The antimicrobial spectrum to manage the co-infections of Pseudomonas aeruginosa and Staphylococcus aureus

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. 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. A pair of biofilm-forming, sensitive, and resistant strains was identified from 52 clinical isolates of P. aeruginosa and 43 of S. aureus using phenotypic, genotypic, antimicrobial susceptibility tests, and colorimetric microtiter plate assays. The antimicrobial susceptibility patterns of the planktonic and biofilm cultures and co-cultures (1:1) from these resistant (PA-14 and PS-107) and sensitive (PA-27 and PS-100) strains were determined for the 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. In the drug combination studies, 33.3% (4/12) of drug combinations showed synergy against resistant and 41.7% (5/12) against sensitive strain planktonic co-cultures among the shortlisted drug combinations. Furthermore, 8.3% (2/24) of drug combinations were found to be effective against the biofilm co-cultures of resistant strains and 80% (4/5) of drug combinations showed synergy against sensitive strains. Drug combination studies revealed a few effective drug combinations that demonstrated synergy against the planktonic and biofilm co-cultures. Despite their synergistic effects against the bacterial co-cultures, the drugs involved in these combinations (colistin, linezolid, trimethoprim, nitrofurantoin, and vancomycin) displayed inhibitory effects against the pure cultures of P. aeruginosa and S. aureus within the susceptible ranges noted in the initial studies. Owing to this, however, mitigates the synergistic effect of these drug combinations. Conversely, it shows a notable decrease in the MICs (≥ 50%) when compared to the MICs of these drugs against the pure bacterial cultures, suggesting the therapeutic benefits of adjusted doses of the combined drugs over monotherapy in treating these coinfections.