Microbiology of drugs for treating multiply drug-resistant Gram-positive bacteria

Pharmacotherapies for multidrug-resistant gram-positive infections: current options and beyond

INTRODUCTION

Infections due to multidrug-resistant organisms (MDRO) are a serious concern for public health with high morbidity and mortality. Though many antibiotics have been introduced to manage these infections, there are remaining concerns regarding the optimal management of Gram-positive MDROs.

AREAS COVERED

A literature search on the PubMed/Medline database was conducted. We applied no language and time limits for the search strategy. In this narrative review, we discuss the current options for managing Gram-positive MDROs as well as non-traditional antibacterial agents in development.

EXPERT OPINION

Despite their introduction more than 70 years ago, glycopeptides are still the cornerstone in treating Gram-positive infections: all registrative studies of new antibiotics have glycopeptides as control; these studies are designed as not inferior studies, therefore it is almost impossible to give recommendations other than the use of glycopeptides in the treatment of Gram-positive infections. The best evidence on treatments different from glycopeptides comes from post-hoc analysis and meta-analysis. Non-traditional antibacterial agents are being studied to aid in short and effective antibiotic therapies. The use of non-traditional antibacterial agents is not restricted to replacing traditional antibacterial agents with alternative therapies; instead, they should be used in combination with antibiotic therapies.

From Diospyros kaki L. (Persimmon) Phytochemical Profile and Health Impact to New Product Perspectives and Waste Valorization

Persimmon (Diospyros kaki L.) fruit's phytochemical profile includes carotenoids, proanthocyanidins, and gallic acid among other phenolic compounds and vitamins. A huge antioxidant potential is present given this richness in antioxidant compounds. These bioactive compounds impact on health benefits. The intersection of nutrition and sustainability, the key idea behind the EAT-Lancet Commission, which could improve human health and decrease the global impact of food-related health conditions such as cancer, heart disease, diabetes, and obesity, bring the discussion regarding persimmon beyond the health effects from its consumption, but also on the valorization of a very perishable food that spoils quickly. A broad option of edible products with better storage stability or solutions that apply persimmon and its byproducts in the reinvention of old products or even creating new products, or with new and better packaging for the preservation of food products with postharvest technologies to preserve and extend the shelf-life of persimmon food products. Facing a global food crisis and the climate emergency, new and better day-to-day solutions are needed right now. Therefore, the use of persimmon waste has also been discussed as a good solution to produce biofuel, eco-friendly alternative reductants for fabric dyes, green plant growth regulator, biodegradable and edible films for vegetable packaging, antimicrobial activity against foodborne methicillin-resistant Staphylococcus aureus found in retail pork, anti-Helicobacter pylori agents from pedicel extracts, and persimmon pectin-based emulsifiers to prevent lipid peroxidation, among other solutions presented in the revised literature. It has become clear that the uses for persimmon go far beyond the kitchen table and the health impact consumption demonstrated over the years. The desired sustainable transition is already in progress, however, mechanistic studies and clinical trials are essential and scaling-up is fundamental to the future.

Synthesis and evaluation of isatin-β-thiosemicarbazones as novel agents against antibiotic-resistant Gram-positive bacterial species

Methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant Enterococcus (VRE) have caused an increasing mortality rate, which means that antibiotic resistance is becoming an important health issue. In the course to screen new agents for resistant bacteria, we identified that a series of isatin-β-thiosemicarbazones (IBTs) could inhibit the growth of MRSA and VRE. This was the first time that the "familiar" IBT compounds exhibited significant anti Gram-positive pathogen activity. Against a clinical isolated MRSA strain, 20 of the 51 synthesized compounds showed minimum inhibitory concentration (MIC) data of 0.78 mg/L and another 12 novel compounds had MICs of 0.39 mg/L. Moreover, these compounds also inhibited Enterococcus faecalis and VRE at similar levels, indicating that IBTs might have different mode of action compared with vancomycin. For these IBTs, comparative field analysis (CoMFA) models were further established to understand the structure-activity relationships in order to design new compounds from steric and electrostatic contributions. This work has suggested that IBTs can be considered as potential lead compounds to discover antibacterial inhibitors to combat drug resistance.

