Mechanisms of antibiotic resistance in bacterial biofilms

Monitoring Growth and Removal of Pseudomonas Biofilms on Cellulose-Based Fabrics

Biofilms are often tolerant towards routine cleaning and disinfection processes. As they can grow on fabrics in household or healthcare settings, resulting in odors and serious health problems, it is necessary to contain biofilms through eradication strategies. The current study proposes a novel test model for the growth and removal of biofilms on textiles with Pseudomonas fluorescens and the opportunistic nosocomial pathogen Pseudomonas aeruginosa as model organisms. To assess the biofilm removal on fabrics, (1) a detergent-based, (2) enzyme-based, and (3) combined formulation of both detergent and enzymes (F1/2) were applied. Biofilms were analyzed microscopically (FE-SEM, SEM, 3D laser scanning- and epifluorescence microscopy), via a quartz crystal microbalance with mass dissipation monitoring (QCM-D) as well as plate counting of colonies. This study indicated that Pseudomonas spp. form robust biofilms on woven cellulose that can be efficiently removed via F1/2, proven by a significant reduction (p < 0.001) of viable bacteria in biofilms. Moreover, microscopic analysis indicated a disruption and almost complete removal of the biofilms after F1/2 treatment. QCM-D measurements further confirmed a maximal mass dissipation change after applying F1/2. The combination strategy applying both enzymes and detergent is a promising antibiofilm approach to remove bacteria from fabrics.

Cytotoxic and Antibacterial Prenylated Acylphloroglucinols from Hypericum olympicum L

Two new bicyclo[3.3.1]nonane type bicyclic polyprenylated acylphloroglucinol derivatives (BPAPs), olympiforin A and B as well as three known prenylated phloroglucinols, were isolated from the aerial parts of Hypericum olympicum L. The structures of the isolated compounds were established by means of spectral techniques (HRESIMS and 1D and 2D NMR). All compounds were tested on a panel of human tumor (MDA-MB-231, EJ, K-562, HL-60 and HL-60/DOX) and non- tumorigenic (HEK-293 and EA.hy926) cell lines using the MTT assay. All tested compounds exerted significant in vitro cytotoxicity with IC₅₀ values ranging from 1.2 to 24.9 μM and from 0.9 to 34 μM on tumor and non-cancerous cell lines, respectively. Most of the compounds had good selectivity and were more cytotoxic to the tumor cell lines than to the normal ones. A degradation of the precursor caspase 9 for some of the compounds was observed; therefore, the intrinsic pathway of apoptosis is the most likely mechanism of cytotoxic activity. The BPAPs were examined for antibacterial and antibiofilm activity through the broth microdilution method and the protocol of Stepanović. They showed a moderate effect against Enterococcus faecalis and Streptococcus pyogenes but a very profound activity against Staphylococcus aureus with minimum inhibitory concentrations (MIC) in the range of 0.78-2 mg/L. Olympiforin B also had a great effect against methicillin-resistant S. aureus (MRSA) with an MIC value of 1 mg/L and a very significant antibiofilm activity on that strain with a minimum biofilm inhibition concentration (MBIC) value of 0.5 mg/L. The structures of the isolated compounds were in silico evaluated using ADME and drug likeness tests.

Distinct Screening Approaches Uncover PA14_36820 and RecA as Negative Regulators of Biofilm Phenotypes in Pseudomonas aeruginosa PA14

Pseudomonas aeruginosa commonly infects hospitalized patients and the lungs of individuals with cystic fibrosis. This species is known for forming biofilms, which are communities of bacterial cells held together and encapsulated by a self-produced extracellular matrix. The matrix provides extra protection to the constituent cells, making P. aeruginosa infections challenging to treat. We previously identified a gene, PA14_16550, which encodes a DNA-binding TetR-type repressor and whose deletion reduced biofilm formation. Here, we assessed the transcriptional impact of the 16550 deletion and found six differentially regulated genes. Among them, our results implicated PA14_36820 as a negative regulator of biofilm matrix production, while the remaining 5 had modest effects on swarming motility. We also screened a transposon library in a biofilm-impaired ΔamrZ Δ16550 strain for restoration of matrix production. Surprisingly, we found that disruption or deletion of recA increased biofilm matrix production, both in biofilm-impaired and wild-type strains. Because RecA functions both in recombination and in the DNA damage response, we asked which function of RecA is important with respect to biofilm formation by using point mutations in recA and lexA to specifically disable each function. Our results implied that loss of either function of RecA impacts biofilm formation, suggesting that enhanced biofilm formation may be one physiological response of P. aeruginosa cells to loss of either RecA function. IMPORTANCE Pseudomonas aeruginosa is a notorious human pathogen well known for forming biofilms, communities of bacteria that protect themselves within a self-secreted matrix. Here, we sought to find genetic determinants that impacted biofilm matrix production in P. aeruginosa strains. We identified a largely uncharacterized protein (PA14_36820) and, surprisingly, RecA, a widely conserved bacterial DNA recombination and repair protein, as negatively regulating biofilm matrix production. Because RecA has two main functions, we used specific mutations to isolate each function and found that both functions influenced matrix production. Identifying negative regulators of biofilm production may suggest future strategies to reduce the formation of treatment-resistant biofilms.

Functionalization of 3D Printed Scaffolds Using Polydopamine and Silver Nanoparticles for Bone-Interfacing Applications

The prevention of bacterial colonization and the stimulation of osseointegration are two major requirements for bone-interfacing materials to reduce the incidence of complications and promote the restoration of the patient's health. The present investigation developed an effective, two-step functionalization of 3D printed scaffolds intended for bone-interfacing applications using a simple polydopamine (PDA) dip-coating method followed by the formation of silver nanoparticles (AgNPs) after a second coating step in silver nitrate. 3D printed polymeric substrates coated with a ∼20 nm PDA layer and 70 nm diameter AgNPs proved effective in hindering Staphylococcus aureus biofilm formation, with a 3000-8000-fold reduction in the number of bacterial colonies formed. The implementation of porous geometries significantly accelerated osteoblast-like cell growth. Microscopy characterization further elucidated homogeneity, features, and penetration of the coating inside the scaffold. A proof-of-concept coating on titanium substrates attests to the transferability of the method to other materials, broadening the range of applications both in and outside the medical sector. The antibacterial efficiency of the coating is likely to lead to a decrease in the number of bacterial infections developed after surgery in the presence of these coatings on prosthetics, thus translating to a reduction in revision surgeries and improved health outcomes.

Antibacterial and Antibiofilm Activities of β-Lapachone by Modulating the Catalase Enzyme

Background: Bacterial infections constantly have a large impact on public health, because of increased rates of resistance and reduced frequency of development of novel antibiotics. The utility of conventional antibiotics for treating bacterial infections has become increasingly challenging. The aim of the study was to assess the antibacterial effect of β-Lapachone (β-Lap), a novel synthetic compound. Methods: The antibacterial activity of the β-Lap compound was examined against laboratory strains by agar well diffusion method and broth dilution assay. Growth kinetics in presence of β-Lap on Staphylococcus aureus, Staphylococcus epidermidis, and Pseudomonas aeruginosa (ATCC 27853) were assessed by microplate alamarBlue assay. Crystal violet blue assay was used for biofilm inhibition and biofilm eradication. P. aeruginosa catalase (KatA) complexed with β-Lap was modeled using molecular docking approach. Results: β-Lap exhibited potent antimicrobial activity against laboratory strains of bacteria with MIC of 0.2 mM for S. saprophyticus and Staphylococcus aureus, and 0.04 mM for Staphylococcus epidermidis and Pseudomonas aeruginosa ATCC 27853. The inhibition of catalase enzyme was found to be the cause for its antibacterial activity. Bioinformatics analysis suggests that β-Lap can inhibit KatA activity by interacting with catalase proximal active site and heme binding site. The activity of some commercial antibiotics was enhanced in association with β-Lap. In addition, β-Lap inhibited the biofilm formation and eradicated the already formed and ultra-mature biofilms of aforesaid bacterial strains. Conclusion: These observations indicated that β-Lap could be a promising antibacterial agent for the treatment and prevention of infectious diseases.

