Effect of antibiotics on biofilm inhibition and induction measured by real-time cell analysis

Antimicrobial Sub-MIC induces Staphylococcus aureus biofilm formation without affecting the bacterial count

BACKGROUND

Biofilm formation is an essential virulence factor that creates a highly protected growth mode for Staphylococcus aureus (S. aureus) to survive in any hostile environment. Antibiotic sub-minimal inhibitory concentration (sub-MIC) may modulate the biofilm formation ability of bacterial pathogens, thereby affecting bacterial pathogenesis and infection outcomes. Intense antimicrobial therapy to treat biofilm-associated infections can control the pathogenic infection aggravation but cannot guarantee its complete eradication.

OBJECTIVE

This study aimed to assess the sub-MICs effect of 5 different antimicrobial classes on biofilm-forming capacity among Staphylococcus aureus clinical isolates using three different biofilm quantitation techniques.

METHODS

In this study, the effects of 5 different antimicrobial agents, namely, azithromycin, gentamicin, ciprofloxacin, doxycycline, and imipenem, at sub-MICs of 12.5%, 25%, and 50% were tested on 5 different clinical isolates of S. aureus. The biofilms formed in the absence and presence of different antimicrobial sub-MICs were then assessed using the following three different techniques: the crystal violet (CV) staining method, the quantitative PCR (qPCR) method, and the spread plate method (SPM).

RESULTS

Biofilm formation was significantly induced in 64% of the tested conditions using the CV technique. On the other hand, the qPCR quantifying the total bacterial count and the SPM quantifying the viable bacterial count showed significant induction only in 24% and 17.3%, respectively (Fig. 1). The difference between CV and the other techniques indicates an increase in biofilm biomass without an increase in bacterial growth. As expected, sub-MICs did not reduce the viable cell count, as shown by the SPM. The CV staining method revealed that sub-MICs of imipenem and ciprofloxacin had the highest significance rate (80%) showing an inductive effect on the biofilm development. On the other hand, doxycycline, azithromycin, and gentamicin displayed lower significance rates of 73%, 53%, and 47%, respectively.

CONCLUSION

Exposure to sub-MIC doses of antimicrobial agents induces the biofilm-forming capacity of S. aureus via increasing the total biomass without significantly affecting the bacterial growth of viable count.

Effects of Sucrose and Farnesol on Biofilm Formation by Streptococcus mutans and Candida albicans

Candida albicans (C. albicans) and Streptococcus mutans (S. mutans) are frequently detected in the plaque biofilms of children with early childhood caries. This study investigated the effects of sucrose and farnesol on biofilm formation by the oral pathogens S. mutans and C. albicans, including their synergistic interactions. Biofilm formation dynamics were monitored using the Cell Index (CI). The CI for S. mutans increased in the brain-heart infusion medium, peaking at 10 h; however, the addition of sucrose reduced the CI. For C. albicans yeast cells, the CI increased at sucrose concentrations > 0.5%, peaking at 2 h. Mixed cultures of S. mutans and C. albicans yeast cells showed significantly higher CI values in the presence of sucrose, suggesting a synergistic effect on biofilm formation. Farnesol consistently suppressed biofilm formation by C. albicans yeast cells, even in the presence of sucrose, and higher farnesol concentrations resulted in greater inhibition. Regarding C. albicans hyphal cells, sucrose did not enhance biofilm formation, whereas farnesol significantly reduced biofilm formation at all concentrations tested. These findings elucidate the complex roles of sucrose and farnesol in biofilm formation by S. mutans and C. albicans and emphasize the potential of farnesol as an effective oral biofilm inhibitor.

Single-Use, Metabolite Absorbing, Resonant Transducer (SMART) Culture Vessels for Label-Free, Continuous Cell Culture Progression Monitoring

Secreted metabolites are an important class of bio-process analytical technology (PAT) targets that can correlate to cell conditions. However, current strategies for measuring metabolites are limited to discrete measurements, resulting in limited understanding and ability for feedback control strategies. Herein, a continuous metabolite monitoring strategy is demonstrated using a single-use metabolite absorbing resonant transducer (SMART) to correlate with cell growth. Polyacrylate is shown to absorb secreted metabolites from living cells containing hydroxyl and alkenyl groups such as terpenoids, that act as a plasticizer. Upon softening, the polyacrylate irreversibly conformed into engineered voids above a resonant sensor, changing the local permittivity which is interrogated, contact-free, with a vector network analyzer. Compared to sensing using the intrinsic permittivity of cells, the SMART approach yields a 20-fold improvement in sensitivity. Tracking growth of many cell types such as Chinese hamster ovary, HEK293, K562, HeLa, and E. coli cells as well as perturbations in cell proliferation during drug screening assays are demonstrated. The sensor is benchmarked to show continuous measurement over six days, ability to track different growth conditions, selectivity to transducing active cell growth metabolites against other components found in the media, and feasibility to scale out for high throughput campaigns.

Electrochemical techniques for label-free and early detection of growing microbial cells and biofilms

Over the past decades, the misuse or abuse of antimicrobial agents to prevent and/or control infections has led to increased resistance of microbes to treatments, and antimicrobial resistance is now a subject of major global concern. In some cases, microbes possess the capacity to attach to biotic or abiotic surfaces, and to produce a protective polymeric matrix, forming biofilms of higher resistance and virulence compared to planktonic forms. To avoid further excessive and inappropriate use of antimicrobials, and to propose new effective treatments, it is very important to detect planktonic microbes and microbial biofilms in their early growth stage and at the point of need. In this review, we provide an overview of currently available electrochemical techniques, in particular impedimetric and voltamperometric methods, highlighting recent advances in the field and illustrating with examples in antibiotic susceptibility testing and microbial biofilm monitoring.

Evaluation of Anti-Bacterial and Anti-Biofilm Activity of Native Probiotic Strains of Lactobacillus Extracts

Background

Lactic acid bacteria produce various beneficial metabolites, including antimicrobial agents. Owing to the fast-rising antibiotic resistance among pathogenic microbes, scientists are exploring antimicrobials beyond antibiotics. In this study, we examined four Lactobacillus strains, namely L. plantarum 42, L. brevis 205, L. rhamnosus 239, and L. delbrueckii 263, isolated from healthy human microbiota, to evaluate their antibacterial and antifungal activity.

Methods

Lactobacillus strains were cultivated, and the conditioned media were obtained. The supernatant was then used to treat pathogenic bacteria and applied to the growth media containing fungal and bacterial strains. Additionally, the supernatant was separated to achieve the organic and aqueous phases. The two phases were then examined in terms of bacterial and fungal growth rates. Disk diffusion and MIC tests were conducted to determine strains with the most growth inhibition potential. Finally, the potent strains identified through the MIC test were tested on the pathogenic microorganisms to assess their effects on the formation of pathogenic biofilms.

Results

The organic phase of L. rhamnosus 239 extracts exhibited the highest antibacterial and antibiofilm effects, while that of L. brevis 205 demonstrated the most effective antifungal impact, with a MIC of 125 µg/mL against Saccharomyces cerevisiae.

Conclusion

This study confirms the significant antimicrobial impacts of the lactic acid bacteria strains on pathogenic bacteria and fungi; hence, they could serve as a reliable alternative to antibiotics for a safe and natural protection against pathogenic microorganisms.

Real-time monitoring of biofilm growth identifies andrographolide as a potent antifungal compound eradicating Candida biofilms

Candida species cause life-threatening infections with high morbidity and mortality rates and their resistance to conventional therapy is closely linked to biofilm formation. Thus, the development of new approaches to study Candida biofilms and the identification of novel therapeutic strategies could yield improved clinical outcomes. In the current study, we have set up an impedance-based in vitro system to study Candida spp. biofilms in real-time and to evaluate their sensitivity to two conventional antifungal groups used in clinical practice - azoles and echinocandins. Both fluconazole and voriconazole were unable to inhibit biofilm formation in most strains tested, while echinocandins showed biofilm inhibitory capacity at relatively low concentrations (starting from 0.625 mg/L). However, assays performed on 24 h Candida albicans and C. glabrata biofilms revealed that micafungin and caspofungin failed to eradicate mature biofilms at all tested concentrations, evidencing that once formed, Candida spp. biofilms are extremely difficult to eliminate using currently available antifungals. We then evaluated the antifungal and anti-biofilm effect of andrographolide, a natural compound isolated from the plant Andrographis paniculata with known antibiofilm activity on Gram-positive and Gram-negative bacteria. Optical density measures, impedance evaluation, CFU counts, and electron microscopy data showed that andrographolide strongly inhibits planktonic Candida spp. growth and halts Candida spp. biofilm formation in a dose-dependent manner in all tested strains. Moreover, andrographolide was capable of eliminating mature biofilms and viable cell numbers by up to 99.9% in the C. albicans and C. glabrata strains tested, suggesting its potential as a new approach to treat multi-resistant Candida spp. biofilm-related infections.

