureus col…