The Role of Coagulase-Negative Staphylococci Biofilms on Late-Onset Sepsis: Current Challenges and Emerging Diagnostics and Therapies

Infections are one of the most significant complications of neonates, especially those born preterm, with sepsis as one of the principal causes of mortality. Coagulase-negative staphylococci (CoNS), a group of staphylococcal species that naturally inhabit healthy human skin and mucosa, are the most common cause of late-onset sepsis, especially in preterms. One of the risk factors for the development of CoNS infections is the presence of implanted biomedical devices, which are frequently used for medications and/or nutrient delivery, as they serve as a scaffold for biofilm formation. The major concerns related to CoNS infections have to do with the increasing resistance to multiple antibiotics observed among this bacterial group and biofilm cells’ increased tolerance to antibiotics. As such, the treatment of CoNS biofilm-associated infections with antibiotics is increasingly challenging and considering that antibiotics remain the primary form of treatment, this issue will likely persist in upcoming years. For that reason, the development of innovative and efficient therapeutic measures is of utmost importance. This narrative review assesses the current challenges and emerging diagnostic tools and therapies for the treatment of CoNS biofilm-associated infections, with a special focus on late-onset sepsis.

Biology and Regulation of Staphylococcal Biofilm

Despite continuing progress in medical and surgical procedures, staphylococci remain the major Gram-positive bacterial pathogens that cause a wide spectrum of diseases, especially in patients requiring the utilization of indwelling catheters and prosthetic devices implanted temporarily or for prolonged periods of time. Within the genus, if Staphylococcus aureus and S. epidermidis are prevalent species responsible for infections, several coagulase-negative species which are normal components of our microflora also constitute opportunistic pathogens that are able to infect patients. In such a clinical context, staphylococci producing biofilms show an increased resistance to antimicrobials and host immune defenses. Although the biochemical composition of the biofilm matrix has been extensively studied, the regulation of biofilm formation and the factors contributing to its stability and release are currently still being discovered. This review presents and discusses the composition and some regulation elements of biofilm development and describes its clinical importance. Finally, we summarize the numerous and various recent studies that address attempts to destroy an already-formed biofilm within the clinical context as a potential therapeutic strategy to avoid the removal of infected implant material, a critical event for patient convenience and health care costs.

Potential of nanocarriers using ABC transporters for antimicrobial resistance

Some existing therapies such as antimicrobial regimens, drug combinations, among others, are employed for the treatment of infections that are a threat to the healthcare industry owing to low drug efficacy, increasing dosage regimes, mutation in bacteria and poor pharmacokinetics/pharmacodynamics properties of drugs. Overuse of antibiotics is fostering the emergence and spread of inherent microorganisms that confer temporary and permanent resistance. Nanocarriers accompanying the ABC transporter efflux mechanism are considered 'magic bullets' (i.e., effective antibacterial agents) and can traverse the multidrug-resistant obstacle owing to their multifunctional capabilities (e.g., nanostructure, variability in in vivo functions, etc.) by interfering with normal cell activity. This review focuses on novel applications of the ABC transporter pump by nanocarriers to overcome the resistance caused by the various organs of the body. Teaser: Nanocarriers, the ABC transporter and overcoming multidrug resistance.

The Role of Biofilms in the Pathogenesis of Animal Bacterial Infections

Biofilms are bacterial aggregates embedded in a self-produced, protective matrix. The biofilm lifestyle offers resilience to external threats such as the immune system, antimicrobials, and other treatments. It is therefore not surprising that biofilms have been observed to be present in a number of bacterial infections. This review describes biofilm-associated bacterial infections in most body systems of husbandry animals, including fish, as well as in sport and companion animals. The biofilms have been observed in the auditory, cardiovascular, central nervous, digestive, integumentary, reproductive, respiratory, urinary, and visual system. A number of potential roles that biofilms can play in disease pathogenesis are also described. Biofilms can induce or regulate local inflammation. For some bacterial species, biofilms appear to facilitate intracellular invasion. Biofilms can also obstruct the healing process by acting as a physical barrier. The long-term protection of bacteria in biofilms can contribute to chronic subclinical infections, Furthermore, a biofilm already present may be used by other pathogens to avoid elimination by the immune system. This review shows the importance of acknowledging the role of biofilms in animal bacterial infections, as this influences both diagnostic procedures and treatment.

Perspective: The viscoelastic properties of biofilm infections and mechanical interactions with phagocytic immune cells

Biofilms are viscoelastic materials that are a prominent public health problem and a cause of most chronic bacterial infections, in large part due to their resistance to clearance by the immune system. Viscoelastic materials combine both solid-like and fluid-like mechanics, and the viscoelastic properties of biofilms are an emergent property of the intercellular cohesion characterizing the biofilm state (planktonic bacteria do not have an equivalent property). However, how the mechanical properties of biofilms are related to the recalcitrant disease that they cause, specifically to their resistance to phagocytic clearance by the immune system, remains almost entirely unstudied. We believe this is an important gap that is ripe for a large range of investigations. Here we present an overview of what is known about biofilm infections and their interactions with the immune system, biofilm mechanics and their potential relationship with phagocytosis, and we give an illustrative example of one important biofilm-pathogen (Pseudomonas aeruginosa) which is the most-studied in this context. We hope to inspire investment and growth in this relatively-untapped field of research, which has the potential to reveal mechanical properties of biofilms as targets for therapeutics meant to enhance the efficacy of the immune system.

Natural Polyphenols for Prevention and Treatment of Urinary Tract Infections

Urinary tract infections (UTIs) are the second most common type of bacterial infection worldwide. UTIs are gender-specific diseases, with a higher incidence in women. This type of infection could occur in the upper part of the urogenital tract, leading to pyelonephritis and kidney infections, or in the lower part of the urinary tract, leading to less serious pathologies, mainly cystitis and urethritis. The most common etiological agent is uropathogenic E. coli (UPEC), followed by Pseudomonas aeruginosa and Proteus mirabilis. Conventional therapeutic treatment involves the use of antimicrobial agents, but due to the dramatic increase in antimicrobial resistance (AMR), this strategy has partially lost its therapeutic efficacy. For this reason, the search for natural alternatives for UTI treatment represents a current research topic. Therefore, this review summarized the results of in vitro and animal- or human-based in vivo studies aimed to assess the potential therapeutic anti-UTI effects of natural polyphenol-based nutraceuticals and foods. In particular, the main in vitro studies were reported, describing the principal molecular therapeutic targets and the mechanism of action of the different polyphenols studied. Furthermore, the results of the most relevant clinical trials for the treatment of urinary tract health were described. Future research is needed to confirm and validate the potential of polyphenols in the clinical prophylaxis of UTIs.

Bioactive compounds: a goldmine for defining new strategies against pathogenic bacterial biofilms?

Most human infectious diseases are caused by microorganisms growing as biofilms. These three-dimensional self-organized communities are embedded in a dense matrix allowing microorganisms to persistently inhabit abiotic and biotic surfaces due to increased resistance to both antibiotics and effectors of the immune system. Consequently, there is an urgent need for novel strategies to control biofilm-associated infections. Natural products offer a vast array of chemical structures and possess a wide variety of biological properties; therefore, they have been and continue to be exploited in the search for potential biofilm inhibitors with a specific or multi-locus mechanism of action. This review provides an updated discussion of the major bioactive compounds isolated from several natural sources - such as plants, lichens, algae, microorganisms, animals, and humans - with the potential to inhibit biofilm formation and/or to disperse established biofilms by bacterial pathogens. Despite the very large number of bioactive products, their exact mechanism of action often remains to be clarified and, in some cases, the identity of the active molecule is still unknown. This knowledge gap should be filled thus allowing development of these products not only as novel drugs to combat bacterial biofilms, but also as antibiotic adjuvants to restore the therapeutic efficacy of current antibiotics.

