The threat of vancomycin resistance

Antibiotics and probiotics impact gut antimicrobial resistance gene reservoir in COVID-19 patients

Dysbiosis of gut microbiota is well-described in patients with coronavirus 2019 (COVID-19), but the dynamics of antimicrobial resistance genes (ARGs) reservoir, known as resistome, is less known. Here, we performed longitudinal fecal metagenomic profiling of 142 patients with COVID-19, characterized the dynamics of resistome from diagnosis to 6 months after viral clearance, and reported the impact of antibiotics or probiotics on the ARGs reservoir. Antibiotic-naive patients with COVID-19 showed increased abundance and types, and higher prevalence of ARGs compared with non-COVID-19 controls at baseline. Expansion in resistome was mainly driven by tetracycline, vancomycin, and multidrug-resistant genes and persisted for at least 6 months after clearance of SARS-CoV-2. Patients with expanded resistome exhibited increased prevalence of Klebsiella sp. and post-acute COVID-19 syndrome. Antibiotic treatment resulted in further increased abundance of ARGs whilst oral probiotics (synbiotic formula, SIM01) significantly reduced the ARGs reservoir in the gut microbiota of COVID-19 patients during the acute infection and recovery phase. Collectively, these findings shed new insights on the dynamic of ARGs reservoir in COVID-19 patients and the potential role of microbiota-directed therapies in reducing the burden of accumulated ARGs.

Burden of Antibiotic Resistance at Wolaita Sodo University Comprehensive Specialized Hospital

Background

Antibiotic resistance is a serious threat to the human population everywhere. However, less attention is given to its concern in sub-Saharan Africa including Ethiopia. There is an information gap concerning antibiotic resistance and its pattern in Wolaita Sodo University Teaching Referral Hospital. This study is aimed at investigating the prevalence of antimicrobial resistance in the study area.

Methods

Five-year retrospective data of cultures and records of 581 patients were utilized to analyze the pattern of antibiotic resistance. The statistical software including SPSS version 25 and Microsoft excel 2013 were used. Laboratory records with incompletely registered age, sex, culture isolation, or drug susceptibility test data were excluded.

Results

Out of the total of 581 samples extracted from the microbiology laboratory, 237 (40.8%) samples were culture positive for bacteria. From positive culture growth, 165 (69.6%) were gram-positive bacteria whereas 72 (30.4%) were gram negative. Staphylococcus aureus was the most prevalent isolate among gram-positive isolates as Escherichia coli was for gram-negative isolates. Overall antibiotic resistance of gram-positive isolates was 57.2% whereas that of gram-negative bacteria was 58.8%.

Conclusion

S. aureus and E. coli were found to be the most prevalent pathogenic isolates among gram-positive and gram-negative bacteria, respectively. Most of the isolated pathogens showed high resistance towards the commonly prescribed antibiotic agents. The overall antibiotic resistance in this study was 57.7%, and the overall MDR prevalence was 72.2%.

Pharmacokinetics and pharmacodynamics of peptide antibiotics

Antimicrobial resistance is a major global health challenge. As few new efficacious antibiotics will become available in the near future, peptide antibiotics continue to be major therapeutic options for treating infections caused by multidrug-resistant pathogens. Rational use of antibiotics requires optimisation of the pharmacokinetics and pharmacodynamics for the treatment of different types of infections. Toxicodynamics must also be considered to improve the safety of antibiotic use and, where appropriate, to guide therapeutic drug monitoring. This review focuses on the pharmacokinetics/pharmacodynamics/toxicodynamics of peptide antibiotics against multidrug-resistant Gram-negative and Gram-positive pathogens. Optimising antibiotic exposure at the infection site is essential for improving their efficacy and minimising emergence of resistance.

Overcoming the rising incidence and evolving mechanisms of antibiotic resistance by novel drug delivery approaches - An overview

Antimicrobial resistance is a normal evolutionary process for microorganisms. Antibiotics exerted accelerated selective pressure that hasten bacterial resistance through mutation, and acquisition external genes. These genes often carry multiple antibiotic resistant determinants allowing the recipient microbe an instant "super-bug" status. The extent of Antimicrobial Resistance (AMR) has reached a level of global crisis, existing antimicrobials are no long effective in treating infections caused by AMR pathogens. The great majority of clinically available antimicrobial agents are administered through oral and intra-venous routes. Overcoming antibacterial resistance by novel drug delivery approach offered new hopes, particularly in the treatment of AMR pathogens in sites less assessible through systemic circulation such as the lung and skin. In the current review, we will revisit the mechanism and incidence of important AMR pathogens. Finally, we will discuss novel drug delivery approaches including novel local antibiotic delivery systems, hybrid antibiotics, and nanoparticle-based antibiotic delivery systems.

Elimination from wastewater of antibiotics reserved for hospital settings, with a Fenton process based on zero-valent iron

The Fenton process activated by Zero Valent Iron (ZVI-Fenton) is shown here to effectively remove antibiotics reserved for hospital settings (specifically used to treat antibiotic-resistant infections) from wastewater, thereby helping in the fight against bacterial resistance. Effective degradation of cefazolin, imipenem and vancomycin in real urban wastewater was achieved at pH 5, which is quite near neutrality when compared with classic Fenton that works effectively at pH 3-4. The possibility to operate successfully at pH 5 has several advantages compared to operation at lower pH values: (i) lower reagent costs for pH adjustment; (ii) insignificant impact on wastewater conductivity, because lesser acid is required to acidify and lesser or no base for neutralization; (iii) undetectable release of dissolved Fe, which could otherwise be an issue for wastewater quality. The cost of reagents for the treatment ranges between 0.04 and 0.07 $ m^-3, which looks very suitable for practical applications. The structures of the degradation intermediates of the studied antibiotics and their likely abundance suggest that, once the primary compound is eliminated, most of the potential to trigger antibiotic action has been removed. Application of the ZVI-Fenton technique to wastewater treatment could considerably lower the possibility for antibiotics to trigger the development of resistance in bacteria.

