Nosocomial bacterial infections in Intensive Care Units. I: Organisms and mechanisms of antibiotic resistance

High Prevalence of Multidrug-Resistant Bacteria in the Trachea of Intensive Care Units Admitted Patients: Evidence from a Bangladeshi Hospital

Recent research has shown that antibiotic-resistant microorganisms are becoming more prevalent in intensive care units (ICUs) at an exponential rate. Patients in the ICU can get infected by pathogens due to invasive operation procedures and critical health conditions. This study primarily emphasized tracheal samples from ICU patients due to their reliance on ventilators, increasing their susceptibility to Ventilator-Associated Pneumonia (VAP). Moreover, the rise of multidrug-resistant (MDR) pathogens makes treatment strategies more challenging for these patients. In this study, we tested 200 tracheal specimens to determine the prevalence of microorganisms and analyzed the antibiotic susceptibility of these isolates against regular antibiotics, including 4th generation drugs. Among the 273 isolates, 81% were gram-negative bacteria, 10% were gram-positive bacteria, and 9% were fungi. The most prevalent gram-negative bacteria were Acinetobacter spp. (34%), Klebsiella spp. (22%), Pseudomonas spp. (14%), and Escherichia coli (9.2%). The most prevalent gram-positive bacteria were Staphylococcus aureus (5.9%), and the fungi were Candida spp. (7.3%). Among the most prevalent bacteria, except Staphylococcus aureus isolates, around 90% were resistant to multiple drugs, whereas 60% of Acinetobacter spp. and Pseudomonas spp. were extensively drug resistant. Sensitivity analysis against the gram-negative and gram-positive drug panel using a one-way ANOVA test followed by Tukey's post hoc test showed that in the in vitro assay, colistin was the most effective antibiotic against all gram-negative bacteria. In contrast, linezolid, vancomycin, and fusidic acid were most effective against all gram-positive bacteria. Regular monitoring of nosocomial infections and safe management of highly resistant bacteria can help prevent future pandemics.

Recent Advancement in Bioactive Chalcone Hybrids as Potential Antimicrobial Agents in Medicinal Chemistry

Chalcones are flavonoid-related aromatic ketones and enones generated from plants. The chalcones have a wide range of biological activities, such as anti-tumor, calming, and antimicrobial activities. In the present review, we have focused on the recently published original research articles on chalcones as a unique antibacterial framework in medicinal chemistry. Chalcones are structurally diverse moieties and can be split into simple and hybrid chalcones, with both having core pharmacophore 1,3-diaryl-2-propen-1-one. Chalcones are isolated from natural sources and also synthesized by using various methods. Their structure-activity relationship, mechanisms, and list of patents are also summarized in this paper. This review article outlines the currently published antimicrobial chalcone hybrids and suggests that chalcone derivatives may be potential antimicrobial agents in the future.

Drug repositioning: doxazosin attenuates the virulence factors and biofilm formation in Gram-negative bacteria

The resistance development is an increasing global health risk that needs innovative solutions. Repurposing drugs to serve as anti-virulence agents is suggested as an advantageous strategy to diminish bacterial resistance development. Bacterial virulence is controlled by quorum sensing (QS) system that orchestrates the expression of biofilm formation, motility, and virulence factors production as enzymes and virulent pigments. Interfering with QS could lead to bacterial virulence mitigation without affecting bacterial growth that does not result in bacterial resistance development. This study investigated the probable anti-virulence and anti-QS activities of α-adrenoreceptor blocker doxazosin against Proteus mirabilis and Pseudomonas aeruginosa. Besides in silico study, in vitro and in vivo investigations were conducted to assess the doxazosin anti-virulence actions. Doxazosin significantly diminished the biofilm formation and release of QS-controlled Chromobacterium violaceum pigment and virulence factors in P. aeruginosa and P. mirabilis, and downregulated the QS encoding genes in P. aeruginosa. Virtually, doxazosin interfered with QS proteins, and in vivo protected mice against P. mirabilis and P. aeruginosa. The role of the membranal sensors as QseC and PmrA was recognized in enhancing the Gram-negative virulence. Doxazosin downregulated the membranal sensors PmR and QseC encoding genes and could in silico interfere with them. In conclusion, this study preliminary documents the probable anti-QS and anti-virulence activities of doxazosin, which indicate its possible application as an alternative or in addition to antibiotics. However, extended toxicological and pharmacological investigations are essential to approve the feasible clinical application of doxazosin as novel efficient anti-virulence agent. KEY POINTS: • Anti-hypertensive doxazosin acquires anti-quorum sensing activities • Doxazosin diminishes the virulence of Proteus mirabilis and Pseudomonas aeruginosa • Doxazosin could dimmish the bacterial espionage.

Antimicrobial and Antibiofilm Activity of Copper-Based Metallic Compounds Against Bacteria Related with Healthcare-Associated Infections

Health care-associated infections (HAIs) contribute to a significant rate of morbidity, mortality, and financial burden on health systems. These infections are caused by multidrug-resistant bacteria that produce biofilm as the main virulence factor. This study aimed to evaluate the effect of the copper-based metallic compounds [Cu(phen)(pz)NO₂]Cl (I), [Cu(bpy)(pz)(NO₂)]Cl (II), and [Cu(phen)(INA)NO₂]Cl (III), where phen = phenanthroline, bpy = bipyridine, pz = pyrazinamide, and INA = isonicotinic acid, against planktonic cells and biofilms formation of Staphylococcus aureus, Staphylococcus epidermidis, and Escherichia coli. The susceptibility of the microorganisms was evaluated by minimum inhibitory concentration (MIC), minimum bacterial concentration (MBC), and time-kill curve assay on planktonic cells. The biofilm formation was evaluated by biomass quantification through staining with crystal violet (CV), colony-forming units (CFUs) quantification, and biofilm metabolic activity determination by XTT assay. The compounds showed bacteriostatic and bactericidal activity on all microorganisms analyzed. Regarding the antibiofilm activity, all metallic compounds were able to reduce significantly the biofilm biomass, colony-forming units, and the metabolic activity of remaining cells, varying the efficient concentration according to the strain analyzed. Interestingly, compounds (I), (II) and (III) did not exhibit DNA degradation activity even with up to 100 µM of these metal complexes. On the other hand, complexes (I) and (III) showed a remarkable capacity to cleave DNA upon addition of glutathione, a reducing agent (Cu^II/Cu^I) that leads to reactive oxygen species (ROS) formation. The results presented in this study showed promising antimicrobial and antibiofilm effects.

Hiring of the Anti-Quorum Sensing Activities of Hypoglycemic Agent Linagliptin to Alleviate the Pseudomonas aeruginosa Pathogenesis

Bacteria communicate with each other using quorum sensing (QS) which works in an inducer/receptor manner. QS plays the main role in orchestrating diverse bacterial virulence factors. Pseudomonas aeruginosa is one of the most clinically important bacterial pathogens that can cause infection in almost all body tissues. Besides its efficient capability to develop resistance to different antibiotics, P. aeruginosa acquires a huge arsenal of virulence factors that are controlled mainly by QS. Challenging QS with FDA-approved drugs and natural products was proposed as a promising approach to mitigate bacterial virulence enabling the host immunity to complete the eradication of bacterial infection. The present study aims to evaluate the dipeptidase inhibitor-4 inhibitor hypoglycemic linagliptin anti-QS and anti-virulence activities against P. aeruginosa in vitro, in vivo, and in silico. The current results revealed the significant ability to diminish the production of protease and pyocyanin, motility, and biofilm formation in P. aeruginosa. Furthermore, the histopathological examination of liver and kidney tissues of mice injected with linagliptin-treated bacteria showed an obvious reduction of pathogenesis. Linagliptin downregulation to QS-encoding genes, besides the virtual ability to interact with QS receptors, indicates its anti-QS activities. In conclusion, linagliptin is a promising anti-virulence and anti-QS candidate that can be used solely or in combination with traditional antimicrobial agents in the treatment of P. aeruginosa aggressive infections.