Surveillance of multidrug resistant uropathogenic bacteria in hospitalized patients in Indian

OBJECTIVE

To record surveillance, antibiotic resistance of uropathogens of hospitalized patients over a period of 18 months.

METHODS

Urine samples from wards and cabins were used for isolating urinary tract infection (UTI)-causing bacteria that were cultured on suitable selective media and identified by biochemical tests; and their antibiograms were ascertained by Kirby-Bauer's disc diffusion method, in each 6-month interval of the study period, using 18 antibiotics of five different classes.

RESULTS

From wards and cabins, 1 245 samples were collected, from which 996 strains of bacteria belonging to 11 species were isolated, during April 2011 to September 2012. Two Gram-positive, Staphylococcus aureus (S. aureus) and Enterococcus faecalis (E. faecalis), and nine Gram-negative bacteria, Acinetobacter baumannii, Citrobacter sp., Escherichia coli, Enterobacter aerogenes, Klebsiella pneumoniae, Klebsiella oxytoca, Proteus mirabilis, Proteus vulgaris and Pseudomonas aeruginosa were isolated. Both S. aureus and E. faecalis were vancomycin resistant, and resistant-strains of all pathogens increased in each 6-month period of study. Particularly, all Gram-negatives were resistant to nitrofurantoin and co-trimoxazole, the most preferred antibiotics of empiric therapy for UTI.

CONCLUSIONS

Antibiograms of 11 UTI-causing bacteria recorded in this study indicated moderately higher numbers of strains resistant to each antibiotic studied, generating the fear of precipitating fervent episodes in public health particularly with bacteria, Acinetobacter baumannii, Escherichia coli, Klebsiella pneumoniae and S. aureus. Moreover, vancomycin resistance in strains of S. aureus and E. faecalis is a matter of concern.

Inspecting the potential physiological and biomedical value of 44 conserved uncharacterised proteins of Streptococcus pneumoniae

BACKGROUND

The major Gram-positive coccoid pathogens cause similar invasive diseases and show high rates of antimicrobial resistance. Uncharacterised proteins shared by these organisms may be involved in virulence or be targets for antimicrobial therapy.

RESULTS

Forty four uncharacterised proteins from Streptococcus pneumoniae with homologues in Enterococcus faecalis and/or Staphylococcus aureus were selected for analysis. These proteins showed differences in terms of sequence conservation and number of interacting partners. Twenty eight of these proteins were monodomain proteins and 16 were modular, involving domain combinations and, in many cases, predicted unstructured regions. The genes coding for four of these 44 proteins were essential. Genomic and structural studies showed one of the four essential genes to code for a promising antibacterial target. The strongest impact of gene removal was on monodomain proteins showing high sequence conservation and/or interactions with many other proteins. Eleven out of 40 knockouts (one for each gene) showed growth delay and 10 knockouts presented a chaining phenotype. Five of these chaining mutants showed a lack of putative DNA-binding proteins. This suggest this phenotype results from a loss of overall transcription regulation. Five knockouts showed defective autolysis in response to penicillin and vancomycin, and attenuated virulence in an animal model of sepsis.

CONCLUSIONS

Uncharacterised proteins make up a reservoir of polypeptides of different physiological importance and biomedical potential. A promising antibacterial target was identified. Five of the 44 examined proteins seemed to be virulence factors.