Probiotics impact the antibiotic resistance gene reservoir along the human GI tract in a person-specific and antibiotic-dependent manner

Antimicrobial resistance poses a substantial threat to human health. The gut microbiome is considered a reservoir for potential spread of resistance genes from commensals to pathogens, termed the gut resistome. The impact of probiotics, commonly consumed by many in health or in conjunction with the administration of antibiotics, on the gut resistome is elusive. Reanalysis of gut metagenomes from healthy antibiotics-naïve humans supplemented with an 11-probiotic-strain preparation, allowing direct assessment of the gut resistome in situ along the gastrointestinal (GI) tract, demonstrated that probiotics reduce the number of antibiotic resistance genes exclusively in the gut of colonization-permissive individuals. In mice and in a separate cohort of humans, a course of antibiotics resulted in expansion of the lower GI tract resistome, which was mitigated by autologous faecal microbiome transplantation or during spontaneous recovery. In contrast, probiotics further exacerbated resistome expansion in the GI mucosa by supporting the bloom of strains carrying vancomycin resistance genes but not resistance genes encoded by the probiotic strains. Importantly, the aforementioned effects were not reflected in stool samples, highlighting the importance of direct sampling to analyse the effect of probiotics and antibiotics on the gut resistome. Analysing antibiotic resistance gene content in additional published clinical trials with probiotics further highlighted the importance of person-specific metagenomics-based profiling of the gut resistome using direct sampling. Collectively, these findings suggest opposing person-specific and antibiotic-dependent effects of probiotics on the resistome, whose contribution to the spread of antimicrobial resistance genes along the human GI tract merit further studies.

The Galactose-Binding Lectin Isolated from Vatairea macrocarpa Seeds Enhances the Effect of Antibiotics Against Staphylococcus aureus-Resistant Strain

The use of natural products together with standard antimicrobial drugs has recently received more attention as a strategy to combat infectious diseases caused by multidrug-resistant (MDR) microorganisms. This study aimed to evaluate the capacity of a galactose-binding lectin from Vatairea macrocarpa seeds (VML) to modulate antibiotic activity against standard and MDR Staphylococcus aureus and Escherichia coli bacterial strains. The minimum inhibitory concentration (MIC) obtained for VML against all strains was not clinically relevant (MIC ≥ 1024 μg/mL). However, when VML was combined with the antibacterial drugs gentamicin, norfloxacin and penicillin, a significant increase in antibiotic activity was observed against S. aureus, whereas the combination of VML and norfloxacin presented decreased and, hence, antagonistic antibiotic activity against E. coli. By its inhibition of hemagglutinating activity, gentamicin (MIC = 50 mM) revealed its interaction with the carbohydrate-binding site (CBS) of VML. Using molecular docking, it was found that gentamicin interacts with residues that constitute the CBS of VML with a score of - 120.79 MDS. It is this interaction between the antibiotic and the lectin's CBS that may be responsible for the enhanced activity of gentamicin in S. aureus. Thus, our results suggest that the VML can be an effective modulating agent against S. aureus. This is the first study to report the effect of lectins as modulators of bacterial sensitivity, and as such, the outcome of this study could lay the groundwork for future research involving the use of lectins and conventional antibiotics against such infectious diseases such as community-acquired methicillin-resistant S. aureus (MRSA).

Comparison of Vancomycin versus Cefazolin as Initial Therapy for Peritonitis in Peritoneal Dialysis Patients

The incidence of peritonitis ranges from 1 episode every 24 patient treatment months to 1 episode every 60 patient treatment months [Keane WF, et al. ISPD Guidelines/Recommendations. Adult peritoneal dialysis-related peritonitis treatment recommendations: 2000 update. Perit Dial Int 2000; 20:396–411.]. Gram-positive organisms account for over 80% of continuous ambulatory peritoneal dialysis (PD)-associated peritonitis. Recent fear of vancomycin-resistant enterococci (VRE) has prompted suggestions of limiting vancomycin use.

Fifty-one episodes of peritonitis in 30 patients studied over 2 years were evaluated. Cloudiness of the PD fluid and/or abdominal pain were considered suggestive of peritonitis and were confirmed by cell count and culture. Baseline cell count, Gram stain, and cultures were obtained, with periodic follow-up. Patients were randomized to receive either vancomycin 1 g/L intraperitoneally (IP) as loading dose, repeated on day 5 or day 8, depending on residual renal function, for 2 weeks, or cefazolin 1 g in the first PD bag and continued with 125 mg/L every exchange for 2 or 3 weeks, depending on culture results. All patients also received gentamicin 40 mg IP every day until the culture results were available. A similar randomized trial comparing vancomycin and cefazolin in the past used a lower concentration of cefazolin 50 mg/L [Flanigan MJ, Lim VS. Initial treatment of dialysis associated peritonitis: a controlled trial of vancomycin versus cefazolin. Perit Dial Int 1991; 11:31–7.].

Peritoneal dialysate fluid cultures revealed 31 (60.7%) gram-positive organisms, 7 (13.7%) gram-negative organisms, and 2 (3.9%) cultured yeast; 11 (21.5%) cultures yielded no growth.