Toward Pathogenic Biofilm Suppressors: Synthesis of Amino Derivatives of Pillar[5]arene and Supramolecular Assembly with DNA

New amino derivatives of pillar[5]arene were obtained in three stages with good yields. It was shown that pillar[5]arene containing thiaether and tertiary amino groups formed supramolecular complexes with low molecular weight model DNA. Pillar[5]arene formed complexes with a DNA nucleotide pair at a ratio of 1:2 (macrocycle/DNA base pairs), as demonstrated by UV-visible and fluorescence spectroscopy. The association constants of pillar[5]arene with DNA were lgKass1:1 = 2.38 and lgKass1:2 = 5.07, accordingly. By using dynamic light scattering and transmission electron microscopy, it was established that the interaction of pillar[5]arene containing thiaether and tertiary amino groups (concentration of 10-5 M) with a model nucleic acid led to the formation of stable nanosized macrocycle/DNA associates with an average particle size of 220 nm. It was shown that the obtained compounds did not exhibit a pronounced toxicity toward human adenocarcinoma cells (A549) and bovine lung epithelial cells (LECs). The hypothesis about a possible usage of the synthesized macrocycle for the aggregation of extracellular bacterial DNA in a biofilm matrix was confirmed by the example of St. Aureus. It was found that pillar[5]arene at a concentration of 10^-5 M was able to reduce the thickness of the St. Aureus biofilm by 15%.

Exploring the Microbial Community and Functional Characteristics of the Livestock Feces Using the Whole Metagenome Shotgun Sequencing

The foodborne illness is the important public health concerns, and the livestock feces are known to be one of the major reservoirs of foodborne pathogens. Also, it was reported that 45.5% of foodborne illness outbreaks have been associated with the animal products contaminated with the livestock feces. In addition, it has been known that the persistence of a pathogens depends on many potential virulent factors including the various virulent genes. Therefore, the first step to understanding the public health risk of livestock feces is to identify and describe microbial communities and potential virulent genes that contribute to bacterial pathogenicity. We used the whole metagenome shotgun sequencing to evaluate the prevalence of foodborne pathogens and to characterize the virulence associated genes in pig and chicken feces. Our data showed that the relative abundance of potential foodborne pathogens, such as Bacillus cereus was higher in chickens than pigs at the species level while the relative abundance of foodborne pathogens including Campylobacter coli was only detected in pigs. Also, the microbial functional characteristics of livestock feces revealed that the gene families related to "Biofilm formation and quorum sensing" were highly enriched in pigs than chicken. Moreover, the variety of gene families associated with "Resistance to antibiotics and toxic compounds" were detected in both animals. These results will help us to prepare the scientific action plans to improve awareness and understanding of the public health risks of livestock feces.

Antibacterial and antibiofilm mechanisms of carbon dots: a review

Due to the increasing bacterial resistance to conventional antibiotics, developing safe and effective approaches to combat infections caused by bacteria and biofilms has become an urgent clinical problem. Recently, carbon dots (CDs) have received great attention as a promising alternative to conventional antimicrobial agents due to their excellent antimicrobial efficacy and biocompatibility. Although CDs have been widely used in the field of antibacterial applications, their antibacterial and antibiofilm mechanisms have not been systematically discussed. This review provides a systematic overview on the complicated mechanisms of antibacterial and antibiofilm CDs based on recent development.

The first case of Escherichia fergusonii with biofilm in China and literature review

BACKGROUND

Escherichia fergusonii is a rare opportunistic pathogen in humans and animals, especially with biofilm.

METHODS

In one case, E. fergusonii with biofilm was detected in the bile, and silver staining was used to prove it had biofilm. The clinical characteristics and drug susceptibility of eight cases of E. fergusonii retrieved from the literature were also summarized.

RESULTS

This is a case of E. fergusonii with biofilm, which has not been reported in China. The 8 cases retrieved from the literature did not specify whether they had biofilm, but we analyzed their clinical characteristics and drug susceptibility. All patients were treated with antimicrobial drugs. 8 cases showed sensitivity to piperacillin/tazobactam and imipenem in 6 cases (75%), but poor sensitivity to levofloxacin and ciprofloxacin.

CONCLUSION

The silver staining method proved biofilm in this case, which is the first case of E. fergusonii with biofilm in China.

Tetracycline accumulation in biofilms enhances the selection pressure on Escherichia coli for expression of antibiotic resistance

Microorganisms are present as either biofilm or planktonic species in natural and engineered environments. Little is known about the selection pressure emanating from exposure to sub-minimal inhibitory concentration of antibiotics on planktonic vs. biofilm bacteria. In this study, an E. coli bioreporter was used to develop biofilms on glass and high-density polyethylene (HDPE) surfaces, and compared with the corresponding planktonic bacteria in antibiotic resistance expression when exposed to a range of μg/L levels of tetracycline. The antibiotic resistance-associated fluorescence emissions from biofilm E. coli reached up to 1.6 times more than those from planktonic bacteria. The intensively developed biofilms on glass surfaces caused the embedded bacteria to experience higher selection pressure and express more antibiotic resistance than those on HDPE surfaces. The temporal pattern of fluorescence emissions from biofilm E. coli was consistent with the biofilm-developing processes during the experimental period. The increased expression of antibiotic resistance from biofilm bacteria could be attributed to the high affinity of tetracycline with extracellular polymeric substances (EPS). The enhanced accumulation of tetracycline in biofilms could exert higher selection pressure on the embedded bacteria. These results suggest that in many natural and engineered systems the higher antibiotic resistance in biofilm bacteria could be attributed partially to the retention antibiotics by the EPS in biofilms.

A cascade nanozyme with antimicrobial effects against nontypeable Haemophilus influenzae

Otitis media (OM) is the main cause of pediatric antibiotic prescriptions. Nontypeable Haemophilus influenzae (NTHi) is a major OM pathogen, which forms a biofilm that resists conventional antimicrobials and immune clearance. Thus, novel treatments that are effective against NTHi and its biofilm are urgently required. Nanozymes (often inorganic nanoparticles) mimic natural enzymes' catalytic activities to generate strong antimicrobials at the site of infection, and thus represent one of the emerging solutions to the crisis of antimicrobial resistance. They mimic natural enzymes' activities, such as generating strong antimicrobials catalytically at the site of infection, to minimize overexposure. However, that in situ generation often relies on Reactive Oxygen Species (ROS) as precursors, a prerequisite that limits the broad deployment of nanozymes. To address this challenge, we designed a cascade nanozyme that generates an antiseptic, HOBr, from a ubiquitous non-ROS, i.e., O₂, which successfully eradicates NTHi. The cascade nanozyme simultaneously exhibits glucose oxidase (GOx)-like activity from gold nanoparticles (AuNPs) and haloperoxidase (HPO)-mimicking activity from vanadium pentoxide nanowires (V₂O₅ NWs) connected using dopamine (DPA). The cascade nanozyme demonstrated strong antimicrobial efficacy against NTHi and its biofilm, while showing improved biocompatibility compared to the nanozyme of V₂O₅ NWs alone. The cascade nanozyme thus points to a material-oriented infectious disease treatment strategy, where small-molecule antimicrobials are generated in real time at the site of infection for the benefit of autonomous dosing. This strategy potentially mitigates the development of antimicrobial resistance and reduces side effects.