[Resistance to "last resort" antibiotics in Gram-positive cocci: The post-vancomycin era]

New therapeutic alternatives have been developed in the last years for the treatment of multidrug-resistant Gram-positive infections. Infections caused by methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant enterococci (VRE) are considered a therapeutic challenge due to failures and lack of reliable antimicrobial options. Despite concerns related to the use of vancomycin in the treatment of severe MRSA infections in specific clinical scenarios, there is a paucity of solid clinical evidence that support the use of alternative agents (when compared to vancomycin). Linezolid, daptomycin and tigecycline are antibiotics approved in the last decade and newer cephalosporins (such as ceftaroline and ceftobiprole) and novel glycopeptides (dalvavancin, telavancin and oritavancin) have reached clinical approval or are in the late stages of clinical development. This review focuses on discussing these newer antibiotics used in the "post-vancomycin" era with emphasis on relevant chemical characteristics, spectrum of antimicrobial activity, mechanisms of action and resistance, as well as their clinical utility.

The structure and competitive substrate inhibition of dihydrofolate reductase from Enterococcus faecalis reveal restrictions to cofactor docking

We are addressing bacterial resistance to antibiotics by repurposing a well-established classic antimicrobial target, the dihydrofolate reductase (DHFR) enzyme. In this work, we have focused on Enterococcus faecalis, a nosocomial pathogen that frequently harbors antibiotic resistance determinants leading to complicated and difficult-to-treat infections. An inhibitor series with a hydrophobic dihydrophthalazine heterocycle was designed from the anti-folate trimethoprim. We have examined the potency of this inhibitor series based on inhibition of DHFR enzyme activity and bacterial growth, including in the presence of the exogenous product analogue folinic acid. The resulting preferences were rationalized using a cocrystal structure of the DHFR from this organism with a propyl-bearing series member (RAB-propyl). In a companion apo structure, we identify four buried waters that act as placeholders for a conserved hydrogen-bonding network to the substrate and indicate an important role in protein stability during catalytic cycling. In these structures, the nicotinamide of the nicotinamide adenine dinucleotide phosphate cofactor is visualized outside of its binding pocket, which is exacerbated by RAB-propyl binding. Finally, homology models of the TMP^R sequences dfrK and dfrF were constructed. While the dfrK-encoded protein shows clear sequence changes that would be detrimental to inhibitor binding, the dfrF-encoded protein model suggests the protein would be relatively unstable. These data suggest a utility for anti-DHFR compounds for treating infections arising from E. faecalis. They also highlight a role for water in stabilizing the DHFR substrate pocket and for competitive substrate inhibitors that may gain advantages in potency by the perturbation of cofactor dynamics.

IB-367 pre-treatment improves the in vivo efficacy of teicoplanin and daptomycin in an animal model of wounds infected with meticillin-resistant Staphylococcus aureus

Antimicrobial peptides are known as immunomodulators and antibiotic enhancers. We report that administration of an antimicrobial peptide, IB-367, was efficacious in increasing the antimicrobial activity of daptomycin and teicoplanin in a mouse model of wound infection caused by meticillin-resistant Staphylococcus aureus (MRSA). Mice were assigned to seven groups: an IB-367 pre-treated group with no antibiotics given after challenge, two IB-367 pre-treated groups plus daptomycin or teicoplanin given after challenge, two groups treated with daptomycin or teicoplanin only after challenge, and two control groups without infection or that did not receive any treatment. The main outcome measures were quantitative bacterial culture and analysis of natural killer (NK) cytotoxicity and leukocyte phenotype. The wound, established through the panniculus carnosus muscle of mice, was infected by MRSA. Bacterial cultures of mice receiving antibiotics alone showed a −2 log decrease, whilst those for IB-367 plus daptomycin or teicoplanin showed a −4 log decrease. IB-367 plus daptomycin showed the highest efficacy. The higher antimicrobial effect exerted by IB-367 was associated with increased levels of NK cytotoxicity but not of NK cell number. IB-367 increased the number of both CD11b and Gr-1 cells 3 days after MRSA challenge, whereas both of these leukocyte populations were reduced at 10 days after challenge. Our data suggest that a combination of IB-367 with antibiotic exerts a therapeutic effect and may be useful for the management of staphylococcal wounds.