The incidence of peritonitis at our center was 1 episode every 42 patient treatment months. No case of VRE was noted. There was no statistical difference in clinical response or relapse rate for the two protocols. It was the authors’ and nurses’ observation that patient compliance and satisfaction was better with vancomycin, and the cost per treatment was 23% less than cefazolin. Based on these data we believe vancomycin should still be considered for first-line treatment of PD-associated peritonitis.

Eradication of Vancomycin-Resistant Enterococci by Combining Phage and Vancomycin

Currently, effective options are needed to fight vancomycin-resistant Enterococcus faecalis (VRE). The present study shows that combinations of phage and vancomycin are highly efficient against VRE, despite being resistant to the antibiotic. Vancomycin-phage EFLK1 (anti-E. faecalis phage) synergy was assessed against VRE planktonic and biofilm cultures. The effect of the combined treatment on VRE biofilms was determined by evaluating the viable counts and biomass and then visualized using scanning electron microscopy (SEM). The cell wall peptidoglycan was stained after phage treatment, visualized by confocal microscopy and quantified by fluorescence activated cell sorting (FACS) analysis. The combined treatment was synergistically effective compared to treatment with phage or antibiotic alone, both in planktonic and biofilm cultures. Confocal microscopy and FACS analysis showed that fluorescence intensity of phage-treated bacteria increased eight-fold, suggesting a change in the peptidoglycan of the cell wall. Our results indicate that with combined treatment, VRE strains are not more problematic than sensitive strains and thus give hope in the continuous struggle against the current emergence of multidrug resistant pathogens.

Current Insights in the Application of Bone Grafts for Local Antibiotic Delivery in Bone Reconstruction Surgery

Introduction: Bone implant related infection is still one of the biggest challenges in bone and joint surgery. Antibiotic impregnated bone grafts seem to be promising in both treatment and prevention of these infections. However, great variance in methodology predominates this field of research. This paper gives an overview of the published literature.

Methods: The PRISMA-flowchart was used as protocol for article selection. Medline was searched and articles were selected in accordance with predetermined exclusion criteria.

Results: Forty-eight articles were included in the synthesis. Topics including bone graft type, manipulations of the graft, elution profile, bacterial inhibition, osteotoxicity, incorporation, special impregnation methods, clinical use and storage were investigated.

Therapeutically, high initial levels seem appropriate for biofilm eradication. A single stage procedure in the treatment of bone implant related infection seems feasible. Prophylactically, the literature indicates a reduction of postoperative infections when using antibiotic impregnated bone grafts.

Conclusion: Bone grafts are a suitable carrier for local antibiotic application both therapeutically and prophylactically.

Development of Phage Lysins as Novel Therapeutics: A Historical Perspective

Bacteriophage lysins and related bacteriolytic enzymes are now considered among the top antibiotic alternatives for solving the mounting resistance problem. Over the past 17 years, lysins have been widely developed against Gram-positive and recently Gram-negative pathogens, and successfully tested in a variety of animal models to demonstrate their efficacy. A lysin (CF-301) directed to methicillin resistant Staphylococcus aureus (MRSA) has effectively completed phase 1 human clinical trials, showing safety in this novel therapeutic class. To validate efficacy, CF-301 is currently the first lysin to enter phase 2 human trials to treat hospitalized patients with MRSA bacteremia or endocarditis. If successful, it could be the defining moment leading to the acceptance of lysins as an alternative to small molecule antibiotics. This article is a detailed account of events leading to the first therapeutic use and ultimate development of phage-encoded lysins as novel anti-infectives.

Reducing health care-associated infections by implementing separated environmental cleaning management measures by using disposable wipes of four colors

Background

Environmental cleaning is a fundamental principle of infection control in health care settings. We determined whether implementing separated environmental cleaning management measures in MICU reduced the density of HAI.

Methods

We performed a 4-month prospective cohort intervention study between August and December 2013, at the MICU of Cathay General hospital. We arranged a training program for all the cleaning staff regarding separated environmental cleaning management measures by using disposable wipes of four colors to clean the patients' bedside areas, areas at a high risk of contamination, paperwork areas, and public areas. Fifteen high-touch surfaces were selected for cleanliness evaluation by using the adenosine triphosphate (ATP) bioluminescence test. Then data regarding HAI densities in the MICU were collected during the baseline, intervention, and late periods.

Results

A total of 120 ATP readings were obtained. The total number of clean high-touch surfaces increased from 13% to 53%, whereas that of unclean high-touch surface decreased from 47% to 20%. The densities of HAI were 14.32‰ and 14.90‰ during the baseline and intervention periods, respectively. The HAI density did not decrease after the intervention period, but it decreased to 9.07‰ during the late period.

Conclusion

Implementing separated environmental cleaning management measures by using disposable wipes of four colors effectively improves cleanliness in MICU environments. However, no decrease in HAI density was observed within the study period. Considering that achieving high levels of hand-hygiene adherence is difficult, improving environmental cleaning is a crucial adjunctive measure for reducing the incidence of HAIs.

VanA-Type MRSA (VRSA) Emerged in Surface Waters

Due to the widespread occurrence of mecA-encoded methicillin resistance in Staphylococcus aureus (MRSA), treatment of staphylococcal infections is shifted to glycopeptide antibiotics like vancomycin and teicoplanin. The selective pressure of glycopeptides has eventually led to the emergence of staphylococci with increased resistance. Of great concern is vanA-encoded high level vancomycin and teicoplanin resistance in MRSA (VRSA). Therefore, this study aimed at investigating the occurrence of VRSA in surface waters. Out of 290, two staphylococcal isolates identified as MRSA Al11, Ba01, and one as MRS Co11 through 16S rRNA sequencing, also displayed high level resistance towards vancomycin and teicoplanin. These staphylococcal isolates were found to harbor vanA gene with sequence similarities of 99 %-100 % to the vanA gene extracted from vancomycin- and teicoplanin-resistant enterococcal (VRE) surface water isolates of Enterococcus faecalis Cr07, E07, Pb06 and E. faecium E330. High level glycopeptide resistance rendering protein encoded by the vanA gene, D-alanine-D-lactate ligase found in VRE, was also shown to be present in all vanA-type staphylococcal isolates through western blot. Current study elucidated that surface waters provide high potential for enterococcal vanA gene being transferred to MRSA, so called VRSA, and require special scientific consideration.