Dissolvable alginate hydrogel-based biofilm microreactors for antibiotic susceptibility assays

Biofilms are found in many infections in the forms of surface-adhering aggregates on medical devices, small clumps in tissues, or even in synovial fluid. Although antibiotic resistance genes are studied and monitored in the clinic, the structural and phenotypic changes that take place in biofilms can also lead to significant changes in how bacteria respond to antibiotics. Therefore, it is important to better understand the relationship between biofilm phenotypes and resistance and develop approaches that are compatible with clinical testing. Current methods for studying antimicrobial susceptibility are mostly planktonic or planar biofilm reactors. In this work, we develop a new type of biofilm reactor-three-dimensional (3D) microreactors-to recreate biofilms in a microenvironment that better mimics those in vivo where bacteria tend to form surface-independent biofilms in living tissues. The microreactors are formed on microplates, treated with antibiotics of 1000 times of the corresponding minimal inhibitory concentrations (1000 × MIC), and monitored spectroscopically with a microplate reader in a high-throughput manner. The hydrogels are dissolvable on demand without the need for manual scraping, thus enabling measurements of phenotypic changes. Bacteria inside the biofilm microreactors are found to survive exposure to 1000 × MIC of antibiotics, and subsequent comparison with plating results reveals no antibiotic resistance-associated phenotypes. The presented microreactor offers an attractive platform to study the tolerance and antibiotic resistance of surface-independent biofilms such as those found in tissues.

Nitrate and a nitrate-reducing Rothia aeria strain as potential prebiotic or synbiotic treatments for periodontitis

A few studies indicate that nitrate can reduce dysbiosis from a periodontitis point of view. However, these experiments were performed on samples from healthy individuals, and it is unknown if nitrate will be effective in periodontal patients, where the presence of nitrate-reducing bacteria is clearly reduced. The aim of this study was to test the effect of nitrate and a nitrate-reducing R. aeria (Ra9) on subgingival biofilms of patients with periodontitis. For this, subgingival plaque was incubated with 5 mM nitrate for 7 h (n = 20) or 50 mM nitrate for 12 h (n = 10), achieving a ~50% of nitrate reduction in each case. Additionally, Ra9 was combined with 5 mM nitrate (n = 11), increasing the nitrate reduced and nitrite produced (both p < 0.05). The addition of nitrate to periodontitis communities decreased biofilm mass (50 mM > 5 mM, both p < 0.05). Five millimolar nitrate, 50 mM nitrate and 5 mM nitrate + Ra9 led to 3, 28 and 20 significant changes in species abundance, respectively, which were mostly decreases in periodontitis-associated species. These changes led to a respective 15%, 63% (both p < 0.05) and 6% (not significant) decrease in the dysbiosis index. Using a 10-species biofilm model, decreases in periodontitis-associated species in the presence of nitrate were confirmed by qPCR (all p < 0.05). In conclusion, nitrate metabolism can reduce dysbiosis and biofilm growth of periodontitis communities. Five millimolar nitrate (which can be found in saliva after vegetable intake) was sufficient, while increasing this concentration to 50 mM (which could be achieved by topical applications such as a periodontal gel) increased the positive effects. Ra9 increased the nitrate metabolism of periodontitis communities and should be tested in vivo.

Ficin-Cyclodextrin-Based Docking Nanoarchitectonics of Self-Propelled Nanomotors for Bacterial Biofilm Eradication

Development of bioinspired nanomotors showing effective propulsion and cargo delivery capabilities has attracted much attention in the last few years due to their potential use in biomedical applications. However, implementation of this technology in realistic settings is still a barely explored field. Herein, we report the design and application of a multifunctional gated Janus platinum-mesoporous silica nanomotor constituted of a propelling element (platinum nanodendrites) and a drug-loaded nanocontainer (mesoporous silica nanoparticle) capped with ficin enzyme modified with β-cyclodextrins (β-CD). The engineered nanomotor is designed to effectively disrupt bacterial biofilms via H₂O₂-induced self-propelled motion, ficin hydrolysis of the extracellular polymeric matrix (EPS) of the biofilm, and controlled pH-triggered cargo (vancomycin) delivery. The effective synergic antimicrobial activity of the nanomotor is demonstrated in the elimination of Staphylococcus aureus biofilms. The nanomotor achieves 82% of EPS biomass disruption and a 96% reduction in cell viability, which contrasts with a remarkably lower reduction in biofilm elimination when the components of the nanomotors are used separately at the same concentrations. Such a large reduction in biofilm biomass in S. aureus has never been achieved previously by any conventional therapy. The strategy proposed suggests that engineered nanomotors have great potential for the elimination of biofilms.

Subinhibitory concentrations of florfenicol increase the biofilm formation of Piscirickettsia salmonis

Public health is facing a new challenge due to the increased bacterial resistance to most of the conventional antibacterial agents. Inadequate use of antibiotics in the Chilean aquaculture industry leads to the generation of multidrug resistance bacteria. Many fish pathogenic bacteria produce biofilm upon various sources of stress such as antibiotics, which provides several survival advantages for the bacterial life in community and can constitute a reservoir of pathogens in the marine environment. Being florfenicol a broad-spectrum antibiotic commonly used to treat infections in aquaculture, the aim of this study was to assess whether this antibiotic modulates in vitro the biofilm formation in several isolates of Piscirickettsia salmonis. Standard antibiotic-micro broth 96-flat well plates were used to determinate the minimal inhibitory concentration of florfenicol in eight different P. salmonis isolates. In vitro findings, with P. salmonis growing in the presence and absence of the antibiotic, exhibited a statistically significantly increase (p < .05) in biofilm formation in all the bacterial isolates cultivated with sub-MIC (defined as the half of the minimal inhibitory concentration in the presence of antibiotic) of florfenicol compared with controls (antibiotic-free broth). In conclusion, sub-MIC of florfenicol induced an increased biofilm formation in all P. salmonis isolates tested.

Analytical methods for assessing antimicrobial activity of nanomaterials in complex media: advances, challenges, and perspectives

Assessing the antimicrobial activity of engineered nanomaterials (ENMs), especially in realistic scenarios, is of great significance for both basic research and applications. Multiple analytical methods are available for analysis via off-line or on-line measurements. Real-world samples are often complex with inorganic and organic components, which complicates the measurements of microbial viability and/or metabolic activity. This article highlights the recent advances achieved in analytical methods including typical applications and specifics regarding their accuracy, cost, efficiency, and user-friendliness. Methodological drawbacks, technique gaps, and future perspectives are also discussed. This review aims to help researchers select suitable methods for gaining insight into antimicrobial activities of targeted ENMs in artificial and natural complex matrices.

Flagellar motility mediates biofilm formation in Aeromonas dhakensis

Aeromonas dhakensis possesses dual flagellar systems for motility under different environments. Flagella-mediated motility is necessary for biofilm formation through an initial attachment of bacteria to the surface, but this has not been elucidated in A. dhakensis. This study investigates the role of polar (flaH, maf1) and lateral (lafB, lafK and lafS) flagellar genes in the biofilm formation of a clinical A. dhakensis strain WT187 isolated from burn wound infection. Five deletion mutants and corresponding complemented strains were constructed using pDM4 and pBAD33 vectors, respectively, and analyzed for motility and biofilm formation using crystal violet staining and real-time impedance-based assays. All mutants were significantly reduced in swimming (p < 0.0001), swarming (p < 0.0001) and biofilm formation using crystal violet assay (p < 0.05). Real-time impedance-based analysis revealed WT187 biofilm was formed between 6 to 21 h, consisting of early (6-10 h), middle (11-18 h), and late (19-21 h) stages. The highest cell index of 0.0746 was recorded at 22-23 h and biofilms began to disperse starting from 24 h. Mutants Δmaf1, ΔlafB, ΔlafK and ΔlafS exhibited reduced cell index values at 6-48 h when compared to WT187 which indicates less biofilm formation. Two complemented strains cmaf1 and clafB exhibited full restoration to wild-type level in swimming, swarming, and biofilm formation using crystal violet assay, hence suggesting that both maf1 and lafB genes are involved in biofilm formation through flagella-mediated motility and surface attachment. Our study shows the role of flagella in A. dhakensis biofilm formation warrants further investigations.

Real-Time Impedance-Based Monitoring of the Growth and Inhibition of Osteomyelitis Biofilm Pathogen Staphylococcus aureus Treated with Novel Bisphosphonate-Fluoroquinolone Antimicrobial Conjugates

Osteomyelitis is a limb- and life-threatening orthopedic infection predominantly caused by Staphylococcus aureus biofilms. Bone infections are extremely challenging to treat clinically. Therefore, we have been designing, synthesizing, and testing novel antibiotic conjugates to target bone infections. This class of conjugates comprises bone-binding bisphosphonates as biochemical vectors for the delivery of antibiotic agents to bone minerals (hydroxyapatite). In the present study, we utilized a real-time impedance-based assay to study the growth of Staphylococcus aureus biofilms over time and to test the antimicrobial efficacy of our novel conjugates on the inhibition of biofilm growth in the presence and absence of hydroxyapatite. We tested early and newer generation quinolone antibiotics (ciprofloxacin, moxifloxacin, sitafloxacin, and nemonoxacin) and several bisphosphonate-conjugated versions of these antibiotics (bisphosphonate-carbamate-sitafloxacin (BCS), bisphosphonate-carbamate-nemonoxacin (BCN), etidronate-carbamate-ciprofloxacin (ECC), and etidronate-carbamate-moxifloxacin (ECX)) and found that they were able to inhibit Staphylococcus aureus biofilms in a dose-dependent manner. Among the conjugates, the greatest antimicrobial efficacy was observed for BCN with an MIC of 1.48 µg/mL. The conjugates demonstrated varying antimicrobial activity depending on the specific antibiotic used for conjugation, the type of bisphosphonate moiety, the chemical conjugation scheme, and the presence or absence of hydroxyapatite. The conjugates designed and tested in this study retained the bone-binding properties of the parent bisphosphonate moiety as confirmed using high-performance liquid chromatography. They also retained the antimicrobial activity of the parent antibiotic in the presence or absence of hydroxyapatite, albeit at lower levels due to the nature of their chemical modification. These findings will aid in the optimization and testing of this novel class of drugs for future applications to pharmacotherapy in osteomyelitis.