Effect of erythromycin on epiphytic bacterial communities and water quality in wetlands

The occurrence of antibiotics such as erythromycin (ERY) under macrolide group, has long been acknowledged for negatively affecting ecosystems in freshwater environments. However, the effects of ERY on water quality and microbial communities in epiphytic biofilms are poorly understood. Here, Scanning Electron Microscopy (SEM), High-throughput sequencing, and physicochemical analytical methods were employed to unravel the impact of ERY on the water quality and bacterial morphology, biodiversity, composition, interaction, and ecological function in epiphytic biofilms attached to Vallisneria natans and artificial plants in mesocosmic wetlands. The study showed that ERY exposure significantly impaired the nutrient removal capacity (TN, TP, and COD) and altered the epiphytic bacterial morphology of V. natans and artificial plants. ERY did not affect the bacterial α-diversity. Notwithstanding ERY decreased the bacterial composition, but the relative abundance of Proteobacteria and Patescibacteria spiked by 62.2 % and 54 %, respectively, in V. natans, while Desulfobacteria and Chloroflexi increased by 8.9 % and 11.2 %, respectively, in artificial plants. Notably, ERY disturbed the food web structure and metabolic pathways such as carbohydrate metabolism, amino acid metabolism, energy metabolism, cofactor and vitamin metabolism, membrane transport, and signal transduction. This study revealed that ERY exposure disrupted the bacterial morphology, composition, interaction or food web structure, and metabolic functions in epiphytic biofilm. These data underlined that ERY negatively impacts epiphytic bacterial communities and nutrient removal in wetlands.

Physical Approaches to Prevent and Treat Bacterial Biofilm

Prosthetic joint infection (PJI) presents several clinical challenges. This is in large part due to the formation of biofilm which can make infection eradication exceedingly difficult. Following an extensive literature search, this review surveys a variety of non-pharmacological methods of preventing and/or treating biofilm within the body and how they could be utilized in the treatment of PJI. Special attention has been paid to physical strategies such as heat, light, sound, and electromagnetic energy, and their uses in biofilm treatment. Though these methods are still under study, they offer a potential means to reduce the morbidity and financial burden related to multiple stage revisions and prolonged systemic antibiotic courses that make up the current gold standard in PJI treatment. Given that these options are still in the early stages of development and offer their own strengths and weaknesses, this review offers an assessment of each method, the progress made on each, and allows for comparison of methods with discussion of future challenges to their implementation in a clinical setting.

Biofilm formation of pathogenic bacteria isolated from aquatic animals

Bacterial biofilm formation is one of the dynamic processes, which facilitates bacteria cells to attach to a surface and accumulate as a colony. With the help of biofilm formation, pathogenic bacteria can survive by adapting to their external environment. These bacterial colonies have several resistance properties with a higher survival rate in the environment. Especially, pathogenic bacteria can grow as biofilms and can be protected from antimicrobial compounds and other substances. In aquaculture, biofilm formation by pathogenic bacteria has emerged with an increased infection rate in aquatic animals. Studies show that Vibrio anguillarum, V. parahaemolyticus, V. alginolyticus, V. harveyi, V. campbellii, V. fischeri, Aeromonas hydrophila, A. salmonicida, Yersinia ruckeri, Flavobacterium columnare, F. psychrophilum, Piscirickettsia salmonis, Edwardsiella tarda, E. ictaluri, E. piscicida, Streptococcus parauberis, and S. iniae can survive in the environment by transforming their planktonic form to biofilm form. Therefore, the present review was intended to highlight the principles behind biofilm formation, major biofilm-forming pathogenic bacteria found in aquaculture systems, gene expression of those bacterial biofilms and possible controlling methods. In addition, the possibility of these pathogenic bacteria can be a serious threat to aquaculture systems.

A Review of Biofilm Formation of Staphylococcus aureus and Its Regulation Mechanism

Bacteria can form biofilms in natural and clinical environments on both biotic and abiotic surfaces. The bacterial aggregates embedded in biofilms are formed by their own produced extracellular matrix. Staphylococcus aureus (S. aureus) is one of the most common pathogens of biofilm infections. The formation of biofilm can protect bacteria from being attacked by the host immune system and antibiotics and thus bacteria can be persistent against external challenges. Therefore, clinical treatments for biofilm infections are currently encountering difficulty. To address this critical challenge, a new and effective treatment method needs to be developed. A comprehensive understanding of bacterial biofilm formation and regulation mechanisms may provide meaningful insights against antibiotic resistance due to bacterial biofilms. In this review, we discuss an overview of S. aureus biofilms including the formation process, structural and functional properties of biofilm matrix, and the mechanism regulating biofilm formation.

Adhesion and Anti-Adhesion Abilities of Potentially Probiotic Lactic Acid Bacteria and Biofilm Eradication of Honeybee (Apis mellifera L.) Pathogens

Lactic acid bacteria (LAB) naturally inhabits the organisms of honeybees and can exhibit adhesive properties that protect these insects against various pathogenic microorganisms. Thus, cell surface (auto-aggregation, co-aggregation, hydrophobicity) and adhesive properties of LAB to two abiotic (polystyrene and glass) and four biotic (collagen, gelatin, mucus, and intestinal Caco-2 cells) surfaces were investigated. Additionally, anti-adhesion activity and the eradication of honeybee pathogen biofilms by LAB metabolites (culture supernatants) were determined. The highest hydrophobicity was demonstrated by Pediococcus pentosaceus 19/1 (63.16%) and auto-aggregation by Lactiplantibacillus plantarum 18/1 (71.91%). All LAB showed a broad spectrum of adhesion to the tested surfaces. The strongest adhesion was noted for glass. The ability to co-aggregate with pathogens was tested for the three most potently adherent LAB strains. All showed various levels of co-aggregation depending on the pathogen. The eradication of mature pathogen biofilms by LAB metabolites appeared to be weaker than their anti-adhesive properties against pathogens. The most potent anti-adhesion activity was observed for L. plantarum 18/1 (98.80%) against Paenibacillus apiarius DSM 5582, while the strongest biofilm eradication was demonstrated by the same LAB strain against Melissococcus plutonius DSM 29964 (19.87%). The adhesive and anti-adhesive activity demonstrated by LAB can contribute to increasing the viability of honeybee colonies and improving the conditions in apiaries.

Proof-of-Concept Standardized Approach Using a Single-Disk Method Analogous to Antibiotic Disk Diffusion Assays for Routine Phage Susceptibility Testing in Diagnostic Laboratories

Application of bacteriophages is increasingly being implemented in clinical therapies. Prior susceptibility testing should be regarded as mandatory, but standards are lacking. The objective of this research was to develop a highly standardized methodology to facilitate phage susceptibility testing (PST) in clinical microbiology routine laboratories. Therefore, EUCAST methods established for single disk-based antibiotic susceptibility testing (AST) were adapted. In a first step, basic parameters were evaluated using well-studied Escherichia phage T4-Escherichia coli combinations. In addition, test results were compared to those from conventional spot test and efficiency of plating (EOP) approaches. In a second step, the applicability of the methodology and the most promising test parameters were demonstrated for five other frequently isolated clinical bacterial species and their corresponding phages. At present, the method predominantly leads to qualitative rather than quantitative results. This disk-based approach provides a standardized, easy-to-handle, reproducible and reliable PST protocol by relying on well-established routine procedures in diagnostic laboratories. IMPORTANCE Application of bacteriophages in clinical therapies is attractive due to increasing rates of isolation of multidrug-resistant bacteria worldwide. As the phage effect is highly specific, prior susceptibility testing of target bacteria is mandatory. Of note, established standards are lacking. In this research, we adapted the single-disk method for antibiotic susceptibility testing to phage susceptibility testing (PST) in order to provide a standardized, easy-to-handle, reproducible, and reliable PST protocol for application in diagnostic routine laboratories.

