Bacterial-fungal Biofilms Research Articles

Synergistic effects of quorum-sensing molecules and antimicrobials against Candida albicans and Pseudomonas aeruginosa biofilms: in vitro and in vivo studies.

Candida albicans can form polymicrobial biofilms with other microorganisms, such as Pseudomonas aeruginosa, at infection sites. As biofilms are highly resistant to antibiotics there is a need for new antibiofilm agents that have unique targets and modes of action. In this study the antibiofilm effects of two quorum-sensing molecules (QSMs), farnesol and tyrosol, were investigated alone and in combination with antibiotics (aztreonam, colistin, tobramycin) and antifungals (fluconazole, amphotericin B, caspofungin), against single- and dual-species biofilms of C. albicans and P. aeruginosa in in vitro and in vivo systems. It was observed that QSMs alone, especially farnesol, showed at least a 1-log reduction against preformed single- and dual-species biofilms of C. albicans and P. aeruginosa. Combination of QSMs with colistin or fluconazole was found to be effective against both single- and dual-species biofilms in vitro. Increased survival was observed in C. elegans when treated with colistin or fluconazole in combination with QSMs, compared with no treatment. Additionally, the QSMs and colistin and farnesol combinations effectively inhibited biofilm formation by C. albicans and P. aeruginosa on bronchial epithelial cells, and reduced IL-1β expression in lung bronchial epithelial cells. There is a need for effective treatments for bacterial-fungal biofilm infections and, to our knowledge, there have been no studies of QSMs and antimicrobial combinations against dual-species biofilms involving C. albicans and P. aeruginosa. Hence these findings will make a significant contribution to the literature.

Potential of Bouea macrophylla kernel extract as an intracanal medicament against mixed-species bacterial-fungal biofilm. An in vitro and ex vivo study

ObjectiveTo investigate the antimicrobial activity of B. macrophylla kernel extract against mixed-species biofilms of E. faecalis, S. gordonii and C. albicans in vitro. To evaluate the efficacy of the extract as an intracanal medicament compared with Ca(OH)2 and chlorhexidine in ex vivo tooth model. MethodsThe antibiofilm effect of B. macrophylla kernel extract was determined by AlamarBlue™ assay and the effect on biofilms was visualized by LIVE/DEAD® BacLight™ viability test. Mixed-species biofilms were incubated into the tooth model (N = 42) for 21 days. The teeth were randomly divided into 4 medicament groups for 7 days: (i) normal saline, (ii) calcium hydroxide (Ca(OH)2), (iii) chlorhexidine gel, (iv) B. macrophylla kernel extract. Dentine samples were collected, qPCR with PMA was used to quantify the viability and species composition of each sample. SEM was used to visualize the effect of medicament on biofilm structure. ResultsThe MBIC was 6.25 mg/mL and the MBEC was 50 mg/mL. The integrity of microbial cells was progressively compromised as concentration increased, resulting in greater cell death. Ex vivo tooth model revealed that biofilm treated with 50 mg/mL of the B. macrophylla extract demonstrated a significantly higher proportions of dead cells than in Ca(OH)2, chlorhexidine and normal saline groups (p < 0.01). Disruption of biofilm structure and enlargement of dentinal tubules was observed in B. macrophylla group on SEM. ConclusionThe extract of B. macrophylla kernel exhibited significant antibiofilm effect against the mixed-species biofilms of E. faecalis, S. gordonii and C. albicans.

Farnesol delivery via polymeric nanoparticle carriers inhibits cariogenic cross-kingdom biofilms and prevents enamel demineralization.

