Innate and induced resistance mechanisms of bacterial biofilms

Competitive behaviors in Serratia marcescens are coordinately regulated by a lifestyle switch frequently inactivated in the clinical environment

Opportunistic bacterial pathogens must compete with other bacteria and switch between host- and environment-adapted states. Type VI secretion systems (T6SSs) occur widely in gram-negative bacteria and can efficiently kill neighboring competitors. We determined the distribution of T6SSs across the genus Serratia and observed that a highly conserved antibacterial T6SS is differentially active between closely related clinical isolates of Serratia marcescens. By combining genomic and experimental approaches, we identified a genus-core two-component system, BetR-Reg1-Reg2, that controls T6SS activity and exhibits frequent inactivating mutations, exclusively in S. marcescens isolates of clinical origin. This regulatory system controls a number of lifestyle-related traits at transcriptional and post-translational levels, including T6SS activity, antibiotic production, motility, and adhesion, with loss of BetR increasing virulence in an in vivo infection model. Our data support a model whereby this system represents a conserved, modular switch from sessile to pioneering and aggressive behavior, which is subject to selection pressure in clinical environments.

The pathogenicity traits of avian pathogenic Escherichia coli O25-ST131 associated with avian colibacillosis in Georgia poultry and their genotypic and phenotypic overlap with other extraintestinal pathogenic E. coli

AIMS

To characterize Escherichia coli O25 ST131 (O25-ST131) isolated from Georgia poultry-a "global high-risk" clonal strain.

METHODS AND RESULTS

Using multiplex PCR to detect target genes in 98 isolates of avian pathogenic E. coli (APEC) O25 recovered from avians diagnosed with colibacillosis (n = 87) and healthy chicks (n = 11) in Georgia, USA. Eighty-eight isolates were classified as sequence type ST131 clade b and 56% (n = 49) belong to the phylogenetic group B2. Overall, 17% were identified as uropathogenic E. coli (UPEC)-like and 94% of the isolates formed strong to moderate biofilms. The extended-spectrum β-lactamases encoding genes, blaCTX M-15 (24%), carbapenemases encoding genes, and blaOXA48 (16%) were also detected. The isolates harbored FIB (88%), FIC (28%), A/C (14%), and FIIA (6%) plasmid replicons. Interestingly, 78% of the isolates were found to be resistant to chicken serum and 92% showed capabilities for growth in human urine. The isolates showed phenotypic resistance to several antibiotics including chloramphenicol (63%), ciprofloxacin (57%), trimethoprim-sulfamethoxazole (28%), streptomycin (17%), and cefoxitin and meropenem (14%) using the national antimicrobial resistance monitoring system panel.

CONCLUSIONS

Overall, our study provides evidence of the virulence of these global "high-risk" clones in Georgia poultry with some isolates showing genotypic overlap between APEC and UPEC. Also, this clone harbored several virulence genes, antimicrobial-resistant genes, and plasmids. Interestingly, the majority of APEC O25-ST131 isolates can survive and grow in both chicken serum and human urine and warrant further investigation of their potential pathogenicity for both chickens and humans.

H-NOX Influences Biofilm Formation, Central Metabolism, and Quorum Sensing in Paracoccus denitrificans

The transition from planktonic to biofilm growth in bacteria is often accompanied by greater resistance to antibiotics and other stressors, as well as distinct alterations in physical traits, genetic activity, and metabolic restructuring. In many species, the heme nitric oxide/oxygen binding proteins (H-NOX) play an important role in this process, although the signaling mechanisms and pathways in which they participate are quite diverse and largely unknown. In Paracoccus denitrificans, deletion of the hnox gene results in a severe biofilm-deficient phenotype. Quantitative proteomics was used to assemble a comprehensive data set of P. denitrificans proteins showing altered abundance of those involved in several important metabolic pathways. Further, decreased levels of pyruvate and elevated levels of C16 homoserine lactone were detected for the Δhnox strain, associating the biofilm deficiency with altered central carbon metabolism and quorum sensing, respectively. These results expand our knowledge of the important role of H-NOX signaling in biofilm formation.

Carbazole and Quinazolinone Derivatives from a Fluoride-Tolerant Streptomyces Strain OUCMDZ-5511

Six new 9H-carbazole derivatives (1-6) and nine previously reported compounds (7-15) were isolated from a fermented solid medium of the Thailand mangrove-derived Streptomyces strain, OUCMDZ-5511, under fluoride stress. Compounds 2-5, 12, and 15 were exclusively present in the fluoride-supplemented fermentation medium, while compounds 7-9, 13, and 14 were newly discovered natural products. The molecular structures of the compounds were identified by a spectroscopic analysis. The new compound 2 displayed antiquorum sensing activity against Chromobacterium violaceum ATCC 12472 by reducing the violacein production and inhibiting the biofilm formation in a concentration-dependent manner. The study revealed that compound 2 could be a novel potential inhibitor of quorum sensing.

In vitro lung epithelial cell model reveals novel roles for Pseudomonas aeruginosa siderophores

The multidrug-resistant pathogen Pseudomonas aeruginosa is a common nosocomial respiratory pathogen that continues to threaten the lives of patients with mechanical ventilation in intensive care units and those with underlying comorbidities such as cystic fibrosis or chronic obstructive pulmonary disease. For over 20 years, studies have repeatedly demonstrated that the major siderophore pyoverdine is an important virulence factor for P. aeruginosa in invertebrate and mammalian hosts in vivo. Despite its physiological significance, an in vitro, mammalian cell culture model that can be used to characterize the impact and molecular mechanisms of pyoverdine-mediated virulence has only been developed very recently. In this study, we adapt a previously-established, murine macrophage-based model to use human bronchial epithelial (16HBE) cells. We demonstrate that conditioned medium from P. aeruginosa induced rapid 16HBE cell death through the pyoverdine-dependent secretion of cytotoxic rhamnolipids. Genetic or chemical disruption of pyoverdine biosynthesis decreased rhamnolipid production and mitigated cell death. Consistent with these observations, chemical depletion of lipids or genetic disruption of rhamnolipid biosynthesis abrogated the toxicity of the conditioned medium. Furthermore, we also examine the effects of exposure to purified pyoverdine on 16HBE cells. While pyoverdine accumulated within cells, it was largely sequestered within early endosomes, resulting in minimal cytotoxicity. More membrane-permeable iron chelators, such as the siderophore pyochelin, decreased epithelial cell viability and upregulated several pro-inflammatory genes. However, pyoverdine potentiated these iron chelators in activating pro-inflammatory pathways. Altogether, these findings suggest that the siderophores pyoverdine and pyochelin play distinct roles in virulence during acute P. aeruginosa lung infection.

IMPORTANCE

Multidrug-resistant Pseudomonas aeruginosa is a versatile bacterium that frequently causes lung infections. This pathogen is life-threatening to mechanically-ventilated patients in intensive care units and is a debilitating burden for individuals with cystic fibrosis. However, the role of P. aeruginosa virulence factors and their regulation during infection are not fully understood. Previous murine lung infection studies have demonstrated that the production of siderophores (e.g., pyoverdine and pyochelin) is necessary for full P. aeruginosa virulence. In this report, we provide further mechanistic insight into this phenomenon. We characterize distinct and novel ways these siderophores contribute to virulence using an in vitro human lung epithelial cell culture model.

Antibiotic Resistant Biofilms and the Quest for Novel Therapeutic Strategies

Antimicrobial resistance (AMR) is one of the major leading causes of death around the globe. Present treatment pipelines are insufficient to overcome the critical situation. Prominent biofilm forming human pathogens which can thrive in infection sites using adaptive features results in biofilm persistence. Considering the present scenario, prudential investigations into the mechanisms of resistance target them to improve antibiotic efficacy is required. Regarding this, developing newer and effective treatment options using edge cutting technologies in medical research is the need of time. The reasons underlying the adaptive features in biofilm persistence have been centred on different metabolic and physiological aspects. The high tolerance levels against antibiotics direct researchers to search for novel bioactive molecules that can help combat the problem. In view of this, the present review outlines the focuses on an opportunity of different strategies which are in testing pipeline can thus be developed into products ready to use.