Suicidal chemotaxis in bacteria

Bacteria commonly live in surface-associated communities where steep gradients of antibiotics and other chemical compounds can occur. While many bacterial species move on surfaces, we know surprisingly little about how such antibiotic gradients affect cell motility. Here, we study the behaviour of the opportunistic pathogen Pseudomonas aeruginosa in stable spatial gradients of several antibiotics by tracking thousands of cells in microfluidic devices as they form biofilms. Unexpectedly, these experiments reveal that bacteria use pili-based ('twitching') motility to navigate towards antibiotics. Our analyses suggest that this behaviour is driven by a general response to the effects of antibiotics on cells. Migrating bacteria reach antibiotic concentrations hundreds of times higher than their minimum inhibitory concentration within hours and remain highly motile. However, isolating cells - using fluid-walled microfluidic devices - reveals that these bacteria are terminal and unable to reproduce. Despite moving towards their death, migrating cells are capable of entering a suicidal program to release bacteriocins that kill other bacteria. This behaviour suggests that the cells are responding to antibiotics as if they come from a competing colony growing nearby, inducing them to invade and attack. As a result, clinical antibiotics have the potential to lure bacteria to their death.

The Quinone-Derived Small Molecule M5N32 Is an Effective Anti-Helicobacter pylori Agent Both In Vivo and In Vitro

BACKGROUND

Helicobacter pylori has become increasingly resistant to all commonly used clinical antibiotics. Therefore, new anti-H. pylori drugs need to be identified. Recently, quinones were found to inhibit growth of H. pylori with quinone-derived small-molecule compounds identified as having antitumor effects.

METHODS

The minimum inhibitory concentrations of the compounds against H. pylori were measured by agar plate dilution method. The inhibition of biofilm formation by the compounds was assessed by SYTO9-PI double staining. The reactive oxygen species induced by the compounds were detected by DCFH-DA stain. The clearance effects of the compounds for H. pylori in mouse were evaluated by counting colony-forming units and hematoxylin and eosin staining.

RESULTS

Our results revealed strong inhibition of M5N32 in vitro against H. pylori in both the planktonic and biofilm-forming states. Resistance to M5N32 was not developed in successive generations of the bacteria. In vivo, the combination of M5N32 and omeprazole showed enhanced effects in comparison to the standard triple therapy. M5N32 was nontoxic to normal tissues.

CONCLUSIONS

M5N32 is effective in the treatment of H. pylori infections, providing potential development of anti-H. pylori medicines in the treatment of H. pylori infections.

Multispecies biofilm architecture determines bacterial exposure to phages

Numerous ecological interactions among microbes-for example, competition for space and resources, or interaction among phages and their bacterial hosts-are likely to occur simultaneously in multispecies biofilm communities. While biofilms formed by just a single species occur, multispecies biofilms are thought to be more typical of microbial communities in the natural environment. Previous work has shown that multispecies biofilms can increase, decrease, or have no measurable impact on phage exposure of a host bacterium living alongside another species that the phages cannot target. The reasons underlying this variability are not well understood, and how phage-host encounters change within multispecies biofilms remains mostly unexplored at the cellular spatial scale. Here, we study how the cellular scale architecture of model 2-species biofilms impacts cell-cell and cell-phage interactions controlling larger scale population and community dynamics. Our system consists of dual culture biofilms of Escherichia coli and Vibrio cholerae under exposure to T7 phages, which we study using microfluidic culture, high-resolution confocal microscopy imaging, and detailed image analysis. As shown previously, sufficiently mature biofilms of E. coli can protect themselves from phage exposure via their curli matrix. Before this stage of biofilm structural maturity, E. coli is highly susceptible to phages; however, we show that these bacteria can gain lasting protection against phage exposure if they have become embedded in the bottom layers of highly packed groups of V. cholerae in co-culture. This protection, in turn, is dependent on the cell packing architecture controlled by V. cholerae biofilm matrix secretion. In this manner, E. coli cells that are otherwise susceptible to phage-mediated killing can survive phage exposure in the absence of de novo resistance evolution. While co-culture biofilm formation with V. cholerae can confer phage protection to E. coli, it comes at the cost of competing with V. cholerae and a disruption of normal curli-mediated protection for E. coli even in dual species biofilms grown over long time scales. This work highlights the critical importance of studying multispecies biofilm architecture and its influence on the community dynamics of bacteria and phages.

Characterization of amniotic fluid sludge in preterm and term gestations

OBJECTIVE

To describe the characteristics of amniotic fluid sludge obtained from patients in term and preterm gestations.

METHODS

This cross-sectional study included patients with dense aggregates of particulate matter detected in amniotic fluid, observed with transvaginal sonography. All patients were in labor and had an impending delivery, either preterm or at term. Echogenic material contained within amniotic fluid was retrieved transvaginally by needle amniotomy under direct visualization. The amniotic fluid analysis consisted of a Gram stain, cultures for aerobic/anaerobic bacteria and genital mycoplasmas, and a white blood cell count.

RESULTS

Twenty-five patients ranging from 18 to 41 weeks of gestation were included in the study. We observed the following: (1) the appearance of amniotic fluid was consistent with pus-like material, vernix, or meconium by naked eye examination; (2) samples collected before 33 weeks of gestation (n = 13) had a pus-like appearance; however, after this gestational age, most of the samples [83% (10/12)] appeared to be consistent with vernix; (3) amniotic fluid cultures were positive for microorganisms in 13 patients, of which 10 were preterm gestations before 33 weeks; (4) the most frequent microorganisms retrieved by culture were genital mycoplasmas (Ureaplasma urealyticum [46% (6/13)]), followed by Mycoplasma hominis [31% (4/13)] and Candida albicans [15% (2/13)]; and (5) patients with sonographic particulate matter in preterm gestations frequently presented acute histologic chorioamnionitis and funisitis, but these conditions were rare in patients at term.

CONCLUSION

The nature of amniotic fluid particulate material varies as a function of gestational age. The material obtained in preterm gestations is frequently related to an inflammatory process, while that obtained at term is often consistent with vernix and appears to represent a maturational process.

Serious Risk of Tigecycline Resistance in Escherichia coli Isolated from Swine Manure

The emergence of the plasmid-mediated tigecycline resistance gene tetX family in pig farms has attracted worldwide attention. The use of tetracycline antibiotics in pig farms has a facilitating effect on the prevalence of the tetX family, but the relationship among its presence, expression, and resistance phenotype in resistant bacteria is unknown. In this study, the presence and expression characteristics of tetracycline resistance genes (TRGs) in 89 strains of doxycycline-resistant E. coli (DRE) isolated from pig manure samples from 20 pig farms under low concentrations of doxycycline stress (2 μg/mL) were analyzed. The detection rate of tetO was 96.63%, which is higher than those of other TRGs, such as tetA (94.38%), tetX (76.40%), tetB (73.03%), and tet(X4) (69.66%). At least three TRG types were present in DRE strains, which thus showed extensive resistance to tetracycline antibiotics, and 37% of these strains were resistant to tigecycline. In the presence of a low concentration of doxycycline, tetA played an important role, and the expression and existence ratio of TRGs indicated low expression of TRGs. Furthermore, the doxycycline resistance of DRE was jointly determined by the total absolute abundance of TRGs, and the absolute abundance of tetX and tet(X4) was significantly positively associated with tigecycline resistance in DRE (P < 0.05). Overall, DRE isolated from swine manure is an important reservoir of the tetX family, which suggests that DRE in swine manure has a high risk of tigecycline resistance, poses a potential threat to human health, and should be of public concern.

