Coexistence of Pseudomonas aeruginosa With Candida albicans Enhances Biofilm Thickness Through Alginate-Related Extracellular Matrix but Is Attenuated by N-acetyl-l-cysteine

A growing battlefield in the war against biofilm-induced antimicrobial resistance: insights from reviews on antibiotic resistance

Biofilms are a common survival strategy employed by bacteria in healthcare settings, which enhances their resistance to antimicrobial and biocidal agents making infections difficult to treat. Mechanisms of biofilm-induced antimicrobial resistance involve reduced penetration of antimicrobial agents, increased expression of efflux pumps, altered microbial physiology, and genetic changes in the bacterial population. Factors contributing to the formation of biofilms include nutrient availability, temperature, pH, surface properties, and microbial interactions. Biofilm-associated infections can have serious consequences for patient outcomes, and standard antimicrobial therapies are often ineffective against biofilm-associated bacteria, making diagnosis and treatment challenging. Novel strategies, including antibiotics combination therapies (such as daptomycin and vancomycin, colistin and azithromycin), biofilm-targeted agents (such as small molecules (LP3134, LP3145, LP4010, LP1062) target c-di-GMP), and immunomodulatory therapies (such as the anti-PcrV IgY antibodies which target Type IIIsecretion system), are being developed to combat biofilm-induced antimicrobial resistance. A multifaceted approach to diagnosis, treatment, and prevention is necessary to address this emerging problem in healthcare settings.

Therapeutic Approach Targeting Gut Microbiome in Gastrointestinal Infectious Diseases

While emerging evidence highlights the significance of gut microbiome in gastrointestinal infectious diseases, treatments like Fecal Microbiota Transplantation (FMT) and probiotics are gaining popularity, especially for diarrhea patients. However, the specific role of the gut microbiome in different gastrointestinal infectious diseases remains uncertain. There is no consensus on whether gut modulation therapy is universally effective for all such infections. In this comprehensive review, we examine recent developments of the gut microbiome's involvement in several gastrointestinal infectious diseases, including infection of Helicobacter pylori, Clostridium difficile, Vibrio cholerae, enteric viruses, Salmonella enterica serovar Typhimurium, Pseudomonas aeruginosa Staphylococcus aureus, Candida albicans, and Giardia duodenalis. We have also incorporated information about fungi and engineered bacteria in gastrointestinal infectious diseases, aiming for a more comprehensive overview of the role of the gut microbiome. This review will provide insights into the pathogenic mechanisms of the gut microbiome while exploring the microbiome's potential in the prevention, diagnosis, prediction, and treatment of gastrointestinal infections.

Interkingdom interactions between Pseudomonas aeruginosa and Candida albicans affect clinical outcomes and antimicrobial responses

Infections that involve interkingdom microbial communities, such as those between bacteria and yeast pathogens, are difficult to treat, associated with worse patient outcomes, and may be a source of antimicrobial resistance. In this review, we address co-occurrence and co-infections of Candida albicans and Pseudomonas aeruginosa, two pathogens that occupy multiple infection niches in the human body, especially in immunocompromised patients. The interaction between the pathogen species influences microbe-host interactions, the effectiveness of antimicrobials and even infection outcomes, and may thus require adapted treatment strategies. However, the molecular details of bacteria-fungal interactions both inside and outside the infection sites, are insufficiently characterised. We argue that comprehensively understanding the P. aeruginosa-C. albicans interaction network through integrated systems biology approaches will capture the highly dynamic and complex nature of these polymicrobial infections and lead to a more comprehensive understanding of clinical observations such as reshaped immune defences and low antimicrobial treatment efficacy.

Ca-EDTA restores the activity of ceftazidime-avibactam or aztreonam against carbapenemase-producing Klebsiellapneumoniae infections

Developing an effective therapy to overcome carbapenemase-positive Klebsiella pneumoniae (CPKp) is an important therapeutic challenge that must be addressed urgently. Here, we explored a Ca-EDTA combination with aztreonam or ceftazidime-avibactam in vitro and in vivo against diverse CPKp clinical isolates. The synergy testing of this study demonstrated that novel aztreonam-Ca-EDTA or ceftazidime-avibactam-Ca-EDTA combination was significantly effective in eliminating planktonic and mature biofilms in vitro, as well as eradicating CPKp infections in vivo. Both combinations revealed significant therapeutic efficacies in reducing bacterial load in internal organs and protecting treated mice from mortality. Conclusively, this is the first in vitro and in vivo study to demonstrate that novel aztreonam-Ca-EDTA or ceftazidime-avibactam-Ca-EDTA combinations provide favorable efficacy and safety for successful eradication of carbapenemase-producing Klebsiella pneumoniae planktonic and biofilm infections.