Streptococcus mutans and Candida albicans are frequently detected together in the plaque from patients with early childhood caries (ECC) and synergistically interact to form a cariogenic cross-kingdom biofilm. However, this biofilm is difficult to control. Thus, to achieve maximal efficacy within the complex biofilm microenvironment, nanoparticle carriers have shown increased interest in treating oral biofilms in recent years. Here, we assessed the anti-biofilm efficacy of farnesol (Far), a hydrophobic antibacterial drug and repressor of Candida filamentous forms, against cross-kingdom biofilms employing drug delivery via polymeric nanoparticle carriers (NPCs). We also evaluated the effect of the strategy on teeth enamel demineralization. The farnesol-loaded NPCs (NPC+Far) resulted in a 2-log CFU/mL reduction of S. mutans and C. albicans (hydroxyapatite disc biofilm model). High-resolution confocal images further confirmed a significant reduction in exopolysaccharides, smaller microcolonies of S. mutans, and no hyphal form of C. albicans after treatment with NPC+Far on human tooth enamel (HT) slabs, altering the biofilm 3D structure. Furthermore, NPC+Far treatment was highly effective in preventing enamel demineralization on HT, reducing lesion depth (79% reduction) and mineral loss (85% reduction) versus vehicle PBS-treated HT, while NPC or Far alone had no differences with the PBS. The drug delivery via polymeric NPCs has the potential for targeting bacterial-fungal biofilms associated with a prevalent and costly pediatric oral disease, such as ECC.

Efficacy of alpha-mangostin for antimicrobial activity against endodontopathogenic microorganisms in a multi-species bacterial-fungal biofilm model

ObjectiveTo determine the activity of alpha-mangostin on preformed bacterial-fungal multi-species biofilms in vitro, and to ascertain the impact on metabolic activity, biofilm structure and viability. DesignInhibitory concentrations (ICs) for alpha-mangostin against planktonic cultures of Candida albicans, Enterococcus faecalis, Lactobacillus rhamnosus, and Streptococcus gordonii were determined using a standard broth microdilution method. Single and multi-species (all species 1:1:1:1) biofilms were grown on polystyrene coverslips in Roswell Park Memorial Institute Medium for 48 h. The biofilms were then exposed to 0.2% (w/v) alpha-mangostin for 24 h. These concentrations were selected based on pilot experiments and the solubility of these compounds. 2% (v/v) chlorhexidine was used as a positive control and Roswell Park Memorial Institute Medium as a negative control. The metabolic activity of the biofilms after exposure was measured using metabolic (XTT) assays. Biofilms were visualised and quantified using fluorescent BacLight™ LIVE/DEAD staining. The biofilms were assessed for cell viability by culture and colony counting (CFU/mL). Results8 mg/L of alpha-mangostin was cidal against planktonic bacteria and 1000 mg/L for Candida. Alpha-mangostin was most active against L. rhamonosus biofilms and least active against C. albicans biofilm (metabolism inhibited by 99% and 78%, respectively). Alpha-mangostin exposure reduced the number of viable cells in the biofilms. ConclusionAlpha-mangostin inhibited the metabolic activity of bacterial-fungal biofilms effectively. The anti-biofilm activity of alpha-mangostin was comparable to chlorhexidine and thus has potential as a novel agent for endodontic therapy.

Effectiveness of D,L-2-hydroxyisocaproic acid (HICA) and alpha-mangostin against endodontopathogenic microorganisms in a multispecies bacterial-fungal biofilm in an ex vivo tooth model.

To develop a defined multispecies root canal biofilm model ex vivo, and to perform viable compositional analysis following D,L-2-hydroxyisocaproic acid (HICA), alpha-mangostin, Calcicur® , and Odontopaste® exposure. Time-kill assays were conducted in vitro using HICA, alpha-mangostin, Calcicur® , Odontopaste® , and saline solution on the planktonic cultures of C.albicans, E.faecalis, L.rhamnosus, and S.gordonii. Human root dentine blocks were prepared (n=100) ex vivo, and multispecies suspensions containing each of 1.5×108 CFU/mL C.albicans, E.faecalis, L.rhamnosus, and S.gordonii in brain heart infusion (BHI) were incubated within the root canals for 21days. Canals (n=20/group) were then exposed to medicaments for 7days. Samples taken from the inner (first 0.1mm) and deeper (second 0.1mm) dentine by drilling with Ash Steel Burs No. 5 and No. 6, and residual roots were cultured in broth for 24h. Cell growth was detected by spectrophotometry and confirmed by culture on agar. The other set of inner dentine, deeper dentine, and residual root samples were sonicated, and then exposed with 50μM PMA before DNA was extracted using the QIAamp DNA mini kit. Real-time quantitative PCR was performed to determine the biofilm composition as well as the number of live and total cells remaining in the biofilm following each treatment. The OD data were analysed with Kruskal-Wallis and Friedman with Wilcoxon signed-rank test between and within groups, respectively, agar culture and qPCR data with Pearson chi-square with Mann-Whitney and Cochran with McNemar tests, respectively (p<.0001). Time-kill assays revealed that HICA and Calcicur® killed all planktonic organisms within 24h, whilst alpha-mangostin killed the organisms within 72h. However, Odontopaste® was a slow-killing agent: 10 cells of planktonic organisms survived after exposure to the agent for 7days. The ex vivo tooth model demonstrated that HICA and alpha-mangostin significantly inhibited the cell growth in all sampling depths (p<.0001). All species-specific data revealed the effectiveness of each medicament on the biofilm composition. D,L-2-hydroxyisocaproic acid and alpha-mangostin had antimicrobial activity against multispecies bacterial-fungal biofilms.