Drug-Repurposing Approach To Combat Staphylococcus aureus: Biomolecular and Binding Interaction Study

Staphylococcus aureus is considered as one of the most widespread bacterial pathogens and continues to be a prevalent cause of mortality and morbidity across the globe. FmtA is a key factor linked with methicillin resistance in S. aureus. Consequently, new antibacterial compounds are crucial to combat S. aureus resistance. Here, we present the virtual screening of a set of compounds against the available crystal structure of FmtA. The findings indicate that gemifloxacin, paromomycin, streptomycin, and tobramycin were the top-ranked potential drug molecules based on the binding affinity. Furthermore, these drug molecules were analyzed with molecular dynamics simulations, which showed that the identified molecules formed highly stable FmtA-inhibitor(s) complexes. Molecular mechanics Poisson-Boltzmann surface area and quantum mechanics/molecular mechanics calculations suggested that the active site residues (Ser127, Lys130, Tyr211, and Asp213) of FmtA are crucial for the interaction with the inhibitor(s) to form stable protein-inhibitor(s) complexes. Moreover, fluorescence- and isothermal calorimetry-based binding studies showed that all the molecules possess dissociation constant values in the micromolar scale, revealing a strong binding affinity with FmtA^Δ80, leading to stable protein-drug(s) complexes. The findings of this study present potential beginning points for the rational development of advanced, safe, and efficacious antibacterial agents targeting FmtA.

Quantum Mechanics/Molecular Mechanics Studies on the Catalytic Mechanism of a Novel Esterase (FmtA) of Staphylococcus aureus

FmtA is a novel esterase that shares the penicillin-binding protein (PBP) core structural folding but found to hydrolyze the removal of d-Ala from teichoic acids. Molecular docking, dynamics, and MM-GBSA of FmtA and its variants S127A, K130A, Y211A, D213A, and K130AY211A, in the presence or absence of wall teichoic acid (WTA), suggest that active site residues S127, K130, Y211, D213, N343, and G344 play a role in substrate binding. Quantum mechanics (QM)/molecular mechanics (MM) calculations reveal that during WTA catalysis, K130 deprotonates S127, and the nucleophilic S127 attacks the carbonyl carbon of d-Ala bound to WTA. The tetrahedral intermediate (TI) complex is stabilized by hydrogen bonding to the oxyanion holes. The TI complex displays a high energy gap and collapses to an energetically favorable acyl-enzyme complex.

A review on disinfection technologies for controlling the antibiotic resistance spread

The occurrence of antibiotic-resistant bacteria (ARB) in water bodies poses a sanitary and environmental risk. These ARB and other mobile genetic elements can be easily spread from hospital facilities, the point in which, for sure, they are more concentrated. For this reason, novel clean and efficient technologies are being developed for allowing to remove these ARB and other mobile genetic elements before their uncontrolled spread. In this paper, a review on the recent knowledge about the state of the art of the main disinfection technologies to control the antibiotic resistance spread from natural water, wastewater, and hospital wastewater (including urine matrices) is reported. These technologies involve not only conventional processes, but also the recent advances on advanced oxidation processes (AOPs), including electrochemical advanced oxidation processes (EAOPs). This review summarizes the state of the art on the applicability of these technologies and also focuses on the description of the disinfection mechanisms by each technology, highlighting the promising impact of EAOPs on the remediation of this important environmental and health problem.

Tackling Virulence of Pseudomonas aeruginosa by the Natural Furanone Sotolon

The bacterial resistance development due to the incessant administration of antibiotics has led to difficulty in their treatment. Natural adjuvant compounds can be co-administered to hinder the pathogenesis of resistant bacteria. Sotolon is the prevailing aromatic compound that gives fenugreek its typical smell. In the current work, the anti-virulence activities of sotolon on Pseudomonas aeruginosa have been evaluated. P. aeruginosa has been treated with sotolon at sub-minimum inhibitory concentration (MIC), and production of biofilm and other virulence factors were assessed. Moreover, the anti-quorum sensing (QS) activity of sotolon was in-silico evaluated by evaluating the affinity of sotolon to bind to QS receptors, and the expression of QS genes was measured in the presence of sotolon sub-MIC. Furthermore, the sotolon in-vivo capability to protect mice against P. aeruginosa was assessed. Significantly, sotolon decreased the production of bacterial biofilm and virulence factors, the expression of QS genes, and protected mice from P. aeruginosa. Conclusively, the plant natural substance sotolon attenuated the pathogenicity of P. aeruginosa, locating it as a plausible potential therapeutic agent for the treatment of its infections. Sotolon can be used in the treatment of bacterial infections as an alternative or adjuvant to antibiotics to combat their high resistance to antibiotics.

Increased Antimicrobial and Multidrug Resistance Downstream of Wastewater Treatment Plants in an Urban Watershed

Development and spread of antimicrobial resistance (AMR) and multidrug resistance (MDR) through propagation of antibiotic resistance genes (ARG) in various environments is a global emerging public health concern. The role of wastewater treatment plants (WWTPs) as hot spots for the dissemination of AMR and MDR has been widely pointed out by the scientific community. In this study, we collected surface water samples from sites upstream and downstream of two WWTP discharge points in an urban watershed in the Bryan-College Station (BCS), Texas area, over a period of nine months. E. coli isolates were tested for resistance to ampicillin, tetracycline, sulfamethoxazole, ciprofloxacin, cephalothin, cefoperazone, gentamycin, and imipenem using the Kirby-Bauer disc diffusion method. Antimicrobial resistant heterotrophic bacteria were cultured on R2A media amended with ampicillin, ciprofloxacin, tetracycline, and sulfamethoxazole for analyzing heterotrophic bacteria capable of growth on antibiotic-containing media. In addition, quantitative real-time polymerase chain reaction (qPCR) method was used to measure eight ARG – tetA, tetW, aacA, ampC, mecA, ermA, blaTEM, and intI1 in the surface water collected at each time point. Significant associations (p < 0.05) were observed between the locations of sampling sites relative to WWTP discharge points and the rate of E. coli isolate resistance to tetracycline, ampicillin, cefoperazone, ciprofloxacin, and sulfamethoxazole together with an increased rate of isolate MDR. The abundance of antibiotic-resistant heterotrophs was significantly greater (p < 0.05) downstream of WWTPs compared to upstream locations for all tested antibiotics. Consistent with the results from the culture-based methods, the concentrations of all ARG were substantially higher in the downstream sites compared to the upstream sites, particularly in the site immediately downstream of the WWTP effluent discharges (except mecA). In addition, the Class I integron (intI1) genes were detected in high amounts at all sites and all sampling points, and were about ∼20 times higher in the downstream sites (2.5 × 10⁷ copies/100 mL surface water) compared to the upstream sites (1.2 × 10⁶ copies/100 mL surface water). Results suggest that the treated WWTP effluent discharges into surface waters can potentially contribute to the occurrence and prevalence of AMR in urban watersheds. In addition to detecting increased ARG in the downstream sites by qPCR, findings from this study also report an increase in viable AMR (HPC) and MDR (E. coli) in these sites. This data will benefit establishment of improved environmental regulations and practices to help manage AMR/MDR and ARG discharges into the environment, and to develop mitigation strategies and effective treatment of wastewater.

