Differential effects of Pseudomonas aeruginosa on biofilm formation by different strains of Staphylococcus epidermidis.

Pseudomonas aeruginosa and Staphylococcus epidermidis are common opportunistic pathogens associated with medical device-related biofilm infections. 16S rRNA-FISH and confocal laser scanning microscopy were used to study these two bacteria in dual-species biofilms. Two of the four S. epidermidis strains used were shown to form biofilms more avidly on polymer surfaces than the other two strains. In dual-species biofilms, the presence of P. aeruginosa reduced biofilm formation by S. epidermidis, although different clinical isolates differed in their susceptibility to this effect. The most resistant isolate coexisted with P. aeruginosa for up to 18 h and was also resistant to the effects of the culture supernatant from P. aeruginosa biofilms, which caused dispersal from established biofilms of other S. epidermidis strains. Thus, different strains of S. epidermidis differed in their capacity to withstand the action of P. aeruginosa, with some being better equipped than others to coexist in biofilms with P. aeruginosa. Our data suggest that where S. epidermidis and P. aeruginosa are present on abiotic surfaces such as medical devices, S. epidermidis biofilm formation can be inhibited by P. aeruginosa through two mechanisms: disruption by extracellular products, possibly polysaccharides, and, in the later stages, by cell lysis.