Gum Arabic polysaccharide embedded L-cysteine capped copper oxide nanocarriers selectively inhibit fluconazole-resistant C. albicans biofilm and remove the toxic dye from wastewater

Copper oxide nanocarriers have attracted increasing interest in the scientific community, including antimicrobial applications. Candida biofilm developed causes serious clinical problems, leading to drug failure caused by its inherent drug tolerance. Nanocarriers are a good alternative approach to solving this challenge because of their excellent penetration power inside biofilms. Hence, main objectives of this research were to prepare gum arabic-embedded L-cysteine-capped copper oxide nanocarriers (GCCuO NCs) and tested against C. albicans and explore another application. To achieve the main research objectives, GCCuO NCs were synthesized and investigated for antibiofilm potency against C. albicans. Various methods were employed to measure antibiofilm potency such as biofilm assay etc., of NCs. The nano size of GCCuO NCs is advantageous for augmenting penetration power and retention into biofilms. GCCuO NCs at 100 μg/mL exhibited significant antibiofilm activity against the C. albicans DAY185 by switching of yeast-to-hyphae and gene perturbation. The level of CR dye adsorption was 58.96 % using 30 μg/mL of NCs. Based on effective C. albicans biofilm inhibition and CR dye adsorption capacity of NCs, it can be suggested that present research work opens an innovative path to treat biofilm-associated fungal infections, and these NCs can be used for environmental remedies.

Genetic and environmental determinants of surface adaptations in Pseudomonas aeruginosa

Pseudomonas aeruginosa is a well-studied Gram-negative opportunistic bacterium that thrives in markedly varied environments. It is a nutritionally versatile microbe that can colonize a host as well as exist in the environment. Unicellular, planktonic cells of P. aeruginosa can come together to perform a coordinated swarming movement or turn into a sessile, surface-adhered population called biofilm. These collective behaviours produce strikingly different outcomes. While swarming motility rapidly disseminates the bacterial population, biofilm collectively protects the population from environmental stresses such as heat, drought, toxic chemicals, grazing by predators, and attack by host immune cells and antibiotics. The ubiquitous nature of P. aeruginosa is likely to be supported by the timely transition between planktonic, swarming and biofilm lifestyles. The social behaviours of this bacteria viz biofilm and swarm modes are controlled by signals from quorum-sensing networks, LasI-LasR, RhlI-RhlR and PQS-MvfR, and several other sensory kinases and response regulators. A combination of environmental and genetic cues regulates the transition of the P. aeruginosa population to specific states. The current review is aimed at discussing key factors that promote physiologically distinct transitioning of the P. aeruginosa population.

The leaky gut and the gut microbiome in sepsis - targets in research and treatment

Both a leaky gut (a barrier defect of the intestinal surface) and gut dysbiosis (a change in the intestinal microbial population) are intrinsic to sepsis. While sepsis itself can cause dysbiosis, dysbiosis can worsen sepsis. The leaky gut syndrome refers to a status with which there is an increased intestinal permeability allowing the translocation of microbial molecules from the gut into the blood circulation. It is not just a symptom of gastrointestinal involvement, but also an underlying cause that develops independently, and its presence could be recognized by the detection, in blood, of lipopolysaccharides and (1→3)-β-D-glucan (major components of gut microbiota). Gut-dysbiosis is the consequence of a reduction in some bacterial species in the gut microbiome, as a consequence of intestinal mucosal immunity defect, caused by intestinal hypoperfusion, immune cell apoptosis, and a variety of enteric neuro-humoral-immunity responses. A reduction in bacteria that produce short-chain fatty acids could change the intestinal barriers, leading to the translocation of pathogen molecules, into the circulation where it causes systemic inflammation. Even gut fungi might be increased in human patients with sepsis, even though this has not been consistently observed in murine models of sepsis, probably because of the longer duration of sepsis and also antibiotic use in patients. The gut virobiome that partly consists of bacteriophages is also detectable in gut contents that might be different between sepsis and normal hosts. These alterations of gut dysbiosis altogether could be an interesting target for sepsis adjuvant therapies, e.g., by faecal transplantation or probiotic therapy. Here, current information on leaky gut and gut dysbiosis along with the potential biomarkers, new treatment strategies, and future research topics are mentioned.

