Matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry (MS) fingerprinting has recently become an effective instrument for rapid microbiological diagnostics and in particular for identification of micro-organisms directly in a positive blood culture. The aim of the study was to evaluate a collection of 82 stored yeast isolates from bloodstream infection, by MALDI-TOF MS; 21 isolates were identified also directly from positive blood cultures and in the presence of other co-infecting micro-organisms. Of the 82 isolates grown on plates, 64 (76%) were correctly identified by the Vitek II system and 82 (100%) by MALDI-TOF MS; when the two methods gave different results, the isolate was identified by PCR. MALDI-TOF MS was unreliable in identifying two isolates (Candida glabrata and Candida parapsilosis) directly from blood culture; however, direct analysis from positive blood culture samples was fast and effective for the identification of yeast, which is of great importance for early and adequate treatment.

Many pathogens involved in human infection have rapidly increased their antibiotic resistance, reducing the effectiveness of therapies in recent decades. Most of them can form biofilms and effective drugs are not available to treat these formations. Natural products could represent an efficient solution in discovering and developing new drugs to overcome antimicrobial resistance and treat biofilm-related infections. In this study, 20 secondary metabolites produced by pathogenic fungi of forest plants and belonging to diverse classes of naturally occurring compounds were evaluated for the first time against clinical isolates of antibiotic-resistant Gram-negative and Gram-positive bacteria. epi-Epoformin, sphaeropsidone, and sphaeropsidin A showed antimicrobial activity on all test strains. In particular, sphaeropsidin A was effective at low concentrations with Minimum Inhibitory Concentration (MIC) values ranging from 6.25 μg/mL to 12.5 μg/mL against all reference and clinical test strains. Furthermore, sphaeropsidin A at sub-inhibitory concentrations decreased methicillin-resistant S. aureus (MRSA) and P. aeruginosa biofilm formation, as quantified by crystal violet staining. Interestingly, mixtures of sphaeropsidin A and epi-epoformin have shown antimicrobial synergistic effects with a concomitant reduction of cytotoxicity against human immortalized keratinocytes. Our data show that sphaeropsidin A and epi-epoformin possess promising antimicrobial properties.

Nowadays, silver nanoparticles are in the limelight to control infection during wound healing process, and a vast variety of antimicrobial dressings based on colloidal silver have been marketed to fight wound invasion of pathogen bacteria, which represents one of the main adverse effects limiting the repair process. Here we propose a biofunctional hydrogel based on alginate (ALG) and hyaluronic acid (HA) embedding ultrasmall silver nanoparticles (usSN, <1 nm) as antimicrobial component. The hydrogels were fabricated in different size by a straightforward internal gelation method using CaCO₃ and glucono-δ-lactone. To follow usSN release from the hydrogels in aqueous media, catalytic activity of usSN-loaded hydrogels was evaluated. Results suggested that catalytic activity was low in intact hydrogels and high when hydrogels dissolved, which suggests that usSN firmly interact with polymer chains and are available in the medium depending on the extent of hydrogel degradation. HA-containing hydrogels showed faster dissolution in simulated physiological conditions and higher antibiofouling properties as compared to hydrogels made only of ALG. Free usSN were not toxic toward human mesenchymal stem cells (Ad-MSCs), previously isolated from subcutaneous adipose tissue biopsies, up to 50 µg/mL. At this concentration, viability of Ad-MSCs was unaffected whereas their motility was significantly higher as compared to control (p<0.01) for both free usSN and hydrogel integrating. Antimicrobial activity on clinical isolates of both Gram-positive and Gram-negative bacteria demonstrated that usSN at 50 µg/mL were able to kill all the bacteria tested after 24 and 48 h of contact time. In the case of hydrogels, a matrix effect was found and bacterial killing was significant only at 24 h and dependent on bacterial strain, being Gram-negative bacteria more susceptible. These results clearly indicate that usSN interaction with polymer network and exposure time can strongly affect usSN antimicrobial profile in the hydrogel and, in turn, timing of hydrogel change at injured site in a clinical setting. On the whole, ALG/HA hydrogels integrating usSN can be considered a suitable option to fabricate biofunctional dressings for hospitalized patients and worth of further in vivo investigation. GRAPHICAL ABSTRACT