Summary Although several therapeutic approaches are available for wound and burn treatment and much progress has been made in this area, room for improvement still exists, driven by the urgent need of better strategies to accelerate wound healing and recovery, mostly for cases of severe burned patients. Bacterial cellulose (BC) is a biopolymer produced by bacteria with several advantages over vegetal cellulose, such as purity, high porosity, permeability to liquid and gases, elevated water uptake capacity and mechanical robustness. Besides its biocompatibility, BC can be modified in order to acquire antibacterial response and possible local drug delivery features. Due to its intrinsic versatility, BC is the perfect example of a biotechnological response to a clinical problem. In this review, we assess the BC main features and emphasis is given to a specific biomedical application: wound dressings. The production process and the physical–chemical properties that entitle this material to be used as wound dressing namely for burn healing are highlighted. An overview of the most common BC composites and their enhanced properties, in particular physical and biological, is provided, including the different production processes. A particular focus is given to the biochemistry and genetic manipulation of BC. A summary of the current marketed BC‐based wound dressing products is presented, and finally, future perspectives for the usage of BC as wound dressing are foreseen.

Antimicrobial resistance is one of the most worrying threats to humankind with extremely high healthcare costs associated. The current technologies used in clinical microbiology to identify the bacterial agent and profile antimicrobial susceptibility are time-consuming and frequently expensive. As a result, physicians prescribe empirical antimicrobial therapies. This scenario is often the cause of therapeutic failures, causing higher mortality rates and healthcare costs, as well as the emergence and spread of antibiotic resistant bacteria. As such, new technologies for rapid identification of the pathogen and antimicrobial susceptibility testing are needed. This review summarizes the current technologies, and the promising emerging and future alternatives for the identification and profiling of antimicrobial resistance bacterial agents, which are expected to revolutionize the field of clinical diagnostics.

Antibiotic resistance in bacterial pathogens threatens the future of modern medicine. One such resistant pathogen is methicillin-resistant Staphylococcus aureus (MRSA), which is resistant to nearly all β-lactam antibiotics, limiting treatment options. Here, we show that a significant proportion of MRSA isolates from different lineages, including the epidemic USA300 lineage, are susceptible to penicillins when used in combination with β-lactamase inhibitors such as clavulanic acid. Susceptibility is mediated by a combination of two different mutations in the mecA promoter region that lowers mecA-encoded penicillin binding protein 2a (PBP2a) expression, and in the majority of isolates by either one of two substitutions in PBP2a (E246G or M122I) that increase the affinity of PBP2a for penicillin in the presence of clavulanic acid. Treatment of S. aureus infections in wax moth and mouse models demonstrate that penicillin/β-lactamase inhibitor susceptibility can be exploited as an effective therapeutic choice for 'susceptible' MRSA infection. Finally, we show that isolates with the PBP2a E246G substitution have a growth advantage in the presence of penicillin, but the absence of clavulanic acid, which suggests that penicillin/βlactamase susceptibility is an example of collateral sensitivity (resistance to one antibiotic increases sensitivity to another). Our findings suggest that widely available and currently disregarded antibiotics could be effective in a significant proportion of MRSA infections.

Peptidoglycan (PGN) is the major component of the bacterial cell wall, a structure essential for the physical integrity and shape of the cell. Bacteria maintain cell shape by directing PGN incorporation to distinct regions of the cell, namely through the localisation of the late stage PGN synthesis proteins. These include two key protein families, SEDS transglycosylases and the bPBP transpeptidases, proposed to function in cognate pairs. Rod-shaped bacteria have two SEDS-bPBP pairs, involved in cell elongation and cell division. Here, we elucidate why coccoid bacteria, such as Staphylococcus aureus, also possess two SEDS-bPBP pairs. We determined that S. aureus RodA-PBP3 and FtsW-PBP1 likely constitute cognate pairs of interacting proteins. Lack of RodA-PBP3 decreased cell eccentricity due to deficient pre-septal PGN synthesis, whereas the depletion of FtsW-PBP1 arrested normal septal PGN incorporation. Although PBP1 is an essential protein, a mutant lacking PBP1 transpeptidase activity is viable, showing that this protein has a second function. We propose that the FtsW-PBP1 pair has a role in stabilising the divisome at midcell. In the absence of these proteins, the divisome appears as multiple rings/arcs that drive lateral PGN incorporation, leading to cell elongation. We conclude that RodA-PBP3 and FtsW-PBP1 mediate lateral and septal PGN incorporation, respectively, and that the activity of these pairs must be balanced in order to maintain coccoid morphology. Peptidoglycan (PGN) synthesis is an essential process that is both spatially and temporally regulated to ensure that the bacterial cell shape is maintained 1 . Rod-shaped bacteria elongate by synthesising PGN along the length of the cell in a process directed by the cytoskeletal protein MreB 2 . In Escherichia coli and Bacillus subtilis, this protein polymerises into short filaments that move processively around the cell diameter, and organise a multi-protein machinery, including PGN synthesis proteins, referred to as the elongasome or the Rod system [3][4][5] . Cell division is dependent on another cytoskeletal protein, FtsZ, which polymerises to form the Z-ring and recruits a multi-protein complex responsible for septum synthesis, known as the divisome 6,7 . This complex directs PGN incorporation to the midcell, resulting in inward PGN synthesis, and eventually bisects the mother cell, leading to daughter cell separation.Ovococci such as Streptococcus pneumoniae and Lactococcus lactis lack MreB, and FtsZ is proposed to coordinate both elongation and septation 8,9 . In these organisms PGN is