Rapid Synergistic Biofilm Production of Pseudomonas and Candida on the Pulmonary Cell Surface and in Mice, a Possible Cause of Chronic Mixed Organismal Lung Lesions

Due to the possible co-presence of Pseudomonas aeruginosa and Candida albicans (the most common nosocomial pathogens) in lungs, rapid interkingdom biofilm production is possible. As such, PA+CA produced more dominant biofilms on the pulmonary epithelial surface (NCI-H292) (confocal fluorescent extracellular matrix staining) with dominant psl upregulation, as demonstrated by polymerase chain reaction (PCR), after 8 h of experiments than PA alone. With a proteomic analysis, rhamnosyltransferase RhlB protein (Psl-associated quorum-sensing protein) was found to be among the high-abundance proteins in PA+CA than in PA biofilms, supporting psl-mediated biofilms in PA+CA on the cell surface. Additionally, PA+CA increased supernatant cytokines (IL-8 and IL-13, but not TNF-α, IL-6, and IL-10) with a similar upregulation of TLR-4, TLR-5, and TLR-9 (by PCR) compared with PA-stimulated cells. The intratracheal administration of PA+CA induced a greater severity of sepsis (serum creatinine, alanine transaminase, serum cytokines, and histology score) and prominent biofilms (fluorescent staining) with psl upregulation (PCR). In comparison with PA+CA biofilms on glass slides, PA+CA biofilms on biotic surfaces were more prominent (fluorescent staining). In conclusion, PA+CA induced Psl-predominant biofilms on the pulmonary cell surface and in mice with acute pneumonia, and these biofilms were more prominent than those induced by PA alone, highlighting the impact of Candida on rapid interkingdom biofilm production.

Helicobacter pylori, Protected from Antibiotics and Stresses Inside Candida albicans Vacuoles, Cause Gastritis in Mice

Due to (i) the simultaneous presence of Helicobacter pylori (ulcer-induced bacteria) and Candida albicans in the stomach and (ii) the possibility of prokaryotic–eukaryotic endosymbiosis (intravacuolar H. pylori in the yeast cells) under stresses, we tested this symbiosis in vitro and in vivo. To that end, intravacuolar H. pylori were induced by the co-incubation of C. albicans with H. pylori under several stresses (acidic pH, non-H. pylori-enrichment media, and aerobic environments); the results were detectable by direct microscopy (wet mount) and real-time polymerase chain reaction (PCR). Indeed, intravacuolar H. pylori were predominant under all stresses, especially the lower pH level (pH 2–3). Interestingly, the H. pylori (an amoxicillin-sensitive strain) inside C. albicans were protected from the antibiotic (amoxicillin), while extracellular H. pylori were neutralizable, as indicated by the culture. In parallel, the oral administration of intravacuolar H. pylori in mice caused H. pylori colonization in the stomach resulting in gastritis, as indicated by gastric histopathology and tissue cytokines, similar to the administration of free H. pylori (extra-Candida bacteria). In conclusion, Candida protected H. pylori from stresses and antibiotics, and the intravacuolar H. pylori were able to be released from the yeast cells, causing gastric inflammation with neutrophil accumulations.

