Figure 1 – Cell viability of dual-species biofilms after treatment with several antimicrobial interactions. Bars represent the average of three independent assays ± standard deviation. Symbol indicate statistically different reduction values between positive control (0 mg/L) and different antimicrobials concentrations combined for each strain (* p<0.05).
Ventilator associated pneumonia (VAP), an usual nosocomial infection in the intensive care units and the most common in mechanically ventilated patients, is a serious problem due to high mortality and morbidity rates associated (Kollef, 2013). The presence of the endotracheal tube is the principal determinant for developing VAP because its surface is prone to microbial adhesion and the formation of biofilms, deserving thus high attention in clinical settings. Cell-to-cell communication is an important mechanism of interaction between VAP microorganisms, being involved in the process known as quorum-sensing (QS) that regulate the expression of resistance and virulence. Polymicrobial biofilm infections with Pseudomonas aeruginosa and Candida albicans have being recently reported in VAP (De Sordi and Mühlschlegel 2009; Ader et al. 2011; Hall et al. 2011; Hamet et al. 2012; Morales et al. 2013). The antimicrobial resistance profiles of these binary biofilms represent a serious impact on the treatment of the disease by reducing the effective therapies and affecting the state of health of patients.
To evaluate the role of bacteria fungi cross-talk in co-infection and in their behavior towards antimicrobials and their interactions, the dynamics of mono- and dual- species biofilms of P. aeruginosa and C. albicans, before and after antibiotic and antifungal co-treatment, was examined. Biofilms were characterized in terms of total mass and cell viability. Four clinically important antimicrobials, amphotericin B (AmB), tobramycin (ToB), colistin (CoL) and polymyxin B (PolyB), were tested. Results showed that very few antimicrobial interactions were successful in dual-species biofilms eradication (Figure 1). Some AmB/PolyB and ToB/PolyB interactions promoted a significant reduction of the biofilm-cells viability but only at very high concentrations of PolyB. In some cases, the tolerance of the polymicrobial consortia was higher than that of single biofilms, highlighting that P. aeruginosa and C. albicans established synergistic relationships.
To gain knowledge helping to explain the responses of P.aeruginosa C. albicans consortia to antimicrobials and the interactions that these microorganisms establish among themselves, a transcriptomics analysis approach is being followed to inspect the expression profiles of some cell-cell communication genes involved in biofilm resistance. To overcome the tolerance issues, new antimicrobial combinatorial approaches using QS-inhibitors are being tested. Some interactions involving chlorogenic acid and ciprofloxacin displayed promising anti-biofilm potential.
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