Characteristics of gut bacterial microbiota of black soldier fly (Diptera: Stratiomyidae) larvae effected by typical antibiotics

As agents in an emerging technology, Hermetia illucens (Linnaeus, 1758) (Diptera: Stratiomyidae) larvae, black soldier fly, have shown exciting potential for degrading antibiotics in organic solid waste, a process for which gut microorganisms play an important role. This study investigated the characteristics of larval gut bacterial communities effected by typical antibiotics. Initially, antibiotics significantly reduced the diversity of gut bacterial species. After 8 days, diversity recovered to similar to that of the control group in the chlortetracycline, tylosin, and sulfamethoxazole groups. Proteobacteria, Firmicutes, and Actinobacteriota were the dominant phyla at the initial BSFL gut. However, after 4 days treatment, the proportion of Actinobacteriota significantly decreased, but Bacteroidota notably increased. During the conversion process, 18, 18, 17, 21, and 19 core genera were present in the chlortetracycline, sulfamethoxazole, tylosin, norfloxacin, and gentamicin groups, respectively. Pseudomonas, Actinomyces, Morganella, Providencia and Klebsiella might be the important genera with extraordinary resistance and degradation to antibiotics. Statistical analyses of COGs showed that antibiotics changed the microbial community functions of BSFL gut. Compared with the control group, (i) the chlortetracycline, sulfamethoxazole, and tylosin groups showed significant increase in the classification functions of transcription, RNA processing and modification，and so on, (ii) the norfloxacin and gentamicin groups showed significant increase in defense mechanisms and other functions. Note that we categorized the response mechanisms of these classification functions to antibiotics into resistance and degradation. This provides a new perspective to deeply understand the joint biodegradation behavior of antibiotics in environments, and serves as an important reference for further development and utilization of microorganisms-assisted larvae for efficient degradation of antibiotics.

DNase improves the efficacy of antimicrobial photodynamic therapy in the treatment of candidiasis induced with Candida albicans

The study evaluated the association of DNase I enzyme with antimicrobial photodynamic therapy (aPDT) in the treatment of oral candidiasis in mice infected with fluconazole-susceptible (CaS) and -resistant (CaR) Candida albicans strains. Mice were inoculated with C. albicans, and after the infection had been established, the tongues were exposed to DNase for 5 min, followed by photosensitizer [Photodithazine®(PDZ)] and light (LED), either singly or combined. The treatments were performed for 5 consecutive days. Treatment efficacy was evaluated by assessing the tongues via fungal viable population, clinical evaluation, histopathological and fluorescence microscopy methods immediately after finishing treatments, and 7 days of follow-up. The combination of DNase with PDZ-aPDT reduced the fungal viability in mice tongues immediately after the treatments by around 4.26 and 2.89 log10 for CaS and CaR, respectively (versus animals only inoculated). In the fluorescence microscopy, the polysaccharides produced by C. albicans and fungal cells were less labeled in animals treated with the combination of DNase with PDZ-aPDT, similar to the healthy animals. After 7 days of the treatment, DNase associated with PDZ-aPDT maintained a lower count, but not as pronounced as immediately after the intervention. For both strains, mice treated with the combination of DNase with PDZ-aPDT showed remission of oral lesions and mild inflammatory infiltrate in both periods assessed, while animals treated only with PDZ-aPDT presented partial remission of oral lesions. DNase I enzyme improved the efficacy of photodynamic treatment.

In vitro Lung Epithelial Cell Model Reveals Novel Roles for Pseudomonas aeruginosa Siderophores

Multidrug-resistant Pseudomonas aeruginosa is a common nosocomial respiratory pathogen that continues to threaten the lives of patients with mechanical ventilation in intensive care units and those with underlying comorbidities such as cystic fibrosis or chronic obstructive pulmonary disease. For over 20 years, studies have repeatedly demonstrated that the major siderophore pyoverdine is an important virulence factor for P. aeruginosa in invertebrate and mammalian hosts in vivo. Despite its physiological significance, an in vitro, mammalian cell culture model to characterize the impact and molecular mechanism of pyoverdine-mediated virulence has only been developed very recently. In this study, we adapt a previously-established, murine macrophage-based model for human bronchial epithelial cells (16HBE). We demonstrate that conditioned medium from P. aeruginosa induced rapid 16HBE cell death through the pyoverdine-dependent secretion of cytotoxic rhamnolipids. Genetic or chemical disruption of pyoverdine biosynthesis decreased rhamnolipid production and mitigated cell death. Consistent with these observations, chemical depletion of lipid factors or genetic disruption of rhamnolipid biosynthesis was sufficient to abrogate conditioned medium toxicity. Furthermore, we also examine the effects of purified pyoverdine exposure on 16HBE cells. While pyoverdine accumulated within cells, the siderophore was largely sequestered within early endosomes, showing minimal cytotoxicity. More membrane-permeable iron chelators, such as the siderophore pyochelin, decreased epithelial cell viability and upregulated several proinflammatory genes. However, pyoverdine potentiated these iron chelators in activating proinflammatory pathways. Altogether, these findings suggest that the siderophores pyoverdine and pyochelin play distinct roles in virulence during acute P. aeruginosa lung infection.

Antibody-Drug Conjugates to Treat Bacterial Biofilms via Targeting and Extracellular Drug Release

The treatment of implant-associated bacterial infections and biofilms is an urgent medical need and a grand challenge because biofilms protect bacteria from the immune system and harbor antibiotic-tolerant persister cells. This need is addressed herein through an engineering of antibody-drug conjugates (ADCs) that contain an anti-neoplastic drug mitomycin C, which is also a potent antimicrobial against biofilms. The ADCs designed herein release the conjugated drug without cell entry, via a novel mechanism of drug release which likely involves an interaction of ADC with the thiols on the bacterial cell surface. ADCs targeted toward bacteria are superior by the afforded antimicrobial effects compared to the non-specific counterpart, in suspension and within biofilms, in vitro, and in an implant-associated murine osteomyelitis model in vivo. The results are important in developing ADC for a new area of application with a significant translational potential, and in addressing an urgent medical need of designing a treatment of bacterial biofilms.

Mechanisms of iron homeostasis in Pseudomonas aeruginosa and emerging therapeutics directed to disrupt this vital process

Pseudomonas aeruginosa is an opportunistic pathogen able to infect any human tissue. One of the reasons for its high adaptability and colonization of host tissues is its capacity of maintaining iron homeostasis through a wide array of iron acquisition and removal mechanisms. Due to their ability to cause life-threatening acute and chronic infections, especially among cystic fibrosis and immunocompromised patients, and their propensity to acquire resistance to many antibiotics, the World Health Organization (WHO) has encouraged the scientific community to find new strategies to eradicate this pathogen. Several recent strategies to battle P. aeruginosa focus on targeting iron homeostasis mechanisms, turning its greatest advantage into an exploitable weak point. In this review, we discuss the different mechanisms used by P. aeruginosa to maintain iron homeostasis and the strategies being developed to fight this pathogen by blocking these mechanisms. Among others, the use of iron chelators and mimics, as well as disruption of siderophore production and uptake, have shown promising results in reducing viability and/or virulence of this pathogen. The so-called 'Trojan-horse' strategy taking advantage of the siderophore uptake systems is emerging as an efficient method to improve delivery of antibiotics into the bacterial cells. Moreover, siderophore transporters are considered promising targets for the developing of P. aeruginosa vaccines.