Ex vivo evaluation of antibiotic sensitivity in samples from endodontic infections

Objective

To develop an in vitro model for real-time monitoring of endodontic biofilm growth and evaluate the ex vivo effect of antibiotics on biofilm growth.

Material and Methods

Root canal samples were taken from 40 patients and inoculated into 96-well plates in a system that measures biofilm growth through electrical impedance. Biofilm bacterial composition at the genus and species level was analyzed by Illumina sequencing. ANCOM-BC corrected data were used to compare bacterial composition after antibiotic treatment through compositional analysis, and to compare microbiological with clinical data.

Results

The stationary phase was reached at 8 hours. The biofilm formed had a similar bacterial composition to the inoculum, and Enterococcus faecalis was virtually absent from the samples. The bacterial composition and the effect of antibiotics were sample-dependent. Metronidazole was the antibiotic that most inhibited biofilm formation and azithromycin the one that inhibited it in the highest percentage of cases. The antibiotic effect could not be related to the biofilm original bacterial composition.

Conclusions

The impedance system allowed real-time monitoring of endodontic biofilm formation, and we propose it as a model for ex vivo evaluation of the whole biofilm susceptibility to antimicrobials, as opposed to evaluating antibiotic sensitivity of specific bacterial isolates.

An open-source computational tool for measuring bacterial biofilm morphology and growth kinetics upon one-sided exposure to an antimicrobial source

Bacillus subtilis biofilms are well known for their complex and highly adaptive morphology. Indeed, their phenotypical diversity and intra-biofilm heterogeneity make this gram-positive bacterium the subject of many scientific papers on the structure of biofilms. The “robustness” of biofilms is a term often used to describe their level of susceptibility to antimicrobial agents and various mechanical and molecular inhibition/eradication methods. In this paper, we use computational analytics to quantify Bacillus subtilis morphological response to proximity to an antimicrobial source, in the form of the antiseptic chlorhexidine. Chlorhexidine droplets, placed in proximity to Bacillus subtilis macrocolonies at different distances result in morphological changes, quantified using Python-based code, which we have made publicly available. Our results quantify peripheral and inner core deformation as well as differences in cellular viability of the two regions. The results reveal that the inner core, which is often characterized by the presence of wrinkled formations in the macrocolony, is more preserved than the periphery. Furthermore, the paper describes a crescent-shaped colony morphology which occurs when the distance from the chlorhexidine source is 0.5 cm, as well as changes observed in the growth substrate of macrocolonies exposed to chlorhexidine.

Functional mgrA Influences Genetic Changes within a Staphylococcus aureus Cell Population over Time

Prolonged survival in the host-bacteria microenvironment drives the selection of alternative cell types in Staphylococcus aureus, permitting quasi-dormant sub-populations to develop. These facilitate antibiotic tolerance, long-term growth, and relapse of infection. Small Colony Variants (SCV) are an important cell type associated with persistent infection but are difficult to study in vitro due to the instability of the phenotype and reversion to the normal cell type. We have previously reported that under conditions of growth in continuous culture over a prolonged culture time, SCVs dominated a heterogenous population of cell types and these SCVs harbored a mutation in the DNA binding domain of the gene for the transcription factor, mgrA. To investigate this specific cell type further, S. aureus WCH-SK2-ΔmgrA itself was assessed with continuous culture. Compared to the wild type, the mgrA mutant strain required fewer generations to select for SCVs. There was an increased rate of mutagenesis within the ΔmgrA strain compared to the wild type, which we postulate is the mechanism explaining the increased emergence of SCV selection. The mgrA derived SCVs had impeded metabolism, altered MIC to specific antibiotics and an increased biofilm formation compared to non-SCV strain. Whole genomic sequencing detected single nucleotide polymorphisms (SNP) in phosphoglucosamine mutase glmM and tyrosine recombinase xerC. In addition, several genomic rearrangements were detected which affected genes involved in important functions such as antibiotic and toxic metal resistance and pathogenicity. Thus, we propose a direct link between mgrA and the SCV phenotype. IMPORTANCE Within a bacterial population, a stochastically generated heterogeneity of phenotypes allows continual survival against current and future stressors. The generation of a sub-population of quasi-dormant Small Colony Variants (SCV) in Staphylococcus aureus is such a mechanism, allowing for persistent or relapse of infection despite initial intervention seemingly clearing the infection. The use of continuous culture under clinically relevant conditions has allowed us to introduce time to the growth system and selects SCV within the population. This study provides valuable insights into the generation of SCV which are not addressed in standard laboratory generated models and reveals new pathways for understanding persistent S. aureus infection which can potentially be targeted in future treatments of persistent S. aureus infection.

Antibiofilm Properties of Antiseptic Agents Used on Pseudomonas aeruginosa Isolated from Diabetic Foot Ulcers

In diabetic foot ulcers (DFUs), biofilm formation is a major challenge that promotes wound chronicity and delays healing. Antiseptics have been proposed to combat biofilms in the management of DFUs. However, there is limited evidence on the activity of these agents against biofilms, and there are questions as to which agents have the best efficiency. Here, we evaluated the antibiofilm activity of sodium hypochlorite, polyvinylpyrrolidoneIodine (PVPI), polyhexamethylenebiguanide (PHMB) and octenidine against Pseudomonas aeruginosa strains using static and dynamic systems in a chronic-wound-like medium (CWM) that mimics the chronic wound environment. Using Antibiofilmogram®, a technology assessing the ability of antiseptics to reduce the initial phase of biofilm formation, we observed the significant activity of antiseptics against biofilm formation by P. aeruginosa (at 1:40 to 1:8 dilutions). Moreover, 1:100 to 1:3 dilutions of the different antiseptics reduced mature biofilms formed after 72 h by 10-log, although higher concentrations were needed in CWM (1:40 to 1:2). Finally, in the BioFlux200TM model, after biofilm debridement, sodium hypochlorite and PHMB were the most effective antiseptics. In conclusion, our study showed that among the four antiseptics tested, sodium hypochlorite demonstrated the best antibiofilm activity against P. aeruginosa biofilms and represents an alternative in the management of DFUs.

Investigating Biofilm Formation and Antibiofilm Activity Using Real Time Cell Analysis Method in Carbapenem Resistant Acinetobacter baumannii Strains

Acinetobacter baumannii is a significant nosocomial pathogen, with its biofilm forming capacity playing an important role in its pathogenicity. The fast and reliable detection of the biofilm formation and measurement of antibiofilm activity of various molecules are critical for combating A. baumannii infections. In this study, we aimed to detect biofilm formation by real time cell analyses (RTCA) method in clinical A. baumannii isolates and to investigate antibiofilm activities of tigecycline (TGC), N-acetylcysteine (NAC), and acetylsalicylic acid (ASA). The effect of the tested drugs on expressions of biofilm-related genes bap and csuE in clinical A. baumannii strains was also analyzed by real time quantitative reverse transcription polymerase chain reaction (RT-qPCR). Biofilm forming capacities for strong and weak biofilm producer A. baumannii strains were detected within 10 h by RTCA method (P < 0.05). We also observed that sub-minimum inhibitory concentrations of NAC + TGC and ASA + TGC combinations could significantly reduce biofilm formation and expression of biofilm-related genes in A. baumanii strains. No statistically significant activity of the tested drugs was detected against mature biofilms of the bacterial strains with the RTCA method. These results suggest that reproducible results on biofilm production capacity of A. baumannii strains and antibiofilm activities of various compounds can be obtained in a short time using RTCA method. Therefore, RTCA method seems to be a beneficial technique for biofilm detection and can help in combating A. baumannii infections by giving health providers the opportunity of implementing antibiofilm treatment strategies in a timely manner.

Single and combined effects of antibiotics and nanoplastics from surgical masks and plastic bottles on pathogens

Over the last decade, pollution of plastics and antibiotics has increased in its threat to the environment and human health. However, very limited information is available concerning impact of co-presence of plastics and antibiotics on environment and human health. Moreover, the potential ingestion and inhalation of nano(micro)plastics due to the disposable materials has dramatically increased. With the outbreak and spread of the COVID-19 in the world, disposable surgical masks and plastic bottles have been widely used by the public, and their rapid use and improper dispensing can cause to increase plastic pollution risk on human. However, impacts of co-presence of nano(micro)plastics and antibiotics on pathogens have yet been demonstrated. Therefore, this study aims to investigate the impact the individual and combined influences of nano-sized plastics (surgical mask and plastic bottles) and antibiotics (amoxicillin and spiramycin) towards the main susceptible bacterium (Staphylococcus epidermidis, Staphylococcus aureus, Bacillus subtilis, Escherichia coli, and Pseudomonas aeruginosa) by microbial activity, biofilm formation and their biochemical characteristics. The results showed that antimicrobial efficiencies of the tested antibiotics were reduced (approximately 10-98%) with the plastics. Moreover, the biochemical pathways of the microbial activity changed by the plastics entrance. Polymer structure and sorption play the role on the reduction in the inhibition of pathogens. In the meantime, the biofilm formation changed and characteristic of the extracellular polymeric substance with the co-presence of plastics and antibiotics mostly depended on the polymer structure, exposure time and sorption.

