Biofilms are involved in the recalcitrance of infections due to the presence of persister cells. Although the molecular basis of persistence is still largely unknown, toxin-antitoxin modules (TA) are thought to play a role in this process. In this study, we investigated whether TA modules contribute to persistence toward antibiotics in Burkholderia cenocepacia J2315. Sixteen pairs of genes were identified based on their apparent similarity to TA modules. Overexpression of the putative toxins had various effects on growth, persistence, and biofilm formation. Toxins, whose overexpression resulted in growth inhibition, often increased the number of surviving persisters; in contrast, overexpression of putative toxins showing no effects on growth had no positive influence on the number of surviving persisters. Furthermore, the expression of the TA modules was compared between treated and untreated sessile and planktonic wild-type cultures. For 10 toxin-encoding genes, the expression was higher in untreated sessile cells than in untreated planktonic cells. Nine toxin-encoding genes were upregulated after treatment with tobramycin, but none after treatment with ciprofloxacin. These results indicate that most, but not all TA modules contribute to persistence in B. cenocepacia J2315 and that this contribution depends on the mode of growth and the antibiotic used.

Infections related to fungal biofilms are difficult to treat due to the reduced susceptibility of sessile cells to most antifungal agents. Previous research has shown that 1-10% of sessile Candida cells survive treatment with high doses of miconazole (a fungicidal imidazole). The aim of this study was to identify genes involved in fungal biofilm formation and to unravel the mechanisms of resistance of these biofilms to miconazole. To this end, a screening of a Saccharomyces cerevisiae deletion mutant bank was carried out. Our results revealed that genes involved in peroxisomal transport and the biogenesis of the respiratory chain complex IV play an essential role in biofilm formation. On the other hand, genes involved in transcription and peroxisomal and mitochondrial organization seem to highly influence the susceptibility to miconazole of yeast biofilms. Additionally, our data confirm previous findings on genes involved in biofilm formation and in general stress responses. Our data suggest the involvement of peroxisomes in biofilm formation and miconazole resistance in fungal biofilms.

In young cystic fibrosis (CF) patients, is typically the most prevalent organism, while in adults, is the major pathogen. More recently, it was observed that also plays an important role in exacerbations of respiratory symptoms. These species are often coisolated from CF lungs, yet little is known about whether antibiotic killing of one species is influenced by the presence of others. In the present study, we compared the activities of various antibiotics against, , and when grown in monospecies biofilms with the activity observed in a multispecies biofilm. Our results show that differences in antibiotic activity against species grown in mono- and multispecies biofilms are species and antibiotic dependent. Fewer cells are killed by antibiotics that interfere with cell wall synthesis (amoxicillin plus sulbactam, cefepime, imipenem, meropenem, and vancomycin) in the presence of and , while for ciprofloxacin, levofloxacin, and tobramycin, no difference was observed. In addition, we observed that the cell-free supernatant of, but not that of biofilms, also caused this decrease in killing. Overall, was more affected by antibiotic treatment in a multispecies biofilm, while for , no differences were observed between growth in mono- or multispecies biofilms. The results of the present study suggest that it is important to take the community composition into account when evaluating the effect of antimicrobial treatments against certain species in mixed biofilms.