Methicillin-Resistant Staphylococcus aureus: A 5-Year Review of Surveillance Data in a Tertiary Care Hospital in Saudi Arabia

Background.

Staphylococcus aureus is an important pathogen that leads to serious infections in the community and in hospitals. Evidence has shown that the prevalence of infection and colonization with drug-resistant S. aureus, such as methicillin-resistant S. aureus (MRSA) and glycopeptide intermediately susceptible S. aureus, is increasing. Authorities must be aware of the prevalence of MRSA infection and colonization in their country in order to implement and monitor infection control policies that help curtail further emergence of this pathogen.

Objectives.

To examine the trend of hospital-acquired MRSA infection and colonization in a tertiary care institution in Saudi Arabia during a 5-year period in order to identify specific areas at high risk for MRSA transmission, and to review our MRSA decolonization procedure and outcomes.

Methods.

Surveillance data prospectively collected from January 1, 2000, through December 31, 2004, on hospital-acquired (HA) MRSA were analyzed, with an emphasis on the trend of HA-MRSA infection and colonization, areas of high transmission, risk factors, and effectiveness of the implemented decolonization policy.

Results.

During the study period, 442 cases of HA-MRSA infection and colonization were identified. Of these, 51.2% were infections, and 48.8% were colonizations. An increasing trend in the incidence rates of infection and colonization was noticed during the study period, and most cases were identified on the surgical ward (33.3%) and medical ward (32.1%). Of the 34 infected patients who underwent systematic decolonization, 35.3% were successfully decolonized, and of the 11 who underwent topical decolonization, 63.6% were successfully decolonized.

Conclusion.

The increasing trend of HA-MRSA infections has been a noticeable global problem. We identified a gradual increase in the rates of MRSA colonization and infection in a tertiary care center Saudi Arabia and recognize the importance of abiding by strict infection control policies, including hand hygiene and proper isolation practices. Continued surveillance for MRSA and other emerging multidrug-resistant pathogens is also needed.

Evaluation of the iNtRON VRE vanA/vanB real-time PCR assay for detection of vancomycin-resistant enterococci

BACKGROUND

Recently, the iNtRON VRE vanA/vanB real-time PCR (iNtRON; iNtRON Biotechnology, Korea) assay, a multiplex real-time PCR method, was introduced. In this prospective study, we compared the iNtRON assay with the Seeplex VRE ACE detection kit (Seeplex; Seegene, Korea), a conventional multiplex PCR assay.

METHODS

A chromogenic agar-based culture, in which pre-selected vancomycin-resistant enterococci (VRE) was grown and subsequently plated on blood agar with vancomycin disks, was regarded as the reference method. A total of 304 consecutive rectal swab specimens were tested for VRE by culture and by iNtRON and Seeplex PCR assays. For the PCR assays, specimens were enriched for 16-24 hr before PCR.

RESULTS

VRE were isolated from 44 (14.5%) specimens by chromogenic agar-based culture. The clinical sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of the iNtRON assay were 100% (95% confidence interval: 89.8%-100%), 99.2% (96.9%-99.9%), 95.6% (83.6%-99.2%), and 100% (98.2%-100%), respectively, while those of the Seeplex assay were 97.7% (86.2%-99.9%), 99.6% (97.5%-99.9%), 97.7% (86.2%-99.9%), and 99.6% (97.5%-99.9%), respectively. The iNtRON assay had a detection limit of 3,159 copies/µL and 13,702 copies/µL for the vanA and vanB genes, respectively. No cross-reactivity was observed in 11 non-VRE bacterial culture isolates.

CONCLUSIONS

The overall performance of the iNtRON assay was comparable to that of a chromogenic agar-based culture method for prompt identification of VRE-colonized patients in hospitals. This assay could be an alternative or supportive method for the effective control of nosocomial VRE infection.

Role of efflux pumps in the antibiotic resistance of bacteria embedded in a biofilm

Biofilms are complex microbial associations anchored to abiotic or biotic surfaces, embedded in extracellular matrix produced by the biofilms themselves where they interact with each other and the environment. One of the main properties of biofilms is their capacity to be more resistant to antimicrobial agents than planktonic cells. Efflux pumps have been reported as one of the mechanisms responsible for the antimicrobial resistance in biofilm structures. Evidence of the role of efflux pump in biofilm resistance has been found in several microorganisms such as Pseudomonas aeruginosa, Escherichia coli and Candida albicans. However, in spite of the studies on the importance of efflux pumps in biofilm growth and about their relevance in antimicrobial resistance forming biofilm, the exact role of these efflux systems has not been determined as yet.

Antibacterial nicotinamide adenine dinucleotide synthetase inhibitors: amide- and ether-linked tethered dimers with alpha-amino acid end groups

Tethered dimers incorporating natural alpha-amino acid end groups were synthesized, including examples in which the previously reported esterase-sensitive ester linker was replaced with more stable amide or ether linkers. These compounds remained effective both as inhibitors of NAD synthetase and as potent antibacterial agents for Gram-positive strains. Studies on nonspecific effects, including detergent properties and promiscuous inhibition, suggested little contribution to observed activities.