High prevalence of mgrB-mediated colistin resistance among carbapenem-resistant Klebsiella pneumoniae is associated with biofilm formation, and can be overcome by colistin-EDTA combination therapy

The global prevalence of colistin-resistant Klebsiella pneumoniae (ColRkp) facilitated by chromosomal and plasmid-mediated Ara4N or PEtN-remodeled LPS alterations has steadily increased with increased colistin usage for treating carbapenem-resistant K. pneumoniae (CRkp). Our study demonstrated the rising trend of ColRkp showing extensively and pandrug-resistant characteristics among CRkp, with a prevalence of 28.5%, which was mediated by chromosomal mgrB, pmrB, or phoQ mutations (91.5%), and plasmid-mediated mcr-1.1, mcr-8.1, mcr-8.2 alone or in conjunction with R256G PmrB (8.5%). Several genetic alterations in mgrB (85.1%) with increased expressions of Ara4N-related phoPQ and pmrK were critical for establishing colistin resistance in our isolates. In this study, we discovered the significant associations between extensively drug-resistant bacteria (XDR) and pandrug-resistant bacteria (PDR) ColRkp in terms of moderate, weak or no biofilm-producing abilities, and altered expressions of virulence factors. These ColRkp would therefore be very challenging to treat, emphasizing for innovative therapy to combat these infections. Regardless of the underlying colistin-resistant mechanisms, colistin-EDTA combination therapy in this study produced potent synergistic effects in both in vitro and in vivo murine bacteremia, with no ColRkp regrowth and improved animal survival, implying the significance of colistin-EDTA combination therapy as systemic therapy for unlocking colistin resistance in ColRkp-associated bacteremia.

Chlorhexidine Promotes Psl Expression in Pseudomonas aeruginosa That Enhances Cell Aggregation with Preserved Pathogenicity Demonstrates an Adaptation against Antiseptic

Because Pseudomonas aeruginosa is frequently in contact with Chlorhexidine (a regular antiseptic), bacterial adaptations are possible. In comparison with the parent strain, the Chlorhexidine-adapted strain formed smaller colonies with metabolic downregulation (proteomic analysis) with the cross-resistance against colistin (an antibiotic for several antibiotic-resistant bacteria), partly through the modification of L-Ara4N in the lipopolysaccharide at the outer membrane. Chlorhexidine-adapted strain formed dense liquid–solid interface biofilms with enhanced cell aggregation partly due to the Chlorhexidine-induced overexpression of psl (exopolysaccharide-encoded gene) through the LadS/GacSA pathway (c-di-GMP-independence) in 12 h biofilms and maintained the aggregation with SiaD-mediated c-di-GMP dependence in 24 h biofilms as evaluated by polymerase chain reaction (PCR). The addition of Ca²⁺ in the Chlorhexidine-adapted strain facilitated several Psl-associated genes, indicating an impact of Ca²⁺ in Psl production. The activation by Chlorhexidine-treated sessile bacteria demonstrated a lower expression of IL-6 and IL-8 on fibroblasts and macrophages than the activation by the parent strain, indicating the less inflammatory reactions from Chlorhexidine-exposed bacteria. However, the 14-day severity of the wounds in mouse caused by Chlorhexidine-treated bacteria versus the parent strain was similar, as indicated by wound diameters and bacterial burdens. In conclusion, Chlorhexidine induced psl over-expression and colistin cross-resistance that might be clinically important.

Overcoming addition of phosphoethanolamine to lipid A mediated colistin resistance in Acinetobacter baumannii clinical isolates with colistin–sulbactam combination therapy

Overcoming colistin-resistant Acinetobacter baumannii (CoR-AB) has become a major concern due to the lack of effective antibiotics. This study aimed to explore the prevalence of CoR-AB clinical isolates in Thailand, their mechanisms of resistance, and test the efficacy of colistin plus sulbactam against CoR-AB isolates. The colistin resistance rate among carbapenem-resistant A. baumannii was 15.14%. The mcr gene or its variants were not detected in CoR-AB isolates by PCR screening. The lipid A mass spectra of CoR-AB isolates showed the additional [M–H]⁻ ion peak at m/z = 2034 that correlated to the phosphoethanolamine (pEtN) addition to lipid A (N = 27/30). The important amino acid substitutions were found at position S14P, A138T, A227V in PmrB that are associated with overexpression of the pEtN transferase (PmrC) and contributed the pEtN addition. The lipopolysacccharide production genes (lpxACD) were not related to lipid A mass spectra. A colistin plus sulbactam combination exhibited the synergy rate at 86.7% against CoR-AB isolates compare to sulbactam (85.89% resistance) or colistin (15.14% resistance) alone. The excellent synergistic activity of colistin plus sulbactam combination has the potential for the treatment of CoR-AB infections.

