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

Aim: To investigate antagonistic interactions among pathogens, in ex vivo donor corneas infected with monomicrobial or polymicrobial combinations of antibiotic susceptible and resistant clinical isolates of Staphylococcus aureus (MSSA, MRSA) and Pseudomonas aeruginosa (S-PA, MDR-PA).Materials & methods: 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.Results: 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.Conclusion: Significant antagonistic interactions occur in ocular polymicrobial infections, affecting antibiotic susceptible isolates more than resistant ones.