Bacterial efflux pump inhibitors from natural sources

The rapid spread of bacteria expressing multidrug resistance (MDR) has necessitated the discovery of new antibacterials and resistance-modifying agents. Since the initial discovery of bacterial efflux pumps in the 1980s, many have been characterized in community- and hospital-acquired Gram-positive and Gram-negative pathogens, such as Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli and, more recently, in mycobacteria. Efflux pumps are able to extrude structurally diverse compounds, including antibiotics used in a clinical setting; the latter are rendered therapeutically ineffective. Antibiotic resistance can develop rapidly through changes in the expression of efflux pumps, including changes to some antibiotics considered to be drugs of last resort. It is therefore imperative that new antibiotics, resistance-modifying agents and, more specifically, efflux pump inhibitors (EPIs) are characterized. The use of bacterial resistance modifiers such as EPIs could facilitate the re-introduction of therapeutically ineffective antibiotics back into clinical use such as ciprofloxacin and might even suppress the emergence of MDR strains. Here we review the literature on bacterial EPIs derived from natural sources, primarily those from plants. The resistance-modifying activities of many new chemical classes of EPIs warrant further studies to assess their potential as leads for clinical development.

Efficacy and food safety considerations of poultry competitive exclusion products

Competitive exclusion (CE) products are anaerobic cultures of bacteria that are applied to poultry hatchlings to establish a protective enteric microbiota that excludes intestinal colonization by human food-borne pathogens. For safety of the poultry flock and human consumers, the identities of bacteria in CE products need to be known. A CE product is a culture of intestinal contents from adult chickens. It may be microbiologically defined by analysis of bacteria isolated from the culture, but many bacteria are hard to reliably isolate, identify, and characterize with conventional techniques. Sequence analysis of 16S ribosomal RNA (rRNA) genes may be more reliable than conventional techniques to identify CE bacteria. Bacteria in CE products may contain antimicrobial drug resistance and virulence mechanisms that could be transferred to the enteric bacteria of the food animal and to the human consumer. Detection methods for specific antimicrobial drug resistance and virulence genes and the integrase genes of conjugative transposons, mostly utilizing PCR technology, are being developed that can be applied to assess these risks in CE bacteria. With improvements in efficacy, bacterial identification, and detection and control of the possible risks of gene transfer, CE product technology can be made a more effective food safety tool.

7-O-malonyl macrolactin A, a new macrolactin antibiotic from Bacillus subtilis active against methicillin-resistant Staphylococcus aureus, vancomycin-resistant enterococci, and a small-colony variant of Burkholderia cepacia

We report here the discovery, isolation, and chemical and preliminary biological characterization of a new antibiotic compound, 7-O-malonyl macrolactin A (MMA), produced by a Bacillus subtilis soil isolate. MMA is a bacteriostatic antibiotic that inhibits a number of multidrug-resistant gram-positive bacterial pathogens, including methicillin-resistant Staphylococcus aureus, vancomycin-resistant enterococci, and a small-colony variant of Burkholderia cepacia. MMA-treated staphylococci and enterococci were pseudomulticellular and exhibited multiple asymmetric initiation points of septum formation, indicating that MMA may inhibit a cell division function.

The emergence of vancomycin-intermediate and vancomycin-resistant Staphylococcus aureus

Methicillin-resistant Staphylococcus aureus (MRSA) is well-recognised as a major cause of infection in the health care setting but, even more worryingly, is now emerging in the community. The glycopeptides-notably vancomycin-have traditionally been the mainstay of treatment of MRSA but overuse has led to the emergence of vancomycin-intermediate and vancomycin-resistant MRSA (VISA and VRSA, respectively). Although the mechanisms underlying vancomycin resistance are not yet fully understood, changes to the bacterial cell wall-the site of action of the glycopeptides-are believed to be key. Recent evidence also supports the transfer of genetic material among bacteria as contributing to the development of VRSA. Based on the cases identified to date, risk factors for the development of VRSA may include older age, compromised blood flow to the lower limbs, and the presence of chronic ulcers. The true extent of the problem, however, remains to be determined-it is likely that many cases of VISA and VRSA infection go undetected because of suboptimal screening programmes and possible limitations of automated and non-automated detection methods. Effective screening directed at those patients considered to be most at risk should therefore be a priority. Not surprisingly, the spread of MRSA from the hospital to the community setting, coupled with the emergence of VISA and VRSA, has become a major cause of concern among clinicians and microbiologists. The treatment options available for these infections are now severely compromised and thus new classes of antimicrobial agents effective against MRSA, VISA and VRSA are urgently required.

Control and Outcome of a Large Outbreak of Colonization and Infection with Glycopeptide-Intermediate Staphylococcus aureus in an Intensive Care Unit

BACKGROUND

Glycopeptide-intermediate Staphylococcus aureus (GISA) is emerging as a cause of nosocomial infection and outbreaks of infection and colonization in intensive care units (ICUs). We describe an outbreak of GISA colonization/infection and the ensuing control measures in an ICU and investigate outcomes of the affected patients.

METHODS

We describe an outbreak of GISA colonization and infection that affected 21 patients in a medical ICU at a tertiary care teaching hospital, as well as the measures taken to eradicate the GISA strain.

RESULT

Recognition of the outbreak was difficult. Infections, all of which were severe, were diagnosed in 11 of 21 patients. Patient isolation and barrier precautions failed when used alone. Addition of a stringent policy of restricted admissions, twice daily environmental cleaning, and implementation of hand decontamination with a hydroalcoholic solution led to outbreak termination. This was associated with increases in workload, despite a marked decrease in the number of admissions.

