Polymicrobial Ventilator-Associated Pneumonia: Fighting In Vitro Candida albicans-Pseudomonas aeruginosa Biofilms with Antifungal-Antibacterial Combination Therapy

Abstract

The polymicrobial nature of ventilator-associated pneumonia (VAP) is now evident, with mixed bacterial-fungal biofilms colonizing the VAP endotracheal tube (ETT) surface. The microbial interplay within this infection may contribute for enhanced pathogenesis and exert impact towards antimicrobial therapy. Consequently, the high mortality/morbidity rates associated to VAP and the worldwide increase in antibiotic resistance has promoted the search for novel therapeutic strategies to fight VAP polymicrobial infections. Under this scope, this work aimed to assess the activity of mono- vs combinational antimicrobial therapy using one antibiotic (Polymyxin B; PolyB) and one antifungal (Amphotericin B; AmB) agent against polymicrobial biofilms of Pseudomonas aeruginosa and Candida albicans. The action of isolated antimicrobials was firstly evaluated in single- and polymicrobial cultures, with AmB being more effective against C. albicans and PolyB against P. aeruginosa. Mixed planktonic cultures required equal or higher antimicrobial concentrations. In biofilms, only PolyB at relatively high concentrations could reduce P. aeruginosa in both monospecies and polymicrobial populations, with C. albicans displaying only punctual disturbances. PolyB and AmB exhibited a synergistic effect against P. aeruginosa and C. albicans mixed planktonic cultures, but only high doses (256 mg L-1) of PolyB were able to eradicate polymicrobial biofilms, with P. aeruginosa showing loss of cultivability (but not viability) at 2 h post-treatment, whilst C. albicans only started to be inhibited after 14 h. In conclusion, combination therapy involving an antibiotic and an antifungal agent holds an attractive therapeutic option to treat severe bacterial-fungal polymicrobial infections. Nevertheless, optimization of antimicrobial doses and further clinical pharmacokinetics/pharmacodynamics and toxicodynamics studies underpinning the optimal use of these drugs are urgently required to improve therapy effectiveness and avoid reinfection.

Real-time monitoring of Pseudomonas aeruginosa biofilm formation on endotracheal tubes in vitro

“…Most of our current knowledge of P. aeruginosa biofilm formation on medical devices, such as ETT, derives from in vitro studies on polystyrene or rough plastic sections [ 30 , 42 , 43 ]. Such models suffer from a relevant limitation, i.e.…”

Honey as a Strategy to Fight Candida tropicalis in Mixed-Biofilms with Pseudomonas aeruginosa

“…Susceptibilities of C. tropicalis planktonic-cell cultures were evaluated by determining the minimum inhibitory concentration (MIC) and the minimum fungicidal concentration (MFC). The MIC values were determined according to standard European Committee on Antimicrobial Susceptibility Testing (EUCAST), through the broth microdilution method [32]. Briefly, the initial cell concentration for both microorganisms was adjusted for 1 × 10 6 CFU/mL and dispensed into 96-well plates in a proportion of 1:2 (the final inoculum concentration was 5 × 10 5 CFU/mL) with the working antimicrobial solutions (previously diluted in RPMI 1640 broth with double of the desired final concentration).…”

Virulent Pseudomonas aeruginosa infection converts antimicrobial amyloids into cytotoxic prions

“…4 This colonization comprises a locus that can facilitate the seeding of bacteria into the lower airways as a source of ventilator-associated pneumonia (VAP). 5,6 P aeruginosa is the predominant bacterial agent of VAP; it is responsible for the majority of nosocomial infections. 7,8 Within the distal airways the organism disrupts the alveolar (ie, epithelial)-capillary (ie, capillary endothelial) membrane, leading to exudative edema that impairs oxygenation and promotes bacterial dissemination through the circulation.…”