Biodegradation of acetaminophen and its main by-product 4-aminophenol by Trichoderma harzianum versus mixed biofilm of Trichoderma harzianum/Pseudomonas fluorescens in a fungal microbial fuel cell

Our research aimed to explore the bioremediation of acetaminophen (APAP) and 4-aminophenol (PAP), as well as energy production in a dual-chamber fungal microbial fuel cell (FMFC) device. The pure culture of fungus Trichoderma harzianum and mixed culture of bacteria and fungi (Trichoderma harzianum and Pseudomonas fluorescens) were used as bioanodes. The microorganisms were compared for the first time to examine the removal efficiency of the APAP and its main by-product (PAP). The authors have applied an electrochemical approach to follow the APAP and PAP behavior in the systems. It is interesting to mention that the mixed biofilm culture was able to completely remove the APAP and PAP at around 7 h. These experiments revealed that the biodegradation rate was enhanced in bacterial-fungal biofilms about 5 times higher than in the pure culture of fungus Trichoderma harzianum. The formation of PAP was also observed during the mixed biofilm biodegradation of APAP, which was the result of bacterial degradation. The half-life of APAP biodegradation was 7 h and 1.3 h for pure and mixed biofilm cultures, respectively. Similarly, the higher removal efficiency of PAP was also obtained for the mixed culture biofilms. The PAP biodegradation kinetic constants of 0.116 h−1 and 0.066 h−1 were observed for mixed culture and fungal biofilms, respectively. In terms of MFC performance, a power density of 1.7 mW m−2 was obtained for the FMFC system working with mixed biofilm which is at least 10 times higher than that of pure fungal biofilm (0.13 mW m−2). This work led to the conclusion that a combination of bacterial-fungal biofilm Trichoderma harzianum and Pseudomonas fluorescens could be made use of to remove APAP and PAP with simultaneous electricity production.

Microbial Diversity and Putative Opportunistic Pathogens in Dishwasher Biofilm Communities.

ABSTRACTExtreme habitats are not only limited to natural environments, but also exist in manmade systems, for instance, household appliances such as dishwashers. Limiting factors, such as high temperatures, high and low pHs, high NaCl concentrations, presence of detergents, and shear force from water during washing cycles, define microbial survival in this extreme system. Fungal and bacterial diversity in biofilms isolated from rubber seals of 24 different household dishwashers was investigated using next-generation sequencing. Bacterial genera such as Pseudomonas, Escherichia, and Acinetobacter, known to include opportunistic pathogens, were represented in most samples. The most frequently encountered fungal genera in these samples belonged to Candida, Cryptococcus, and Rhodotorula, also known to include opportunistic pathogenic representatives. This study showed how specific conditions of the dishwashers impact the abundance of microbial groups and investigated the interkingdom and intrakingdom interactions that shape these biofilms. The age, usage frequency, and hardness of incoming tap water of dishwashers had significant impact on bacterial and fungal community compositions. Representatives of Candida spp. were found at the highest prevalence (100%) in all dishwashers and are assumed to be one of the first colonizers in recently purchased dishwashers. Pairwise correlations in tested microbiomes showed that certain bacterial groups cooccur, as did the fungal groups. In mixed bacterial-fungal biofilms, early adhesion, contact, and interactions were vital in the process of biofilm formation, where mixed complexes of bacteria and fungi could provide a preliminary biogenic structure for the establishment of these biofilms.IMPORTANCE Worldwide demand for household appliances, such as dishwashers and washing machines, is increasing, as is the number of immunocompromised individuals. The harsh conditions in household dishwashers should prevent the growth of most microorganisms. However, our research shows that persisting polyextremotolerant groups of microorganisms in household appliances are well established under these unfavorable conditions and supported by the biofilm mode of growth. The significance of our research is in identifying the microbial composition of biofilms formed on dishwasher rubber seals, how diverse abiotic conditions affect microbiota, and which key microbial members were represented in early colonization and contamination of dishwashers, as these appliances can present a source of domestic cross-contamination that leads to broader medical impacts.