Transcriptome analysis of responses to rhodomyrtone in methicillin-resistant Staphylococcus aureus

Rhodomyrtone, purified from Rhodomyrtus tomentosa (Aiton) Hassk, exhibits a high degree of potency against methicillin-resistant Staphylococcus aureus (MRSA). We recently demonstrated that exposure of MRSA to a subinhibitory concentration (0.174 µg/ml) of rhodomyrtone resulted in the alteration of expression of several functional classes of bacterial proteins. To provide further insight into the antibacterial mode of action of this compound, we determined the impact of exposure to rhodomyrtone on the gene transcriptional profile of MRSA using microarray analysis. Exposure of MRSA to subinhibitory concentrations (0.5MIC; 0.5 µg/ml) of rhodomyrtone revealed significant modulation of gene expression, with induction of 64 genes and repression of 35 genes. Prominent changes in response to exposure to rhodomyrtone involved genes encoding proteins essential to metabolic pathways and processes such as amino acid metabolism, membrane function, ATP-binding cassette (ABC) transportation and lipoprotein and nucleotide metabolism. Genes involved in the synthesis of the aspartate family of amino acids, in particular proteins encoded by the dap operon were prominent. The diaminopimelate (DAP) biosynthetic pathway is the precursor of lysine synthesis and is essential for peptidoglycan biosynthesis. However, phenotypic analysis of the peptidoglycan amino acid content of rhodomyrtone-treated MRSA did not differ significantly from that extracted from control cells. Genes involved in the biosynthesis of amino acids and peptidoglycan, and a high affinity ATP-driven K ((+)) transport system, were investigated by quantitative reverse transcription-PCR (qRT-PCR) using EMRSA-16 1, 4, or 18 h after exposure to rhodomyrtone and in general the data concurred with that obtained by microarray, highlighting the relevance of the DAP biosynthetic pathway to the mode of action of rhodomyrtone.

Infectious diseases in the critically ill patients

Infection is common in the critically ill and often results due to the severity of the patient's illness. Recent data suggest 51% of intensive care unit (ICU) patients are infected, and 71% receive antimicrobial therapy. Bacterial infection is the primary concern, although some fungal infections are opportunistic. Infection more than doubles the ICU mortality rate, and the costs associated with infection may be as high as 40% of total ICU expenditures. There are many contemporary antimicrobial resistance concerns that the critical care clinician must consider in managing the pharmacotherapy of infection. Methicillin resistance in Staphylococcus aureus, vancomycin resistance in Enterococci, beta-lactamase resistance in Enterobacteriaceae, multidrug resistance in Pseudomonas aeruginosa and Acinetobacter species, fluoroquinolone resistance in Escherichia coli, and fungal resistance are among the most common issues ICU clinician's must face in managing infection. Critical illness causes changes in pharmacokinetics that influence drug and dosing considerations. Absorption, distribution, metabolism, and excretion may all be affected by the various disease states that define critical illness. Several specific diseases are discussed, including ventilator-associated pneumonia, various fungal infections, gastrointestinal infections due to Clostridium difficile, urinary tract infections, and bloodstream infections. Within each disease section, discussion includes causes and prevention strategies, microbiology, evidence-based guidelines, and important caveats.

Vancomycin tolerance in Gram-positive cocci

Vancomycin, a glycopeptide antimicrobial agent, represents the last line of defence against a wide range of multi-resistant Gram-positive pathogens such as enterococci, staphylococci and streptococci. However, vancomycin-resistant enterococci and staphylococci, along with vancomycin-tolerant clinical isolates, are compromising the therapeutic efficacy of vancomycin. It is conceivable that tolerance may emerge during prolonged vancomycin use. It has not been until recently, however, that the molecular basis of this tolerance began to be understood. Superoxide anions might be involved in the bactericidal activity of vancomycin in enterococci, and recent evidence suggests that the stringent response is partly responsible for vancomycin tolerance in Enterococcus faecalis. The mechanism of vancomycin tolerance in Staphylococcus aureus and Streptococcus pneumoniae is sometimes associated with a reduction of autolysin activity. Vancomycin tolerance in S. aureus and S. pneumoniae also appears to be somehow related with the two-component regulatory systems linked to cell envelope stress, although the precise molecular regulatory pathways remain poorly defined.

