Destruction of Staphylococcus aureus biofilms by combining an antibiotic with subtilisin A or calcium gluconate

Population and pan-genomic analyses of Staphylococcus pseudintermedius identify geographic distinctions in accessory gene content and novel loci associated with AMR

Staphylococcus pseudintermedius is a common representative of the normal skin microbiota of dogs and cats but is also a causative agent of a variety of infections. Although primarily a canine/feline bacterium, recent studies suggest an expanded host range including humans. This paper details population genomic analyses of the largest yet assembled and sequenced collection of S. pseudintermedius isolates from across the USA and Canada and assesses these isolates within a larger global population genetic context. We then employ a pan-genome-wide association study analysis of over 1,700 S. pseudintermedius isolates from sick dogs and cats, covering the period 2017-2020, correlating loci at a genome-wide level, with in vitro susceptibility data for 23 different antibiotics. We find no evidence from either core genome phylogenies or accessory genome content for separate lineages colonizing cats or dogs. Some core genome geographic clustering was evident on a global scale, and accessory gene content was noticeably different between various regions, some of which could be linked to known antimicrobial resistance (AMR) loci for certain classes of antibiotics (e.g., aminoglycosides). Analysis of genes correlated with AMR was divided into different categories, depending on whether they were known resistance mechanisms, on a plasmid, or a putatively novel resistance mechanism on the chromosome. We discuss several novel chromosomal candidates for follow-up laboratory experimentation, including, for example, a bacteriocin (subtilosin), for which the same protein from Bacillus subtilis has been shown to be active against Staphylococcus aureus infections, and for which the operon, present in closely related Staphylococcus species, is absent in S. aureus.IMPORTANCEStaphylococcus pseudintermedius is an important causative agent of a variety of canine and feline infections, with recent studies suggesting an expanded host range, including humans. This paper presents global population genomic data and analysis of the largest set yet sequenced for this organism, covering the USA and Canada as well as more globally. It also presents analysis of in vitro antibiotic susceptibility testing results for the North American (NA) isolates, as well as genetic analysis for the global set. We conduct a pan-genome-wide association study analysis of over 1,700 S. pseudintermedius isolates from sick dogs and cats from NA to correlate loci at a genome-wide level with the in vitro susceptibility data for 23 different antibiotics. We discuss several chromosomal loci arising from this analysis for follow-up laboratory experimentation. This study should provide insight regarding the development of novel molecular treatments for an organism of both veterinary and, increasingly, human medical concern.

Antibiofilm activity of Plumbagin against Staphylococcus aureus

In chronic infections caused by Staphylococcus aureus, biofilm is a major virulence factor. In Staphylococcus aureus biofilms, bacteria are embedded in a matrix of extracellular polymeric substances and are highly tolerant to antimicrobial drugs. However, the lack of effective solutions to inhibit biofilm formation remains a challenge, and the mechanism of inhibition of biofilm formation targeting extracellular polymeric substances is unclear. The aim of the present study was to investigate the inhibitory mechanisms of Plumbagin against Staphylococcus aureus biofilms formation by affecting secretion of extracellular polymeric substances using the high-content screening. Our results showed Plumbagin (16 µg/mL) inhibited biofilm formation, revealing a significant reduction in both biomass and bacterial metabolic activity, and disrupted the biofilm structure, leading to a significant decrease in both biological volume and average thickness (P ≤ 0.01). High-content screening imaging indicated that the Plumbagin treatment induced alterations in the extracellular polymeric substances of Staphylococcus aureus biofilm, significantly reducing the quantities of extracellular polysaccharide, proteins and extracellular DNA. Interestingly, extracellular DNA within the matrix was found to be the most sensitive to Plumbagin treatment. Extracellular DNA formation was significantly inhibited at a concentration of 4 µg/mL, whereas the inhibition of extracellular polysaccharide and proteins required a higher concentration of 8 µg/mL. Overall, these results demonstrated the inhibitory effects of Plumbagin on Staphylococcus aureus biofilm formation and extracellular polymeric substances secretion, suggesting that extracellular DNA may be a potential target for the anti-biofilm activity of Plumbagin. These findings will provide new insights into the mode of action of Plumbagin in treating infections caused by Staphylococcus aureus biofilms.