Evaluating the Antivirulence Effects of New Thiazolidinedione Compounds Against Pseudomonas aeruginosa PAO1

Pseudomonas aeruginosa is an opportunistic pathogen that causes several serious health problems and numerous forms of virulence. During the treatment of P. aeruginosa infections, the development of multidrug-resistant isolates creates significant clinical problems. Using antivirulence compounds to disrupt pathogenicity rather than killing the bacterium may be an interesting strategy to overcome this problem, because less harsh conditions will exist for the development of resistance. To reduce pathogenicity and biofilm formation, newly synthesized analogs of imidazolyl (8n) and previously synthesized analogs (8a-8m) with a similar backbone [the 5-(imidazolyl-methyl) thiazolidinediones] were tested against pyoverdine and pyocyanin production, protease activity, and biofilm formation. Compared to the positive control group, the best compounds reduced the production of pyoverdine (8n) by 89.57% and pyocyanin (8i) by 22.68%, and protease activity (8n) by 2.80% for PAO1 strain, at a concentration of 10 μM. Moreover, the biofilm formation assay showed a reduction of 87.94% (8i) for PAO1, as well as 30.53% (8d) and 44.65% (8m) for 1074 and 1707 strains, respectively. The compounds used in this study did not show any toxicity in the human dermal fibroblasts and 4T1 cells (viability higher than 90%). The in silico study of these compounds revealed that their antivirulence activity could be due to their interaction with the PqsR, PqsE, and LasR receptors.

Biofilms as a microbial hazard in the food industry: A scoping review

Biofilms pose a serious public health hazard with a significant economic impact on the food industry. The present scoping review is designed to analyse the literature published during 2001-2020 on biofilm formation of microbes, their detection methods, and association with antimicrobial resistance (if any). The peer-reviewed articles retrieved from 04 electronic databases were assessed using PRISMA-ScR guidelines. From the 978 preliminary search results, a total of 88 publications were included in the study. On analysis, the commonly isolated pathogens were Listeria monocytogenes, Staphylococcus aureus, Salmonella spp., Escherichia coli, Bacillus spp., Vibrio spp., Campylobacter jejuni and Clostridium perfringens. The biofilm-forming ability of microbes was found to be influenced by various factors such as attachment surfaces, temperature, presence of other species, nutrient availability etc. A total of 18 studies characterized the biofilm-forming genes, particularly for S. aureus, Salmonella spp., and E. coli. In most studies, polystyrene plate and/or stainless-steel coupons were used for biofilm formation, and the detection was carried out by crystal violet assays and/or by plate counting method. The strain-specific significant differences in biofilm formation were observed in many studies, and few studies carried out analysis of multi-species biofilms. The association between biofilm formation and antimicrobial resistance was not clearly defined. Further, viable but non-culturable form of the foodborne pathogens is posing an unseen (by conventional cultivation techniques) but potent threat to the food safety. The present review recommends the need for carrying out systematic surveys and risk analysis of biofilms in food chain to highlight the evidence-based public health concerns, especially in regions where microbiological food hazards are quite prevalent.

Insights Into the Dynamics and Composition of Biofilm Formed by Environmental Isolate of Enterobacter cloacae

Bacterial biofilms are clinically admissible and illustrate an influential role in infections, particularly those related to the implant of medical devices. The characterization of biofilms is important to understand the etiology of the diseases. Enterobacter cloacae are known for causing infections by forming biofilms on various abiotic surfaces, such as medical devices. However, a detailed characterization in terms of morphology and the molecular composition of the formed biofilms by this bacterium is sparse. The present study provides insights into the biofilm formation of E. cloacae SBP-8, an environmental isolate, on various surfaces. We performed assays to understand the biofilm-forming capability of the SBP-8 strain and characterized the adhering potential of the bacteria on the surface of different medical devices (foley latex catheter, enteral feeding tube, and glass) at different temperatures. We found that medical devices exhibited strong colonization by E. cloacae SBP-8. Using field emission-scanning electron microscopy (FE-SEM) studies, we characterized the biofilms as a function of time. It indicated stronger biofilm formation in terms of cellular density and EPS production on the surfaces. Further, we characterized the biofilm employing surface-enhanced Raman spectroscopy (SERS) and identified the vast heterogenic nature of the biofilm-forming molecules. Interestingly, we also found that this heterogeneity varies from the initial stages of biofilm formation until the maturation and dispersion. Our studies provide insights into biofilm composition over a period of time, which might aid in understanding the biofilm dispersion phases, to enhance the presently available treatment strategies.

Oral Dysbiosis and Neurodegenerative Diseases: Correlations and Potential Causations

Biofilms are a heterogenous complex community of vegetative cells and extracellular polymeric substances that can adhere to various surfaces and are responsible for a variety of chronic and acute diseases. The impact of bacterial biofilms on oral and intestinal health is well studied, but the correlation and causations of biofilms and neurodegenerative diseases are still in their infancy. However, the correlations between biofilms and diseases such as Alzheimer’s Disease, Multiple Sclerosis, and even Parkinson’s Disease are starting to demonstrate the role bacterial biofilms have in promoting and exasperating various illnesses. The review article provides insight into the role bacterial biofilms may have on the development and progression of various neurodegenerative diseases and hopefully shine a light on this very important area of research.

mazEF Homologue Has a Minor Role in Staphylococcus epidermidis 1457 Virulence Potential

Staphylococcus epidermidis biofilm cells are characterized by increased antimicrobial tolerance and improved ability to evade host immune system defenses. These features are, in part, due to the presence of viable but non-culturable (VBNC) cells. A previous study identified genes potentially involved in VBNC cells formation in S. epidermidis biofilms, among which SERP1682/1681 raised special interest due to their putative role as a toxin–antitoxin system of the mazEF family. Herein, we constructed an S. epidermidis mutant lacking the mazEF genes homologues and determined their role in (i) VBNC state induction during biofilm formation, (ii) antimicrobial susceptibility, (iii) survival in human blood and plasma, and (iv) activation of immune cells. Our results revealed that mazEF homologue did not affect the proportion of VBNC cells in S. epidermidis 1457, refuting the previous hypothesis that mazEF homologue could be linked with the emergence of VBNC cells in S. epidermidis biofilms. Additionally, mazEF homologue did not seem to influence key virulence factors on this strain, since its deletion did not significantly affect the mutant biofilm formation capacity, antimicrobial tolerance or the response by immune cells. Surprisingly, our data suggest that mazEF does not behave as a toxin–antitoxin system in S. epidermidis strain 1457, since no decrease in the viability and culturability of bacteria was found when only the mazF toxin homologue was being expressed.

Advances in the Sensing and Treatment of Wound Biofilms

Wound biofilms represent a particularly challenging problem in modern medicine. They are increasingly antibiotic resistant and can prevent the healing of chronic wounds. However, current treatment and diagnostic options are hampered by the complexity of the biofilm environment. In this review, we present new chemical avenues in biofilm sensors and new materials to treat wound biofilms, offering promise for better detection, chemical specificity, and biocompatibility. We briefly discuss existing methods for biofilm detection and focus on novel, sensor-based approaches that show promise for early, accurate detection of biofilm formation on wound sites and that can be translated to point-of-care settings. We then discuss technologies inspired by new materials for efficient biofilm eradication. We focus on ultrasound-induced microbubbles and nanomaterials that can both penetrate the biofilm and simultaneously carry active antimicrobials and discuss the benefits of those approaches in comparison to conventional methods.

Advances in the Sensing and Treatment of Wound Biofilms

Wound biofilms represent a particularly challenging problem in modern medicine. They are increasingly antibiotic resistant and can prevent the healing of chronic wounds. However, current treatment and diagnostic options are hampered by the complexity of the biofilm environment. In this review, we present new chemical avenues in biofilm sensors and new materials to treat wound biofilms, offering promise for better detection, chemical specificity, and biocompatibility. We briefly discuss existing methods for biofilm detection and focus on novel, sensor-based approaches that show promise for early, accurate detection of biofilm formation on wound sites and that can be translated to point-of-care settings. We then discuss technologies inspired by new materials for efficient biofilm eradication. We focus on ultrasound-induced microbubbles and nanomaterials that can both penetrate the biofilm and simultaneously carry active antimicrobials and discuss the benefits of those approaches in comparison to conventional methods.