Mycobacterium tuberculosis and Paracoccidioides brasiliensis Formation and Treatment of Mixed Biofilm In Vitro

Co-infection of Mycobacterium tuberculosis and Paracoccidioides brasiliensis, present in 20% in Latin America, is a public health problem due to a lack of adequate diagnosis. These microorganisms are capable of forming biofilms, mainly in immunocompromised patients, which can lead to death due to the lack of effective treatment for both diseases. The present research aims to show for the first time the formation of mixed biofilms of M. tuberculosis and P. brasiliensis (Pb18) in vitro, as well as to evaluate the action of 3’hydroxychalcone (3’chalc) -loaded nanoemulsion (NE) (NE3’chalc) against monospecies and mixed biofilms, the formation of mixed biofilms of M. tuberculosis H37Rv (ATCC 27294), 40Rv (clinical strains) and P. brasiliensis (Pb18) (ATCC 32069), and the first condition of formation (H37Rv +Pb18) and (40Rv + Pb18) and second condition of formation (Pb18 + H37Rv) with 45 days of total formation time under both conditions. The results of mixed biofilms (H37Rv + Pb18) and (40Rv + Pb18), showed an organized network of M. tuberculosis bacilli in which P. brasiliensis yeasts are connected with a highly extracellular polysaccharide matrix. The (Pb18 + H37Rv) showed a dense biofilm with an apparent predominance of P. brasiliensis and fragments of M. tuberculosis. PCR assays confirmed the presence of the microorganisms involved in this formation. The characterization of NE and NE3’chalc displayed sizes from 145.00 ± 1.05 and 151.25 ± 0.60, a polydispersity index (PDI) from 0.20± 0.01 to 0.16± 0.01, and zeta potential -58.20 ± 0.92 mV and -56.10 ± 0.71 mV, respectively. The atomic force microscopy (AFM) results showed lamellar structures characteristic of NE. The minimum inhibitory concentration (MIC) values of 3’hidroxychalcone (3’chalc) range from 0.97- 7.8 µg/mL and NE3’chalc from 0.24 - 3.9 µg/mL improved the antibacterial activity when compared with 3’chalc-free, no cytotoxicity. Antibiofilm assays proved the efficacy of 3’chalc-free incorporation in NE. These findings contribute to a greater understanding of the formation of M. tuberculosis and P. brasiliensis in the mixed biofilm. In addition, the findings present a new possible NE3’chalc treatment alternative for the mixed biofilms of these microorganisms, with a high degree of relevance due to the lack of other treatments for these comorbidities.

Presence of Candida tropicalis on Staphylococcus epidermidis Biofilms Facilitated Biofilm Production and Candida Dissemination: An Impact of Fungi on Bacterial Biofilms

While Staphylococcus epidermidis (SE) is a common cause of infections in implanted prostheses and other indwelling devices, partly due to the biofilm formation, Candida tropicalis (CT) is an emerging Candida spp. with a potent biofilm-producing property. Due to the possible coexistence between SE and CT infection in the same patient, characteristics of the polymicrobial biofilms from both organisms might be different from those of the biofilms of each organism. Then, the exploration on biofilms, from SE with or without CT, and an evaluation on l-cysteine (an antibiofilm against both bacteria and fungi) were performed. As such, Candida incubation in preformed SE biofilms (SE > CT) produced higher biofilms than the single- (SE or CT) or mixed-organism (SE + CT) biofilms as determined by crystal violet staining and fluorescent confocal images with z-stack thickness analysis. In parallel, SE > CT biofilms demonstrated higher expression of icaB and icaC than other groups at 20 and 24 h of incubation, suggesting an enhanced matrix polymerization and transportation, respectively. Although organism burdens (culture method) from single-microbial biofilms (SE or CT) were higher than multi-organism biofilms (SE + CT and SE > CT), macrophage cytokine responses (TNF-α and IL-6) against SE > CT biofilms were higher than those in other groups in parallel to the profound biofilms in SE > CT. Additionally, sepsis severity in mice with subcutaneously implanted SE > CT catheters was more severe than in other groups as indicated by mortality rate, fungemia, serum cytokines (TNF-α and IL-6), and kidney and liver injury. Although CT grows upon preformed SE-biofilm production, the biofilm structures interfered during CT morphogenesis leading to the frailty of biofilm structure and resulting in the prominent candidemia. However, l-cysteine incubation together with the organisms in catheters reduced biofilms, microbial burdens, macrophage responses, and sepsis severity. In conclusion, SE > CT biofilms prominently induced biofilm matrix, fungemia, macrophage responses, and sepsis severity, whereas the microbial burdens were lower than in the single-organism biofilms. All biofilms were attenuated by l-cysteine.