Evaluation of the Use of Antibiofilmogram Technology in the Clinical Evolution of Foot Ulcers Infected by Staphylococcus aureus in Persons Living with Diabetes: A Pilot Study

Infected diabetic foot ulcers (DFUs) represent a serious threat to public health because of their frequency and the severity of their consequences. DFUs are frequently infected by bacteria in biofilms, obstructing antibiotic action. Antibiofilmogram was developed to assess the impact of antibiotics to inhibit biofilm formation. This pilot study aimed to determine the benefits of this technology in predicting antibiotic activity on the outcome of 28 patients with Grade 2 DFUs that were infected by a monomicrobial Staphylococcus aureus. Patients with diabetes were followed during the antibiotic treatment (day 14) and the follow-up period of the study (day 45). The contribution of Antibiofilmogram was compared between patients with non-concordant results (n = 13) between antibiogram and Antibiofilmogram versus concordant results (n = 15). The clinical improvement of wounds (80.0% vs. 38.5%, p = 0.0245) and the absence of exudates (0% vs. 33.3%, p = 0.0282) were observed in concordant vs. discordant groups. This pilot study provides promising results for the interest of Antibiofilmogram in the prescription of antibiotics to prevent biofilm formation in infected DFUs.

Real-time monitoring of Pseudomonas aeruginosa biofilm growth dynamics and persister cells' eradication

Biofilm formation and the appearance of persister cells with low metabolic rates are key factors affecting conventional treatment failure and antibiotic resistance. Using impedance-based measurements, crystal violet staining and traditional culture we have studied the biofilm growth dynamics of 13 Pseudomonas aeruginosa strains under the effect of seven conventional antibiotics. Real-time growth quantifications revealed that the exposure of established P. aeruginosa biofilms to certain concentrations of ciprofloxacin, ceftazidime and tobramycin induced the emergence of persister cells, that showed different morphology and pigmentation, as well increased antibiotic resistance. Whole-genome sequencing of wildtype and persister cells identified several SNPs, a genomic inversion and a genomic duplication in one of the strains. However, these mutations were not uniquely associated with persisters, suggesting that the persistent phenotype may be related to metabolic and transcriptional changes. Given that mannitol has been proposed to activate bacterial metabolism, the synergistic combination of mannitol and ciprofloxacin was evaluated on clinical 48 h P. aeruginosa biofilms. When administered at doses ≥320 mg/L, mannitol was capable of preventing persister cell formation by efficiently activating dormant bacteria and making them susceptible to the antibiotic. These results were confirmed using viable colony counting. As the tested ciprofloxacin-mannitol combination appeared to fully eradicate mature biofilms, we conclude that impedance-based biofilm diagnostics, which permits antibiotic susceptibility testing and the identification of persister cells, is of great potential for the clinical practice and could aid in establishing treatment breakpoints for emerging biofilm-related infections.

Quorum quenching and anti-biofilm activities of halotolerant Bacillus strains isolated in different environments in Algeria

AIMS

The current study aimed to screen Bacillus strains with wide-spectrum quorum quenching (QQ) activity against N-acyl-l-homoserine lactones (AHLs), helpful in controlling virulence traits in Gram-negatives, including biofilm formation and also with anti-biofilm activity against Gram-positives.

METHODS AND RESULTS

A total of 94 halotolerant strains of Bacillus isolated from soil and salt-lake sediment samples in Algeria were examined for the presence of QQ activity against AHLs, the presence of the aiiA gene, encoding an AHL lactonase enzyme typical of Bacillus spp., antimicrobial and anti-biofilm activities against Pseudomonas aeruginosa and Streptococcus mutans. Of all strains of Bacillus spp. isolated, 48.9% showed antibacterial activity. In addition, 40% of these isolates showed a positive QQ activity against long-chain AHLs, of which seven strains presented the aiiA gene. Among the species with broad-spectrum QQ activity, the cell extract of Bacillus thuringiensis DZ16 showed antibiofilm activity against P. aeruginosa PAO1, reducing 60% using the Amsterdam active attachment (AAA) biofilm cultivation model. In addition, the cell extract of B. subtilis DZ17, also presenting a broad-spectrum QQ activity, significantly reduced Strep. mutans ATCC 25175 biofilm formations by 63% and 53% in the xCELLigence and the AAA model, respectively, without affecting growth. Strain DZ17 is of particular interest due to its explicit halophilic nature because it can thrive at salinities in the range of 6%-30%.

CONCLUSIONS

B. thuringiensis DZ16 and B. subtilis DZ17 strains have interesting antibacterial, QQ, and anti-biofilm activities. The high range of salinities accepted by these strains increases their biotechnological potential. This may open up their use as probiotics, the treatment and prevention of conventional and emerging infectious diseases.

SIGNIFICANCE AND IMPACT OF STUDY

The use of safe, economical and effective probiotics is limited to control the infections related to multi-resistant bacteria. In our study, we provide two promising agents with QQ, anti-biofilm and antibacterial activities.

Impacts of antibiotics on biofilm bacterial community and disinfection performance on simulated drinking water supply pipe wall

Overuse of antibiotics is accelerating the spread of resistance risk in the environment. In drinking water supply systems, the effect of antibiotics on the resistance of biofilm is unclear, and there have been few studies in disinfectant-containing systems. Here, we designed a series of drinking water supply reactors to investigate the effects of antibiotics on biofilm and bacteria in the water. At low concentrations, antibiotics could promote the growth of bacteria in biofilm; among the tested antibiotics (tetracycline, sulfadiazine and chloramphenicol), tetracycline had the strongest ability to promote this. And the antibiotic resistant bacteria (ARB) could inhibit the growth of bacteria in drinking water. Results have shown that antibiotics enhanced the bacterial chlorine resistance in the effluent, but reduced that in the biofilm. Furthermore, metagenomic analysis showed that antibiotics reduced the richness of biofilm communities. The dominant phyla in the biofilm were Proteobacteria, Planctomycetes, and Firmicutes. In tetracycline-treated biofilm, the dominant phylum was Planctomycetes. In sulfadiazine- and chloramphenicol-treated groups, bacteria with complex cell structures preferentially accumulated. The dominant class in biofilm in the ARB-added group was Gammaproteobacteria. The abundance of antibiotic resistant genes (ARGs) was correlated with biofilm community structure. This study shows that antibiotics make the biofilm community structure of drinking water more resistant to chlorine. ARGs may be selective for certain bacteria in the process, and there may ultimately be enhanced chlorine and antibiotic resistance of effluent bacteria in drinking water.

Evaluation of the Antimicrobial Efficacy of N-Acetyl-l-Cysteine, Rhamnolipids, and Usnic Acid-Novel Approaches to Fight Food-Borne Pathogens

In the food industry, the increasing antimicrobial resistance of food-borne pathogens to conventional sanitizers poses the risk of food contamination and a decrease in product quality and safety. Therefore, we explored alternative antimicrobials N-Acetyl-l-cysteine (NAC), rhamnolipids (RLs), and usnic acid (UA) as a novel approach to prevent biofilm formation and reduce existing biofilms formed by important food-borne pathogens (three strains of Salmonella enterica and two strains of Escherichia coli, Listeria monocytogenes, Staphylococcus aureus). Their effectiveness was evaluated by determining minimum inhibitory concentrations needed for inhibition of bacterial growth, biofilm formation, metabolic activity, and biofilm reduction. Transmission electron microscopy and confocal scanning laser microscopy followed by image analysis were used to visualize and quantify the impact of tested substances on both planktonic and biofilm-associated cells. The in vitro cytotoxicity of the substances was determined as a half-maximal inhibitory concentration in five different cell lines. The results indicate relatively low cytotoxic effects of NAC in comparison to RLs and UA. In addition, NAC inhibited bacterial growth for all strains, while RLs showed overall lower inhibition and UA inhibited only the growth of Gram-positive bacteria. Even though tested substances did not remove the biofilms, NAC represents a promising tool in biofilm prevention.

Influence of sub-inhibitory concentrations of antimicrobials on micrococcal nuclease and biofilm formation in Staphylococcus aureus

A major contributor to biomaterial associated infection (BAI) is Staphylococcus aureus. This pathogen produces a protective biofilm, making eradication difficult. Biofilms are composed of bacteria encapsulated in a matrix of extracellular polymeric substances (EPS) comprising polysaccharides, proteins and extracellular DNA (eDNA). S. aureus also produces micrococcal nuclease (MN), an endonuclease which contributes to biofilm composition and dispersion, mainly expressed by nuc1. MN expression can be modulated by sub-minimum inhibitory concentrations of antimicrobials. We investigated the relation between the biofilm and MN expression and the impact of the application of antimicrobial pressure on this relation. Planktonic and biofilm cultures of three S. aureus strains, including a nuc1 deficient strain, were cultured under antimicrobial pressure. Results do not confirm earlier findings that MN directly influences total biomass of the biofilm but indicated that nuc1 deletion stimulates the polysaccharide production per CFU in the biofilm in in vitro biofilms. Though antimicrobial pressure of certain antibiotics resulted in significantly increased quantities of polysaccharides per CFU, this did not coincide with significantly reduced MN activity. Erythromycin and resveratrol significantly reduced MN production per CFU but did not affect total biomass or biomass/CFU. Reduction of MN production may assist in the eradication of biofilms by the host immune system in clinical situations.