Elevated Incidences of Antimicrobial Resistance and Multidrug Resistance in the Maumee River (Ohio, USA), a Major Tributary of Lake Erie

Maumee River, the major tributary in the western basin of Lake Erie, serves as one of major sources of freshwater in the area, supplying potable, recreational, and industrial water. In this study we collected water samples from four sites in the Maumee River Bay between 2016–2017 and E. coli was isolated, enumerated, and analyzed for antimicrobial resistance (AMR) and multidrug resistance (MDR). Strikingly, 95% of the total isolates were found to be resistant to at least one antibiotic. A very high resistance to the drugs cephalothin (95.3%), ampicillin (38.3%), tetracycline (8.8%), gentamicin (8.2%), ciprofloxacin (4.2%), cefoperazone (4%), and sulfamethoxazole (1.5%) was observed within isolates from all four sampling sites. Percentages of AMR and MDR was consistently very high in the summer and fall months, whereas it was observed to be lowest in the winter. A remarkably high number of the isolates were detected to be MDR—95% resistant to ≥1 antibiotic, 43% resistant to ≥2 antibiotics, 15% resistant to ≥3 antibiotics, 4.9% resistant to ≥4 antibiotic and 1.2% resistant to ≥5 antibiotics. This data will serve in better understanding the environmental occurrence and dissemination of AMR/MDR in the area and assist in improving and establishing control measures.

Structure-Based Identification of Potential Drugs Against FmtA of Staphylococcus aureus: Virtual Screening, Molecular Dynamics, MM-GBSA, and QM/MM

Staphylococcus aureus is resistant to β-lactam antibiotics and causes several skin diseases to life-threatening diseases. FmtA is found to be one of the main factors involved in methicillin resistance in S. aureus. FmtA exhibits an esterase activity that removes the D-Ala from teichoic acid. Teichoic acids played a significant role in cell wall synthesis, cell division, colonization, biofilm formation, virulence, antibiotic resistance, and pathogenesis. The virtual screening of drug molecules against the crystal structure of FmtA was performed and the binding affinities of top three molecules (ofloxacin, roflumilast, and furazolidone) were predicted using molecular docking. The presence of positive potential and electron affinity regions in screened drug molecules by DFT analysis illustrated that these molecules are reactive in nature. The protein-ligand complexes were subjected to molecular dynamics simulation. Molecular dynamics analysis such as RMSD, RMSF, Rg, SASA, PCA, and FEL results suggested that FmtA-drug(s) complexes are stable. MM-GBSA binding affinity and QM/MM results (ΔG, ΔH, and ΔS) revealed that active site residues (Ser127, Lys130, Tyr211, Asp213, and Asn343) of FmtA played an essential for the binding of the drug(s) to form a lower energy stable protein-ligand complexes. FmtA^Δ42 was purified using cation exchange and gel filtration chromatography. Fluorescence spectroscopy and circular dichroism results showed that interactions of drugs with FmtA^Δ42 affect the tertiary structure and increase the thermostability of the protein. The screened molecules need to be tested and could be further modified to develop the antimicrobial compounds against S. aureus.

Bacterial Resistance: Antibiotics of Last Generation used in Clinical Practice and the Arise of Natural Products as New Therapeutic Alternatives

Bacterial resistance to therapeutical drugs has been a serious issue over the last decades. In fact, the quick development of resistance mechanisms by the microorganisms has been fatal for millions of people around the world, turning into a public health issue. The major cause of the resistance mechanisms is the overuse of antimicrobials. European countries try to implement mechanisms to overcome antimicrobial resistance in the community through the rational use of antimicrobials. The scientific community has been exhaustively dedicated to the discovering of new, safer and efficient drugs, being the exploitation of natural resources, mainly plants and fungi, considered as a hot topic in the field of antimicrobial agents. Innumerous reports have already shown the promising capacity of natural products or molecules extracted from these natural resources, to act as bacteriostatic and bactericidal agents. More importantly, these natural agents present significantly lower harmful effects. Bearing that in mind, this review aims at giving a contribution to the knowledge about the synthetic antibiotics of the last generation. Moreover, it is intended to provide information about the last advances regarding the discovery of new antimicrobial agents. Thus, a compilation of the chemical characteristics, efficiency, harmful outcomes and resistance mechanisms developed by the microorganisms can be consulted in the following sections together with a critical discussion, in line with the recent approaches. Furthermore, modern strategies for the prospection of novel anti-infective compounds for tackling resistant bacteria have been considered as also a current synopsis of plants and mushrooms with relevant antimicrobial potentials.

Synthesis and antimicrobial activity of the hybrid molecules between amoxicillin and derivatives of benzoic acid

Due to the increasing problem of bacterial resistance worldwide, the demand for new antibiotics is becoming increasingly urgent. We wished to: (a) prepare hybrid molecules by linking different pharmacophores by chemical bonds; (b) investigate the antib acterial activity of these hybrids using drug-sensitive and drug-resistant pathogens in vitro and vivo. A series of hybrid molecules with a diester structure were designed and synthesized that linked amoxicillin and derivatives of benzoic acid via a methylene bridge. Synthesized compounds were evaluated for activities against Gram-positive bacteria (Staphylococcus aureus American Type Culture Collection [ATCC] 29213, ATCC 11632; methicillin-resistant S. aureus [MRSA] 11; Escherichia coli ATCC 25922) and Gram-negative bacteria (Salmonella LS677, GD836, GD828, GD3625) by microdilution of broth. Synthesized compounds showed good activity against Gram-positive and Gram-negative bacteria in vitro. In particular, amoxicillin-p-nitrobenzoic acid (6d) showed good activity against Salmonella species and had better activity against methicillin-resistant S. aureus (minimum inhibitory concentration [MIC] = 64 μg/ml) than the reference drug, amoxicillin (MIC = 128 μg/ml). Amoxicillin-p-methoxybenzoic acid (6b) had the best antibacterial activity in vivo (ED₅₀ = 13.2496 μg/ml). The hybrid molecules of amoxicillin and derivatives of benzoic acid synthesized based on a diester structure can improve the activity of amoxicillin against Salmonella species and even improve the activity against MRSA.

Comparing clinical outcomes of piperacillin-tazobactam administration and dosage strategies in critically ill adult patients: a systematic review and meta-analysis

Background

Recently, continuous administration of piperacillin-tazobactam has been proposed as a valuable alternative to traditional intermittent administration especially in critically ill patients. However, antibiotic dosing remains a challenge for clinicians as antibiotic dosing regimens are usually determined in non-critically ill hospitalized adult patients. The aim was to conduct a systematic review to identify and highlight studies comparing clinical outcomes of piperacillin tazobactam dosing regimens, continuous/prolonged infusion vs intermittent infusion in critically ill patients. Meta-analyses were performed to assess the overall effect of dosing regimen on clinical efficacy.

