muramidase and Cross-Infection

Enterococcus faecium has become a nosocomial pathogen of major importance, causing infections that are difficult to treat owing to its multi-drug resistance. In particular, resistance to the β-lactam antibiotic ampicillin has become ubiquitous among clinical isolates. Mutations in the low-affinity penicillin binding protein PBP5 have previously been shown to be important for ampicillin resistance in E. faecium, but the existence of additional resistance determinants has been suggested. Here, we constructed a high-density transposon mutant library in E. faecium and developed a transposon mutant tracking approach termed Microarray-based Transposon Mapping (M-TraM), leading to the identification of a compendium of E. faecium genes that contribute to ampicillin resistance. These genes are part of the core genome of E. faecium, indicating a high potential for E. faecium to evolve towards β-lactam resistance. To validate the M-TraM results, we adapted a Cre-lox recombination system to construct targeted, markerless mutants in E. faecium. We confirmed the role of four genes in ampicillin resistance by the generation of targeted mutants and further characterized these mutants regarding their resistance to lysozyme. The results revealed that ddcP, a gene predicted to encode a low-molecular-weight penicillin binding protein with D-alanyl-D-alanine carboxypeptidase activity, was essential for high-level ampicillin resistance. Furthermore, deletion of ddcP sensitized E. faecium to lysozyme and abolished membrane-associated D,D-carboxypeptidase activity. This study has led to the development of a broadly applicable platform for functional genomic-based studies in E. faecium, and it provides a new perspective on the genetic basis of ampicillin resistance in this organism.

Topics: Ampicillin; Ampicillin Resistance; Cell Proliferation; Cross Infection; DNA Transposable Elements; Enterococcus faecium; Gene Expression Regulation, Bacterial; Genome, Bacterial; Humans; Muramidase; Mutation; Oligonucleotide Array Sequence Analysis; Penicillin-Binding Proteins; Serine-Type D-Ala-D-Ala Carboxypeptidase

Enterococci are commensal organisms in the alimentary tract. However, they can cause a variety of life-threatening infections, especially in nosocomial settings. We hypothesized that induction of cell death might enable these facultative pathogenic bacteria to evade the innate immune response and to cause infections of their host. We demonstrate that E. faecium when exposed to lysozyme induces cell death in macrophages in vitro and in vivo. Flow cytometric analyses of J774A.1 macrophages infected with E. faecium revealed loss of cell membrane integrity indicated by uptake of propidium iodide and decrease of the inner mitochondrial transmembrane potential DeltaPsi(m). Inhibition of caspases, treatment of macrophages with cytochalasin D, or rifampicin did not prevent cells from dying, suggesting cell death mechanisms that are independent of caspase activation, bacterial uptake, and intracellular bacterial replication. Characteristics of necrotic cell death were demonstrated by both lack of procaspase 3 activation and cell shrinkage, electron microscopy, and release of lactate dehydrogenase. Pretreatment of E. faecium with lysozyme and subsequently with broad spectrum protease considerably reduced cell death, suggesting that a bacterial surface protein is causative for cell death induction. Moreover, in a mouse peritonitis model we demonstrated that E. faecium induces cell death of peritoneal macrophages in vivo. Altogether, our results show that enterococci, under specific conditions such as exposure to lysozyme, induce necrotic cell death in macrophages, which might contribute to disseminated infections by these facultative pathogenic bacteria.

Topics: Animals; Apoptosis; Bacterial Proteins; Caspase 3; Caspases; Cell Death; Cross Infection; Enterococcus faecium; Female; Macrophages; Macrophages, Peritoneal; Membrane Potentials; Mice; Mice, Inbred C57BL; Mitochondria; Muramidase; Necrosis