Bicarbonate Evokes Reciprocal Changes in Intracellular Cyclic di-GMP and Cyclic AMP Levels in Pseudomonas aeruginosa

The formation of Pseudomonas aeruginosa biofilms in cystic fibrosis (CF) is one of the most common causes of morbidity and mortality in CF patients. Cyclic di-GMP and cyclic AMP are second messengers regulating the bacterial lifestyle transition in response to environmental signals. We aimed to investigate the effects of extracellular pH and bicarbonate on intracellular c-di-GMP and cAMP levels, and on biofilm formation. P. aeruginosa was inoculated in a brain−heart infusion medium supplemented with 25 and 50 mM NaCl in ambient air (pH adjusted to 7.4 and 7.7 respectively), or with 25 and 50 mM NaHCO3 in 5% CO2 (pH 7.4 and 7.7). After 16 h incubation, c-di-GMP and cAMP were extracted and their concentrations determined. Biofilm formation was investigated using an xCelligence real-time cell analyzer and by crystal violet assay. Our results show that HCO3− exposure decreased c-di-GMP and increased cAMP levels in a dose-dependent manner. Biofilm formation was also reduced after 48 h exposure to HCO3−. The reciprocal changes in second messenger concentrations were not influenced by changes in medium pH or osmolality. These findings indicate that HCO3− per se modulates the levels of c-di-GMP and cAMP, thereby inhibiting biofilm formation and promoting the planktonic lifestyle of the bacteria.

Dalbavancin for the Treatment of Prosthetic Joint Infections: A Narrative Review

Dalbavancin (DAL) is a lipoglycopeptide with bactericidal activity against a very wide range of Gram-positive microorganisms. It also has unique pharmacokinetic properties, namely a prolonged half-life (around 181 h), which allows a convenient weekly dosing regimen, and good diffusion in bone tissue. These features have led to off-label use of dalbavancin in the setting of bone and joint infection, including prosthetic joint infections (PJI). In this narrative review, we go over the pharmacokinetic and pharmacodynamic characteristics of DAL, along with published in vitro and in vivo experimental models evaluating its activity against biofilm-embedded bacteria. We also examine published experience of osteoarticular infection with special attention to DAL and PJI.

AHLs-mediated quorum sensing threshold and its response towards initial adhesion of wastewater biofilms

Quorum sensing (QS) plays a crucial role during initial biofilm formation, however the QS threshold and the response of biofilm formation towards N-acyl-homoserine lactones (AHLs) remains largely unknown due to the limitation of nondestructive online methods for monitoring bacterial adherence and the complexity of QS system, which limits the application of QS signal reagents in biofilm reactors. In this study, bacterial QS threshold and its response of biofilm formation to AHLs in purely cultured Sphingomonas rubra biofilm as well as in three different wastewater biofilms #1-3 were investigated via real time cell analysis (RTCA). The main perspective was to study the biomass adherence in response to 12 different forms of AHLs at different concentrations. Results showed that bacterial adhesion was significantly improved by exogenous AHLs with the maximum increase of 2.26-, 2.36-, 2.52-, and 2.80- times biomass production in the four respective biofilms. Although the preferred form of AHL differed for various biofilms, the long-chain AHLs (12-14 carbons) resulted in an overall improvement of bacterial adhesion due to their stronger hydrophobicity and hydrolysis resistance. In addition, bacterial QS threshold of AHLs was observed to have a wide range of concentration from 10 ng/L to 10 μg/L. Meanwhile, QS response time to AHLs also showed a significant difference in different biofilms. Biofilm #2 inoculated with bulking sludge had lower QS threshold of 10 ng/L and faster response to most AHLs that is less than 6 h. Thus, considering the improvement of biofilm adhesion by AHLs, 10 ng/L of C12-HSL, 10 ng/L of C12-HSL, and 10 ng/L of C6-HSL were preferentially selected for wastewater biofilms #1-3 respectively. Unexpectedly, adding high-concentration of AHLs detected in sludges did not significantly improved the bacterial adhesion. Infact the addition of these AHLs at low concentrations or even undetected concentrations substantially improved bacterial adhesion, which could be explained by bacterial communities composition. According to the Pearson correlation analysis, 62% of the top 50 most abundant genera in bacterial communities were significantly negatively related to the response time of multiple AHLs, representing their fast QS response. The QS bacteria, Dechloromonas and Nitrospira have fast QS response for C4-HSL and C8-HSL while, Comamonadaceae has fast QS response for 3OC8-HSL, 3OC10-HSL, 3OC12-HSL, and 3OC14-HSL. In contrast, the rest 38% of the top most abundant genera, such as Ferruginibacter, Hyphomicrobium, and Terrimonas quickly responded to only one AHL, showing significant negative relationship with the response time of C6-HSL. Overall, this study provides an effective and convenient means to select appropriate AHL reagents to promote bacterial adhesion in biofilm systems. Moreover, it also suggests that exogenous AHLs may be useful in improving the settling property of bulking sludge.

Diagnosis of biofilm infections: current methods used, challenges and perspectives for the future

The diagnosis of biofilms continues to be a challenge, and there is no standardized protocol for such a diagnosis in clinical practice. In addition, some proposed methodologies are expensive to require significant amounts of time and a high number of trained staff, making them impracticable for clinical practice. In recent years, mass spectrophotometry/matrix-assisted laser desorption ionization time of flight (MALDI-TOF) has been applied it in biofilm studies. However, due to several problems and limitations of the technique, MALDI-TOF is far from being the gold standard for identifying biofilm formation. The omics analysis may prove to be a promising strategy for the diagnosis of biofilms in clinical laboratories since it allows the identification of pathogens in less time than needed for conventional techniques and in a more specific manner. However, omic tools are expensive and require qualified technical expertise, and an analysis of the data obtained needs to be careful not to neglect subpopulations in the biofilm. More studies must therefore be developed for creating a protocol that guarantees rapid biofilm identification, ensuring greater chances of success in infection control. This review discusses the current methods of microbial biofilm detection and future perspectives for its diagnosis in clinical practice.

Use of Quorum Sensing Inhibition Strategies to Control Microfouling

Interfering with the quorum sensing bacterial communication systems has been proposed as a promising strategy to control bacterial biofilm formation, a key process in biofouling development. Appropriate in vitro biofilm-forming bacteria models are needed to establish screening methods for innovative anti-biofilm and anti-microfouling compounds. Four marine strains, two Pseudoalteromonas spp. and two Vibrio spp., were selected and studied with regard to their biofilm-forming capacity and sensitivity to quorum sensing (QS) inhibitors. Biofilm experiments were performed using two biofilm cultivation and quantification methods: the xCELLigence^® system, which allows online monitoring of biofilm formation, and the active attachment model, which allows refreshment of the culture medium to obtain a strong biofilm that can be quantified with standard staining methods. Although all selected strains produced acyl-homoserine-lactone (AHL) QS signals, only the P. flavipulchra biofilm, measured with both quantification systems, was significantly reduced with the addition of the AHL-lactonase Aii20J without a significant effect on planktonic growth. Two-species biofilms containing P. flavipulchra were also affected by the addition of Aii20J, indicating an influence on the target bacterial strain as well as an indirect effect on the co-cultured bacterium. The use of xCELLigence^® is proposed as a time-saving method to quantify biofilm formation and search for eco-friendly anti-microfouling compounds based on quorum sensing inhibition (QSI) strategies. The results obtained from these two in vitro biofilm formation methods revealed important differences in the response of biosensor bacteria to culture medium and conditions, indicating that several strains should be used simultaneously for screening purposes and the cultivation conditions should be carefully optimized for each specific purpose.

A chip-based 128-channel potentiostat for high-throughput studies of bioelectrochemical systems: Optimal electrode potentials for anodic biofilms

The presence of microorganisms performing extracellular electron transfer has been established in many environments. Research to determine their role is moving slowly due to the high cost of potentiostats and the variance of data with small number of replicates. Here, we present a 128-channel potentiostat, connected to a 128 gold electrode array. Whereas the system is able to perform simultaneously 128 (bio)electrochemical measurements with an independent electrical signal input, the present manufacturing of the array limited the number of effective channels for this study to 77. We assessed the impact of 11 electrode potentials ranging from -0.45V to +0.2V vs. Ag/AgCl (7 replicates per potential) on the growth and electrochemical characteristics of anodic electroactive biofilms (EABs) formed by acetate-fed microbial communities. After 7 days of growth, maximum current was reached for electrodes poised at -0.3V, closely followed by -0.25V and -0.1V to +0.1V, a range well-fitting the midpoint potential of minerals naturally reduced by electroactive bacteria such as Geobacter Sulfurreducens. There was no significant difference in apparent midpoint potential of the EABs (-0.35V), suggesting that the mechanism of heterogeneous electron transfer was not affected by the electrode potential. The EABs poised below current plateau potential (≤-0.3V) exhibited slower growth but higher charge transfer parameters. The high-throughput and high reproducibility provided by the array may have a major facilitating impact on the field of electromicrobiology. Key aspects to improve are data processing algorithms to deal with the vast amount of generated data, and manufacturing of the electrode array itself.