Methods

Studies were identified systematically through searches of PubMed and Science Direct, in compliance with PRISMA guidelines. Following the systematic literature review, meta-analyses were performed using Review Manager.

Results

Twenty-three studies were included in the analysis involving 3828 critically ill adult participants in total (continuous/prolonged infusion = 2197 and intermittent infusion = 1631) from geographically diverse regions. Continuous/prolonged resulted in significantly: higher clinical cure rates (Odds Ratio 1.56, 95% Confidence Interval 1.28–1.90, P = 0 .0001), lower mortality rates (Odds Ratio 0.68, 95% Confidence Interval 0.55–0.84, P = 0 .0003), higher microbiological success rates (Odds Ratio 1.52, 95% Confidence Interval 1.10–2.11, P = 0.01) and decreasing the length of hospital stay (Mean Difference − 1.27, 95% Confidence Interval − 2.45—0.08, P = 0.04) in critically ill patients.

Conclusion

Results from this study show that there is a significant level of evidence that clinical outcome in critically ill patients is improved in patients receiving piperacillin-tazobactam via continuous/prolonged infusion. However, more rigorous scientific studies in critically ill patients are warranted to reach a sufficient level of evidence and promote further implementation of C/PI as a dosing strategy.

Development of Staphylococcus Enzybiotics: The Ph28 Gene of Staphylococcus epidermidis Phage PH15 Is a Two-Domain Endolysin

Given the worldwide increase in antibiotic resistant bacteria, bacteriophage derived endolysins represent a very promising new alternative class of antibacterials in the fight against infectious diseases. Endolysins are able to degrade the prokaryotic cell wall, and therefore have potential to be exploited for biotechnological and medical purposes. Staphylococcus epidermidis is a Gram-positive multidrug-resistant (MDR) bacterium of human skin. It is a health concern as it is involved in nosocomial infections. Genome-based screening approach of the complete genome of Staphylococcus virus PH15 allowed the identification of an endolysin gene (Ph28; NCBI accession number: YP_950690). Bioinformatics analysis of the Ph28 protein predicted that it is a two-domain enzyme composed by a CHAP (22-112) and MurNAc-LAA (171-349) domain. Phylogenetic analysis and molecular modelling studies revealed the structural and evolutionary features of both domains. The MurNAc-LAA domain was cloned, and expressed in E. coli BL21 (DE3). In turbidity reduction assays, the recombinant enzyme can lyse more efficiently untreated S. epidermidis cells, compared to other Staphylococcus strains, suggesting enhanced specificity for S. epidermidis. These results suggest that the MurNAc-LAA domain from Ph28 endolysin may represent a promising new enzybiotic.

Effects of Pseudomonas aeruginosa on Microglial-Derived Extracellular Vesicle Biogenesis and Composition

The packaging of molecular constituents inside extracellular vesicles (EVs) allows them to participate in intercellular communication and the transfer of biological molecules, however the role of EVs during bacterial infection is poorly understood. The goal of this study was to examine the effects of Pseudomonas aeruginosa (P. aeruginosa) infection on the biogenesis and composition of EVs derived from the mouse microglia cell line, BV-2. BV-2 cells were cultured in exosome-free media and infected with 0, 1.3 × 10⁴, or 2.6 × 10⁴ colony forming units per milliliter P. aeruginosa for 72 h. The results indicated that compared with the control group, BV-2 cell viability significantly decreased after P. aeruginosa infection and BV-2-derived EVs concentration decreased significantly in the P. aeruginosa-infected group. P. aeruginosa infection significantly decreased chemokine ligand 4 messenger RNA in BV-2-derived infected EVs, compared with the control group (p ≤ 0.05). This study also revealed that heat shock protein 70 (p ≤ 0.05) and heat shock protein 90β (p ≤ 0.001) levels of expression within EVs increased after P. aeruginosa infection. EV treatment with EVs derived from P. aeruginosa infection reduced cell viability of BV-2 cells. P. aeruginosa infection alters the expression of specific proteins and mRNA in EVs. Our study suggests that P. aeruginosa infection modulates EV biogenesis and composition, which may influence bacterial pathogenesis and infection.

Analysis of the structures of confirmed and questionable CRISPR loci in 325 Staphylococcus genomes

The CRISPR-Cas (clustered regular interspaced short palindromic repeats and CRISPR-associated proteins) system is a newly discovered immune defense system in the genome of prokaryotes, which can resist the invasion of foreign genetic elements, such as plasmids or phage. In this study, 154 strains of Staphylococcus published in the CRISPRDatabase and 171 strains included in NCBI were downloaded, the confirmed and questionable CRISPR loci of which were analyzed by bioinformatics methods, including their distribution, characteristics of the structure (including the direct repeats, spacers and cas genes), and the relationship between the presence of CRISPR and the mecA gene. Meanwhile, a comprehensive analysis of orphan CRISPR arrays was performed on this basis. A total of 196 confirmed and 1757 questionable CRISPR loci were found in 325 Staphylococcus genomes. Only 25 strains contained cas genes, which were classified into III-A (48.1%) and II-C (51.9%). The difference between the presence of the cas gene and the carrying rate of mecA was statistically significant, and they were negatively correlated. A total of 137 confirmed and 1755 questionable CRISPR loci were assumed to be false-CRISPR. The present study also analyzed the questionable CRISPR array for the first time while analyzing the confirmed CRISPR array in the Staphylococcal genome and screened the false-CRISPR elements in the orphan CRISPR array.

Chalcone derivatives and their antibacterial activities: Current development

The increase in antibiotic resistance due to various factors has encouraged the look for novel compounds which are active against multidrug-resistant pathogens. In this framework, chalcone-based compounds showed a diversity of pharmacological properties, and its derivatives possess a high degree of structural diversity, and it is helpful for the discovery of new therapeutic agents. The growing resistance to antibiotics worldwide has endangered their efficacy. This has led to a surging interest in the discovery of new antibacterial agents. Thus, there is an urgent need for new antibacterial drug candidates with increased strength, new targets, low cost, superior pharmacokinetic properties, and minimum side effects. The present review concluded and focuses on the recent developments in the area of medicinal chemistry to explore the diverse chemical structures of potent antibacterial agents and also describes its structure-activity relationships studies. The various synthetic structures leading to this class of neutral protective compound is common and additional structural optimization is promising for potential drug discovery and development.

Cultivable microbiota and pulmonary lesions in polymicrobial bovine pneumonia

In the present study, the spectrum of bacterial pathogens in the nasal shedding during disease process and in pneumonic lungs of dead animals was studied. A total of 288 clinical samples from cattle and buffaloes comprising of nasal swabs, blood, tracheal swabs, heart blood and lung tissue samples were collected from diseased (n = 190) and dead animals (n = 98). The recovered bacterial isolates were characterized by biochemical reactions, Matrix Assisted Laser Desorption/Ionization Time of Flight Mass Spectrometry (MALDI TOF-MS) and the 16S rRNA sequence analysis. The predominant bacterial isolates associated were Pasteurella multocida, Pseudomonas aeruginosa, Escherichia coli, Klebsiella pneumoniae and Staphylococcus aureus. The emerging pathogens causing bovine pneumonia identified were Leclercia spp., Stenotrophononas maltophila and Staphylococcus sciuri. Bacteriological examination of pneumonic lungs samples revealed 96.9% samples to be positive for polymicrobial isolation. Macroscopical lesions of lungs exhibited various stages and types of pneumonia with variable degree of haemorrhages, oedema and emphysema. Histopathologically, the fibrinous bronchopneumonia was observed to be the most frequent lesions seen in bovine pneumonia. Multi-drug resistance (MDR) was observed in 10% of P. multocida isolates. The resistance was seen for penicillin, cephalosporins and fluoroquinolones. Multi-drug resistance was seen in 90% of the E.coli tested. K. pneumoniae, E. hormaechei, E. cloacae, P. putida and Leclercia spp. identified were found to be multi-drug resistant. Understanding the etiological diversity of bacterial pathogens of bovine pneumonia may provide information for the better choice of therapeutics and health management.