Gradients and consequences of heterogeneity in biofilms

Historically, appreciation for the roles of resource gradients in biology has fluctuated inversely to the popularity of genetic mechanisms. Nevertheless, in microbiology specifically, widespread recognition of the multicellular lifestyle has recently brought new emphasis to the importance of resource gradients. Most microorganisms grow in assemblages such as biofilms or spatially constrained communities with gradients that influence, and are influenced by, metabolism. In this Review, we discuss examples of gradient formation and physiological differentiation in microbial assemblages growing in diverse settings. We highlight consequences of physiological heterogeneity in microbial assemblages, including division of labour and increased resistance to stress. Our impressions of microbial behaviour in various ecosystems are not complete without complementary maps of the chemical and physical geographies that influence cellular activities. A holistic view, incorporating these geographies and the genetically encoded functions that operate within them, will be essential for understanding microbial assemblages in their many roles and potential applications.

H-NOX proteins in the virulence of pathogenic bacteria

Nitric oxide (NO) is a toxic gas encountered by bacteria as a product of their own metabolism or as a result of a host immune response. Non-toxic concentrations of NO have been shown to initiate changes in bacterial behaviors such as the transition between planktonic and biofilm-associated lifestyles. The heme nitric oxide/oxygen binding proteins (H-NOX) are a widespread family of bacterial heme-based NO sensors that regulate biofilm formation in response to NO. The presence of H-NOX in several human pathogens combined with the importance of planktonic–biofilm transitions to virulence suggests that H-NOX sensing may be an important virulence factor in these organisms. Here we review the recent data on H-NOX NO signaling pathways with an emphasis on H-NOX homologs from pathogens and commensal organisms. The current state of the field is somewhat ambiguous regarding the role of H-NOX in pathogenesis. However, it is clear that H-NOX regulates biofilm in response to environmental factors and may promote persistence in the environments that serve as reservoirs for these pathogens. Finally, the evidence that large subgroups of H-NOX proteins may sense environmental signals besides NO is discussed within the context of a phylogenetic analysis of this large and diverse family.

Phylogenetic Group B2 Expressed Significant Biofilm Formation among Drug Resistant Uropathogenic Escherichia coli

Biofilm is an important virulent marker attributed to the development of urinary tract infections (UTIs) by uropathogenic E. coli (UPEC). Drug-resistant and biofilm-producing UPEC are highly problematic causing catheter-associated or recurrent UTIs with significant morbidity and mortality. The aim of the current study was to investigate the prevalence of biofilm formation and phylogenetic groups in drug-resistant UPEC to predict their ability to cause disease. This prospective study was conducted at the Department of Microbiology, University of Karachi from January to June 2019. A total of 50 highly drug-resistant UPEC were selected for this study. UPEC isolates were screened to form biofilm by Congo-red agar (CRA) and microtiter plate (MTP) technique. The representative biofilm-producing isolates were analysed by scanning electron microscopy (SEM) monitoring. Phylogenetic analysis was done by PCR method based on two preserved genes; chuA, yjaA and TspE4-C2 DNA fragment. On CRA 34 (68%) UPEC were slime producers, while on MTP 20 (40%) were strong biofilm producers, 19 (38%) moderate and 11 (22%) were low to negligible biofilm producers. Molecular typing confirmed that phylogenetic group B2 was prevalent in drug resistant UPEC strains. Pathogenic strains belonged to phylogenetic group B2 and D were found to have greater biofilm forming ability as compare to non-pathogenic commensal strains that belonged to phylogenetic group A. Our results indicate that biofilm formation vary in drug resistant UPEC belonged to different phylogenetic groups. This study indicates possible link between in vitro biofilm formation and phylogenetic groups of UPEC, therefore this knowledge might be helpful to predict the pathogenic potential of UPEC and help design strategies for controlling UTIs.

Characterizations of the viability and gene expression of dispersal cells from Pseudomonas aeruginosa biofilms released by alginate lyase and tobramycin

Biofilm infections are hard to manage using conventional antibiotic treatment regimens because biofilm structures discourage antibiotics from reaching the entire bacterial community and allow pathogen cells to persistently colonize and develop a plethora of tolerance mechanisms towards antibiotics. Moreover, the dispersed cells from biofilms can cause further complications by colonizing different sites and establishing new cycles of biofilms. Previously, we showed that alginate lyase enzyme (AlyP1400), purified from a marine Pseudoalteromonas bacterium, reduced Pseudomonas aeruginosa biofilm biomass and boosted bactericidal activity of tobramycin by degrading alginate within the biofilm extracellular polymeric substances matrix. In this work, we used a flow cytometry-based assay to analyze collected dispersal cells and demonstrated the synergy between tobramycin with AlyP1400 in enhancing the release of both live and dead biofilm cells from a mucoid P. aeruginosa strain CF27, which is a clinical isolate from cystic fibrosis (CF) patients. Interestingly, this enhanced dispersal was only observed when AlyP1400 was combined with tobramycin and administered simultaneously but not when AlyP1400 was added in advance of tobramycin in a sequential manner. Moreover, neither the combined nor sequential treatment altered the dispersal of the biofilms from a non-mucoid P. aeruginosa laboratory strain PAK. We then carried out the gene expression and tobramycin survival analyses to further characterize the impacts of the combined treatment on the CF27 dispersal cells. Gene expression analysis indicated that CF27 dispersal cells had increased expression in virulence- and antibiotic resistance-related genes, including algR, bdlA, lasB, mexF, mexY, and ndvB. In the CF27 dispersal cell population, the combinational treatment of AlyP1400 with tobramycin further induced bdlA, mexF, mexY, and ndvB genes more than non-treated and tobramycin-treated dispersal cells, suggesting an exacerbated bacterial stress response to the combinational treatment. Simultaneous to the gene expression analysis, the survival ability of the same batch of biofilm dispersal cells to a subsequent tobramycin challenge displayed a significantly higher tobramycin tolerant fraction of cells (~60%) upon the combinational treatment of AlyP1400 and tobramycin than non-treated and tobramycin-treated dispersal cells, as well as the planktonic cells (all below 10%). These results generate new knowledge about the gene expression and antibiotic resistance profiles of dispersed cells from biofilm. This information can guide the design of safer and more efficient therapeutic strategies for the combinational use of alginate lyase and tobramycin to treat P. aeruginosa biofilm-related infections in CF lungs.

Black-and-White Ruffed Lemur (Varecia variegata) in Captivity: Analysis of the Oral Microbiota in a One Health Perspective

This study aimed to characterize the susceptibility profile to antibiotics and biofilm formation of Gram-negative bacterial isolates obtained from the oral cavity of the black-and-white ruffed lemur (Varecia variegata). From eight individuals from a zoo located in Portugal, samples of the oral microbiota were collected with sterile swabs and then placed in closed tubes with a transport medium. Culture was carried out for media of Gram-negative bacteria. Twenty-two isolates were obtained and subjected to susceptibility tests to twenty-five antimicrobial agents belonging to seven different classes. All tested isolates demonstrated resistance to, at least, one antibiotic, and it was possible to observe multidrug resistance in 11 of the 22 isolates (50%). It should be noted that an isolate showed phenotypic resistance to imipenem, an antibiotic for exclusive use in a hospital environment. All the isolates showed an increasing ability of biofilm formation over time. The obtained results show that wild mammals in captivity could be reservoirs and potential sources of multi-resistant pathogens. In view of this fact and considering the One Health concept, it will be advisable to establish local monitoring programs worldwide that benefit and protect human, animal and environmental health.

Antibiofilm Potential of Medicinal Plants against Candida spp. Oral Biofilms: A Review

The use of natural products to promote health is as old as human civilization. In recent years, the perception of natural products derived from plants as abundant sources of biologically active compounds has driven their exploitation towards the search for new chemical products that can lead to further pharmaceutical formulations. Candida fungi, being opportunistic pathogens, increase their virulence by acquiring resistance to conventional antimicrobials, triggering diseases, especially in immunosuppressed hosts. They are also pointed to as the main pathogens responsible for most fungal infections of the oral cavity. This increased resistance to conventional synthetic antimicrobials has driven the search for new molecules present in plant extracts, which have been widely explored as alternative agents in the prevention and treatment of infections. This review aims to provide a critical view and scope of the in vitro antimicrobial and antibiofilm activity of several medicinal plants, revealing species with inhibition/reduction effects on the biofilm formed by Candida spp. in the oral cavity. The most promising plant extracts in fighting oral biofilm, given their high capacity to reduce it to low concentrations were the essential oils extracted from Allium sativum L., Cinnamomum zeylanicum Blume. and Cymbopogon citratus (DC) Stapf.