Antibiofilm activity of flavonoids on staphylococcal biofilms through targeting BAP amyloids

The opportunistic pathogen Staphylococcus aureus is responsible for causing infections related to indwelling medical devices, where this pathogen is able to attach and form biofilms. The intrinsic properties given by the self-produced extracellular biofilm matrix confer high resistance to antibiotics, triggering infections difficult to treat. Therefore, novel antibiofilm strategies targeting matrix components are urgently needed. The Biofilm Associated Protein, Bap, expressed by staphylococcal species adopts functional amyloid-like structures as scaffolds of the biofilm matrix. In this work we have focused on identifying agents targeting Bap-related amyloid-like aggregates as a strategy to combat S. aureus biofilm-related infections. We identified that the flavonoids, quercetin, myricetin and scutellarein specifically inhibited Bap-mediated biofilm formation of S. aureus and other staphylococcal species. By using in vitro aggregation assays and the cell-based methodology for generation of amyloid aggregates based on the Curli-Dependent Amyloid Generator system (C-DAG), we demonstrated that these polyphenols prevented the assembly of Bap-related amyloid-like structures. Finally, using an in vivo catheter infection model, we showed that quercetin and myricetin significantly reduced catheter colonization by S. aureus. These results support the use of polyphenols as anti-amyloids molecules that can be used to treat biofilm-related infections.

Bacterial assembly during the initial adhesion phase in wastewater treatment biofilms

Biofilm start-up is a critical and time-consuming process in moving bed biofilm reactors (MBBRs), with the procedure beginning with bacteria being statically bound on surfaces. Studies addressing this critical process have mainly focused on constructing models based on single strains, although consideration of the unstable adhesion process of structured bacterial communities remains underexplored. In this study, impedance based real-time cell analysis (RTCA) was employed to quantitatively characterize the unstable adhesion process of structured bacterial communities collected from the aerobic tanks of eight full-scale wastewater treatment plants (WWTPs). The unstable adhesion time ranged from 8.85 ± 1.53 h to 17.06 ± 0.64 h, indicating significant differences in bacterial colonization properties. Using principal components analysis (PCA), Na⁺, K⁺ and proteins were found to significantly influence the biofilm unstable adhesion process. Furthermore, the differences in unstable adhesion times were closely related to the abundance of the most abundant operational taxonomic units (OTUs). The dominant OTUs mainly belonged to Aeromonadaceae and Enterobacteriaceae, with 73% found to be negatively corelated with unstable adhesion time. Furthermore, bacterial assembly during the initial adhesion phase was driven by bacterial interactions and key OTUs (exhibiting maximum connectivity in phylogenetic molecular ecological networks (pMENs)). Analysis of pMENs indicated that bacterial cooperation was a dominant factor in the initial adhesion, which may involve bacterial co-colonization, co-aggregation and communication. Considering keystone taxa were not identified, OTUs with max connectivity in pMENs were considered as key species. Although these key species play important roles in the connection of networks, their relative abundances were low and no significant relationships were observed with the unstable adhesion time. Overall, unstable adhesion in MBBRs is regulated by the dominant bacterial species and the alleviation of environmental variables by repulsive forces, providing potential strategies of dosing quorum sensing signals and key cations at the initial adhesion phase in reactors, to facilitate initial biofilm formation.

An In Vitro Model of Nonattached Biofilm-Like Bacterial Aggregates Based on Magnetic Levitation

Chronic infections are associated with the formation of nonattached biofilm-like aggregates. In vitro models of surface-attached biofilms do not always accurately mimic these processes. Here, we tested a new approach to create in vitro nonattached bacterial aggregates using the principle of magnetic levitation of biological objects placed into a magnetic field gradient. Bacteria grown under magnetic levitation conditions formed nonattached aggregates that were studied with confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM) and characterized quantitatively. Nonattached aggregates consisted of bacteria submerged into an extracellular matrix and demonstrated features characteristic of biofilms, such as a polymeric matrix that binds Ruby Red and Congo red dyes, a prerequisite of bacterial growth, and increased resistance to gentamicin. Three quantitative parameters were explored to characterize strain-specific potential to form nonattached aggregates: geometric sizes, relative quantities of aggregated and free-swimming bacteria, and Congo red binding. Among three tested Escherichia coli strains, one strain formed nonattached aggregates poorly, and for this strain, all three of the considered parameters were different from those of the other two strains (P < 0.05). Further, we characterized biofilm formation on plastic and agar surfaces by these strains and found that good biofilm formation ability does not necessarily indicate good nonattached aggregate formation ability, and vice versa. The model and quantitative methods can be applied for in vitro studies of nonattached aggregates and modeling bacterial behavior in chronic infections, as it is important to increase our understanding of the role that nonattached bacterial aggregates play in the pathogenesis of chronic diseases.IMPORTANCE An increasing amount of evidence indicates that chronic infections are associated with nonattached biofilm-like aggregates formed by pathogenic bacteria. These aggregates differ from biofilms because they form under low-shear conditions within the volume of biological fluids and they do not attach to surfaces. Here, we describe an in vitro model that provides nonattached aggregate formation within the liquid volume due to magnetic levitation. Using this model, we demonstrated that despite morphological and functional similarities of nonattached aggregates and biofilms, strains that exhibit good biofilm formation might exhibit poor nonattached aggregate formation, suggesting that mechanisms underlying the formation of biofilms and nonattached aggregates are not identical. The magnetic levitation approach can be useful for in vitro studies of nonattached aggregate formation and simulation of bacterial behavior in chronic infections.

Inactivation of the gene encoding the cationic antimicrobial peptide resistance factor MprF increases biofilm formation but reduces invasiveness of Listeria monocytogenes

AIMS

To understand the genetics involved in surface attachment and biofilm formation of Listeria monocytogenes.

METHODS AND RESULTS

An in vitro screen of a Himar1 transposon library of L. monocytogenes strain 15G01 identified three transposants that produced significantly different biofilm levels when compared to the wild-type strain; two mutants exhibited enhanced biofilm formation and one produced less biofilm biomass than the wild-type. The mutant 15G01 mprF::Himar1, which had a transposon insertion in the mprF gene, was selected for further analysis. The mutant produced a more densely populated biofilm on solid surfaces such as stainless steel and polystyrene, as determined using scanning electron and light microscopy. The 15G01 mprF::Himar1 mutant remained viable in biofilms, but showed an increase in sensitivity to the cationic antimicrobial gallidermin. The mutant also displayed reduced invasiveness in CaCo-2 intestinal cells, suggesting virulence properties are compromised by the inactivation of mprF.

CONCLUSIONS

Biofilm formation and gallidermin resistance of L. monocytogenes is influenced by mprF, but this trait is associated with a compromise in invasiveness.

SIGNIFICANCE AND IMPACT OF THE STUDY

The presence of pathogenic microorganisms in the food processing environment can cause a significant problem, especially when these microorganisms are established as biofilms. This study shows that the inactivation of the mprF gene results in enhanced biofilm formation and abiotic surface attachment of L. monocytogenes.

Nitrate as a potential prebiotic for the oral microbiome

The salivary glands actively concentrate plasma nitrate, leading to high salivary nitrate concentrations (5–8 mM) after a nitrate-rich vegetable meal. Nitrate is an ecological factor that can induce rapid changes in structure and function of polymicrobial communities, but the effects on the oral microbiota have not been clarified. To test this, saliva of 12 healthy donors was collected to grow in vitro biofilms with and without 6.5 mM nitrate. Samples were taken at 5 h (most nitrate reduced) and 9 h (all nitrate reduced) of biofilm formation for ammonium, lactate and pH measurements, as well as 16S rRNA gene Illumina sequencing. Nitrate did not affect biofilm growth significantly, but reduced lactate production, while increasing the observed ammonium production and pH (all p < 0.01). Significantly higher levels of the oral health-associated nitrate-reducing genera Neisseria (3.1 ×) and Rothia (2.9 ×) were detected in the nitrate condition already after 5 h (both p < 0.01), while several caries-associated genera (Streptococcus, Veillonella and Oribacterium) and halitosis- and periodontitis-associated genera (Porphyromonas, Fusobacterium, Leptotrichia, Prevotella, and Alloprevotella) were significantly reduced (p < 0.05 at 5 h and/or 9 h). In conclusion, the addition of nitrate to oral communities led to rapid modulation of microbiome composition and activity that could be beneficial for the host (i.e., increasing eubiosis or decreasing dysbiosis). Nitrate should thus be investigated as a potential prebiotic for oral health.

In-situ monitoring of the unstable bacterial adhesion process during wastewater biofilm formation: A comprehensive study

The initial bacterial adhesion phase is a pivotal and unstable step in the formation of biofilms. The initiation of biofilm formation is an unstable process caused by the reversible adhesion of bacteria, which is always time-consuming and yet to be elucidated. In this study, impedance-based real time cell analysis (RTCA) was employed to comprehensively investigate the initial bacterial adhesion process. Results showed that the time required for the unstable adhesion process was significantly (p < 0.05) reduced by increasing the initial concentration of bacteria, which is mainly attributed to the large deposition rate of bacteria at high concentrations. In addition, the unstable adhesion process is also regulated by shear stress, derived in this work from orbital shaking. Shear stress improves the reversibility of unstable bacterial attachment. Furthermore, attachment characteristics during the unstable phase vary between different species of bacteria (Sphingomonas rubra, Nakamurella multipartita and mixed bacteria). The S. rubra strain and mixed culture were more prone to adhere to the substratum surface during the unstable process, which was attributed to the smaller xDLVO energy barrier and motility of species in comparison with N. multipartita. Meanwhile, the molecular composition of extracellular polymeric substances (EPS) in the initial attachment phase presented a significant difference in expressed proteins, indicating the important role of proteins in EPS that strengthen bacterial adhesion. Overall, these findings suggest that during the biofilm reactor start-up process, seed sludge conditions, including the bacterial concentration, composition and hydraulics, need to be carefully considered.