Biomimetic Transparent Nanoplasmonic Meshes by Reverse-Nanoimprinting for Bio-Interfaced Spatiotemporal Multimodal SERS Bioanalysis

Multicellular systems, such as microbial biofilms and cancerous tumors, feature complex biological activities coordinated by cellular interactions mediated via different signaling and regulatory pathways, which are intrinsically heterogeneous, dynamic, and adaptive. However, due to their invasiveness or their inability to interface with native cellular networks, standard bioanalysis methods do not allow in situ spatiotemporal biochemical monitoring of multicellular systems to capture holistic spatiotemporal pictures of systems-level biology. Here, a high-throughput reverse nanoimprint lithography approach is reported to create biomimetic transparent nanoplasmonic microporous mesh (BTNMM) devices with ultrathin flexible microporous structures for spatiotemporal multimodal surface-enhanced Raman spectroscopy (SERS) measurements at the bio-interface. It is demonstrated that BTNMMs, supporting uniform and ultrasensitive SERS hotspots, can simultaneously enable spatiotemporal multimodal SERS measurements for targeted pH sensing and non-targeted molecular detection to resolve the diffusion dynamics for pH, adenine, and Rhodamine 6G molecules in agarose gel. Moreover, it is demonstrated that BTNMMs can act as multifunctional bio-interfaced SERS sensors to conduct in situ spatiotemporal pH mapping and molecular profiling of Escherichia coli biofilms. It is envisioned that the ultrasensitive multimodal SERS capability, transport permeability, and biomechanical compatibility of the BTNMMs can open exciting avenues for bio-interfaced multifunctional sensing applications both in vitro and in vivo.

Antibiofilm and Antivirulence Activities of Gold and Zinc Oxide Nanoparticles Synthesized from Kimchi-Isolated Leuconostoc sp. Strain C2

The rapid emergence of antimicrobial resistance (AMR) among bacterial pathogens results in antimicrobial treatment failure and the high mortality rate associated with AMR. The application of nanoparticles synthesized from probiotics will be widely accepted due to their efficacy and biocompatibility in treating microbial infections in humans. The current work sought to isolate and identify lactic acid bacteria (LAB) from Kimchi. Based on 16S rRNA gene sequencing, the LAB isolate C2 was identified as a member of the genus Leuconostoc. The obtained supernatant from Leuconostoc sp. strain C2 was employed for the green synthesis of metal (AuNPs) and metal oxide (ZnONPs) nanoparticles. UV–vis absorption spectra, FTIR analysis, XRD, DLS, FE-TEM, and EDS mapping were used to fully characterize these C2-AuNPs and C2-ZnONPs. The C2-AuNPs were found to be spherical in shape, with a size of 47.77 ± 5.7 nm and zeta potential of −19.35 ± 0.67 mV. The C2-ZnONPs were observed to be rod-shaped and 173.77 ± 14.53 nm in size. The C2-ZnONPs zeta potential was determined to be 26.62 ± 0.35 mV. The C2-AuNPs and C2-ZnONPs were shown to have antimicrobial activity against different pathogens. Furthermore, these nanoparticles inhibited the growth of Candida albicans. The antibiofilm and antivirulence properties of these NPs against Pseudomonas aeruginosa and Staphylococcus aureus were thoroughly investigated. C2-AuNPs were reported to be antibiofilm and antivirulence against P. aeruginosa, whereas C2-ZnONPs were antibiofilm and antivirulence against both P. aeruginosa and S. aureus. Furthermore, these nanoparticles disrupted the preformed mature biofilm of P. aeruginosa and S. aureus. The inhibitory impact was discovered to be concentration-dependent. The current research demonstrated that C2-AuNPs and C2-ZnONPs exhibited potential inhibitory effects on the biofilm and virulence features of bacterial pathogens. Further studies are needed to unravel the molecular mechanism behind biofilm inhibition and virulence attenuation.

pH variation in medical implant biofilms: Causes, measurements, and its implications for antibiotic resistance

The advent of implanted medical devices has greatly improved the quality of life and increased longevity. However, infection remains a significant risk because bacteria can colonize device surfaces and form biofilms that are resistant to antibiotics and the host's immune system. Several factors contribute to this resistance, including heterogeneous biochemical and pH microenvironments that can affect bacterial growth and interfere with antibiotic biochemistry; dormant regions in the biofilm with low oxygen, pH, and metabolites; slow bacterial growth and division; and poor antibody penetration through the biofilm, which may also be regions with poor acid product clearance. Measuring pH in biofilms is thus key to understanding their biochemistry and offers potential routes to detect and treat latent infections. This review covers the causes of biofilm pH changes and simulations, general findings of metabolite-dependent pH gradients, methods for measuring pH in biofilms, effects of pH on biofilms, and pH-targeted antimicrobial-based approaches.

Combating multidrug-resistant Helicobacter pylori with moenomycin A in combination with clarithromycin or metronidazole

Current treatment of Helicobacter pylori involves a triple therapy comprising one proton pump inhibitor and two other antibiotics; however, the outcomes are limited due to the existence of antibiotic resistant strains. We previously reported that moenomycin A, a cell-wall transglycosylase inhibitor, is highly active against multidrug-resistant Helicobacter pylori. Herein we show that combination of moenomycin A with the protein synthesis inhibitor clarithromycin or metronidazole can synergistically achieve almost 95% eradication of multidrug-resistant Helicobacter pylori. We also found that the moenomycin A-non-susceptible strains of Helicobacter pylori with deletion of transglycosylase exhibit moenomycin A hyposensitivity, faster growth and impaired biofilm formation compared to the parental strain. Overall, the combination of moenomycin A and clarithromycin or metronidazole to achieve a synergistic effect on different targets is a promising treatment for multidrug-resistant Helicobacter pylori.

Recent Advances in Antimicrobial Coatings and Material Modification Strategies for Preventing Urinary Catheter-Associated Complications

In recent years, we have witnessed prominent improvements in urinary catheter coatings to tackle the commonly occurring catheter-associated urinary tract infection (CAUTI) in catheterized patients. CAUTIs are claimed to be one of the most frequent nosocomial infections that can lead to various complications, from catheter encrustation to severe septicaemia and pyelonephritis. Besides general prevention hygienic strategies, antimicrobial-coated urinary catheters show great potential in the prevention of urinary catheter-associated complications. The aim of this review is to present and evaluate recent updates on the development of antimicrobial urinary catheters in the context of the aetiology of urinary malfunction. Subsequently, we shed some light on future perspectives of utilizing 3D printing and the surrounding regulatory directions.

The identification of Pseudomonas aeruginosa persisters using flow cytometry

Pseudomonas aeruginosa persisters are a rare and poorly characterized subpopulation of cells that are responsible for many recurrent infections. The lack of knowledge on the mechanisms that lead to persister cell development is mainly a result of the difficulty in isolating and characterizing this rare population. Flow cytometry is an ideal method for identifying such subpopulations because it allows for high-content single-cell analysis. However, there are fewer established protocols for bacterial flow cytometry compared to mammalian cell work. Herein, we describe and propose a flow cytometry protocol to identify and isolate P. aeruginosa persister cells. Additionally, we show that the percentage of potential persister cells increases with increasing antibiotic concentrations above the MIC.

Antibiotics in mastoid and epitympanic obliteration with S53P4 bioactive glass: A retrospective study

Objective

The role of antibiotics in ear surgery is still controversial. The aim of this study was to assess their need in cholesteatoma surgery when performing obliteration with S53P4 bioactive glass, a biocompatible material with antibacterial properties.

Methods

This retrospective cohort study was conducted in a tertiary referral center between January 2017 and May 2019. Sixty-nine consecutive patients, who underwent surgery for cholesteatoma removal and/or rehabilitation of canal-wall-down mastoidectomy with mastoid and epitympanic obliteration using S53P4 granules were included. Before 2019, antibiotics were routinely used (group "w/AB"). Patients received intravenous antibiotics during surgery, oral treatment was continued for 7 days and topical antibiotics for 1 month. After 2019, no antibiotics were administered (group "w/oAB"). The primary outcome was the occurrence of early surgical site infection. Secondary outcomes were late infection, anatomic and functional results at 3 and 12 months.