Functional Integration and Individuality in Prokaryotic Collective Organisations

Both physiological and evolutionary criteria of biological individuality are underpinned by the idea that an individual is a functionally integrated whole. However, a precise account of functional integration has not been provided so far, and current notions are not developed in the details, especially in the case of composite systems. To address this issue, this paper focuses on the organisational dimension of two representative associations of prokaryotes: biofilms and the endosymbiosis between prokaryotes. Some critical voices have been raised against the thesis that biofilms are biological individuals. Nevertheless, it has not been investigated which structural and functional obstacles may prevent them from being fully integrated physiological or evolutionary units. By contrast, the endosymbiotic association of different species of prokaryotes has the potential for achieving a different type of physiological integration based on a common boundary and interlocked functions. This type of association had made it possible, under specific conditions, to evolve endosymbionts into fully integrated organelles. This paper therefore has three aims: first, to analyse the organisational conditions and the physiological mechanisms that enable integration in prokaryotic associations; second, to discuss the organisational differences between biofilms and prokaryotic endosymbiosis and the types of integration they achieve; finally, to provide a more precise account of functional integration based on these case studies.

The Adc regulon mediates zinc homeostasis in Streptococcus mutans

Zinc (Zn²⁺ ) is an essential divalent trace metal for living cells. Intracellular zinc homeostasis is critical to the survival and virulence of bacteria. Thus, the frequent fluctuations of salivary zinc, caused by the low physiological level and the frequent exogenous zinc introduction, present a serious challenge for bacteria colonizing the oral cavity. However, the regulation strategies to keep intracellular Zn²⁺ homeostasis in Streptococcus mutans, an important causative pathogen of dental caries, are unknown. Because zinc uptake is primarily mediated by an ATP-binding ABC transporter AdcABC in Streptococcus strains, we examined the function of AdcABC and transcription factor AdcR in S. mutans in this study. The results demonstrated that deletion of either adcA or adcCB gene impaired the growth but enhanced the extracellular polymeric matrix production in S. mutans, both of which could be relieved after excessive Zn²⁺ supplementation. Using RNA sequencing analysis, quantitative reverse transcription polymerase chain reaction examination, LacZ-reporter studies, and electrophoretic mobility shift assay, we showed that a MarR (multiple antibiotic resistance regulator) family transcription factor, AdcR, negatively regulates the expression of the genes adcR, adcC, adcB, and adcA by acting on the adcRCB and adcA promoters in response to Zn²⁺ concentration in their environmental niches. The deletion of adcR increases the sensitivity of S. mutans to excessive Zn²⁺ supply. Taken together, our findings suggest that Adc regulon, which consists of a Zn²⁺ uptake transporter AdcCBA and a Zn²⁺ -responsive repressor AdcR, plays a prominent role in the maintenance of intracellular zinc homeostasis of S. mutans.

1,4-Naphthoquinone disintegrates the pre-existing biofilm of Staphylococcus aureus by accumulating reactive oxygen species

Staphylococcus aureus causes several nosocomial and community-acquired infections in human host involving biofilm. Thus, strategies need to be explored to curb biofilm threats by either inhibiting the formation of biofilm or disintegrating the pre-existing biofilm. Towards this direction, we had already revealed the biofilm inhibiting properties of 1,4-naphthoquinone against S. aureus. In this study, we have investigated whether this compound can act on pre-existing biofilm. Hence, biofilm of S. aureus was developed first and challenged further with 1,4-naphthoquinone. Experiments such as crystal violet assay, fluorescence microscopy, and estimation of total biofilm protein were performed to confirm the biofilm disintegration properties of 1,4-naphthoquinone. The disintegration of pre-existing biofilm could be attributed to the generation of reactive oxygen species (ROS). To investigate further, we observed that extracellular DNA (eDNA) was found to play an important role in holding the biofilm network as DNaseI treatment could cause an efficient disintegration of the same. To examine the effect of ROS on the eDNA, we exposed pre-existing biofilm to either 1,4-naphthoquinone or a combination of both 1,4-naphthoquinone and ascorbic acid for different length of time. Post-incubation, ROS generation and the amount of eDNA associated with the biofilm were determined wherein an inversely proportional relationship was observed between them. The result indicated that with the increase of ROS generation, the amount of eDNA associated with biofilm got decreased substantially. Thus, the results indicated that the generation of ROS could degrade the eDNA thereby compromising the integrity of biofilm which lead to the disintegration of pre-existing biofilm.

Differential exopolysaccharide production and composition by Herbaspirillum strains from diverse ecological environments

Bacteria belonging to the genus Herbaspirillum are found in many different ecological niches. Some species are typically endophytic, while others were reported as free-living organisms that occupy various environments. Also, opportunistic herbaspirilli have been found infecting humans affected by several diseases. We have analyzed the production of exopolysaccharides (EPS) by Herbaspirillum strains isolated from different sources and with distinct ecological characteristics. The monosaccharide composition was determined for the EPS obtained for selected strains including free-living, plant-associated and clinical isolates, and the relationship with the ecological niches occupied by Herbaspirillum spp. is proposed.

Response of Escherichia coli minimal ter operon to UVC and auto-aggregation: pilot study

Aim

The study of minimal ter operon as a determinant of tellurium resistance (Te^R) is important for the purpose of confirming the relationship of these genes to the pathogenicity of microorganisms. The ter operon is widespread among bacterial species and pathogens, implicated also in phage inhibition, oxidative stress and colicin resistance. So far, there is no experimental evidence for the role of the Escherichia coli (E. coli) minimal ter operon in ultraviolet C (UVC) resistance, biofilm formation and auto-aggregation. To identify connection with UVC resistance of the minimal ter operon, matched pairs of Ter-positive and -negative E. coli cells were stressed and differences in survival and whole genome sequence analysis were performed. This study was aimed also to identify differences in phenotype of cells induced by environmental stress.

Methods

In the current study, a minimal ter operon(terBCDEΔF) originating from the uropathogenic strain E. coli KL53 was used. Clonogenic assay was the method of choice to determine cell reproductive death after treatment with UVC irradiation at certain time intervals. Bacterial suspensions were irradiated with 254 nm UVC-light (germicidal lamp in biological safety cabinet) in vitro. UVC irradiance output was 2.5 mW/cm² (calculated at the UVC device aperture) and plate-lamp distance of 60 cm. DNA damage analysis was performed using shotgun sequencing on Illumina MiSeq platform. Biofilm formation was measured by a crystal violet retention assay. Auto-aggregation assay was performed according to the Ghane, Babaeekhou & Ketabi (2020).

Results

A large fraction of Ter-positive E. coli cells survived treatment with 120-s UVC light (300 mJ/cm²) compared to matched Ter-negative cells; ∼5-fold higher resistance of Ter-positive cells to UVC dose (p = 0.0007). Moreover, UVC surviving Ter-positive cells showed smaller mutation rate as Ter-negative cells. The study demonstrated that a 1200-s exposure to UVC (3,000 mJ/cm²) was sufficient for 100% inhibition of growth for all the Ter-positive and -negative E. coli cells. The Ter-positive strain exhibited of 26% higher auto-aggregation activities and was able to inhibit biofilm formation over than Ter- negative strain (**** P < 0.0001).

Conclusion

Our study shows that Ter-positive cells display lower sensitivity to UVC radiation, corresponding to a presence in minimal ter operon. In addition, our study suggests that also auto-aggregation ability is related to minimal ter operon. The role of the minimal ter operon (terBCDEΔF) in resistance behavior of E. coli under environmental stress is evident.

