Bacterial interaction and indirect pathogenesis of Pseudomonas aeruginosa at the growth of MRSA

Bacterial interactions such as methicillin-resistant Staphylococcus aureus (MRSA) growth inhibition or inactivation of anti-MRSA antibiotics by Pseudomonas aeruginosa as an indirect pathogen were tested by in vitro assay. Paired strains, P. aeruginosa and MRSA, used in this experiment were isolated from 63 respiratory samples at Juntendo University Hospital from 2002 to 2003. Growth inhibitory activities against MRSA by P. aeruginosa were tested with reversed agar plate method. Inactivation of anti-MRSA antibiotics by P. aeruginosa were assayed with disk diffusion method using agar over lay technique. Fifty-six (88.9%) out of 63 samples showed the significant MRSA growth inhibitory activity by co-existed P. aeruginosa. Anti-MRSA antibiotics such as trimetoprim-sulfamethoxazole combination (ST), arbekacin (ABK) and minocycline (MINO) except Vancomycin (VCM) and Teicoplanin (TEIC) were inactivated by the co-existed P. aeruginosa. Our data suggests that P. aeruginosa may play not only as a chronic respiratory pathogen but also as an indirect pathogen. Further, the most P. aeruginosa with anti-MRSA activity isolated respiratory sample may play as a modulator of MRSA infection.