Repurposing niclosamide as a versatile antimicrobial surface coating against device-associated, hospital-acquired bacterial infections

Device-associated and hospital-acquired infections remain amongst the greatest challenges in regenerative medicine. Furthermore, the rapid emergence of antibiotic resistance and lack of new classes of antibiotics has made the treatment of these bacterial infections increasingly difficult. The repurposing of Food and Drug Administration approved drugs for antimicrobial therapies is a powerful means of reducing the time and cost associated with drug discovery and development. In this work, niclosamide, a commercially available anthelmintic drug with recently identified antimicrobial properties, was found to prevent the formation of, and combat existing biofilms of, several relevant Gram-positive bacteria, namely strains of Staphylococcus aureus, including methicillin resistant S. aureus (MRSA), and Staphylococcus epidermidis, all common causes of hospital-acquired and device-associated infections. This anti-biofilm activity was demonstrated at niclosamide concentrations as low as 0.01 μg ml^-1. We then assessed niclosamide activity as an antibacterial coating, which could potentially be applied to medical device surfaces. We developed solvent cast niclosamide coatings on a variety of surfaces common amongst medical devices including glass, titanium, stainless steel, and aluminum. Niclosamide-coated surfaces exhibited potent in vitro activity against S. aureus, MRSA, and S. epidermidis. At niclosamide surface concentrations as low as 1.6 × 10^-2 μg mm^-2, the coatings prevented attachment of these bacteria. The coatings also cleared bacteria inoculated suspensions at niclosamide surface concentrations of 3.1 × 10^-2 μg mm^-2. Hemolysis was not observed at any of the antimicrobial coating concentrations tested. We report a facile, effective means of coating devices with niclosamide to both clear and prevent biofilm formation of common bacteria encountered in hospital-acquired and device-associated infections.

Surveillance of nosocomial infections in the Yaounde University Teaching Hospital, Cameroon

Background

Nosocomial infections (NI) represent a real public health problem in developing countries. Their surveillance is recommended to provide needed information for better control. The aim of this study was to describe the frequency and distribution of NI in the Yaoundé University Teaching Hospital (YUTH).

Methods

It was a longitudinal and descriptive study targeting hospitalized patients in the intensive care, gynaecological, surgical and neonatal units. Each consenting patient was administered a questionnaire at the beginning of the study and followed up daily for the duration of their hospitalization using a standardized grid to detect all nosocomial infections. Cumulative incidence was used to estimate NI frequency.

Results

There were 307 patients included. The cumulative incidence and specific mortality rate of NI were 19.21% (16.9–21.5) and 28% (16.2–42.5) respectively. Septicaemia (20.34%), infection of the skin and soft tissues (20.34%) and urinary tract infections (15.25%) were the most frequent type of NI. Klebsiella spp. was the most frequently isolated bacterium (27%).

Conclusion

Nosocomial infections contribute to high hospital morbidity in the Yaounde University Teaching Hospital. Strategies need to be identified for a sustainable and continuous monitoring of NI in all health facilities of Cameroon. In addition, Further studies should identify NI determinants and interventions for efficient and better control.

Characterization of CRISPR-Cas system in clinical Staphylococcus epidermidis strains revealed its potential association with bacterial infection sites

Staphylococcus epidermidis is considered as a major cause of nosocomial infections, bringing an immense burden to healthcare systems. Virulent phages have been confirmed to be efficient in combating the pathogen, but the prensence of CRISPR-Cas system, which is a bacterial immune system eliminating phages was reported in few S. epidermidis strains. In this study, the CRISPR-Cas system was detected in 12 from almost 300 published genomes in GenBank and by PCR of cas6 gene in 18 strains out of 130 clinical isolates obtained in Copenhagen. Four strains isolated in 1965-1966 harboured CRISPR elements confirming that this immunity system was not recently acquired by S. epidermidis. In these CRISPR-positive strains, 44 and 12 spacers were found to belong to CRISPR1 and CRISPR2 elements, respectively. However, only 15 spacers displayed homology to reported phages and plasmids DNA. Interestingly, 5 different spacers located in the CRISPR1 locus with homolgy to virulent phage 6ec DNA sequences, and 19 strains each carrying 2 or 3 different spacers recognizing this phage, implied that the CRISPR-Cas immunity could be abrogated by nucleotide mismatch between the spacer and its target phage sequence, while new spacers obtained from the evolved phage could recover the CRISPR interference. In addition, phylogenetic analysis of the 29 CRISPR-positive isolates divided them into four lineages, with 81% human blood isolates as a distinct sub-lineage, suggesting that the CRISPR difference is closely related to diverse habitats. Knowledge of CRISPR and its prevalence may ultimately be applied in the understanding of origin and evolution of CRISPR-positive S. epidermidis strains.

Bactericidal and Antibiotic Synergistic Effect of Nanosilver Against Methicillin-Resistant Staphylococcus aureus

Background:

Methicillin-Resistant Staphylococcus aureus (MRSA) are bacteria responsible for several difficult-to-treat infections in humans. These strains have developed, through the process of natural selection. Infections by MRSA are more difficult to treat with standard types of antibiotics and thus more dangerous to human health.

Objectives:

The aim of this study was to evaluate the bactericidal and antibiotic synergistic effect of silver nanoparticles (Ag-NPs) against MRSA.

Materials and Methods:

Methicillin-Resistant Staphylococcus aureus strains were isolated from clinical samples and identified, and their susceptibility was tested using the MicroScan® WalkAway-96® SI System. minimum inhibitory concentration (MIC) was determined by a microdilution method. Time kill assay was performed by exposing the MRSA isolates to different concentrations of Ag-NPs and monitoring bacterial growth, by measuring optical density at 600 nm. Tissue culture plate was used for determination of the efficacy of Ag-NPs and their combination with antibiotics in the elimination of formed biofilm.

Results:

The MIC value of Ag-NPs against MRSA was 100 μg/mL. Methicillin-Resistant Staphylococcus aureus cells were treated with 50, 100 and 200 µg/mL of Ag-NPs and inhibited bacterial growth so that after four hours, almost all treated MRSA cells were dead. All combinations showed effectiveness against MRSA. It was observed that MRSA did not show inhibition zones with ampicillin alone.

Conclusions:

Silver Nanoparticles have high therapeutic activity against MRSA, thus can be suggested as an alternative or adjuvant with antibiotics for MRSA treatment. Further studies are required to understand the synergistic effect of Ag-NPs combinations and to assess the safety and efficacy of new antibiotic-Ag-NPs combinations.

