Caspofungin alone or combined with polymyxin B are effective against mixed biofilm of Aspergillus fumigatus and carbapenem-resistant Pseudomonas aeruginosa.

Aspergillus fumigatus and Pseudomonas aeruginosa biofilms are associated to the recalcitrant and persistent infections due to resistance to antimicrobials. Here, we evaluated the effect of antimicrobials on single and mixed biofilms of A. fumigatus and P. aeruginosa (carbapenem-resistant and susceptible strains) determining total biomass by crystal violet, cell viability by colony forming unit count, and microscopy. Polymyxin B (PMB) had the best action on P. aeruginosa biofilms inhibiting the biomass (2-4 µg/mL) and it was efficient reducing the viable bacterial cells. Amphotericin B (AMB) and caspofungin (CAS) were the best antifungal at inhibiting A. fumigatus biofilms and reducing fungal viability at concentration ≥1 and ≥ 16 µg/mL, respectively. In addition, CAS was able to significantly reduce P. aeruginosa viability in mixed biofilms. CAS combined with PMB also significantly reduced the mixed biofilm biomass and fungal and bacterial viability mainly against carbapenem-resistant bacterium. The light and fluorescence microscopy showed alterations on hyphae morphology and confirmed the increase of fungal and bacterial death cells after combined therapy of mixed biofilms. Taken together, our work showed that CAS alone and its combination with PMB showed better potential in reducing mixed biofilm biomass and fungal and bacterial viability, even for the carbapenem-resistant P. aeruginosa strain.

Caspofungin and Polymyxin B Reduce the Cell Viability and Total Biomass of Mixed Biofilms of Carbapenem-Resistant Pseudomonas aeruginosa and Candida spp.

Pseudomonas aeruginosa and Candida spp. are biofilm-forming pathogens commonly found colonizing medical devices, being mainly associated with pneumonia and bloodstream infections. The coinfection by these pathogens presents higher mortality rates when compared to those caused by a single microbial species. This study aimed to evaluate the antibiofilm activity of echinocandins and polymyxin B (PMB) against polymicrobial biofilms of carbapenem-resistant (CR) Pseudomonas aeruginosa and Candida spp. (C. albicans, C. parapsilosis, C. tropicalis, and C. glabrata). In addition, we tested the antimicrobial effect on their planktonic and monomicrobial biofilm counterparties. Interestingly, beyond inhibition of planktonic [minimum inhibitory concentration (MIC) = 0.5 µg/ml] and biofilm [minimum biofilm inhibitory concentration (MBIC)50 ≤ 2-8 µg/ml] growth of P. aeruginosa, PMB was also effective against planktonic cells of C. tropicalis (MIC = 2 µg/ml), and polymicrobial biofilms of CR P. aeruginosa with C. tropicalis (MBIC50 ≤ 2 µg/ml), C. parapsilosis (MBIC50 = 4-16 µg/ml), C. glabrata (MBIC50 = 8-16 µg/ml), or C. albicans (MBIC50 = 8-64 µg/ml). On the other hand, while micafungin (MFG) showed highest inhibitory activity against planktonic (MIC ≤ 0.008-0.5 µg/ml) and biofilm (MBIC50 ≤ 2-16 µg/ml) growth of Candida spp.; caspofungin (CAS) displays inhibitory activity against planktonic cells (MIC = 0.03-0.25 µg/ml) and monomicrobial biofilms (MBIC50 ≤ 2-64 µg/ml) of Candida spp., and notably on planktonic and monomicrobial biofilms of CR P. aeruginosa (MIC or MBIC50 ≥ 64 µg/ml). Particularly, for mixed biofilms, while CAS reduced significantly viable cell counts of CR P. aeruginosa and Candida spp. at ≥32 and ≥ 2 µg/ml, respectively; PMB was effective in reducing viable cells of CR P. aeruginosa at ≥2 µg/ml and Candida spp. at ≥8 µg/ml. Similar reduction of viable cells was observed for CAS (32-64 µg/ml) combined with PMB (2 µg/ml). These findings highlight the potential of PMB and CAS for the treatment of polymicrobial infections caused by Candida spp. and critical priority CR P. aeruginosa.