Polymicrobial Interactions in the Cystic Fibrosis Airway Microbiome Impact the Antimicrobial Susceptibility of Pseudomonas aeruginosa

Pseudomonas aeruginosa is one of the most dominant pathogens in cystic fibrosis (CF) airway disease and contributes to significant inflammation, airway damage, and poorer disease outcomes. The CF airway is now known to be host to a complex community of microorganisms, and polymicrobial interactions have been shown to play an important role in shaping P. aeruginosa pathogenicity and resistance. P. aeruginosa can cause chronic infections that once established are almost impossible to eradicate with antibiotics. CF patients that develop chronic P. aeruginosa infection have poorer lung function, higher morbidity, and a reduced life expectancy. P. aeruginosa adapts to the CF airway and quickly develops resistance to several antibiotics. A perplexing phenomenon is the disparity between in vitro antimicrobial sensitivity testing and clinical response. Considering the CF airway is host to a diverse community of microorganisms or 'microbiome' and that these microorganisms are known to interact, the antimicrobial resistance and progression of P. aeruginosa infection is likely influenced by these microbial relationships. This review combines the literature to date on interactions between P. aeruginosa and other airway microorganisms and the influence of these interactions on P. aeruginosa tolerance to antimicrobials.

Biofilm-Forming Potential of Ocular Fluid Staphylococcus aureus and Staphylococcus epidermidis on Ex Vivo Human Corneas from Attachment to Dispersal Phase

The biofilm-forming potential of Staphylococcus aureus and Staphylococcus epidermidis, isolated from patients with Endophthalmitis, was monitored using glass cover slips and cadaveric corneas as substrata. Both the ocular fluid isolates exhibited biofilm-forming potential by the Congo red agar, Crystal violet and 2,3-bis (2-methoxy-4-nitro-5-sulfophenyl)-5-(phenylamino) carbonyl-2H-tetra-zolium hydroxide (XTT) methods. Confocal microscopy demonstrated that the thickness of the biofilm increased from 4–120 h of biofilm formation. Scanning electron microscopic studies indicated that the biofilms grown on cover slips and ex vivo corneas of both the isolates go through an adhesion phase at 4 h followed by multilayer clumping of cells with intercellular connections and copious amounts of extracellular polymeric substance. Clumps subsequently formed columns and eventually single cells were visible indicative of dispersal phase. Biofilm formation was more rapid when the cornea was used as a substratum. In the biofilms grown on corneas, clumping of cells, formation of 3D structures and final appearance of single cells indicative of dispersal phase occurred by 48 h compared to 96–120 h when biofilms were grown on cover slips. In the biofilm phase, both were several-fold more resistant to antibiotics compared to planktonic cells. This is the first study on biofilm forming potential of ocular fluid S. aureus and S. epidermidis on cadaveric cornea, from attachment to dispersal phase of biofilm formation.

Microbial Interkingdom Biofilms and the Quest for Novel Therapeutic Strategies

Fungal and bacterial species interact with each other within polymicrobial biofilm communities in various niches of the human body. Interactions between these species can greatly affect human health and disease. Diseases caused by polymicrobial biofilms pose a major challenge in clinical settings because of their enhanced virulence and increased drug tolerance. Therefore, different approaches are being explored to treat fungal-bacterial biofilm infections. This review focuses on the main mechanisms involved in polymicrobial drug tolerance and the implications of the polymicrobial nature for the therapeutic treatment by highlighting clinically relevant fungal-bacterial interactions. Furthermore, innovative treatment strategies which specifically target polymicrobial biofilms are discussed.