Attachment of Proteolytic Enzyme Inhibitors to Vascular Prosthesis-An Analysis of Binding and Antimicrobial Properties

Prosthetic infections are associated with high morbidity, mortality, and relapse rates, making them still a serious problem for implantology. Staphylococcus aureus is one of the most common bacterial pathogens causing prosthetic infections. In response to the increasing rate of bacterial resistance to commonly used antibiotics, this work proposes a method for combating pathogenic microorganisms by modifying the surfaces of synthetic polymeric biomaterials using proteolytic enzyme inhibitors (serine protease inhibitors-4-(2-aminoethyl)benzenesulfonyl fluoride hydrochloride and puromycin). While using techniques based on the immobilization of biologically active molecules, it is important to monitor the changes occurring on the surface of the modified biomaterial, where spectroscopic techniques (e.g., FTIR) are ideal. ATR-FTIR measurements demonstrated that the immobilization of both inhibitors caused large structural changes on the surface of the tested vascular prostheses (polyester or polytetrafluoroethylene) and showed that they were covalently bonded to the surfaces of the biomaterials. Next, the bactericidal and antibiofilm activities of the tested serine protease inhibitors were determined using the CLSM microscopic technique with fluorescent staining. During LIVE/DEAD analyses, a significant decrease in the formation of Staphylococcus aureus biofilm after exposure to selected concentrations of native inhibitors (0.02-0.06 mg/mL for puromycin and 0.2-1 mg/mL for 4-(2-aminoethyl)benzenesulfonyl fluoride hydrochloride) was demonstrated.

In Vitro Activities of Oxazolidinone Antibiotics Alone and in Combination with C-TEMPO against Methicillin-Resistant Staphylococcus aureus Biofilms

Infections caused by methicillin-resistant Staphylococcus aureus (MRSA) are a global health concern. The propensity of MRSA to form biofilms is a significant contributor to its pathogenicity. Strategies to treat biofilms often involve small molecules that disperse the biofilm into planktonic cells. Linezolid and, by extension, theoxazolidinones have been developed to treat infections caused by Gram-positive bacteria such as MRSA. However, the clinical development of these antibiotics has mainly assessed the susceptibility of planktonic cells to the drug. Previous studies evaluating the anti-biofilm activity of theoxazolidinones have mainly focused on the biofilm inhibition of Enterococcus faecalis and methicillin-sensitive Staphylococcus aureus, with only a few studies investigating the activity of oxazolidinones for eradicating established biofilms for these species. Very little is known about the ability of oxazolidinones to eradicate MRSA biofilms. In this work, five oxazolidinones were assessed against MRSA biofilms using a minimum biofilm eradication concentration (MBEC) assay. All oxazolidinones had inherent antibiofilm activity. However, only ranbezolid could completely eradicate MRSA biofilms at clinically relevant concentrations. The susceptibility of the MRSA biofilms to ranbezolid was synergistically enhanced by coadministration with the nitroxide biofilm dispersal agent C-TEMPO. We presume that ranbezolid acts as a dual warhead drug, which combines the mechanism of action of the oxazolidinones with a nitric oxide donor or cytotoxic drug.

Development, systematic optimisation and biofilm disruption activity of eugenol-based nanosized emulsions stabilised with Tween 80

The aims of this study were to systematically optimise a formula for eugenol emulsions via face-centered central composite design and to assess the activity against two-different bacterial strains (Staphylococcus aureus and Propionibacterium acnes) present at planktonic and biofilm forms. The molecular interaction of excipients, mean particle size (MPS) including zeta potential (ZP), drug entrapment efficiency (DEE) and in vitro drug release of optimised emulsions was done using FT-IR, Malvern Zetasizer, ultracentrifugation technique and membrane-free dissolution model, respectively. The emulsions consisted of 151.3 ± 1.45 nm MPS, -21.3 ± 1.25 mV ZP and 93.98 ± 1.41% DEE values. On storage of emulsions at 25 °C for 3 months, the value of DEE was found to be 72.12 ± 2.82%. The Tween 80 emulsifier film coverage onto the dispersed eugenol droplets of emulsions delayed significantly the drug release (12%-19%) compared to the drug release occurred from pure eugenol. The treatment of planktonic S. aureus and P. acnes with diluted eugenol emulsions showed the minimum inhibitory concentration and minimum bactericidal concentration values at 1.25-2.5 mg/ml whereas it occurred at 10 mg/ml for pure eugenol. Treating the biofilms with eugenol emulsions (1-2 mg/ml) yielded 59-70% minimum biofilm eradication concentration but 10 mg/ml pure eugenol showed 60%. Hence, the eugenol emulsions displayed antibacterial activity and could be projected as an antibiofilm or biofilm disruption agent.