A murF conditional mutant was used to evaluate the effect of suboptimal transcription of this gene on the transcriptome of the methicillin-resistant Staphylococcus aureus strain COL. The mutant was grown in the presence of optimal and suboptimal concentrations of the inducer, and the relative levels of transcription of genes were evaluated genome wide with an Affymetrix DNA microarray that included all open reading frames (ORFs) as well as intergenic sequences derived from four sequenced S. aureus strains. Using a sensitivity threshold value of 1.5, suboptimal expression of murF altered the transcription of a surprisingly large number of genes, i.e., 668 out of the 2,740 ORFs (close to one-fourth of all ORFs), of the genome of S. aureus strain COL. The genes with altered transcription were distributed evenly around the S. aureus chromosome, and groups of genes involved with distinct metabolic functions responded in unique and operon-specific manners to modulation in murF transcription. For instance, all genes belonging to the isd operon and all but 2 of the 35 genes of prophage L54a were down-regulated, whereas all but one of the 21 members of the vraSR regulon and most of the 79 virulence-related genes (those for fibronectin binding proteins A and B, clumping factor A, gamma hemolysin, enterotoxin B, etc.) were up-regulated in cells with suboptimal expression of murF. Most importantly, the majority of these altered gene expression profiles were reversible by resupplying the optimal concentration of IPTG (isopropyl-␤-D-thiogalactopyranoside) to the culture. The observations suggest the coordinate regulation of a large sector of the S. aureus transcriptome in response to a disturbance in cell wall synthesis.Transcriptomic approaches are powerful tools for the identification of groups of genes with similar expression patterns and for the establishment of putative regulatory relations between them. Using microarray technology, recent reports have described extensive changes in gene expression profiles when Staphylococcus aureus was challenged by different cell wall inhibitors such as oxacillin, bacitracin, D-cycloserine, and vancomycin (12, 19, 20, 34). The group of genes whose transcription was altered during treatment with antibiotics that target different steps in cell wall synthesis was proposed to represent members of a cell wall stimulon responding to a specific form of stress in a coordinate manner.The large number and diversity of genes that respond to cell wall inhibitors by altered transcription suggest that many functions of the bacterial cell are connected through regulatory loops to one or more steps in cell wall synthesis which may also serve as control points of metabolism. Such a control should also be operational in the absence of antibiotic treatment, and we searched for a system in which the existence of such a regulatory system could be experimentally demonstrated.The method of choice became available with the isolation of an S. aureus murF conditional mutant in which the rate of transcription o...

The epidemiologically most important mechanism of antibiotic resistance in Staphylococcus aureus is associated with mecA–an acquired gene encoding an extra penicillin-binding protein (PBP2a) with low affinity to virtually all β-lactams. The introduction of mecA into the S. aureus chromosome has led to the emergence of methicillin-resistant S. aureus (MRSA) pandemics, responsible for high rates of mortality worldwide. Nonetheless, little is known regarding the origin and evolution of mecA. Different mecA homologues have been identified in species belonging to the Staphylococcus sciuri group representing the most primitive staphylococci. In this study we aimed to identify evolutionary steps linking these mecA precursors to the β-lactam resistance gene mecA and the resistance phenotype. We sequenced genomes of 106 S. sciuri, S. vitulinus and S. fleurettii strains and determined their oxacillin susceptibility profiles. Single-nucleotide polymorphism (SNP) analysis of the core genome was performed to assess the genetic relatedness of the isolates. Phylogenetic analysis of the mecA gene homologues and promoters was achieved through nucleotide/amino acid sequence alignments and mutation rates were estimated using a Bayesian analysis. Furthermore, the predicted structure of mecA homologue-encoded PBPs of oxacillin-susceptible and -resistant strains were compared. We showed for the first time that oxacillin resistance in the S. sciuri group has emerged multiple times and by a variety of different mechanisms. Development of resistance occurred through several steps including structural diversification of the non-binding domain of native PBPs; changes in the promoters of mecA homologues; acquisition of SCCmec and adaptation of the bacterial genetic background. Moreover, our results suggest that it was exposure to β-lactams in human-created environments that has driven evolution of native PBPs towards a resistance determinant. The evolution of β-lactam resistance in staphylococci highlights the numerous resources available to bacteria to adapt to the selective pressure of antibiotics.