Developments for improved diagnosis of bacterial bloodstream infections

Bloodstream infections (BSIs) are associated with high mortality and increased healthcare costs. Optimal management of BSI depends on several factors including recognition of the disease, laboratory tests and treatment. Rapid and accurate identification of the etiologic agent is crucial to be able to initiate pathogen specific antibiotic therapy and decrease mortality rates. Furthermore, appropriate treatment might slow down the emergence of antibiotic resistant strains. Culture-based methods are still considered to be the "gold standard" for the detection and identification of pathogens causing BSI. Positive blood cultures are used for Gram-staining. Subsequently, positive blood culture material is subcultured on solid media, and (semi-automated) biochemical testing is performed for species identification. Finally, a complete antibiotic susceptibility profile can be provided based on cultured colonies, which allows the start of pathogen-tailored antibiotic therapy. This conventional workflow is extremely time-consuming and can take up to several days. Furthermore, fastidious and slow-growing microorganisms, as well as antibiotic pre-treated samples can lead to false-negative results. The main aim of this review is to present different strategies to improve the conventional laboratory diagnostic steps for BSI. These approaches include protein-based (MALDI-TOF mass spectrometry) and nucleic acid-based (polymerase chain reaction [PCR]) identification from subculture, blood cultures, and whole blood to decrease time to results. Pathogen enrichment and DNA isolation methods, to enable optimal pathogen DNA recovery from whole blood, are described. In addition, the use of biomarkers as patient pre-selection tools for molecular assays are discussed.

Quantitative analysis of biofilm formed on vascular prostheses by Staphylococcus epidermidis with different ica and aap genetic status

OBJECTIVES

This study aims to examine biofilm formed on vascular prostheses by Staphylococcus epidermidis with different ica and aap genetic status, and to evaluate the effect of antibiotic-modified prostheses on bacterial colonization.

METHODS

Biofilm formation was determined using fluorescence microscopy imaging. Quantitative analysis was conducted using the biofilm coverage ratio (BCR) calculations.

RESULTS

Our investigations prove that the BCR method with fluorescent dye enabled an accurate assessment of biofilm coverage and comparison of the obtained results. The ica+ aap+ strains formed a biofilm on all of the examined vascular prostheses. Uni-Graft(®) modified with covalently immobilized amikacin was effective in preventing bacterial adherence.

CONCLUSIONS

Molecular biology techniques combined with phenotype studies give a broad insight into biofilm formation mechanisms. On the other hand, fluorescence microscopy imaging along with BCR calculations are reliable and simple tools to quantitatively estimate biofilm formation, as well as the effectiveness of antimicrobial prosthesis modification.

The skin microbiome: current perspectives and future challenges

Complex communities of bacteria, fungi, and viruses thrive on our skin. The composition of these communities depends on skin characteristics, such as sebaceous gland concentration, moisture content, and temperature, as well as on host genetics and exogenous environmental factors. Recent metagenomic studies have uncovered a surprising diversity within these ecosystems and have fostered a new view of commensal organisms as playing a much larger role in immune modulation and epithelial health than previously expected. Understanding microbe-host interactions and discovering the factors that drive microbial colonization will help us understand the pathogenesis of skin diseases and develop new promicrobial and antimicrobial therapeutics.

Detection of methicillin-resistance gene in Staphylococcus epidermidis strains isolated from patients in Al-Zahra Hospital using polymerase chain reaction and minimum inhibitory concentration methods

Background:

In recent years, antibiotic resistance of Staphylococcus epidermidis to methicillin has significantly increased, making it essential to study resistance to methicillin, which is a determining factor in the appropriate treatment pattern. The purpose of this study was to identify methicillin-resistant genes in S. epidermidis strains using polymerase chain reaction (PCR) and to determine their mean minimum inhibitory concentration (MIC) to methicillin using E-test method.

Materials and Methods:

MIC was determined on 146 samples of S. epidermidis using E-test method. Moreover, all samples were tested for the presence of mecA gene using PCR.

Results:

PCR test showed 75.34% of the samples to contain mecA gene. Methicillin resistance test was performed using E-test on all the samples, which showed resistance in different dilutions.

Conclusion:

The frequency of mecA gene in S. epidermidis isolates was 75.34%. Among the various applied tests used for determining methicillin resistance, sensitivity and specificity of PCR were the highest and reached 100%. Sensitivity and specificity were found to be 95.3% and 94.7%, respectively, for phenotypic test (E-test) and 86.5% and 80.9%, respectively, for disk diffusion method. Based on the above results, it seems that resistance of S. epidermidis to methicillin is on the rise, and therefore more research is warranted.

CRISPR interference: RNA-directed adaptive immunity in bacteria and archaea

Sequence-directed genetic interference pathways control gene expression and preserve genome integrity in all kingdoms of life. The importance of such pathways is highlighted by the extensive study of RNA interference (RNAi) and related processes in eukaryotes. In many bacteria and most archaea, clustered, regularly interspaced short palindromic repeats (CRISPRs) are involved in a more recently discovered interference pathway that protects cells from bacteriophages and conjugative plasmids. CRISPR sequences provide an adaptive, heritable record of past infections and express CRISPR RNAs - small RNAs that target invasive nucleic acids. Here, we review the mechanisms of CRISPR interference and its roles in microbial physiology and evolution. We also discuss potential applications of this novel interference pathway.

Sequencing and comparative analysis of IncP-1α antibiotic resistance plasmids reveal a highly conserved backbone and differences within accessory regions

Although IncP-1 plasmids are important for horizontal gene transfer among bacteria, in particular antibiotic resistance spread, so far only three plasmids from the subgroup IncP-1α have been completely sequenced. In this study we doubled this number. The three IncP-1α plasmids pB5, pB11 and pSP21 were isolated from bacteria of two different sewage treatment plants and sequenced by a combination of next-generation and capillary sequencing technologies. A comparative analysis including the previously analysed IncP-1α plasmids RK2, pTB11 and pBS228 revealed a highly conserved plasmid backbone (at least 99.9% DNA sequence identity) comprising 54 core genes. The accessory elements of the plasmid pB5 constitute a class 1 integron interrupting the parC gene and an IS6100 copy inserted into the integron. In addition, the tetracycline resistance genes tetAR and the ISTB11-like element are located between the klc operon and the trfA-ssb operon. Plasmid pB11 is loaded with a Tn5053-like mercury resistance transposon between the parCBA and parDE operons and contains tetAR that are identical to those identified in plasmid pB5 and the insertion sequence ISSP21. Plasmid pSP21 harbours an ISPa7 element in a Tn402 transposon including a class 1 integron between the partitioning genes parCBA and parDE. The IS-element ISSP21 (99.89% DNA sequence identity to ISSP21 from pB11), inserted downstream of the tetR gene and a copy of ISTB11 (identical to ISTB11 on pTB11) inserted between the genes pncA and pinR. On all three plasmids the accessory genes are almost always located between the backbone modules confirming the importance of the backbone functions for plasmid maintenance. The striking backbone conservation among the six completely sequenced IncP-1α plasmids is in contrast to the much higher diversity within the IncP-1β subgroup.