Microbiology of removable dentures plaque in patients with chronic obstructive pulmonary disease

Introduction. The role of bacterial infection in the exacerbation of chronic obstructive pulmonary disease (COPD) has been the subject of numerous studies. The plaque of removable dentures in COPD patients is an example of bacterial-fungal biofilm that serves as a reservoir of potential pathogenic microorganisms of the respiratory system. Inadequate and improper cleaning of dentures may become a cause of COPD exacerbations. Aim of the study. To evaluate the impact of the respiratory pathogens in the denture plaque on the condition of the oral mucosa. Material and methods. The clinical status of the oral mucous membrane and the hygienic condition of dentures were assessed in 86 COPD patients and in 30 generally healthy removable denture-wearers. Microbiological and mycological examinations were conducted on the basis of material collected using direct swab from the surface of the denture. Results. Twenty-three species of potentially pathogenic microorganisms were isolated and analysed in the course of tests performed for the purpose of this study. The most frequently isolated strain, in all groups of COPD patients, was Candida albicans (from 47.6 to 60%), while in�the control group it accounted for 36.7% of the cases. In the group of COPD patients, the main isolated strains were: Candida tropicalis, Klebsiella pneumoniae, Enterobacter cloacae and Staphylococcus epidermidis. Stomatopathy complicated by fungal infections was observed both in patients with COPD (from 76% to 90%) and in the control group (53.3%). Conclusions. Denture plaque may be a potential source of bacterial and fungal infections in COPD patients. The elimination of the plaque from dentures can be an effective way of reducing the risk of exacerbations. A higher incidence of prosthetic stomatopathy complicated by fungal infection among COPD patients may be associated with the chronic use of inhaled glucocorticotherapy and home oxygen therapy.

Sequence of inoculation influences the nature of extracellular polymeric substances and biofilm formation in Azotobacter chroococcum and Trichoderma viride.

Extracellular polymeric substances (EPS) are important structural components of biofilms. In the present study, the EPS in biofilms developed using two agriculturally beneficial organisms-Azotobacter chroococcum (Az) and Trichoderma viride (Tv) were quantified and characterised. Time course experiments were undertaken to optimise the EPS yield of biofilm samples resulting from coculture and staggered inoculation. The EPS produced during biofilm formation was found to differ quantitatively and qualitatively in individual cultures (Az alone, Tv alone), and in treatments differing in the sequence of inoculation of bacterium and fungus (Az + Tv coculture, staggered inoculation of Az followed by Tv i.e. Az - Tv, or Tv followed by Az i.e. Tv - Az). Significant enhancement in terms of growth and biofilm formation, as compared to individual inoculation was recorded, with Tv - Az exhibiting higher values of these attributes. The EPS from biofilms showed significantly higher concentrations of protein, acetyl, and uronic acids, while planktonic EPS recorded higher total carbohydrates. Fourier transform infrared spectroscopy analyses illustrated the significant influence on chemical and structural aspects of EPS (planktonic and biofilm). This represents a first report correlating EPS production, cell aggregation and biofilm formation during bacterial-fungal biofilm development, which can have implications in the colonisation of soil and plants.

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

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.

A novel antifungal is active against Candida albicans biofilms and inhibits mutagenic acetaldehyde production in vitro.