The Staphylococcus aureus murF gene was placed under the control of a promoter inducible by IPTG (isopropyl-␤-D-thiogalactopyranoside). It was demonstrated that murF is an essential gene; it is cotranscribed with ddlA and growth rate, level of beta-lactam antibiotic resistance, and rates of transcription of the mecA and pbpB genes paralleled the rates of transcription of murF. At suboptimal concentrations of the inducer, a UDP-linked muramyl tripeptide accumulated in the cytoplasm in parallel with the decline in the amounts of the normal pentapeptide cell wall precursor. The abnormal tripeptide component incorporated into the cell wall as a monomeric muropeptide, accompanied by a decrease in the oligomerization degree of the peptidoglycan. However, incorporation of the tripeptide into the cell wall was limited to a relatively low threshold value. Further reduction of the amounts of pentapeptide cell wall precursor caused a gradual decrease in the cellular amounts of peptidoglycan, the production of a thinner peripheral cell wall, aberrant septae, and an overall increase in the diameter of the cells. The observations suggest that the role of murF exceeds its primary function in peptidoglycan biosynthesis and may also be involved in the control of cell division.The cell wall of Staphylococcus aureus contains a highly cross-linked peptidoglycan in which most of the muropeptide units have pentaglycine branches attached to the aminogroup of the lysine residue, and virtually all monomeric and acceptor muropeptides carry a carboxy-terminal D-alanyl-D-alanine residue (3). The biosynthesis and attachment of this dipeptide is catalyzed by the protein product of the genes ddlA and murF, with the first, DdlA, producing the dipeptide and the second, MurF, attaching the dipeptide to the UDP-N-acetylmuramic acid (MurNAc)-tripeptide, thus completing the formation of the peptidoglycan building block, the UDP-linked MurNAcpentapeptide.The D-alanyl-D-alanine C-terminal residues of the peptidoglycan precursor unit are essential for important reactions which take place at the cell wall level such as peptide crosslinking, recognition by penicillin-binding proteins (PBPs) or recognition by the glycopeptide class of antibiotics (1, 2). The study of a murF insertion mutant (27) has allowed this gene to be added to the extensive list of auxiliary genes that are essential for the optimal expression of methicillin resistance in Staphylococcus aureus (4, 5).MurF and its biochemical function are unique to bacteria; thus, such an enzyme is a potential antimicrobial target. Compounds with specific inhibitory action against MurF have been developed, but so far none with in vivo antibacterial activity has been described (9).The purpose of the study described here was to construct a conditional mutant of murF and use it for the exploration of the physiological role of this determinant in growth, cell wall synthesis, and antibiotic susceptibility of S. aureus. MATERIALS AND METHODSBacterial strains, plasmids, and growth conditions. Bacterial strai...

A carboxy-terminal fragment of murF was used to construct and insert a suicide plasmid into the chromosomal copy of the gene in the highly and homogeneously methicillin-resistant Staphylococcus aureus (MRSA) strain COL by Campbell type integration. The plasmid insertion generated a mutant in which the MIC value for oxacillin was reduced from 400 microg/ml of the parental strain to 0.75 microg/ml in 90% of the cells of the mutant cultures that were heterogeneous: they contained subpopulations of bacteria with a frequency of 10(-3) that were capable of expressing resistance at nearly the parental level. The impact of the murF mutation on antibiotic resistance was selective for beta-lactam antibiotics: there was no change in the susceptibility of the mutant to D-cycloserine, fosfomycin, beta-D-chloro-alanine, moenomycin, bacitracin, or vancomycin. Analysis of the mutant peptidoglycan showed decrease in the percentage of oligomeric components in rough proportion to the accumulation of several abnormal muropeptide components, which were identified as structural variants of the disaccharide tripeptide monomer. An abnormal cell wall precursor identified as UDP MurNac tripeptide was also detected in the cytoplasmic pool of the mutant strain. A normal proportion of oligomers and a greatly reduced representation of the disaccharide tripeptide were demonstrated in the cell wall of the murF mutant's subpopulation that has retained the parental level of resistance. Northern analysis demonstrated a drastic reduction in the transcription rate of mecA in mutant F9 whereas mecA transcription increased in the subpopulation of bacteria that retained high-level resistance.