Results

Twenty-three patients were included in group "w/oAB" and 46 in group "w/AB", with no significant differences in demographics, medical history or follow-up. Five ears (22%) in group "w/oAB" developed an early infection compared with 2 (4%) in group "w/AB" (p = .03). The relative risk was 6.11, 95CI%[1.09;31.96]. Infections were successfully treated with antibiotics, and no patient underwent surgical removal of the granules. No late infections or complications were observed. There was no difference in graft failure or air-bone gap closure at 1 year.

Conclusion

Peri-/post-operative antibiotics prevent early infection in obliteration surgery with S53P4 granules. Infections can be treated medically without complications or require removal of the implanted material.

Level of evidence

4.

Biofilm formation and its impact on environmental survival and antibiotic resistance of Mycoplasma anserisalpingitidis strains

Several Mycoplasma species can form biofilm, facilitating their survival in the environment, and shielding them from therapeutic agents. The aim of this study was to examine the biofilm-forming ability and its potential effects on environmental survival and antibiotic resistance in Mycoplasma anserisalpingitidis, the clinically and economically most important waterfowl Mycoplasma species. The biofilm-forming ability of 32 M. anserisalpingitidis strains was examined by crystal violet assay. Biofilms and planktonic cultures of the selected strains were exposed to a temperature of 50 °C (20 and 30 min), to desiccation at room temperature (16 and 24 h), or to various concentrations of eight different antibiotics. Crystal violet staining revealed great diversity in the biofilm-forming ability of the 32 tested M. anserisalpingitidis strains, with positive staining in more than half of them. Biofilms were found to be more resistant to heat and desiccation than planktonic cultures, while no correlation was shown between biofilm formation and antibiotic susceptibility. Our results indicate that M. anserisalpingitidis biofilms may contribute to the persistence of the organisms in the environment, which should be taken into account for proper management. Antibiotic susceptibility was not affected by biofilm formation; however, it is important to note that correlations were examined only in vitro.

The evolution of spectrum in antibiotics and bacteriocins

A key property of many antibiotics is that they will kill or inhibit a diverse range of microbial species. This broad-spectrum of activity has its evolutionary roots in ecological competition, whereby bacteria and other microbes use antibiotics to suppress other strains and species. However, many bacteria also use narrow-spectrum toxins, such as bacteriocins, that principally target conspecifics. Why has such a diversity in spectrum evolved? Here, we develop an evolutionary model to understand antimicrobial spectrum. Our first model recapitulates the intuition that broad-spectrum is best, because it enables a microbe to kill a wider diversity of competitors. However, this model neglects an important property of antimicrobials: They are commonly bound, sequestered, or degraded by the cells they target. Incorporating this toxin loss reveals a major advantage to narrow-spectrum toxins: They target the strongest ecological competitor and avoid being used up on less important species. Why then would broad-spectrum toxins ever evolve? Our model predicts that broad-spectrum toxins will be favored by natural selection if a strain is highly abundant and can overpower both its key competitor and other species. We test this prediction by compiling and analyzing a database of the regulation and spectrum of toxins used in inter-bacterial competition. This analysis reveals a strong association between broad-spectrum toxins and density-dependent regulation, indicating that they are indeed used when strains are abundant. Our work provides a rationale for why bacteria commonly evolve narrow-spectrum toxins such as bacteriocins and suggests that the evolution of antibiotics proper is a signature of ecological dominance.

Medicinal Chemistry of Inhibitors Targeting Resistant Bacteria

The discovery of antibiotics was a revolutionary feat that provided countless health benefits. The identification of penicillin by Alexander Fleming initiated the era of antibiotics, represented by constant discoveries that enabled effective treatments for the different classes of diseases caused by bacteria. However, the indiscriminate use of these drugs allowed the emergence of resistance mechanisms of these microorganisms against the available drugs. In addition, the constant discoveries in the 20th century generated a shortage of new molecules, worrying health agencies and professionals about the appearance of multidrug-resistant strains against available drugs. In this context, the advances of recent years in molecular biology and microbiology have allowed new perspectives in drug design and development, using the findings related to the mechanisms of bacterial resistance to generate new drugs that are not affected by such mechanisms and supply new molecules to be used to treat resistant bacterial infections. Besides, a promising strategy against bacterial resistance is the combination of drugs through adjuvants, providing new expectations in designing new antibiotics and new antimicrobial therapies. Thus, this manuscript will address the main mechanisms of bacterial resistance under the understanding of medicinal chemistry, showing the main active compounds against efflux mechanisms, and also the application of the use of drug delivery systems, and finally, the main potential natural products as adjuvants or with promising activity against resistant strains.

E-mail: khanzad.jarjees@su.edu.krd, Department of Pharmacy, Erbil Medical Technical Institute, Erbil Polytechnic University, Erbil, Kurdistan Region, Iraq. Molecular detection of Metallo-Beta-Lactamase and alginate in multidrug resistance Pseudomonas aeruginosa isolated from the clinical specimen

Pseudomonas aeruginosa pathogen is opportunistic. Several virulence factors and biofilms can cause its pathogenicity. Furthermore, infections triggered via multidrug-resistant P. aeruginosa among hospitalized patients are a public health concern. The primary antimicrobial agents in treating Gram-negative infection include Meropenem and Imipenem. Moreover, the spread of Carbapenem-resistant P. aeruginosa is a focal concern worldwide. The present research aims to determine the spread of Carbapenem-resistant P. aeruginosa, and the distribution of the Alginate and Metallo-beta-lactamase encoding gene in clinical isolates. In the present cross-sectional descriptive research, 50 wound and sputum clinical specimens were obtained. Isolates were all identified by applying cultural characteristics and biochemical tests. The Polymerase Chain Reaction (PCR) was conducted to distinguish algD, BLA-VIM, BLA-IMP, and 16SrRNA genes. Moreover, the phenotypic method was used to detect hemolysin. The disk diffusion technique was applied to screen clinical isolates for eight antimicrobial agents. The PCR results showed all isolates to be positive for algD and negative for BLA-VIM and BLA-IMP genes. Hemolysin and multidrug resistance prevalence was 100% and 76%, respectively. Furthermore, Meropenem proved to be the most efficient antibiotic against clinical isolates. Alginate and hemolysin are considered significant virulence factors for P. aeruginosa, playing a key role in triggering diseases and tissue or skin lesions. The emergence of Multidrug Resistant (MDR) isolates indicates that developing antibiotic stewardship in our regional community hospital is a top priority. Infection control measures could help control the distribution of virulence genes in P. aeruginosa isolates. Moreover, regular observation is needed to decrease public health threats, distributing virulence factors and Imipenem-resistance patterns in clinical isolates of P. aeruginosa.

Optimal dose of lactoferrin reduces the resilience of in vitro Staphylococcus aureus colonies

The rise in antibiotic resistance has stimulated research into adjuvants that can improve the efficacy of broad-spectrum antibiotics. Lactoferrin is a candidate adjuvant; it is a multifunctional iron-binding protein with antimicrobial properties. It is known to show dose-dependent antimicrobial activity against Staphylococcus aureus through iron sequestration and repression of β-lactamase expression. However, S. aureus can extract iron from lactoferrin through siderophores for their growth, which confounds the resolution of lactoferrin's method of action. We measured the minimum inhibitory concentration (MIC) for a range of lactoferrin/ β-lactam antibiotic dose combinations and observed that at low doses (< 0.39 μM), lactoferrin contributes to increased S. aureus growth, but at higher doses (> 6.25 μM), iron-depleted native lactoferrin reduced bacterial growth and reduced the MIC of the β-lactam-antibiotic cefazolin. This differential behaviour points to a bacterial population response to the lactoferrin/ β-lactam dose combination. Here, with the aid of a mathematical model, we show that lactoferrin stratifies the bacterial population, and the resulting population heterogeneity is at the basis of the dose dependent response seen. Further, lactoferrin disables a sub-population from β-lactam-induced production of β-lactamase, which when sufficiently large reduces the population's ability to recover after being treated by an antibiotic. Our analysis shows that an optimal dose of lactoferrin acts as a suitable adjuvant to eliminate S. aureus colonies using β-lactams, but sub-inhibitory doses of lactoferrin reduces the efficacy of β-lactams.