CONCLUSION

This first description of a large outbreak of GISA colonization and infection underlines the importance of routine GISA-strain detection when methicillin-resistant S. aureus is isolated. Outbreak control may be difficult to achieve.

Clinical trial results with linezolid, an oxazolidinone, in the treatment of soft tissue and postoperative gram-positive infections

BACKGROUND

Infectious complications encountered after major surgery include operative site infections and nosocomial pneumonia. Recent infection surveillance programs have identified the increasing pathogenic role of gram-positive bacteria in these infections and the high prevalence of methicillin-resistant Staphylococcus aureus (MRSA) in the United States and abroad. Surgical site infections and nosocomial pneumonia, often serious infections, are associated with adverse clinical outcomes including bacteremia and its resultant complications, as well as the socioeconomic consequences of excess hospitalization and discharge to nursing care.

METHODS

The essential triad for management of postoperative soft tissue infection consists of thorough appraisal of the infection site for reintervention, culture of drainage or infected tissue, and prompt initiation of empiric antimicrobial therapy designed to cover the most probable causative pathogens. Broad-spectrum antimicrobial regimens are often necessary for empiric therapy of skin and soft tissue infections or nosocomial pneumonia; however, regimens should be tailored to the most effective and clinically appropriate agent based on results of susceptibility testing.

RESULTS

Results of the clinical trial experience with the first United States Food and Drug Administration (FDA)-approved antimicrobial in the new class of oxazolidinones, linezolid, are reviewed.

CONCLUSION

In randomized, controlled trials, linezolid 600 mg twice daily (intravenously or orally) provided effective antimicrobial therapy for gram-positive soft tissue infections, including MRSA, and nosocomial pneumonia in which S. aureus was a causative pathogen.

Mannopeptimycins, a novel class of glycopeptide antibiotics active against gram-positive bacteria

Mannopeptimycins alpha-epsilon, novel glycopeptides with activity against methicillin-resistant staphylococci and vancomycin-resistant enterococci, are purified from the fermentation broth of a strain of Streptomyces hygroscopicus, LL-AC98, and their structures characterized using spectroscopic analyses and chemical methods. The SAR data of the natural and synthetic esters demonstrate that the presence of hydrophobic groups near the terminal mannosyl moiety is critical for antibacterial potency. Scalable syntheses of 4,6-cyclic acetals and ketals on this moiety are used to produce significant quantities of the respective mannopeptimycin derivatives. These acetal and ketal derivatives exhibit potent activities against susceptible and resistant Gram-positive bacteria in both in vitro and in vivo experiments, comparable with or exceeding the activity of vancomycin. Studies on the mechanism of action suggest that the mannopeptimycins interfere with the late stages of bacterial cell wall biosynthesis. It is believed that these antibiotics inhibit the transglycosylation by binding to the transglycosylase substrate, lipid II.

A retrospective drug utilization evaluation of vancomycin usage in paediatric patients

OBJECTIVE

To evaluate the appropriateness of use of vancomycin in paediatric patients at KK Women's and Children's Hospital, the major paediatric hospital in Singapore to identify potential problems in prescribing practices that may necessitate intervention to optimize vancomycin usage.

METHODS

A retrospective drug utilization evaluation was performed for paediatric patients who received intravenous vancomycin from 1 June 1998 to 31 June 1999. The outcome measures were consistency of vancomycin indication with recommended guidelines, dosing regimens, microbiological data, monitoring of serum drug levels, renal function, clinical outcomes and adverse drug reactions (ADRs).

RESULTS

A total of 96 cases was available for evaluation. Sixty-two (64.6%) courses of vancomycin were consistent with guidelines for indication of therapy. Eighty-six (89.6%) of the dosing regimen were consistent. All infusion times that were recorded (56.3%) were consistent with criteria. Of the patients treated with vancomycin for more than 1 day, peak and/or trough serum vancomycin levels were ordered for 70 cases. Of the 56 cases with paired levels ordered, 46 cases had at least one level that fell outside the therapeutic range. Nineteen (19.8%) cases of ADRs were documented. Fifty-eight (60.4%) cases received concurrent nephrotoxic drugs. However, a substantial portion of vancomycin courses were apparently not prescribed for appropriate indications, and there was poor recording of vancomycin administration information and sampling time.

CONCLUSION

The majority of dosing regimens of vancomycin was consistent with guideline criteria. The most evident problem was the sub-optimal use of the monitoring of vancomycin serum levels. The information derived from this study may be used as a for further study and for the development of strategies for optimize vancomycin usage.

Diabetic foot ulcer and multidrug-resistant organisms: risk factors and impact

AIMS

The primary objective was to characterize factors allowing the colonization of diabetic foot wounds by multidrug-resistant organisms (MDRO), and the secondary objective was to evaluate the influence of MDRO colonization/infection on wound healing.

METHODS

In 180 patients admitted to a specialized diabetic foot unit, microbiological specimens were taken on admission. Potential risk factors for MDRO-positive specimens were examined using univariate and multivariate analyses. Prospective follow-up data from 75 patients were used to evaluate the influence of MDRO colonization/infection on time to healing.

RESULTS

Eighteen per cent of admission specimens were positive for MDRO. MDRO-positive status was not associated with patient characteristics (age, sex, type of diabetes, complications of diabetes), wound duration, or wound type (neuropathic or ischaemic). In the multivariate analysis, the only factors significantly associated with positive MDRO status on admission were a history of previous hospitalization for the same wound (21/32 compared with 48/148; P = 0.0008) or the presence of osteomyelitis (22/32 compared with 71/148; P = 0.025). In the longitudinal study of 75 wounds, MDRO-positive status on admission or during follow-up (6 months at least or until healing, mean 9 +/- 7 months) was not associated with time to healing (P = 0.71).