Enhanced Electrochemical Impedance Spectroscopy Analysis of Microbial Biofilms on an Electrochemically In Situ Generated Graphene Interface

Biofilms can cause many bacterial diseases, such as dental disease. An in vitro detection of biofilms may help to screen antibiofilm drugs. An impedance measurement based on an Au electrode has been successfully used for in vitro real-time monitoring of animal and human cell growth. However, microbial growth on the Au electrode produced a poor signal because of the small size of microbial cells. We have recently demonstrated that graphene derivatives can be produced on a carbon electrode through facile electrochemical activation, thus forming a reduced graphene oxide-carbon electrode (rGO-CE). Based on this fact, we hypothesized that an in vitro formed rugose graphene layer of rGO-CE may provide a large surface area for the growth of microbial biofilms and can therefore produce a strong impedance signal in response to a change in the biomass. In this study, three oral bacteria, Streptococcus mutans (S. mutans), Actinomyces viscosus (A. viscosus), and Lactobacillus fermentum (L. fermentum), were cultured on the surfaces of rGO-CE. As a result, the impedance response signal of the rGO-CE for the growth of S. mutans and A. viscosus was found to be 3.3 times and 6.0 times stronger than that of the Au electrode at 1.17 and 54.7 kHz, respectively. In particular, the poorly adhering strain of L. fermentum also produced a detectable signal on the graphene electrode but not on the Au electrode at 1.17 kHz. Furthermore, destructions of the biofilms grown on the rGO-CE by cetylpyridinium chloride were successfully monitored by impedance changes. Overall, it is promising to develop a graphene-based impedance biosensor platform for biofilm study and antibiofilm drug screening.

Effect of Dalbavancin on Staphylococcal Biofilms When Administered Alone or in Combination With Biofilm-Detaching Compounds

Microorganisms grown in biofilms are more resistant to antimicrobial treatment and immune system attacks compared to their planktonic forms. In fact, infections caused by biofilm-forming Staphylococcus aureus and Staphylococcus epidermidis are a large threat for public health, including patients with medical devices. The aim of the current manuscript was to test the effect of dalbavancin, a recently developed lipoglycopeptide antibiotic, alone or in combination with compounds contributing to bacterial cell disaggregation, on staphylococcal biofilm formation and elimination. We used real-time impedance measurements in microtiter plates to study biofilm growth dynamics of S. aureus and S. epidermidis strains, in the absence or presence of dalbavancin, linezolid, vancomycin, cloxacillin, and rifampicin. Further experiments were undertaken to check whether biofilm-detaching compounds such as N-acetylcysteine (NAC) and ficin could enhance dalbavancin efficiency. Real-time dose–response experiments showed that dalbavancin is a highly effective antimicrobial, preventing staphylococcal biofilm formation at low concentrations. Minimum biofilm inhibitory concentrations were up to 22 higher compared to standard E-test values. Dalbavancin was the only antimicrobial that could halt new biofilm formation on established biofilms compared to the other four antibiotics. The addition of NAC decreased dalbavancin efficacy while the combination of dalbavancin with ficin was more efficient than antibiotic alone in preventing growth once the biofilm was established. Results were confirmed by classical biofilm quantification methods such as crystal violet (CV) staining and viable colony counting. Thus, our data support the use of dalbavancin as a promising antimicrobial to treat biofilm-related infections. Our data also highlight that synergistic and antagonistic effects between antibiotics and biofilm-detaching compounds should be carefully tested in order to achieve an efficient treatment that could prevent both biofilm formation and disruption.

Peculiarities of Biofilms Formation by Campylobacter Bacteria in Mixed Populations with Other Microbial Contaminants of Food Products

Peculiarities of biofilms formation by Campylobacter bacteria in mixed populations with other microbial contaminants was studied by real-time impedance spectroscopy on an automated xCelligence real time cell analyzer (RTCA). This method is based on measuring the medium resistance in special plates (E-plates) with interdigitated microelectrodes. Coculturing of campylobacter with coliform bacteria is accompanied by film formation; the intensity of this process varies depending on the type of the test cultures and the nature of their interaction in mixed populations. Film formation by C. jejuni during co-culturing with enterobacteria is maximum during the first hours and depends on the presence of stress factors in the environment. The biomatrix film was synthesized by 3 times more intensively in the presence of oxygen than in microaerobic conditions, and also by 1.7-4.3 times more active in the mixed culture with Enterobacter cloacae, E. coli, and K. pneumoniae. During co-culturing of campylobacter with salmonella, no enhanced film formation by the tested strains was observed. Unlike members of the genus Enterobacter intensively producing exopolysaccharides, pathogenic member of Enterobacteriaceae, salmonella, demonstrated weak capacity to form film matrix. The study of film formation by Campylobacter allows more accurate assessment of the effectiveness of sanitary bactericidal treatment of food industry facilities, predict the appearance of biofilms and the intensity of their formation depending son the nature of the antimicrobial effect and the used means.

N-alkylimidazolium Salts Functionalized with p-Coumaric and Cinnamic Acid: A Study of Their Antimicrobial and Antibiofilm Effects

The bacterial resistance to antibiotics has compromised the therapies used for bacterial infections. Nowadays, many strategies are being carried out to address this problem. Among them, the use of natural compounds like cinnamic and p-coumaric acids stands out. Nevertheless, their utilization is limited because of their unfavorable physicochemical properties. Due to the lack of new therapeutic alternatives for bacterial infections, novel strategies have emerged, such as the use of ionic liquids; given that they can show a broad spectrum of antibacterial activity, this is why we herein report the antibacterial and antibiofilm activity of a series of N-alkylimidazolium salts functionalized with p-coumaric and cinnamic acids. The results from this study showed better antibacterial activity against Gram-positive bacteria, with a predominance of the salts derived from coumaric acid and a correlation with the chain length. Additionally, a lower efficacy was observed in the inhibition of biofilm formation, highlighting the antibiofilm activity against Staphylococcus aureus, which decreased the production of the biofilm by 52% over the control. In conclusion, we suggest that the salts derived from p-coumaric acid are good alternatives as antibacterial compounds. Meanwhile, the salt derived from cinnamic acid could be a good alternative as an antibiofilm compound.

Design, synthesis, and discovery of novel oxindoles bearing 3-heterocycles as species-specific and combinatorial agents in eradicating Staphylococcus species

A series of new functionalized 3-indolylindolin-2-ones, 3-(1-methylpyrrol-2-yl)indolin-2-ones, and 3-(thiophen-2-yl)indolin-2-ones were synthesized by using novel indium (III)-catalysed reaction of various 3-diazoindolin-2-ones with indoles, 1-methylpyrrole, or thiophene via one-pot procedure. The newly synthesized compounds were characterized and screened for their in vitro antibacterial activity against various Staphylococcus species, including methicillin-resistant Staphylococcus aureus. results revealed that five compounds KS15, KS16, KS17, KS19, and KS20 exhibited potent and specific antibacterial activity against Staphylococcus species albeit inactive against Gram-negative bacteria. Especially, compounds exhibited superior antibacterial potency against Staphylococcus epidermidis compared to the reference drug streptomycin. The most potential compound KS16 also increased the susceptibility of Staphylococcus aureus to ciprofloxacin, gentamicin, kanamycin, and streptomycin. Among them, KS16 was found to be a synergistic compound with gentamicin and kanamycin. Furthermore, the cellular level of autolysin protein was increased from the KS16-treated Staphylococcus aureus cells. Finally, in vitro CCK-8 assays showed that KS16 exhibited no cytotoxicity at the minimum inhibitory concentrations used for killing Staphylococcus species. From all our results, novel oxindole compounds directly have lethal action or boost existing antibiotic power with the reduction of doses and toxicity in the treatment of multidrug-resistant Staphylococcus species.

Antimicrobial efficacy of the supernatant of Streptococcus dentisani against microorganisms implicated in root canal infections

The present study aimed to test the antimicrobial activity of Streptococcus dentisani (S. dentisani) supernatant against a collection of microorganisms implicated in dental root infections, and to analyze morphological changes induced in a selection of the tested microorganisms. A total of 22 microbial species were selected, and their growth was monitored by spectrophotometry in the presence and absence of the supernatant of S. dentisani at different assay concentrations (0.2×, 1×, 2×). The generation time and maximum growth rates were evaluated under every tested condition. Scanning electron microscope (SEM) images were obtained to assess the effect on the cell surface following incubation of the pathogens with the concentrated (2×) supernatant of S. dentisani. The supernatant of S. dentisani was found to exert effective inhibitory activity against most of the studied microorganisms implicated in dental root infections (20 out of 22). Total growth inhibition was observed in the case of Streptococcus oralis, Streptococcus sobrinus, Streptococcus salivarius, Prevotella intermedia, and Streptococcus mutans, while the rest of the microorganisms showed an increase in the generation time (between 30 min and 4 h). SEM images revealed structural changes in the membrane consistent with bacteriocin activity, although the effects were heterogeneous among the different species tested.