Bactericidal and anti-biofilm effects of uncharged and cationic ultrasound-responsive nitric oxide microbubbles on Pseudomonas aeruginosa biofilms

Bacterial biofilms are a major and ongoing concern for public health, featuring both inherited genetic resistance traits and a conferred innate tolerance to traditional antibiotic therapies. Consequently, there is a growing need for novel methods of drug delivery, to increase the efficacy of antimicrobial agents. This research evaluated the anti-biofilm and bactericidal effects of ultrasound responsive gas-microbubbles (MBs) of either air or nitric oxide, using an in vitro Pseudomonas aeruginosa biofilm model grown in artificial wound medium. The four lipid-based MB formulations evaluated were room-air MBs (RAMBs) and nitric oxide MBs (NOMBs) with no electrical charge, as well as cationic (+) RAMBs⁺ and NOMBs⁺. Two principal treatment conditions were used: i) ultrasound stimulated MBs only, and ii) ultrasound stimulated MBs with a sub-inhibitory concentration (4 µg/mL) of the antibiotic gentamicin. The total treatment time was divided into a 60 second passive MB interaction period prior to 40 second ultrasound exposure; each MB formulation was tested in triplicate. Ultrasound stimulated RAMBs and NOMBs without antibiotic achieved reductions in biofilm biomass of 93.3% and 94.0%, respectively. Their bactericidal efficacy however was limited, with a reduction in culturable cells of 26.9% and 65.3%, respectively. NOMBs with sub-inhibitory antibiotic produced the most significant reduction in biofilm biomass, corresponding to a 99.9% (SD ± 5.21%); and a 99.9% (SD ± 0.07%) (3-log) reduction in culturable bacterial cells. Cationic MBs were initially manufactured to promote binding of MBs to negatively charged biofilms, but these formulations also demonstrated intrinsic bactericidal properties. In the absence of antibiotic, the bactericidal efficacy of RAMB⁺ and NOMB⁺ was greater that of uncharged counterparts, reducing culturable cells by 84.7% and 86.1% respectively; increasing to 99.8% when combined with antibiotic. This study thus demonstrates the anti-biofilm and bactericidal utility of ultrasound stimulated MBs, and specifically is the first to demonstrate the efficacy of a NOMB for the dispersal and potentiation of antibiotics against bacterial biofilms in vitro. Importantly the biofilm system and complex growth-medium were selected to recapitulate key morphological features of in vivo biofilms. The results us offer new insight for the development of new clinical treatments, for example, in chronic wounds.

Engineering Antimicrobial Polymer Nanocomposites: In Situ Synthesis, Disruption of Polymicrobial Biofilms, and In Vivo Activity

The increasing incidence of microbial infections and a limited arsenal of effective antibacterial and antifungal agents have entailed the need for new broad-spectrum therapeutics. Polymer-inorganic nanocomposites have emerged as an integral choice of antimicrobials but are limited by complicated synthesis, narrow-spectrum activity, and poor in vivo efficacy. Herein, chloride counterions of a nontoxic, moderately antibacterial polymer have been explored for in situ nanoprecipitation-based synthesis of water-soluble polymer-silver chloride nanocomposites. With the controlled release of silver ions, the nanocomposites were highly active against multidrug-resistant bacteria as well as fluconazole-resistant fungi. Alongside the elimination of metabolically inactive bacterial cells, the nanocomposites disrupted polymicrobial biofilms, unlike antibiotics and only silver-based ointments. This underlined the role of the engineered composite design, where the polymer interacted with the biofilm matrix, facilitating the penetration of nanoparticles to kill microbes. Further, the nanocomposite diminished Pseudomonas aeruginosa burden in mice skin infection (>99.9%) with no dermal toxicity proving its potential for clinical translation.

Biofilms with a Dash of Color: A Hands-On Activity for School Students to Build a Biofilm Model and Use It to Understand Antibiotic Tolerance in Biofilms

It is increasingly recognized that microbes such as bacteria exist in communities or biofilms, both in the environment and human body. However, school biology curricula continue to focus on the free-floating form of bacterial life, with minimal descriptions of biofilms. Consequently, there is a need to introduce biofilms to school students, to not only to develop a fundamental understanding of microbial life but also to highlight the challenges posed by biofilm infections to antibiotic treatment. We have developed a hands-on activity for students to build a biofilm model and use it in comparison with a model of free-living (planktonic) bacteria, to test the role of the extracellular matrix in the antibiotic tolerance of biofilms. The activity uses simple, easy-to-obtain supplies and is designed to be conducted in an in-person or virtual format for elementary and middle school students in the age group of 6 to 13 years. We conducted the activity in virtual mode (via Zoom) for 59 school students across India, and we present feedback and acquired knowledge that could be used to execute and adapt this accessible and engaging science experience.

Biofilm-i: A Platform for Predicting Biofilm Inhibitors Using Quantitative Structure-Relationship (QSAR) Based Regression Models to Curb Antibiotic Resistance

Antibiotic drug resistance has emerged as a major public health threat globally. One of the leading causes of drug resistance is the colonization of microorganisms in biofilm mode. Hence, there is an urgent need to design novel and highly effective biofilm inhibitors that can work either synergistically with antibiotics or individually. Therefore, we have developed a recursive regression-based platform “Biofilm-i” employing a quantitative structure–activity relationship approach for making generalized predictions, along with group and species-specific predictions of biofilm inhibition efficiency of chemical(s). The platform encompasses eight predictors, three analysis tools, and data visualization modules. The experimentally validated biofilm inhibitors for model development were retrieved from the “aBiofilm” resource and processed using a 10-fold cross-validation approach using the support vector machine and andom forest machine learning techniques. The data was further sub-divided into training/testing and independent validation sets. From training/testing data sets the Pearson’s correlation coefficient of overall chemicals, Gram-positive bacteria, Gram-negative bacteria, fungus, Pseudomonas aeruginosa, Staphylococcus aureus, Candida albicans, and Escherichia coli was 0.60, 0.77, 0.62, 0.77, 0.73, 0.83, 0.70, and 0.71 respectively via Support Vector Machine. Further, all the QSAR models performed equally well on independent validation data sets. Additionally, we also checked the performance of the random forest machine learning technique for the above datasets. The integrated analysis tools can convert the chemical structure into different formats, search for a similar chemical in the aBiofilm database and design the analogs. Moreover, the data visualization modules check the distribution of experimentally validated biofilm inhibitors according to their common scaffolds. The Biofilm-i platform would be of immense help to researchers engaged in designing highly efficacious biofilm inhibitors for tackling the menace of antibiotic drug resistance.

Lineage dynamics in growing biofilms: Spatial patterns of standing vs. de novo diversity

Microbial biofilms show high phenotypic and genetic diversity, yet the mechanisms underlying diversity generation and maintenance remain unclear. Here, we investigate how spatial patterns of growth activity within a biofilm lead to spatial patterns of genetic diversity. Using individual-based computer simulations, we show that the active layer of growing cells at the biofilm interface controls the distribution of lineages within the biofilm, and therefore the patterns of standing and de novo diversity. Comparing biofilms of equal size, those with a thick active layer retain more standing diversity, while de novo diversity is more evenly distributed within the biofilm. In contrast, equal-sized biofilms with a thin active layer retain less standing diversity, and their de novo diversity is concentrated at the top of the biofilm, and in fewer lineages. In the context of antimicrobial resistance, biofilms with a thin active layer may be more prone to generate lineages with multiple resistance mutations, and to seed new resistant biofilms via sloughing of resistant cells from the upper layers. Our study reveals fundamental "baseline" mechanisms underlying the patterning of diversity within biofilms.