The antimicrobial spectrum to manage the co-infections of P. aeruginosa and S. aureus

Background: Coinfections of Pseudomonas aeruginosa and Staphylococcus aureus usually fail to respond to antibiotic treatment, and combination therapy may prove to be a substantial approach to prevent the spread of antimicrobial resistance. Objectives: To evaluate the antimicrobial and antibiofilm effects of drugs against the sensitive as well as resistant strain co-cultures of P. aeruginosa and S. aureus . Methods: 52 clinical isolates of P. aeruginosa and 43 of S. aureus were studied. The planktonic and biofilm co-cultures of the resistant (PA-14 and PS-107) and sensitive (PA-27 and PS-100) biofilm-forming strains of P. aeruginosa and S. aureus were determined for a specific set of drugs. Based on the Minimum Inhibitory Concentration (MIC), and Minimum Biofilm Inhibitory Concentration (MBIC) data, the different drug combinations were shortlisted and tested against the co-cultures. Results: 33.3% of drug combinations showed synergy against resistant and 41.7% against sensitive strain planktonic co-culturesamong the shortlisted drug combinations. Furthermore, 8.3% were found to be effective against the biofilm co-cultures of resistant strains and 80% against sensitive strains. The drug combinations, although synergistic against the co-cultures, the pure cultures of P. aeruginosa and S. aureus were found to be susceptible to the participating drugs (colistin, linezolid, trimethoprim, nitrofurantoin, and vancomycin) in the initial studies. Conclusions: This, however, alleviates the synergistic effect of these drug combinations. In contrast, it demonstrates a significant reduction in the MICs (≥50%) compared to the MICs of these drugs against the pure cultures of bacteria, indicating the therapeutic benefits of adjusted doses of the combining drugs over monotherapy in treating these coinfections.