The study aimed to describe the patterns and density of early tracheal colonization among intubated patients and to correlate colonization status with levels of antimicrobial peptides and inflammatory cytokines.. The was a prospective cohort study.. The study was conducted in medical and cardiovascular intensive care units of a tertiary referral hospital.. Seventy-four adult patients admitted between March 2003 and May 2006 were recruited for the study.. Tracheal aspirates were collected daily for the first 4 days of intubation using standardized, sterile technique and sent for quantitative culture and cytokines, lactoferrin and lysozyme measurements.. The mean acute physiology and chronic health evaluation (APACHE II) score in this cohort was 24 +/- 7. Proportion of subjects colonized by any microorganism increased over the first 4 days of intubation (47%, 60%, 70%, 70%, P = .08), but density of colonization for bacteria or yeast did not change significantly. No known risk factors predicted tracheal colonization on day 1 of intubation. Several patterns of colonization were observed (persistent, transient, new colonization, and clearance of initial colonization).The most common organisms cultured were Candida albicans and coagulase-negative Staphylococcus. Levels of cytokines, lactoferrin, or lysozyme did not change over time and were not correlated with tracheal colonization status. Four subjects (6%) had ventilator-associated pneumonia.. The density of tracheal colonization did not change significantly over the first 4 days of intubation in medical intensive care unit patients. There was no correlation between tracheal colonization and the levels of antimicrobial peptides or cytokines. Several different patterns of colonization may have to be considered while planning interventions to reduce airway colonization.

Topics: Adult; APACHE; Candidiasis; Case-Control Studies; Colony Count, Microbial; Cross Infection; Cytokines; Female; Humans; Inflammation; Intensive Care Units; Intubation, Intratracheal; Lactoferrin; Logistic Models; Male; Middle Aged; Multivariate Analysis; Muramidase; Pneumonia, Ventilator-Associated; Prospective Studies; Respiration, Artificial; Respiratory Mucosa; Risk Factors; Staphylococcal Infections; Statistics, Nonparametric; Suction; Time Factors; Trachea

The authors have compared the antimicrobial resistance patterns and plasmid profiles of Gram-negative isolates in an intensive care unit over a 7-month period in order to identify epidemiologically related isolates. Bacterial plasmids were found to be valuable markers for the comparison of strains of nosocomial Gram-negative bacilli. Thirty-nine mechanically ventilated patients in an ICU were included. From bronchoaspiratus, the authors isolated 58 strains of Gram-negative bacilli (24 Ps. aeruginosa and 34 Enterobacteria). Common plasmids were found in most Enterobacteria. The interspecies plasmid exchange suggests that interstate spread of these strains may have occurred. Twenty-six Enterobacteria carried plasmids, 11 of which proved transmissible. The R-factors were transferred to other genera that were isolated in the hospital, thereby adding to the pool of multiresistant nosocomial isolates. Larger plasmids transferred ampicillin and carbenicillin resistance, while gentamycin and cephalotin resistance was carried by smaller plasmids. Only 4 Ps. aeruginosa carried plasmids, one of which was transmissible. Pseudomonas plasmid DNA is extracted with difficulty by the simple lysis method, due to the roughness of the colonies. All Pseudomonas isolates belonged to the same biotype which can be regarded as an epidemiological marker. Therefore, plasmid profiling is a useful tool for epidemiological surveillance of Enterobacteria and is a good method for determining the relatedness of isolates in a nosocomial environment.

Topics: Biomarkers; Cross Infection; DNA Restriction Enzymes; Electrophoresis, Polyacrylamide Gel; Gram-Negative Bacteria; Gram-Negative Bacterial Infections; Humans; Intensive Care Units; Microbial Sensitivity Tests; Middle Aged; Muramidase; Plasmids; Pyocins; R Factors; Serotyping

A study was made of 111 strains of plasma-negative spathylococci isolated from the blood, pleural fluid, urine, and exudate of the abdominal cavity of 30 patients. The studies were carried out by 18 criteria. A variety of biological properties and signs characteristic of pathogenic staphylococci (hemolytic activity, anaerobic splitting of mannite, the presence of phosphatase, lysozyme, protease, alpha-toxin, fibrinolysin) were noted. A high resistance to tetracycline and penicillin was found in the strains isolated from the blood and the pleural cavity.

Topics: Animals; Ascitic Fluid; Bacteriophage Typing; Bacteriuria; Cross Infection; Erythrocytes; Fibrinolysin; Hemolysis; Humans; Mannitol; Muramidase; Penicillin Resistance; Penicillins; Phospholipases; Phosphoric Monoester Hydrolases; Pleural Effusion; Pyelonephritis; Rabbits; Sepsis; Staphylococcal Infections; Staphylococcus; Surgical Procedures, Operative; Tetracycline; Toxins, Biological

Topics: Cross Infection; Eye Diseases; Humans; Muramidase; Ophthalmic Solutions; Pseudomonas Infections; Staphylococcal Infections; Sterilization