The ability of C. albicans to form biofilms is a major virulence factor and a challenge for management. This is evident in biofilm-associated chronic oral-oesophageal candidosis, which has been shown to be potentially carcinogenic in vivo. We have previously shown that most Candida spp. can produce significant levels of mutagenic acetaldehyde (ACH). ACH is also an important mediator of candidal biofilm formation. We have also reported that D,L-2-hydroxyisocaproic acid (HICA) significantly inhibits planktonic growth of C. albicans. The aim of the present study was to investigate the effect of HICA on C. albicans biofilm formation and ACH production in vitro. Inhibition of biofilm formation by HICA, analogous control compounds or caspofungin was measured using XTT to measure biofilm metabolic activity and PicoGreen as a marker of biomass. Biofilms were visualised by scanning electron microscopy (SEM). ACH levels were measured by gas chromatography. Transcriptional changes in the genes involved in ACH metabolism were measured using RT-qPCR. The mean metabolic activity and biomass of all pre-grown (4, 24, 48 h) biofilms were significantly reduced after exposure to HICA (p<0.05) with the largest reductions seen at acidic pH. Caspofungin was mainly active against biofilms pre-grown for 4 h at neutral pH. Mutagenic levels (>40 μM) of ACH were detected in 24 and 48 h biofilms at both pHs. Interestingly, no ACH production was detected from D-glucose in the presence of HICA at acidic pH (p<0.05). Expression of genes responsible for ACH catabolism was up-regulated by HICA but down-regulated by caspofungin. SEM showed aberrant hyphae and collapsed hyphal structures during incubation with HICA at acidic pH. We conclude that HICA has potential as an antifungal agent with ability to inhibit C. albicans cell growth and biofilm formation. HICA also significantly reduces the mutagenic potential of C. albicans biofilms, which may be important when treating bacterial-fungal biofilm infections.

A novel antifungal is active against Candida albicans biofilms and inhibits mutagenic acetaldehyde production in vitro.

The ability of C. albicans to form biofilms is a major virulence factor and a challenge for management. This is evident in biofilm-associated chronic oral-oesophageal candidosis, which has been shown to be potentially carcinogenic in vivo. We have previously shown that most Candida spp. can produce significant levels of mutagenic acetaldehyde (ACH). ACH is also an important mediator of candidal biofilm formation. We have also reported that D,L-2-hydroxyisocaproic acid (HICA) significantly inhibits planktonic growth of C. albicans. The aim of the present study was to investigate the effect of HICA on C. albicans biofilm formation and ACH production in vitro. Inhibition of biofilm formation by HICA, analogous control compounds or caspofungin was measured using XTT to measure biofilm metabolic activity and PicoGreen as a marker of biomass. Biofilms were visualised by scanning electron microscopy (SEM). ACH levels were measured by gas chromatography. Transcriptional changes in the genes involved in ACH metabolism were measured using RT-qPCR. The mean metabolic activity and biomass of all pre-grown (4, 24, 48 h) biofilms were significantly reduced after exposure to HICA (p<0.05) with the largest reductions seen at acidic pH. Caspofungin was mainly active against biofilms pre-grown for 4 h at neutral pH. Mutagenic levels (>40 µM) of ACH were detected in 24 and 48 h biofilms at both pHs. Interestingly, no ACH production was detected from D-glucose in the presence of HICA at acidic pH (p<0.05). Expression of genes responsible for ACH catabolism was up-regulated by HICA but down-regulated by caspofungin. SEM showed aberrant hyphae and collapsed hyphal structures during incubation with HICA at acidic pH. We conclude that HICA has potential as an antifungal agent with ability to inhibit C. albicans cell growth and biofilm formation. HICA also significantly reduces the mutagenic potential of C. albicans biofilms, which may be important when treating bacterial-fungal biofilm infections.

Bacterial-fungal biofilms in flowing water photo-processing tanks

A complex seven species model community, including bacteria and fungi, was selected from organisms isolated from the walls of an industrial flowing water system. Growth rates of the species were determined in single and mixed batch culture growth. The rates were found to be significantly higher in mixed culture for Pseudomonas alcaligenes and Flavobacterium indologenes and higher in single culture for Xanthomonas maltophilia, Rhodotorula glutinis and Fusarium solani, whereas no significant difference was recorded for Alcaligenes denitrificans and Fusarium oxysporum. All species attached to PVC in single and mixed culture to form biofilms. Xanthomonas maltophilia, Alc. denitrificans, Ps. alcaligenes and F. solani biofilm cell densities cm-2 were significantly higher than attachment of the component species in mixed culture. Statistical analyses showed a significant difference in rate of colonization between single and mixed cultures for some species. No significant difference was noted between mixed culture cell densities cm-2 at laminar flows of Reynolds number 2.7 and 5.4.