Tn502 and Tn512 are res site hunters that provide evidence of resolvase-independent transposition to random sites

In this study, we report on the transposition behavior of the mercury(II) resistance transposons Tn502 and Tn512, which are members of the Tn5053 family. These transposons exhibit targeted and oriented insertion in the par region of plasmid RP1, since par-encoded components, namely, the ParA resolvase and its cognate res region, are essential for such transposition. Tn502 and, under some circumstances, Tn512 can transpose when par is absent, providing evidence for an alternative, par-independent pathway of transposition. We show that the alternative pathway proceeds by a two-step replicative process involving random target selection and orientation of insertion, leading to the formation of cointegrates as the predominant product of the first stage of transposition. Cointegrates remain unresolved because the transposon-encoded (TniR) recombination system is relatively inefficient, as is the host-encoded (RecA) system. In the presence of the res-ParA recombination system, TniR-mediated (and RecA-mediated) cointegrate resolution is highly efficient, enabling resolution both of cointegrates involving functional transposons (Tn502 and Tn512) and of defective elements (In0 and In2). These findings implicate the target-encoded accessory functions in the second stage of transposition as well as in the first. We also show that the par-independent pathway enables the formation of deletions in the target molecule.

Qualitative risk assessment of the acquisition of Meticillin-resistant staphylococcus aureus in pet dogs

This article presents a qualitative risk assessment of the acquisition of meticillin-resistant Staphylococcus aureus (MRSA) in pet dogs, representing an important first step in the exploration of risk of bidirectional MRSA transfer between dogs and humans. A conceptual model of the seven potential pathways for MRSA acquisition in a dog in any given 24-hour period was developed and the data available to populate that model were considered qualitatively. Humans were found to represent the most important source of MRSA for dogs in both community and veterinary hospital settings. The environment was found to be secondary to humans in terms of importance and other dogs less still. This study highlights some important methodological limitations of a technique that is heavily relied upon for qualitative risk assessments and applies a novel process, the use of relative risk ranking, to enable the generation of a defensible output using a matrix combination approach. Given the limitations of the prescribed methods as applied to the problem under consideration, further validation, or repudiation, of the findings contained herein is called for using a subsequent quantitative assessment.

Attributable hospital cost and length of stay associated with health care-associated infections caused by antibiotic-resistant gram-negative bacteria

Determination of the attributable hospital cost and length of stay (LOS) are of critical importance for patients, providers, and payers who must make rational and informed decisions about patient care and the allocation of resources. The objective of the present study was to determine the additional total hospital cost and LOS attributable to health care-associated infections (HAIs) caused by antibiotic-resistant, gram-negative (GN) pathogens. A single-center, retrospective, observational comparative cohort study was performed. The study involved 662 patients admitted from 2000 to 2008 who developed HAIs caused by one of following pathogens: Acinetobacter spp., Enterobacter spp., Escherichia coli, Klebsiella spp., or Pseudomonas spp. The attributable total hospital cost and LOS for HAIs caused by antibiotic-resistant GN pathogens were determined by comparison with the hospital costs and LOS for a control group with HAIs due to antibiotic-susceptible GN pathogens. Statistical analyses were conducted by using univariate and multivariate analyses. Twenty-nine percent of the HAIs were caused by resistant GN pathogens, and almost 16% involved a multidrug-resistant GN pathogen. The additional total hospital cost and LOS attributable to antibiotic-resistant HAIs caused by GN pathogens were 29.3% (P < 0.0001; 95% confidence interval, 16.23 to 42.35) and 23.8% (P = 0.0003; 95% confidence interval, 11.01 to 36.56) higher than those attributable to HAIs caused by antibiotic-susceptible GN pathogens, respectively. Significant covariates in the multivariate analysis were age >or=12 years, pneumonia, intensive care unit stay, and neutropenia. HAIs caused by antibiotic-resistant GN pathogens were associated with significantly higher total hospital costs and increased LOSs compared to those caused by their susceptible counterparts. This information should be used to assess the potential cost-efficacy of interventions aimed at the prevention of such infections.

Detection of 140 clinically relevant antibiotic-resistance genes in the plasmid metagenome of wastewater treatment plant bacteria showing reduced susceptibility to selected antibiotics

To detect plasmid-borne antibiotic-resistance genes in wastewater treatment plant (WWTP) bacteria, 192 resistance-gene-specific PCR primer pairs were designed and synthesized. Subsequent PCR analyses on total plasmid DNA preparations obtained from bacteria of activated sludge or the WWTP's final effluents led to the identification of, respectively, 140 and 123 different resistance-gene-specific amplicons. The genes detected included aminoglycoside, beta-lactam, chloramphenicol, fluoroquinolone, macrolide, rifampicin, tetracycline, trimethoprim and sulfonamide resistance genes as well as multidrug efflux and small multidrug resistance genes. Some of these genes were only recently described from clinical isolates, demonstrating genetic exchange between clinical and WWTP bacteria. Sequencing of selected resistance-gene-specific amplicons confirmed their identity or revealed that the amplicon nucleotide sequence is very similar to a gene closely related to the reference gene used for primer design. These results demonstrate that WWTP bacteria are a reservoir for various resistance genes. Moreover, detection of about 64 % of the 192 reference resistance genes in bacteria obtained from the WWTP's final effluents indicates that these resistance determinants might be further disseminated in habitats downstream of the sewage plant.

CRISPR interference limits horizontal gene transfer in staphylococci by targeting DNA

Horizontal gene transfer (HGT) in bacteria and archaea occurs through phage transduction, transformation, or conjugation, and the latter is particularly important for the spread of antibiotic resistance. Clustered, regularly interspaced, short palindromic repeat (CRISPR) loci confer sequence-directed immunity against phages. A clinical isolate of Staphylococcus epidermidis harbors a CRISPR spacer that matches the nickase gene present in nearly all staphylococcal conjugative plasmids. Here we show that CRISPR interference prevents conjugation and plasmid transformation in S. epidermidis. Insertion of a self-splicing intron into nickase blocks interference despite the reconstitution of the target sequence in the spliced mRNA, which indicates that the interference machinery targets DNA directly. We conclude that CRISPR loci counteract multiple routes of HGT and can limit the spread of antibiotic resistance in pathogenic bacteria.

Bench-to-bedside review: Bacterial virulence and subversion of host defences

Bacterial pathogens possess an array of specific mechanisms that confer virulence and the capacity to avoid host defence mechanisms. Mechanisms of virulence are often mediated by the subversion of normal aspects of host biology. In this way the pathogen modifies host function so as to promote the pathogen's survival or proliferation. Such subversion is often mediated by the specific interaction of bacterial effector molecules with host encoded proteins and other molecules. The importance of these mechanisms for bacterial pathogens that cause infections leading to severe community-acquired infections is well established. In contrast, the importance of specialised mechanisms of virulence in the genesis of nosocomial bacterial infections, which occur in the context of local or systemic defects in host immune defences, is less well established. Specific mechanisms of bacterial resistance to host immunity might represent targets for therapeutic intervention. The clinical utility of such an approach for either prevention or treatment of bacterial infection, however, has not been determined.