Testing Anti-Biofilm Polymeric Surfaces: Where to Start?

Present day awareness of biofilm colonization on polymeric surfaces has prompted the scientific community to develop an ever-increasing number of new materials with anti-biofilm features. However, compared to the large amount of work put into discovering potent biofilm inhibitors, only a small number of papers deal with their validation, a critical step in the translation of research into practical applications. This is due to the lack of standardized testing methods and/or of well-controlled in vivo studies that show biofilm prevention on polymeric surfaces; furthermore, there has been little correlation with the reduced incidence of material deterioration. Here an overview of the most common methods for studying biofilms and for testing the anti-biofilm properties of new surfaces is provided.

Clinical Pharmacokinetics and Pharmacodynamics of Oxazolidinones

Oxazolidinones are a class of synthetic antimicrobial agents with potent activity against a wide range of multidrug-resistant Gram-positive pathogens including methicillin-resistant Staphylococcus aureus and vancomycin-resistant enterococci. Oxazolidinones exhibit their antibacterial effects by inhibiting protein synthesis acting on the ribosomal 50S subunit of the bacteria and thus preventing formation of a functional 70S initiation complex. Currently, two oxazolidinones have been approved by the US Food and Drug Administration: linezolid and more recently tedizolid. Other oxazolidinones are currently under investigation in clinical trials. These antimicrobial agents exhibit a favourable pharmacokinetic profile with an excellent bioavailability and a good tissue and organ penetration. In-vitro susceptibility studies have shown that oxazolidinones are bacteriostatic against enterococci and staphylococci, and bactericidal for the majority of strains of streptococci. In the context of emergence of resistance to glycopeptides, oxazolidinones have become an effective alternative to vancomycin treatment frequently associated with nephrotoxicity. However, oxazolidinones, and linezolid in particular, are associated with significant adverse events, myelosuppression representing the main unfavourable side effect. More recently, tedizolid has been shown to effectively treat acute bacterial skin and skin structure infections. This newer oxazolidinone offers the advantages of once-daily dosing and a better safety profile in healthy volunteer studies (fewer gastrointestinal and haematological side effects). The potential use of tedizolid for other infections that could require longer therapy warrants further studies for positioning this new oxazolidinone in the available antimicrobial armamentarium. Moreover, other oxazolidinones are currently under active investigation.

Development of an in vitro system to study oral biofilms in real time through impedance technology: validation and potential applications

Background and objectives: We have developed a standardized, easy-to-use in vitro model to study single- and multiple-species oral biofilms in real time through impedance technology, which elucidates the kinetics of biofilm formation in 96-well plates, without the requirement for any further manipulation.

Design and Results: Using this system, biofilms of Streptococcus mutans appear to be sugar-dependent and highly resistant to amoxicilin, an antibiotic to which this oral pathogen is highly sensitive in a planktonic state. Saliva, tongue and dental plaque samples were also used as inocula to form multiple-species biofilms. DNA isolation and Illumina sequencing of the biofilms showed that the multi-species biofilms were formed by tens or hundreds of species, had a similar composition to the original inoculum, and included fastidious microorganisms which are important for oral health and disease. As an example of the potential applications of the model, we show that oral biofilms can be inhibited by amoxicilin, but in some cases they are induced by the antibiotic, suggesting the existence of responders and non-responders to a given antibiotic.

Conclusions: We therefore propose the system as a valid in vitro model to study oral biofilm dynamics, including their susceptibility to antibiotics, antiseptics or anti-adhesive compounds.

Advances in online methods for monitoring microbial growth

Understanding the characteristics of microbial growth is of great significance to many fields including in scientific research, the food industry, health care, and agriculture. Many methods have been established to characterize the process of microbial growth. Online and automated methods, in which sample transfer is avoided, are popular because they can facilitate the development of simple, safe, and effective growth monitoring. This review focuses on advances in online monitoring methods over the last decade (2008-2018). We specifically focus on optic- and electrochemistry-based techniques, either through contact measurements or contactless measurement. Strengths and weaknesses of each set of methods are described and we also speculate on forthcoming trends in the field.

Assessment of in vivo versus in vitro biofilm formation of clinical methicillin-resistant Staphylococcus aureus isolates from endotracheal tubes

Our aim was to demonstrate that biofilm formation in a clinical strain of methicillin-resistant Staphylococcus aureus (MRSA) can be enhanced by environment exposure in an endotracheal tube (ETT) and to determine how it is affected by systemic treatment and atmospheric conditions. Second, we aimed to assess biofilm production dynamics after extubation. We prospectively analyzed 70 ETT samples obtained from pigs randomized to be untreated (controls, n = 20), or treated with vancomycin (n = 32) or linezolid (n = 18). A clinical MRSA strain (MRSA-in) was inoculated in pigs to create a pneumonia model, before treating with antibiotics. Tracheally intubated pigs with MRSA severe pneumonia, were mechanically ventilated for 69 ± 16 hours. All MRSA isolates retrieved from ETTs (ETT-MRSA) were tested for their in vitro biofilm production by microtiter plate assay. In vitro biofilm production of MRSA isolates was sequentially studied over the next 8 days post-extubation to assess biofilm capability dynamics over time. All experiments were performed under ambient air (O₂) or ambient air supplemented with 5% CO₂. We collected 52 ETT-MRSA isolates (placebo N = 19, linezolid N = 11, and vancomycin N = 22) that were clonally identical to the MRSA-in. Among the ETT-MRSA isolates, biofilm production more than doubled after extubation in 40% and 50% under 5% CO₂ and O₂, respectively. Systemic antibiotic treatment during intubation did not affect this outcome. Under both atmospheric conditions, biofilm production for MRSA-in was at least doubled for 9 ETT-MRSA isolates, and assessment of these showed that biofilm production decreased progressively over a 4-day period after extubation. In conclusion, a weak biofilm producer MRSA strain significantly enhances its biofilm production within an ETT, but it is influenced by the ETT environment rather than by the systemic treatment used during intubation or by the atmospheric conditions used for bacterial growth.

Inhibition of Steptococcus mutans biofilm formation by extracts of Tenacibaculum sp. 20J, a bacterium with wide-spectrum quorum quenching activity

Background: Previous studies have suggested the quorum sensing signal AI-2 as a potential target to prevent the biofilm formation by Streptococcus mutans, a pathogen involved in tooth decay.

Objective: To obtain inhibition of biofilm formation by S. mutans by extracts obtained from the marine bacterium Tenacibaculum sp. 20J interfering with the AI-2 quorum sensing system.

Design: The AI-2 inhibitory activity was tested with the biosensors Vibrio harveyi BB170 and JMH597. S. mutans ATCC25175 biofilm formation was monitored using impedance real-time measurements with the xCELLigence system®, confocal laser microscopy, and the crystal violet quantification method.

Results: The addition of the cell extract from Tenacibaculum sp. 20J reduced biofilm formation in S. mutans ATCC25175 by 40–50% compared to the control without significantly affecting growth. A decrease of almost 40% was also observed in S. oralis DSM20627 and S. dentisani 7747 biofilms.

Conclusions: The ability of Tenacibaculum sp. 20J to interfere with AI-2 and inhibit biofilm formation in S. mutans was demonstrated. The results indicate that the inhibition of quorum sensing processes may constitute a suitable strategy for inhibiting dental plaque formation, although additional experiments using mixed biofilm models would be required.

Alterations of growth rate and gene expression levels of UPEC by antibiotics at sub-MIC

The host is the main environment for bacteria, and they also expose to many antibiotics during the treatment of infectious diseases in host body. In this study, it was aimed to investigate possible changes in growth rate and expression levels of three virulence genes (foc/foc, cnf1, and usp) in a uropathogenic E. coli standard strain within the presence of ciprofloxacin, nitrofurantoin, and trimethoprim-sulfamethoxazole. The UPEC C7 strain was grown on tryptic soy broth-TSB (control), TSB + ciprofloxacin, TSB + nitrofurantoin, and TSB + trimethoprim-sulfamethoxazole for determination of both growth rate and gene expression level. Antibiotics were added according to their sub-minimal inhibition concentrations. E-test was used to determine MIC values of antibiotics. Growth changes were measured in absorbance 600 nm during 24-h period. Total RNA isolations were performed after incubation for 24 h at 37 °C. Gene expression levels were determined by quantitative PCR. Tukey's post hoc test was used for statistical analysis. According to absorbance values, it has been shown that only ciprofloxacin and trimethoprim-sulfamethoxazole have lead significant decrease on growth rate. We also detected statistically significant differences in each gene expression levels for all antibiotics via relative quantification analysis. Fold changes in gene expression was found 0.65, 1.42, 0.23 for foc/foc gene; 0.01, 0.01, 2.84 for cnf1 gene; and 0.1, 0.01, 0.01 for usp gene in the presence of ciprofloxacin, nitrofurantoin, and trimethoprim/sulfamethoxazole, respectively. This investigation has shown that antibiotics can play a role as an environmental factor which may determine the pathogenicity of bacteria in vivo.