High-Throughput Approaches for the Identification of Pseudomonas aeruginosa Antivirulents

Antimicrobial resistance is a serious medical threat, particularly given the decreasing rate of discovery of new treatments. Although attempts to find new treatments continue, it has become clear that merely discovering new antimicrobials, even if they are new classes, will be insufficient. It is essential that new strategies be aggressively pursued. Toward that end, the search for treatments that can mitigate bacterial virulence and tilt the balance of host-pathogen interactions in favor of the host has become increasingly popular. In this review, we will discuss recent progress in this field, with a special focus on synthetic small molecule antivirulents that have been identified from high-throughput screens and on treatments that are effective against the opportunistic human pathogen Pseudomonas aeruginosa.

Extracellular Polymeric Substance Protects Some Cells in an Escherichia coli Biofilm from the Biomechanical Consequences of Treatment with Magainin 2

Bacterial biofilms have long been recognized as a source of persistent infections and industrial contamination with their intransigence generally attributed to their protective layer of extracellular polymeric substances (EPS). EPS, consisting of secreted nucleic acids, proteins, and polysaccharides, make it difficult to fully eliminate biofilms by conventional chemical or physical means. Since most bacteria are capable of forming biofilms, understanding how biofilms respond to new antibiotic compounds and components of the immune system has important ramifications. Antimicrobial peptides (AMPs) are both potential novel antibiotic compounds and part of the immune response in many different organisms. Here, we use atomic force microscopy to investigate the biomechanical changes that occur in individual cells when a biofilm is exposed to the AMP magainin 2 (MAG2), which acts by permeabilizing bacterial membranes. While MAG2 is able to prevent biofilm initiation, cells in an established biofilm can withstand exposure to high concentrations of MAG2. Treated cells in the biofilm are classified into two distinct populations after treatment: one population of cells is indistinguishable from untreated cells, maintaining cellular turgor pressure and a smooth outer surface, and the second population of cells are softer than untreated cells and have a rough outer surface after treatment. Notably, the latter population is similar to planktonic cells treated with MAG2. The EPS likely reduces the local MAG2 concentration around the stiffer cells since once the EPS was enzymatically removed, all cells became softer and had rough outer surfaces. Thus, while MAG2 appears to have the same mechanism of action in biofilm cells as in planktonic ones, MAG2 cannot eradicate a biofilm unless coupled with the removal of the EPS.

Relevance of Biofilm Models in Periodontal Research: From Static to Dynamic Systems

Microbial biofilm modeling has improved in sophistication and scope, although only a limited number of standardized protocols are available. This review presents an example of a biofilm model, along with its evolution and application in studying periodontal and peri-implant diseases. In 2011, the ETEP (Etiology and Therapy of Periodontal and Peri-Implant Diseases) research group at the University Complutense of Madrid developed an in vitro biofilm static model using representative bacteria from the subgingival microbiota, demonstrating a pattern of bacterial colonization and maturation similar to in vivo subgingival biofilms. When the model and its methodology were standardized, the ETEP research group employed the validated in vitro biofilm model for testing in different applications. The evolution of this model is described in this manuscript, from the mere observation of biofilm growth and maturation on static models on hydroxyapatite or titanium discs, to the evaluation of the impact of dental implant surface composition and micro-structure using the dynamic biofilm model. This evolution was based on reproducing the ideal microenvironmental conditions for bacterial growth within a bioreactor and reaching the target surfaces using the fluid dynamics mimicking the salivary flow. The development of this relevant biofilm model has become a powerful tool to study the essential processes that regulate the formation and maturation of these important microbial communities, as well as their behavior when exposed to different antimicrobial compounds.

A Heterogeneously Expressed Gene Family Modulates the Biofilm Architecture and Hypoxic Growth of Aspergillus fumigatus

The genus Aspergillus encompasses human pathogens such as Aspergillus fumigatus and industrial powerhouses such as Aspergillus niger In both cases, Aspergillus biofilms have consequences for infection outcomes and yields of economically important products. However, the molecular components influencing filamentous fungal biofilm development, structure, and function remain ill defined. Macroscopic colony morphology is an indicator of underlying biofilm architecture and fungal physiology. A hypoxia-locked colony morphotype of A. fumigatus has abundant colony furrows that coincide with a reduction in vertically oriented hyphae within biofilms and increased low oxygen growth and virulence. Investigation of this morphotype has led to the identification of the causative gene, biofilm architecture factor A (bafA), a small cryptic open reading frame within a subtelomeric gene cluster. BafA is sufficient to induce the hypoxia-locked colony morphology and biofilm architecture in A. fumigatus Analysis across a large population of A. fumigatus isolates identified a larger family of baf genes, all of which have the capacity to modulate hyphal architecture, biofilm development, and hypoxic growth. Furthermore, introduction of A. fumigatusbafA into A. niger is sufficient to generate the hypoxia-locked colony morphology, biofilm architecture, and increased hypoxic growth. Together, these data indicate the potential broad impacts of this previously uncharacterized family of small genes to modulate biofilm architecture and function in clinical and industrial settings.IMPORTANCE The manipulation of microbial biofilms in industrial and clinical applications remains a difficult task. The problem is particularly acute with regard to filamentous fungal biofilms for which molecular mechanisms of biofilm formation, maintenance, and function are only just being elucidated. Here, we describe a family of small genes heterogeneously expressed across Aspergillus fumigatus strains that are capable of modifying colony biofilm morphology and microscopic hyphal architecture. Specifically, these genes are implicated in the formation of a hypoxia-locked colony morphotype that is associated with increased virulence of A. fumigatus Synthetic introduction of these gene family members, here referred to as biofilm architecture factors, in both A. fumigatus and A. niger additionally modulates low oxygen growth and surface adherence. Thus, these genes are candidates for genetic manipulation of biofilm development in aspergilli.

Modelling experimentally measured of ciprofloxacin antibiotic diffusion in Pseudomonas aeruginosa biofilm formed in artificial sputum medium

We study the experimentally measured ciprofloxacin antibiotic diffusion through a gel-like artificial sputum medium (ASM) mimicking physiological conditions typical for a cystic fibrosis layer, in which regions occupied by Pseudomonas aeruginosa bacteria are present. To quantify the antibiotic diffusion dynamics we employ a phenomenological model using a subdiffusion-absorption equation with a fractional time derivative. This effective equation describes molecular diffusion in a medium structured akin Thompson's plumpudding model; here the 'pudding' background represents the ASM and the 'plums' represent the bacterial biofilm. The pudding is a subdiffusion barrier for antibiotic molecules that can affect bacteria found in plums. For the experimental study we use an interferometric method to determine the time evolution of the amount of antibiotic that has diffused through the biofilm. The theoretical model shows that this function is qualitatively different depending on whether or not absorption of the antibiotic in the biofilm occurs. We show that the process can be divided into three successive stages: (1) only antibiotic subdiffusion with constant biofilm parameters, (2) subdiffusion and absorption of antibiotic molecules with variable biofilm transport parameters, (3) subdiffusion and absorption in the medium but the biofilm parameters are constant again. Stage 2 is interpreted as the appearance of an intensive defence build-up of bacteria against the action of the antibiotic, and in the stage 3 it is likely that the bacteria have been inactivated. Times at which stages change are determined from the experimentally obtained temporal evolution of the amount of antibiotic that has diffused through the ASM with bacteria. Our analysis shows good agreement between experimental and theoretical results and is consistent with the biologically expected biofilm response. We show that an experimental method to study the temporal evolution of the amount of a substance that has diffused through a biofilm is useful in studying the processes occurring in a biofilm. We also show that the complicated biological process of antibiotic diffusion in a biofilm can be described by a fractional subdiffusion-absorption equation with subdiffusion and absorption parameters that change over time.