CONCLUSION

MDROs are often present in severe diabetic foot wounds. About one-third of patients with a history of previous hospitalization for the same wound, and 25% of patients with osteomyelitis, had MDRO-positive specimens. This suggests that hygiene measures, or isolation precautions in the case of admission of patients presenting with these characteristics, should be aggressively implemented to prevent cross-transmission. Positive MDRO status is not associated with a longer time to healing.

Incidence of methicillin-resistant Staphylococcus aureus causing chronic rhinosinusitis

OBJECTIVE/HYPOTHESIS

To identify the incidence of methicillin-resistant Staphylococcus aureus (MRSA) causing chronic rhinosinusitis (CRS) and identify whether antibiotic use and previous endoscopic sinus surgeries (ESS) contribute to its development.

STUDY DESIGN

A retrospective case control analysis, with the control group randomly selected and matched for age and sex.

METHODS

All patients undergoing an endonasal culture in a tertiary otolaryngology center between April 2001 and March 2003 for mucopurulent rhinosinusitis were identified. A chart review was undertaken to identify those patients with a positive MRSA culture result. An age- and sex-matched control group was randomly chosen, and an interview was conducted to identify antibiotic use and previous ESS. A statistical analysis on these two variables was carried out using a t test and the Wilcoxon rank-sum test.

RESULTS

Two hundred eighty cultures were identified in 188 patients, and of these, 264 cultures in 173 patients met the inclusion criteria. There were 141 positive cultures and 13 positive MRSA cultures. The overall incidence of MRSA in this population was 9.22%. The mean number of antibiotic courses in the MRSA and the control groups was 33.2 and 26.7, respectively, which was not statistically significant (P =.43). The 95% confidence interval (CI) for this mean difference of 6.5 is -9.8 to 22.8. The mean number of ESS in the MRSA and control groups was 2.0 and 1.9, respectively, which was not statistically significant (P =.93). The 95% CI for this mean difference of 0.06 is -1.3 to 1.4.

CONCLUSIONS

We identified a 9.22% incidence of MRSA-causing CRS. The frequency of antibiotic use and previous ESS were found not to be statistically significant causes of MRSA sinusitis. However, the 95% CI for antibiotic usage is skewed to the right, indicating a possible role for its contribution to the emergence of MRSA-causing CRS.

Hydrophobic Acetal and Ketal Derivatives of Mannopeptimycin-α and Desmethylhexahydromannopeptimycin-α: Semisynthetic Glycopeptides with Potent Activity Against Gram-Positive Bacteria

The effect of introducing hydrophobic groups onto the disaccharide portion of the mannopeptimycins has been examined. Under acid-catalyzed conditions dimethyl acetals and ketals react on the terminal mannose of the disaccharide moiety of mannopeptimycin-alpha and the cyclohexylalanyl analogue 2. The preferentially formed monofunctionalized 4,6-acetals and -ketals display potent antibacterial activities against Gram-positive microorganisms, including MRSA, PRSP, and VRE pathogens.

Synthesis and biological evaluations of novel benzimidazoles as potential antibacterial agents

A series of novel benzimidazole derivatives were synthesized via parallel solution-phase chemistry. Many of these compounds were found to inhibit the growth of Staphylococcus aureus and Escherichia coli. Several analogues exhibited low micromolar minimal inhibitory concentrations (MIC) against both Gram-positive and Gram-negative bacteria of clinical relevance and could serve as leads for further optimizations for antibacterial research.

MexAB-OprM-Specific efflux pump inhibitors in Pseudomonas aeruginosa. Part 1: Discovery and early strategies for lead optimization

The identification of a series of compounds that specifically inhibit efflux by the MexAB-OprM pump system in Pseudomonas aeruginosa is described. Synthesis and in vitro structure-activity relationships (SARs) are outlined. Early leads lacked activity in animal models, and efforts to improve solubility and reduce serum protein binding by the introduction of polar groups are discussed.

2-piperidin-4-yl-benzimidazoles with broad spectrum antibacterial activities

A series of 2-piperidin-4-yl-benzimidazoles were synthesized and evaluated for antibacterial activities. Certain compounds inhibit bacterial growth with low micromolar minimal inhibitory concentration (MIC). These benzimidazoles are effective against both Gram-positive and Gram-negative bacteria of clinical importance, particularly enterococci, and represent a new class of potential antibacterial agents.

Activity of Zanthoxylum clava-herculis extracts against multi-drug resistant methicillin-resistant Staphylococcus aureus (mdr-MRSA)

In a continuing search for compounds with antibiotic activity against methicillin-resistant Staphylococcus aureus (MRSA) possessing multidrug ef flux systems, we have demonstrated activity associated with extracts from Southern prickly ash bark, Zanthoxylum clava-herculis. Bioassay-guided isolation of an alkaloid extract led to the characterization of the benzo[c]phenanthridine alkaloid chelerythrine as the major active principle. This compound exhibited potent activity against strains of MRSA, which were highly resistant to clinically useful antibiotics via multidrug ef flux mechanisms.

Vancomycin-resistant enterococci: 15 years and counting

We review the history of vancomycin-resistant enterococci (VRE) and propose a causal model illustrating the roles of exposure to VRE reservoirs, patient characteristics, antimicrobial exposure, and prevalence of VRE in the progression from potential VRE reservoirs to active disease in hospitalized patients. Differences in VRE colonization and VRE infection are discussed with respect to hospital surveillance methodology and implications for interventions. We further document clonal transmission of VRE in a large, urban, teaching hospital and demonstrate VRE susceptibility to a wide array of antimicrobial agents. This model can guide the identification of mutable factors that are focal points for intervention.