Improved adsorption of an Enterococcus faecalis bacteriophage ΦEF24C with a spontaneous point mutation

Some bacterial strains of the multidrug-resistant Gram-positive bacteria Enterococcus faecalis can significantly reduce the efficacy of conventional antimicrobial chemotherapy. Thus, the introduction of bacteriophage (phage) therapy is expected, where a phage is used as a bioagent to destroy bacteria. E. faecalis phage ΦEF24C is known to be a good candidate for a therapeutic phage against E. faecalis. However, this therapeutic phage still produces nonuniform antimicrobial effects with different bacterial strains of the same species and this might prove detrimental to its therapeutic effects. One solution to this problem is the preparation of mutant phages with higher activity, based on a scientific rationale. This study isolated and analyzed a spontaneous mutant phage, ΦEF24C-P2, which exhibited higher infectivity against various bacterial strains when compared with phage ΦEF24C. First, the improved bactericidal effects of phage ΦEF24C-P2 were attributable to its increased adsorption rate. Moreover, genomic sequence scanning revealed that phage ΦEF24C-P2 had a point mutation in orf31. Proteomic analysis showed that ORF31 (mw, 203 kDa) was present in structural components, and immunological analysis using rabbit-derived antibodies showed that it was a component of a long, flexible fine tail fiber extending from the tail end. Finally, phage ΦEF24C-P2 also showed higher bactericidal activity in human blood compared with phage ΦEF24C using the in vitro assay system. In conclusion, the therapeutic effects of phage ΦEF24C-P2 were improved by a point mutation in gene orf31, which encoded a tail fiber component.

Metabolic flux analysis and principal nodes identification for daptomycin production improvement by Streptomyces roseosporus

In the present work, a comprehensive metabolic network of Streptomyces roseosporus LC-54-20 was proposed for daptomycin production. The analysis of extracellular metabolites throughout the batch fermentation was evaluated in addition to daptomycin and biomass production. Metabolic flux distributions were based on stoichiometrical reaction as well as the extracellular metabolites fluxes. Experimental and calculated values for both the specific growth rate and daptomycin production rate indicated that the in silico model proved a powerful tool to analyze the metabolic behaviors based on the analysis under different initial glucose concentrations throughout the fermentation. Through manipulating different pH values, the production rates of various extracellular metabolites were also presented in this paper. Flux distribution variations revealed that the daptomycin production could be significantly influenced by the branch points of glucose 6-phosphate, 3-phosphoglycerate, phosphoenolpyruvate, pyruvate, and oxaloacetate. The five principal metabolites were certified as the flexible nodes and could form potential bottlenecks for a further enhancement of daptomycin production. Furthermore, various concentrations of the five precursors were added into the batch fermentation and led to the enhancement of daptomycin concentration and production rate.

Structure-guided design of cell wall biosynthesis inhibitors that overcome β-lactam resistance in Staphylococcus aureus (MRSA)

β-Lactam antibiotics have long been a treatment of choice for bacterial infections since they bind irreversibly to Penicillin-Binding Proteins (PBPs), enzymes that are vital for cell wall biosynthesis. Many pathogens express drug-insensitive PBPs rendering β-lactams ineffective, revealing a need for new types of PBP inhibitors active against resistant strains. We have identified alkyl boronic acids that are active against pathogens including methicillin-resistant S. aureus (MRSA). The crystal structures of PBP1b complexed to 11 different alkyl boronates demonstrate that in vivo efficacy correlates with the mode of inhibitor side chain binding. Staphylococcal membrane analyses reveal that the most potent alkyl boronate targets PBP1, an autolysis system regulator, and PBP2a, a low β-lactam affinity enzyme. This work demonstrates the potential of boronate-based PBP inhibitors for circumventing β-lactam resistance and opens avenues for the development of novel antibiotics that target Gram-positive pathogens.