Understanding the physiology and adaptation of staphylococci: A post-genomic approach

Staphylococcus aureus as well as coagulase-negative staphylococci are medically highly important pathogens characterized by an increasing resistance rate toward many antibiotics. Although normally being skin and mucosa commensals, some staphylococcal species and strains have the capacity to cause a wide range of infectious diseases. Many of these infections affect immunocompromised patients in hospitals. However, community-acquired staphylococcal infections due to resistant strains are also currently on the rise. In the light of this development, there is an urgent need for novel anti-staphylococcal therapeutic and prevention strategies for which a better understanding of the physiology of these bacteria is an essential prerequisite. Within the past years, staphylococci have been in the focus of genomic research, resulting in the determination and publication of a range of full-genome sequences of different staphylococcal species and strains which provided the basis for the design and application of DNA microarrays and other genomic tools. Here we summarize the results of the project group 'Staphylococci' within the research network 'Pathogenomics' giving new insights into the genome structure, molecular epidemiology, physiology, and genetic adaptation of both S. aureus and coagulase-negative staphylococci.

Diversity of penicillin-binding proteins. Resistance factor FmtA of Staphylococcus aureus

Antibiotic-resistant Staphylococcus aureus is a major concern to public health. Methicillin-resistant S. aureus strains are completely resistant to all beta-lactams antibiotics. One of the main factors involved in methicillin resistance in S. aureus is the penicillin-binding protein, PBP2a. This protein is insensitive to inactivation by beta-lactam antibiotics such as methicillin. Although other proteins are implicated in high and homogeneous levels of methicillin resistance, the functions of these other proteins remain elusive. Herein, we report for the first time on the putative function of one of these proteins, FmtA. This protein specifically interacts with beta-lactam antibiotics forming covalently bound complexes. The serine residue present in the sequence motif Ser-X-X-Lys (which is conserved among penicillin-binding proteins and beta-lactamases) is the active-site nucleophile during the formation of acyl-enzyme species. FmtA has a low binding affinity for beta-lactams, and it experiences a slow acylation rate, suggesting that this protein is intrinsically resistant to beta-lactam inactivation. We found that FmtA undergoes conformational changes in presence of beta-lactams that may be essential to the beta-lactam resistance mechanism. FmtA binds to peptidoglycan in vitro. Our findings suggest that FmtA is a penicillin-binding protein, and as such, it may compensate for suppressed peptidoglycan biosynthesis under beta-lactam induced cell wall stress conditions.

A pharmacodynamic analysis of resistance trends in pathogens from patients with infection in intensive care units in the United States between 1993 and 2004

Background

Increasing nosocomial pathogen resistance to available antimicrobial agents is of growing concern. While higher MICs can diminish antimicrobial effectiveness, dose adjustments often mitigate this effect. This study's objective was to ascertain whether MICs among major pathogens in the ICU to several commonly used agents have increased enough to significantly impact their ability to achieve bactericidal effect.

Methods

Cefepime, ceftriaxone, imipenem and piperacillin-tazobactam MICs were determined with 74,394 Gram-negative bacilli obtained from ICU patients with various infections in the US between 1993 and 2004. Results were grouped into four 3-year periods. The predicted cumulative fraction of response (CFR) was estimated based on patient-derived pharmacokinetic values and Monte Carlo simulation. Trends in CFR over the four study periods were assessed using the Cochran-Armitage test. The primary analysis included all organisms combined; Pseudomonas aeruginosa and Acinetobacter species were also evaluated individually.

Results

In the primary analysis, imipenem 500 mg q6h showed CFRs from 87% to 90% across all four study periods, with a trend toward slightly improved bactericidal target attainment (p < 0.01). CFRs for cefepime 2 g q12h and piperacillin-tazobactam 4.5 g q6h both declined by 2% (p < 0.01 and p < 0.05, respectively), reflecting upward shifts in the underlying MIC distributions. Ceftriaxone had <52% CFR for all regimens in all periods, with no significant trend. Against P. aeruginosa, significant declines in CFR were seen for (range, p-value): imipenem 1 g q8h (82%–79%, p < 0.01), cefepime 1 g q12h (70%–67%, p < 0.01), cefepime 2 g q12h (84%–82%, p < 0.05), piperacillin-tazobactam 3.375 g q6h (76%–73%, p < 0.01), piperacillin-tazobactam 4.5 g q8h (71%–68%, p < 0.01), and piperacillin-tazobactam 4.5 g q6h (80%–77%, p < .01). Against Acinetobacter spp., all regimens of imipenem, cefepime and piperacillin-tazobactam showed significant declines in CFR over time (p < 0.01).

Conclusion

Our observations suggest that as a result of increasing antimicrobial resistance among ICU pathogens in the US, drug effectiveness, assessed as a function of individual agents' ability to attain pharmacodynamic targets, has declined, especially with P. aeruginosa and Acinetobacter spp. Cefepime 2 g q8h and imipenem were the most potent agents against these species, respectively. More aggressive dosing of all of the agents characterized could preserve their clinical utility, but this must be balanced with safety and tolerability issues by the physician.

Genomics of IncP-1 antibiotic resistance plasmids isolated from wastewater treatment plants provides evidence for a widely accessible drug resistance gene pool

The dramatic spread of antibiotic resistance is a crisis in the treatment of infectious diseases that affect humans. Several studies suggest that wastewater treatment plants (WWTP) are reservoirs for diverse mobile antibiotic resistance elements. This review summarizes findings derived from genomic analysis of IncP-1 resistance plasmids isolated from WWTP bacteria. Plasmids that belong to the IncP-1 group are self-transmissible, and transfer to and replicate in a wide range of hosts. Their backbone functions are described with respect to their impact on vegetative replication, stable maintenance and inheritance, mobility and plasmid control. Accessory genetic modules, mainly representing mobile genetic elements, are integrated in-between functional plasmid backbone modules. These elements carry determinants conferring resistance to nearly all clinically relevant antimicrobial drug classes, to heavy metals, and quaternary ammonium compounds used as disinfectants. All plasmids analysed here contain integrons that potentially facilitate integration, exchange and dissemination of resistance gene cassettes. Comparative genomics of accessory modules located on plasmids from WWTP and corresponding modules previously identified in other bacterial genomes revealed that animal, human and plant pathogens and other bacteria isolated from different habitats share a common pool of resistance determinants.

Polymyxin antibiotics for gram-negative infections

PURPOSE

The role of polymyxin antibiotics in the treatment of multidrug-resistant gram-negative infections is reviewed.

SUMMARY

Antimicrobial resistance is an increasing problem across hospitals worldwide, especially in intensive care settings, where nosocomial infections are 5-10 times more likely to occur than on the general wards. The polymyxins, a group of basic polypeptide antibiotics, were first isolated from Bacillus species in the late 1940s and appear to have a surface detergent effect, making them active against most gram-negative organisms. Early clinical reports suggested a high rate of toxicity associated with the polymyxins, specifically nephrotoxicity (20%) and neurotoxicity (7%); thus the polymyxins had largely fallen out of favor. However, recent studies have suggested that the toxicities associated with the polymyxins may be less severe and less frequent than earlier reports. The emergence of multidrug-resistant gram-negative organisms has led to a reemergence in the use of this antibiotic class. Various clinical trials that evaluated the polymyxins for the treatment of multidrug-resistant gram-negative organisms found that these antibiotics have acceptable effectiveness and may be used if necessary.

CONCLUSION

The polymyxins have become a last resort for the treatment of infections caused by multidrug-resistant gram-negative organisms. Recent studies have suggested that the frequency of polymyxin-associated nephrotoxicity and neurotoxicity may not be as high as was once thought. The polymyxins seem to be effective in treating various infections caused by multidrug-resistant gram-negative organisms but should not be used as first-line therapy until more is known about this class of antibiotics.