Exopolysaccharide II Is Relevant for the Survival of Sinorhizobium meliloti under Water Deficiency and Salinity Stress

Sinorhizobium meliloti is a soil bacterium of great agricultural importance because of its ability to fix atmospheric nitrogen in symbiotic association with alfalfa (Medicago sativa) roots. We looked into the involvement of exopolysaccharides (EPS) in its survival when exposed to different environmental stressors, as well as in bacteria-bacteria and bacteria-substrate interactions. The strains used were wild-type Rm8530 and two strains that are defective in the biosynthesis of EPS II: wild-type Rm1021, which has a non-functional expR locus, and mutant Rm8530 expA. Under stress by water deficiency, Rm8530 remained viable and increased in number, whereas Rm1021 and Rm8530 expA did not. These differences could be due to Rm8530's ability to produce EPS II. Survival experiments under saline stress showed that viability was reduced for Rm1021 but not for Rm8530 or Rm8530 expA, which suggests the existence of some regulating mechanism dependent on a functional expR that is absent in Rm1021. The results of salinity-induced stress assays regarding biofilm-forming capacity (BFC) and autoaggregation indicated the protective role of EPS II. As a whole, our observations demonstrate that EPS play major roles in rhizobacterial survival.

A New Antibacterial N-Halamine Coating Based on Polydopamine

To prevent the formation of biofilms on material surfaces, the latter must have antibacterial properties. The aim of this study is to investigate the synthesis and the antibacterial effect of a new N-halamine coating based on polydopamine (PDA). The benefits of this coating are multiple, notably the green process used to prepare it and the wide variety of organic or inorganic materials that can be functionalized. First, the formation of the PDA coating by oxidative polymerization of dopamine in weak alkaline aqueous solution was studied and characterized. Then, these PDA films were exposed to a NaOCl solution in order to form chloramine functions into the coating, i.e., to immobilize oxidative chlorine on and into the coating. The PDA film chlorination was notably followed in situ by a quartz crystal microbalance (QCM). The influence of the NaOCl solution pH and concentration on chlorination kinetics and on PDA film degradation was evidenced. Finally, the antibacterial properties of the modified PDA coatings were highlighted by testing their antiadhesion and bactericidal properties toward the Escherichia coli bacterial strain.

Transcriptional portrait of M. bovis BCG during biofilm production shows genes differentially expressed during intercellular aggregation and substrate attachment

Mycobacterium tuberculosis and M. smegmatis form drug-tolerant biofilms through dedicated genetic programs. In support of a stepwise process regulating biofilm production in mycobacteria, it was shown elsewhere that lsr2 participates in intercellular aggregation, while groEL1 was required for biofilm maturation in M. smegmatis. Here, by means of RNA-Seq, we monitored the early steps of biofilm production in M. bovis BCG, to distinguish intercellular aggregation from attachment to a surface. Genes encoding for the transcriptional regulators dosR and BCG0114 (Rv0081) were significantly regulated and responded differently to intercellular aggregation and surface attachment. Moreover, a M. tuberculosis H37Rv deletion mutant in the Rv3134c-dosS-dosR regulon, formed less biofilm than wild type M. tuberculosis, a phenotype reverted upon reintroduction of this operon into the mutant. Combining RT-qPCR with microbiological assays (colony and surface pellicle morphologies, biofilm quantification, Ziehl–Neelsen staining, growth curve and replication of planktonic cells), we found that BCG0642c affected biofilm production and replication of planktonic BCG, whereas ethR affected only phenotypes linked to planktonic cells despite its downregulation at the intercellular aggregation step. Our results provide evidence for a stage-dependent expression of genes that contribute to biofilm production in slow-growing mycobacteria.

Impact of nanosystems in Staphylococcus aureus biofilms treatment

Staphylococcus aureus (S. aureus) is considered by the World Health Organization as a high priority pathogen for which new therapies are needed. This is particularly important for biofilm implant-associated infections once the only available treatment option implies a surgical procedure combined with antibiotic therapy. Consequently, these infections represent an economic burden for Healthcare Systems. A new strategy has emerged to tackle this problem: for small bugs, small particles. Here, we describe how nanotechnology-based systems have been studied to treat S. aureus biofilms. Their features, drawbacks and potentialities to impact the treatment of these infections are highlighted. Furthermore, we also outline biofilm models and assays required for preclinical validation of those nanosystems to smooth the process of clinical translation.

Innovative Strategies Toward the Disassembly of the EPS Matrix in Bacterial Biofilms

Bacterial biofilms represent a major concern at a worldwide level due to the high demand for implantable medical devices and the rising numbers of bacterial resistance. The complex structure of the extracellular polymeric substances (EPS) matrix plays a major role in this phenomenon, since it protects bacteria from antibiotics, avoiding drug penetration at bactericidal concentrations. Besides, this structure promotes bacterial cells to adopt a dormant lifestyle, becoming less susceptible to antibacterial agents. Currently, the available treatment for biofilm-related infections consists in the administration of conventional antibiotics at high doses for a long-term period. However, this treatment lacks efficiency against mature biofilms and for implant-associated biofilms it may be necessary to remove the medical device. Thus, biofilm-related infections represent an economical burden for the healthcare systems. New strategies focusing on the matrix are being highlighted as alternative therapies to eradicate biofilms. Here, we outline reported matrix disruptive agents, nanocarriers, and technologies, such as application of magnetic fields, photodynamic therapy, and ultrasounds, that have been under investigation to disrupt the EPS matrix of clinically relevant bacterial biofilms. In an ideal therapy, a synergistic effect between antibiotics and the explored innovated strategies is aimed to completely eradicate biofilms and avoid antimicrobial resistance phenomena.

Access to a Library of 1,3-disubstituted-1,2,3-triazenes and Evaluation of their Antimicrobial Properties

Background:

Due to the rapid development of microbial resistance, finding new molecules became urgent to counteract this problem.

Objective:

The objective of this work is to access 1,2,3-triazene-1,3-disubstituted, a class of molecule with high therapeutic potential.

Methods:

Here we describe the access to 17 new triazene including six with an imidazole-1,2,3-triazene moiety and eleven with an alkyl-1,2,3-triazene moiety and their evaluation against five strains: two gram (-): Escherichia coli ATCC 25921 and Pseudomonas aeruginosa ATCC 27253; two gram (+) : Staphylococcus aureus ATCC 38213 and Enterococcus faecalis ATCC 29212; and one fungi: Candida albicans ATCC 24433.

Results:

All strains were sensitive and the best MIC, 0.28 µM, is observed for 4c against Escherichia coli ATCC 25921. Compound 9, 3-isopropynyltriazene, appears to be the most interesting since it is active on the five evaluated strains with satisfactory MIC 0.32 µM against Escherichia coli and Pseudomonas aeruginosa and 0.64 µM against Enterococcus faecalis and Pseudomonas aeruginosa.

Conclusion:

Comparing the structure activity relationship, electron withdrawing groups appear to increase antimicrobial activity.

Controlling biofilms using synthetic biology approaches

Bacterial biofilms are formed by the complex but ordered regulation of intra- or inter-cellular communication, environmentally responsive gene expression, and secretion of extracellular polymeric substances. Given the robust nature of biofilms due to the non-growing nature of biofilm bacteria and the physical barrier provided by the extracellular matrix, eradicating biofilms is a very difficult task to accomplish with conventional antibiotic or disinfectant treatments. Synthetic biology holds substantial promise for controlling biofilms by improving and expanding existing biological tools, introducing novel functions to the system, and re-conceptualizing gene regulation. This review summarizes synthetic biology approaches used to eradicate biofilms via protein engineering of biofilm-related enzymes, utilization of synthetic genetic circuits, and the development of functional living agents. Synthetic biology also enables beneficial applications of biofilms through the production of biomaterials and patterning biofilms with specific temporal and spatial structures. Advances in synthetic biology will add novel biofilm functionalities for future therapeutic, biomanufacturing, and environmental applications.