Incorporation of collagen into Pseudomonas aeruginosa and Staphylococcus aureus biofilms impedes phagocytosis by neutrophils

Biofilms are communities of microbes embedded in a matrix of extracellular polymeric substances (EPS). Matrix components can be produced by biofilm organisms and can also originate from the environment and then be incorporated into the biofilm. For example, we have recently shown that collagen, a host-produced protein that is abundant in many different infection sites, can be taken up into the biofilm matrix, altering biofilm mechanics. The biofilm matrix protects bacteria from clearance by the immune system, and some of that protection likely arises from the mechanical properties of the biofilm. Pseudomonas aeruginosa and Staphylococcus aureus are common human pathogens notable for forming biofilm infections in anatomical sites rich in collagen. Here, we show that the incorporation of Type I collagen into P. aeruginosa and S. aureus biofilms significantly hinders phagocytosis of biofilm bacteria by human neutrophils. However, enzymatic treatment with collagenase, which breaks down collagen, can partly or entirely negate the protective effect of collagen and restore the ability of neutrophils to engulf biofilm bacteria. From these findings, we suggest that enzymatic degradation of host materials may be a potential way to compromise biofilm infections and enhance the efficacy of the host immune response without promoting antibiotic resistance. Such an approach might be beneficial both in cases where the infecting species is known and also in cases wherein biofilm components are not readily known, such as multispecies infections or infections by unknown species.

Synergy of Antibiotics and Antibiofilm Agents against Methicillin-Resistant Staphylococcus aureus Biofilms

Methicillin-resistant Staphylococcus aureus (MRSA) infections are some of the most common antibiotic-resistant infections, often exacerbated by the formation of biofilms. Here, we evaluated six compounds, three common antibiotics used against MRSA and three antibiofilm compounds, in nine combinations to investigate the mechanisms of synergistic eradication of MRSA biofilms. Using metabolic assessment, colony enumeration, confocal fluorescence microscopy, and scanning electron microscopy, we identified two promising combinations of antibiotics with antibiofilm agents against preformed MRSA biofilms. The broad-spectrum protease, proteinase K, and membrane-targeting antibiotic, daptomycin, worked in synergy against MRSA biofilms by manipulating the protein content, increasing access to the cell membrane of biofilm bacteria. We also found that the combination of cationic peptide, IDR-1018, with the cell wall cross-linking inhibitor, vancomycin, exhibited synergy against MRSA biofilms by causing bacterial damage and preventing repair. Our findings identify synergistic combinations of antibiotics and antibiofilm agents, providing insight into mechanisms that may be explored further for the development of effective treatments against MRSA biofilm.

Drug delivery strategies for antibiofilm therapy

Although new antibiofilm agents have been developed to prevent and eliminate pathogenic biofilms, their widespread clinical use is hindered by poor biocompatibility and bioavailability, unspecific interactions and insufficient local concentrations. The development of innovative drug delivery strategies can facilitate penetration of antimicrobials through biofilms, promote drug dispersal and synergistic bactericidal effects, and provide novel paradigms for clinical application. In this Review, we discuss the potential benefits of such emerging techniques for improving the clinical efficacy of antibiofilm agents, as well as highlighting the existing limitations and future prospects for these therapies in the clinic.

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.

