Ultrastructural polymicrobial <i>Staphylococcus aureus–Pseudomonas aeruginosa</i> interactions and antimicrobial resistance in <i>ex vivo</i> cornea model

<b>Aim:</b> To investigate antagonistic interactions among pathogens, in <i>ex vivo</i> donor corneas infected with monomicrobial or polymicrobial combinations of antibiotic susceptible and resistant clinical isolates of <i>Staphylococcus aureus</i> (MSSA, MRSA) and <i>Pseudomonas aeruginosa</i> (S-PA, MDR-PA).<b>Materials & methods:</b> Scanning electron microscopy and antimicrobial susceptibility testing (AST, broth microdilution for minimum inhibitory and bactericidal concentrations [MIC/MBC]) pre-and post-polymicrobial interactions, in infected donor corneas.<b>Results:</b> MSSA lost viability with S-PA/MDR-PA, while MRSA formed larger cells, biofilm and lower MIC (teicoplanin) with S-PA, but lost viability with MDR-PA. S-PA had lower MIC (ceftazidime, meropenem, chloramphenicol) with MSSA, and lower MBC (cefoperazone, ciprofloxacin) and fewer cells with MRSA. MDR-PA had abundant cells and no change in AST with MSSA or MRSA.<b>Conclusion:</b> Significant antagonistic interactions occur in ocular polymicrobial infections, affecting antibiotic susceptible isolates more than resistant ones.