The airways of individuals with cystic fibrosis (CF) are abundantly colonised by
Staphylococcus aureus
and
Pseudomonas aeruginosa
. Co-infecting hypoxic regions of static mucus within CF airways, together with decreases in pulmonary function, mucus plugging and oxygen consumption by host neutrophils gives rise to regions of anoxia. This study determined the impact of anaerobiosis upon
S. aureus
-
P. aeruginosa
interactions in planktonic co-culture and mixed species biofilms
in vitro
. Whilst anoxia reduced the ability for
P. aeruginosa
CF isolates to dominate over
S. aureus
, this occurred in an isolate dependent manner. Investigations into the underlying mechanisms suggest that the anti-staphylococcal compound facilitating
P. aeruginosa
dominance under normoxia and anoxia is greater than 3 kDa in size and is heat-stable. Not all interspecies interactions studied were antagonistic, as
S. aureus
exoproducts were shown to restore and enhance
P. aeruginosa
motility under normoxia and anoxia in an isolate dependent manner. Collectively, this study suggests changes in oxygen availability within regions of the CF lung is likely to influence interspecies interactions and in turn, potentially influence disease progression.