Nanoscale in silico classification of ligand functionalised surfaces for protein adsorption resistance

Non-specific protein adsorption represents a significant challenge for the design of efficient and safe nanoparticles for biomedical applications since it may prevent functional ligands to target the desired specific receptors which can limit the efficacy of novel drug delivery systems and biosensors. The biofilm formation initiated by protein adsorption on surfaces limits the lifetime and safety of medical implants and tissue regenerative scaffolds. The development of biofouling resistant surfaces is therefore a major goal for the widespread uptake of nanomedicine. Here, we provide a relatively simple computational screening method based on the rational physically grounded criteria that may suffice in selection of surface grafted ligands for protein rejection, and test whether these criteria can be extrapolated from a specific protein to generic protein-resistant surfaces. Using all-atom molecular dynamics simulations we characterise four types of ligand functionalised surfaces at aqueous interfaces in terms of the surface hydrophobicity and ligand dynamics. We demonstrate how our hypothesised interfacial design based on the select physical characteristics of the ligated surfaces can enable the rejection of a protein from the surface. The ligand screening procedure and the detailed atomistic characterisation of the protein rejection process presented suggest that minimizing the adsorption of surface active proteins requires specific surface topographies and ligand chemistries that are able to maximise the entropic penalty associated with the restriction of the ligand dynamics and trapping interfacial water by adsorbed proteins.

Pf Bacteriophage and Their Impact on Pseudomonas Virulence, Mammalian Immunity, and Chronic Infections

Pf bacteriophage are temperate phages that infect the bacterium Pseudomonas aeruginosa, a major cause of chronic lung infections in cystic fibrosis (CF) and other settings. Pf and other temperate phages have evolved complex, mutualistic relationships with their bacterial hosts that impact both bacterial phenotypes and chronic infection. We and others have reported that Pf phages are a virulence factor that promote the pathogenesis of P. aeruginosa infections in animal models and are associated with worse skin and lung infections in humans. Here we review the biology of Pf phage and what is known about its contributions to pathogenesis and clinical disease. First, we review the structure, genetics, and epidemiology of Pf phage. Next, we address the diverse and surprising ways that Pf phages contribute to P. aeruginosa phenotypes including effects on biofilm formation, antibiotic resistance, and motility. Then, we cover data indicating that Pf phages suppress mammalian immunity at sites of bacterial infection. Finally, we discuss recent literature implicating Pf in chronic P. aeruginosa infections in CF and other settings. Together, these reports suggest that Pf bacteriophage have direct effects on P. aeruginosa infections and that temperate phages are an exciting frontier in microbiology, immunology, and human health.

Assembly and substrate recognition of curli biogenesis system

A major component of bacterial biofilms is curli amyloid fibrils secreted by the curli biogenesis system. Understanding the curli biogenesis mechanism is critical for developing therapeutic agents for biofilm-related infections. Here we report a systematic study of the curli biogenesis system, highlighted by structural, biochemical and functional analysis of the secretion channel complexes (CsgF-CsgG) with and without the curli substrate. The dual-pore architecture of the CsgF-CsgG complex was observed and used to develop an approach to inhibit the curli secretion by physically reducing the size of the CsgF pore. We further elucidated the assembly of the CsgFG complex with curli components (CsgA and CsgB) and curli-cell association through CsgF. Importantly, the recognition of the CsgA substrate by CsgG was uncovered. Nine crevices outside of the CsgG channel provide specific and highly-conserved recognition sites for CsgA N-terminus. Together with analysis of CsgE, our study provides comprehensive insights into curli biogenesis.

A major component of bacterial biofilms is curli amyloid fibrils secreted by the curli biogenesis system. Here authors use cryo-EM to visualize the secretion channel complexes (CsgF-CsgG) with and without the curli substrate and provide insights into curli biogenesis.

Using Atomic Force Microscopy To Illuminate the Biophysical Properties of Microbes

Since its invention in 1986, atomic force microscopy (AFM) has grown from a system designed for imaging inorganic surfaces to a tool used to probe the biophysical properties of living cells and tissues. AFM is a scanning probe technique and uses a pyramidal tip attached to a flexible cantilever to scan across a surface, producing a highly detailed image. While many research articles include AFM images, fewer include force-distance curves, from which several biophysical properties can be determined. In a single force-distance curve, the cantilever is lowered and raised from the surface, while the forces between the tip and the surface are monitored. Modern AFM has a wide variety of applications, but this review will focus on exploring the mechanobiology of microbes, which we believe is of particular interest to those studying biomaterials. We briefly discuss experimental design as well as different ways of extracting meaningful values related to cell surface elasticity, cell stiffness, and cell adhesion from force-distance curves. We also highlight both classic and recent experiments using AFM to illuminate microbial biophysical properties.

Bacterial Biofilm Eradication Agents: A Current Review

Most free-living bacteria can attach to surfaces and aggregate to grow into multicellular communities encased in extracellular polymeric substances called biofilms. Biofilms are recalcitrant to antibiotic therapy and a major cause of persistent and recurrent infections by clinically important pathogens worldwide (e.g., Pseudomonas aeruginosa, Escherichia coli, and Staphylococcus aureus). Currently, most biofilm remediation strategies involve the development of biofilm-inhibition agents, aimed at preventing the early stages of biofilm formation, or biofilm-dispersal agents, aimed at disrupting the biofilm cell community. While both strategies offer some clinical promise, neither represents a direct treatment and eradication strategy for established biofilms. Consequently, the discovery and development of biofilm eradication agents as comprehensive, stand-alone biofilm treatment options has become a fundamental area of research. Here we review our current understanding of biofilm antibiotic tolerance mechanisms and provide an overview of biofilm remediation strategies, focusing primarily on the most promising biofilm eradication agents and approaches. Many of these offer exciting prospects for the future of biofilm therapeutics for a large number of infections that are currently refractory to conventional antibiotics.

Betaproteobacteria are predominant in drinking water: are there reasons for concern?

Betaproteobacteria include some of the most abundant and ubiquitous bacterial genera that can be found in drinking water, including mineral water. The combination of physiology and ecology traits place some Betaproteobacteria in the list of potential, yet sometimes neglected, opportunistic pathogens that can be transmitted by water or aqueous solutions. Indeed, some drinking water Betaproteobacteria with intrinsic and sometimes acquired antibiotic resistance, harbouring virulence factors and often found in biofilm structures, can persist after water disinfection and reach the consumer. This literature review summarises and discusses the current knowledge about the occurrence and implications of Betaproteobacteria in drinking water. Although the sparse knowledge on the ecology and physiology of Betaproteobacteria thriving in tap or bottled natural mineral/spring drinking water (DW) is an evidence of this review, it is demonstrated that DW holds a high diversity of Betaproteobacteria, whose presence may not be innocuous. Frequently belonging to genera also found in humans, DW Betaproteobacteria are ubiquitous in different habitats, have the potential to resist antibiotics either due to intrinsic or acquired mechanisms, and hold different virulence factors. The combination of these factors places DW Betaproteobacteria in the list of candidates of emerging opportunistic pathogens. Improved bacterial identification of clinical isolates associated with opportunistic infections and additional genomic and physiological studies may contribute to elucidate the potential impact of these bacteria.

Pyoverdine-Dependent Virulence of Pseudomonas aeruginosa Isolates From Cystic Fibrosis Patients

The development of therapies that modulate or prevent pathogen virulence may be a key strategy for circumventing antimicrobial resistance. Toward that end, we examined the production of pyoverdine, a key virulence determinant, in ∼70 Pseudomonas aeruginosa isolates from pediatric cystic fibrosis patients. Pyoverdine production was heterogeneous and showed a clear correlation with pathogenicity in Caenorhabditis elegans and an acute murine pneumonia model. Examination showed pyoverdine accumulation in host tissues, including extrapharyngeal tissues of C. elegans and lung tissues of mice, where accumulation correlated with host death. Many of the isolates tested were resistant to multiple antimicrobials, so we assayed the ability of pyoverdine inhibitors to mitigate virulence and rescue pyoverdine-mediated host pathology. Representatives from three different classes of pyoverdine inhibitors (gallium, fluoropyrimidines, and LK11) significantly improved survival. Our findings highlight the utility of targeting virulence factors in general, and pyoverdine in particular, as a promising method to control bacterial pathogenesis as the utility of antimicrobials continues to diminish.