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Abstract

Burkholderia cepacia, Pseudomonas aeruginosa and Staphylococcus aureus are important pathogens of cystic fibrosis patients. The lungs of these patients are usually infected by more than one of these microorganisms, but individual species dominante at certain states of disease. A proteomics approach, using two dimensional-polyacrylamide gel electrophoresis followed by mass spectrometry, was taken to understand the population dynamics within a mixed culture of the three strains. The susceptibilities to antibiotic were also analyzed. P. aeruginosa became dominant in the mixed culture under chosen conditions of cultivation. S. aureus was inhibited in growth, while B. cepacia growth was relatively constant. A total of 194 differentially expressed proteins were detected as a result of interactions in the mixed culture or by the influence of the antibiotic Ceftazidime. The predicted functions of 47 identified proteins gave insights into the reactions in the mixed culture concerning antimicrobial, virulent, and stress response mechanisms. PhzS was identified as a potential biomarker of P. aeruginosa that correlates with the inhibition of S. aureus. The enzyme leads to an increased production of pyocyanine which induces oxidative stress. Also, there was evidence of defence against oxidative stress through increased expression of an alkyl-hydroperoxide-reductase in S. aureus. II