Production of Gluconic Acid and Its Derivatives by Microbial Fermentation: Process Improvement Based on Integrated Routes

Gluconic acid (GA) and its derivatives, as multifunctional biological chassis compounds, have been widely used in the food, medicine, textile, beverage and construction industries. For the past few decades, the favored production means of GA and its derivatives are microbial fermentation using various carbon sources containing glucose hydrolysates due to high-yield GA production and mature fermentation processes. Advancements in improving fermentation process are thriving which enable more efficient and economical industrial fermentation to produce GA and its derivatives, such as the replacement of carbon sources with agro-industrial byproducts and integrated routes involving genetically modified strains, cascade hydrolysis or micro- and nanofiltration in a membrane unit. These efforts pave the way for cheaper industrial fermentation process of GA and its derivatives, which would expand the application and widen the market of them. This review summarizes the recent advances, points out the existing challenges and provides an outlook on future development regarding the production of GA and its derivatives by microbial fermentation, aiming to promote the combination of innovative production of GA and its derivatives with industrial fermentation in practice.

Hydrolytic Enzymes as Potentiators of Antimicrobials against an Inter-Kingdom Biofilm Model

Biofilms are recalcitrant to antimicrobials, partly due to the barrier effect of their matrix. The use of hydrolytic enzymes capable to degrade matrix constituents has been proposed as an alternative strategy against biofilm-related infections. This study aimed to determine whether hydrolytic enzymes could potentiate the activity of antimicrobials against hard-to-treat interkingdom biofilms comprising two bacteria and one fungus. We studied the activity of a series of enzymes alone or in combination, followed or not by antimicrobial treatment, against single-, dual- or three-species biofilms of Staphylococcus aureus, Escherichia coli, and Candida albicans, by measuring their residual biomass or culturable cells. Two hydrolytic enzymes, subtilisin A and lyticase, were identified as the most effective to reduce the biomass of C. albicans biofilm. When targeting interkingdom biofilms, subtilisin A alone was the most effective enzyme to reduce biomass of all biofilms, followed by lyticase combined with an enzymatic cocktail composed of cellulase, denarase, and dispersin B that proved previously active against bacterial biofilms. The subsequent incubation with antimicrobials further reduced the biomass. Enzymes alone did not reduce culturable cells in most cases and did not interfere with the cidal effects of antimicrobials. Therefore, this work highlights the potential interest of pre-exposing interkingdom biofilms to hydrolytic enzymes to reduce their biomass besides the number of culturable cells, which was not achieved when using antimicrobials alone. IMPORTANCE Biofilms are recalcitrant to antimicrobial treatments. This problem is even more critical when dealing with polymicrobial, interkingdom biofilms, including both bacteria and fungi, as these microorganisms cooperate to strengthen the biofilm and produce a complex matrix. Here, we demonstrate that the protease subtilisin A used alone, or a cocktail containing lyticase, cellulase, denarase, and dispersin B markedly reduce the biomass of interkingdom biofilms and cooperate with antimicrobials to act upon these recalcitrant forms of infection. This work may open perspectives for the development of novel adjuvant therapies against biofilm-related infections.

Enhancement of Antibiofilm Activity of Ciprofloxacin against Staphylococcus aureus by Administration of Antimicrobial Peptides

Staphylococcus aureus can develop resistance by mutation, transfection or biofilm formation. Resistance was induced in S. aureus by growth in sub-inhibitory concentrations of ciprofloxacin for 30 days. The ability of the antimicrobials to disrupt biofilms was determined using crystal violet and live/dead staining. Effects on the cell membranes of biofilm cells were evaluated by measuring release of dyes and ATP, and nucleic acids. None of the strains developed resistance to AMPs while only S. aureus ATCC 25923 developed resistance (128 times) to ciprofloxacin after 30 passages. Only peptides reduced biofilms of ciprofloxacin-resistant cells. The antibiofilm effect of melimine with ciprofloxacin was more (27%) than with melimine alone at 1X MIC (p < 0.001). Similarly, at 1X MIC the combination of Mel4 and ciprofloxacin produced more (48%) biofilm disruption than Mel4 alone (p < 0.001). Combinations of either of the peptides with ciprofloxacin at 2X MIC released ≥ 66 nM ATP, more than either peptide alone (p ≤ 0.005). At 2X MIC, only melimine in combination with ciprofloxacin released DNA/RNA which was three times more than that released by melimine alone (p = 0.043). These results suggest the potential use of melimine and Mel4 with conventional antibiotics for the treatment of S. aureus biofilms.