Proteome analyses of cellular proteins in methicillin-resistant Staphylococcus aureus treated with rhodomyrtone, a novel antibiotic candidate

The ethanolic extract from Rhodomyrtus tomentosa leaf exhibited good antibacterial activities against both methicillin-resistant Staphylococcus aureus (MRSA) and S. aureus ATCC 29213. Its minimal inhibitory concentration (MIC) values ranged from 31.25–62.5 µg/ml, and the minimal bactericidal concentration (MBC) was 250 µg/ml. Rhodomyrtone, an acylphloroglucinol derivative, was 62.5–125 times more potent at inhibiting the bacteria than the ethanolic extract, the MIC and MBC values were 0.5 µg/ml and 2 µg/ml, respectively. To provide insights into antibacterial mechanisms involved, the effects of rhodomyrtone on cellular protein expression of MRSA have been investigated using proteomic approaches. Proteome analyses revealed that rhodomyrtone at subinhibitory concentration (0.174 µg/ml) affected the expression of several major functional classes of whole cell proteins in MRSA. The identified proteins involve in cell wall biosynthesis and cell division, protein degradation, stress response and oxidative stress, cell surface antigen and virulence factor, and various metabolic pathways such as amino acid, carbohydrate, energy, lipid, and nucleotide metabolism. Transmission electron micrographs confirmed the effects of rhodomyrtone on morphological and ultrastructural alterations in the treated bacterial cells. Biological processes in cell wall biosynthesis and cell division were interrupted. Prominent changes including alterations in cell wall, abnormal septum formation, cellular disintegration, and cell lysis were observed. Unusual size and shape of staphylococcal cells were obviously noted in the treated MRSA. These pioneer findings on proteomic profiling and phenotypic features of rhodomyrtone-treated MRSA may resolve its antimicrobial mechanisms which could lead to the development of a new effective regimen for the treatment of MRSA infections.

Daptomycin nonsusceptible enterococci: an emerging challenge for clinicians

Daptomycin is the only antibiotic with in vitro bactericidal activity against vancomycin-resistant Enterococcus (VRE) that is approved by the Food and Drug Administration (FDA). Data on the potential emergence of daptomycin nonsusceptibility among enterococci remain limited. We systematically reviewed the published literature for reports of isolates of enterococci that were daptomycin nonsusceptible and assessed the clinical significance and outcome of therapy. Based on susceptibility breakpoints approved by the Clinical Laboratory Standards Institute (CLSI), daptomycin has in vitro activity against >90% of enterococcal isolates. Less than 2% of enterococcal isolates were daptomycin nonsusceptible, with minimum inhibitory concentrations (MICs) >4 μg/mL. The prevalence of nonsusceptibility of VRE isolates to daptomycin may be overestimated due to the spread of clonally related isolates in health care settings. Clinicians should be aware of the possibility of the emergence of daptomycin nonsusceptibility and should closely monitor daptomycin MICs of enterococci isolated during treatment.

Emerging drugs for complicated skin and skin-structure infections

IMPORTANCE OF THE FILED: With the worldwide surge of MRSA, skin and skin-structure infection (SSTI) treatment has become a challenge for physicians. Cultures and antibiotic susceptibility tests for SSTIs are the rule due to the implication in morbidity and mortality rates associated with MRSA infections. The need for new antibiotics is evident and the effort to decrease antibiotic resistance is a world priority.