Mannopeptimycins, new cyclic glycopeptide antibiotics produced by Streptomyces hygroscopicus LL-AC98: antibacterial and mechanistic activities

Mannopeptimycins alpha, beta, gamma, delta, and epsilon are new cyclic glycopeptide antibiotics produced by Streptomyces hygroscopicus LL-AC98. Mannopeptimycins gamma, delta, and epsilon, which have an isovaleryl substitution at various positions on the terminal mannose of the disaccharide moiety, demonstrated moderate to good antibacterial activities. Mannopeptimycin epsilon was the most active component against methicillin-resistant staphylococci and vancomycin-resistant enterococci (MICs, 2 to 4 micro g/ml for staphylococci and streptococci and 4 to 32 micro g/ml for enterococci), while mannopeptimycins gamma and delta were two- to fourfold less active. Mannopeptimycins alpha and beta, which lack the isovaleryl substitution and the disaccharide moiety, respectively, had poor antibacterial activities. The in vivo efficacies of the mannopeptimycins in Staphylococcus aureus mouse protection studies paralleled their in vitro activities. The median effective doses of mannopeptimycins gamma, delta, and epsilon were 3.8, 2.6, and 0.59 mg/kg of body weight, respectively. The mannopeptimycins were inactive against cell wall-deficient S. aureus and caused spheroplasting of Escherichia coli imp similar to that observed with penicillin G in an osmotically protective medium. Mannopeptimycin delta rapidly inhibited [(3)H]N-acetylglucosamine incorporation into peptidoglycan in Bacillus subtilis and had no effect on DNA, RNA, or protein biosynthesis. On the basis of the observations presented above, an effect on cell wall biosynthesis was suggested as the primary mode of action for mannopeptimycin delta. The mannopeptimycins were inactive against Candida albicans, did not initiate hemolysis of human erythrocytes, and did not promote potassium ion leakage from E. coli imp, suggesting a lack of membrane damage to prokaryotic or eukaryotic cells.

To gown or not to gown: the effect on acquisition of vancomycin-resistant enterococci

Infection-control recommendations include the use of gowns and gloves to prevent horizontal transmission of vancomycin-resistant enterococci (VRE). This study sought to determine whether the use of a gown and gloves gives greater protection than glove use alone against VRE transmission in a medical intensive care unit (MICU). From 1 July 1997 through 30 June 1998 and from 1 July 1999 through 31 December 1999, health care personnel and visitors were required to don gloves and gowns upon entry into rooms where there were patients infected with nosocomial pathogens. From 1 July 1998 through 30 June 1999, only gloves were required under these same circumstances. During the gown period, 59 patients acquired VRE (9.1 cases per 1000 MICU-days), and 73 patients acquired VRE during the no-gown period (19.6 cases per 1000 MICU-days; P<.01). The adjusted risk estimate indicated that gowns were protective in reducing VRE acquisition in an MICU with high VRE colonization pressure.

Vancomycin resistance in staphylococci

Vancomycin resistance has been reported in clinical isolates of both coagulase-negative staphylococci and Staphylococcus aureus. The emerging threat of widespread vancomycin resistance poses a serious public health concern given the fact that vancomycin has long been the preferred treatment of antibiotic-resistant gram-positive organisms. Though major efforts are now being focused on improving our understanding of vancomycin resistance, there is much that remains unknown at this time. This article reviews the major epidemiologic, microbiologic, and clinical characteristics of vancomycin resistance in both coagulase-negative staphylococci and S. aureus. The review begins with a discussion of issues common to both coagulase-negative staphylococci and S. aureus, such as definitions, laboratory detection of vancomycin resistance, and infection control issues related to vancomycin-resistant staphylococci. The rest of the article is then devoted to a discussion of issues unique to each organism, including epidemiology, risk factors for infection, mechanisms of resistance, and management options.

The genus Hypericum--a valuable resource of anti-Staphylococcal leads

In the present study, extracts of 34 species and varieties of the genus Hypericum were screened for activity against a clinical isolate of methicillin-resistant Staphylococcus aureus, which in addition possessed a multidrug efflux mechanism conferring a high level of resistance to therapeutically useful antibiotics. Thirty-three of the 34 chloroform extracts showed significant activity in a disk diffusion assay, and five extracts had minimum inhibitory concentrations of 64 microg/ml, indicating that this genus has great potential to yield compounds with potent activity against multidrug-resistant bacteria.

Combination of quinupristin-dalfopristin (Synercid) and rifampin is highly synergistic in experimental Staphylococcus aureus joint prosthesis infection

We compared the efficacies of quinupristin-dalfopristin (Q-D; 30 mg/kg of body weight every 8 h) and vancomycin (60 mg/kg twice daily), alone or in combination with rifampin (10 mg/kg twice daily), in a rabbit model of methicillin-resistant Staphylococcus aureus knee prosthesis infection. In contrast to vancomycin, Q-D significantly reduced the mean log(10) CFU per gram of bone versus that for the controls. The combination of rifampin with either Q-D or vancomycin was significantly more effective than monotherapy.

Antibody-catalyzed cleavage of the D-Ala-D-Lac depsipeptide: an immunological approach to the problem of vancomycin resistance

Vancomycin resistance is currently a major healthcare problem. The development of a catalytic monoclonal antibody (mAb) that hydrolyzes the D-Ala-D-Lac depsipeptide provides a potentially novel antibiotic strategy. A phosphonate hapten design was used to program antibody catalysis. The characteristics of the hapten were shown to be important for obtaining a viable immune response and several catalytic mAbs that cleave a peptidoglycan model substrate. The best mAb afforded a >500-fold rate enhancement over background.