AREAS COVERED IN THIS REVIEW

This manuscript accesses the actual treatments and the developing of antibiotics for MRSA SSTIs.

WHAT THE READER WILL GAIN

This is a review of the data on the available and emerging treatments for MRSA SSTIs.

TAKE HOME MESSAGE

There is an unmet medical need for new antibiotics in the new millennium. As physicians, we must assure all appropriate procedures are completed in order to reduce the bacterial resistance, especially for MRSA.

Characterization of lytic enzyme open reading frame 9 (ORF9) derived from Enterococcus faecalis bacteriophage phiEF24C

In bacteriophage (phage) therapy against Gram-positive bacteria, such as Staphylococcus aureus, Listeria monocytogenes, and Enterococcus faecalis, members of a genus of SPO1-like viruses are typically employed because of their extreme virulence and broad host spectrum. Phage φEF24C, which is a SPO1-like virus infecting E. faecalis, has previously been characterized as a therapeutic phage candidate. In addition to the phage itself, phage endolysin is also recognized as an effective antimicrobial agent. In this study, a putative endolysin gene (orf9) of E. faecalis phage φEF24C was analyzed in silico, and its activity was characterized using the recombinant form. First, bioinformatics analysis predicted that the open reading frame 9 (ORF9) protein is N-acetylmuramoyl-l-alanine amidase. Second, bacteriolytic and bactericidal activities of ORF9 against E. faecalis were confirmed by zymography, decrease of peptidoglycan turbidity, decrease of the viable count, and morphological analysis of ORF9-treated cells. Third, ORF9 did not appear to require Zn(2+) ions for its activity, contrary to the bioinformatics prediction of a Zn(2+) ion requirement. Fourth, the lytic spectrum was from 97.1% (34 out of 35 strains, including vancomycin-resistant strains) of E. faecalis strains to 60% (6 out of 10 strains) of Enterococcus faecium strains. Fifth, N-acetylmuramoyl-l-alanine amidase activity of ORF9 was confirmed by matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) and the subsequent MALDI-postsource decay (PSD) analyses. Finally, functional analysis using N- or C-terminally deleted ORF9 mutants suggested that a complete ORF9 molecule is essential for its activity. These results suggested that ORF9 is an endolysin of phage φEF24C and can be a therapeutic alternative to antibiotics.

Antibiotic optimization in the difficult-to-treat patient with complicated intra-abdominal or complicated skin and skin structure infections: focus on tigecycline

Complicated intra-abdominal and skin and skin structure infections are widely varied in presentation. These infections very often lead to an increase in length of hospital stay, with a resulting increase in costs and mortality. In addition, these infections may be caused by a wide variety of bacteria and are often polymicrobial with the possibility of the presence of antimicrobial-resistant strains, such as methicillin-resistant Staphylococcus aureus, vancomycin-resistant enterococci, extended-spectrum β-lactamase strains (Escherichia coli, Klebsiella pneumoniae), and K. pneumoniae carbapenemase-producing strains. In combination with patients’ immunosuppression or comorbidities, the treatment and management options for initial therapy success are few. Tigecycline, a new glycylcyline antimicrobial from the tetracycline drug class, represents a viable option for the successful treatment of these infections. It has been shown to have activity against a wide variety of bacteria, including the antimicrobial-resistant strains. As with all tetracycline drugs, it is not recommended for pregnant or nursing women. The potential side effects are those typical of tetracycline drugs: nausea, vomiting, and headaches. Drug–drug interactions are not expected, and renal function monitoring is not necessary.

Biocidal efficacy of copper alloys against pathogenic enterococci involves degradation of genomic and plasmid DNAs

The increasing incidence of nosocomial infections caused by glycopeptide-resistant enterococci is a global concern. Enterococcal species are also difficult to eradicate with existing cleaning regimens; they can survive for long periods on surfaces, thus contributing to cases of reinfection and spread of antibiotic-resistant strains. We have investigated the potential use of copper alloys as bactericidal surfaces. Clinical isolates of vancomycin-resistant Enterococcus faecalis and Enterococcus faecium were inoculated onto copper alloy and stainless steel surfaces. Samples were assessed for the presence of viable cells by conventional culture, detection of actively respiring cells, and assessment of cell membrane integrity. Both species survived for up to several weeks on stainless steel. However, no viable cells were detected on any alloys following exposure for 1 h at an inoculum concentration of <or=10(4) CFU/cm(2). Analysis of genomic and plasmid DNA from bacterial cells recovered from metal surfaces indicates substantial disintegration of the DNA following exposure to copper surfaces that is not evident in cells recovered from stainless steel. The DNA fragmentation is so extensive, and coupled with the rapid cell death which occurs on copper surfaces, that it suggests that mutation is less likely to occur. It is therefore highly unlikely that genetic information can be transferred to receptive organisms recontaminating the same area. A combination of effective cleaning regimens and contact surfaces containing copper could be useful not only to prevent the spread of viable pathogenic enterococci but also to mitigate against the occurrence of potential resistance to copper, biocides, or antibiotics and the spread of genetic determinants of resistance to other species.

Insertion of epicatechin gallate into the cytoplasmic membrane of methicillin-resistant Staphylococcus aureus disrupts penicillin-binding protein (PBP) 2a-mediated beta-lactam resistance by delocalizing PBP2

Epicatechin gallate (ECg) sensitizes methicillin-resistant Staphylococcus aureus (MRSA) to oxacillin and other beta-lactam agents; it also reduces the secretion of virulence-associated proteins, prevents biofilm formation, and induces gross morphological changes in MRSA cells without compromising the growth rate. MRSA is resistant to oxacillin because of the presence of penicillin-binding protein 2a (PBP2a), which allows peptidoglycan synthesis to continue after oxacillin-mediated acylation of native PBPs. We show that ECg binds predominantly to the cytoplasmic membrane (CM), initially decreasing the fluidity of the bilayer, and induces changes in gene expression indicative of an attempt to preserve and repair a compromised cell wall. On further incubation, the CM is reorganized; the amount of lysylphosphatidylglycerol is markedly reduced, with a concomitant increase in phosphatidylglycerol, and the proportion of branched chain fatty acids increases, resulting in a more fluid structure. We found no evidence that ECg modulates the enzymatic activity of PBP2a through direct binding to the protein but determined that PBP2 is delocalized from the FtsZ-anchored cell wall biosynthetic machinery at the septal division site following intercalation into the CM. We argue that many features of the ECg-induced phenotype can be explained by changes in the fluid dynamics of the CM.

Decreased susceptibility to teicoplanin and vancomycin in coagulase-negative Staphylococci isolated from orthopedic-device-associated infections

We studied 315 coagulase-negative Staphylococcus strains recovered prospectively during 240 surgical procedures (206 subjects) from proven or suspected device-associated bone and joint infections. Sixteen strains (5.1%) had decreased susceptibility to glycopeptides: 15 (12 S. epidermidis strains, 2 S. capitis strains, and 1 S. haemolyticus strain) to teicoplanin alone (MIC of 16 mg/liter, n = 9; MIC of 32 mg/liter, n = 6) and one (S. epidermidis) to both teicoplanin and vancomycin (MIC, 16 and 8 mg/liter, respectively). Decreased susceptibility to teicoplanin was more prevalent in "infecting" strains (i.e., strains recovered from >/=2 distinct intraoperative samples) than in "contaminants" (i.e., strains not fulfilling this criterion) (8.1% [12/149] versus 2.4% [4/166], respectively [P = 0.022]). One hundred percent (13/13) of S. epidermidis strains with decreased susceptibility to teicoplanin were resistant to methicillin (versus 112/173 [64.7%] for S. epidermidis strains susceptible to teicoplanin; P = 0.021).