Mechanism of action of the novel aminomethylcycline antibiotic omadacycline.

Omadacycline is a novel first-in-class aminomethylcycline with potent activity against important skin and pneumonia pathogens, including community-acquired methicillin-resistant Staphylococcus aureus (MRSA), ß-hemolytic streptococci, penicillin-resistant Streptococcus pneumoniae, Haemophilus influenzae, and Legionella. In this work, the mechanism of action for omadacycline was further elucidated using a variety of models. Functional assays demonstrated that omadacycline is active against strains expressing the two main forms of tetracycline resistance (efflux and ribosomal protection). Macromolecular synthesis experiments confirmed that the primary effect of omadacycline is on bacterial protein synthesis, inhibiting protein synthesis with a potency greater than that of tetracycline. Biophysical studies with isolated ribosomes confirmed that the binding site for omadacycline is similar to that for tetracycline. In addition, unlike tetracycline, omadacycline is active in vitro in the presence of the ribosomal protection protein Tet(O).

In vitro and in vivo antibacterial activities of omadacycline, a novel aminomethylcycline.

Omadacycline is the first intravenous and oral 9-aminomethylcycline in clinical development for use against multiple infectious diseases including acute bacterial skin and skin structure infections (ABSSSI), community-acquired bacterial pneumonia (CABP), and urinary tract infections (UTI). The comparative in vitro activity of omadacycline was determined against a broad panel of Gram-positive clinical isolates, including methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant Enterococcus (VRE), Lancefield groups A and B beta-hemolytic streptococci, penicillin-resistant Streptococcus pneumoniae (PRSP), and Haemophilus influenzae (H. influenzae). The omadacycline MIC90s for MRSA, VRE, and beta-hemolytic streptococci were 1.0 µg/ml, 0.25 µg/ml, and 0.5 µg/ml, respectively, and the omadacycline MIC90s for PRSP and H. influenzae were 0.25 µg/ml and 2.0 µg/ml, respectively. Omadacycline was active against organisms demonstrating the two major mechanisms of resistance, ribosomal protection and active tetracycline efflux. In vivo efficacy of omadacycline was demonstrated using an intraperitoneal infection model in mice. A single intravenous dose of omadacycline exhibited efficacy against Streptococcus pneumoniae, Escherichia coli, and Staphylococcus aureus, including tet(M) and tet(K) efflux-containing strains and MRSA strains. The 50% effective doses (ED50s) for Streptococcus pneumoniae obtained ranged from 0.45 mg/kg to 3.39 mg/kg, the ED50s for Staphylococcus aureus obtained ranged from 0.30 mg/kg to 1.74 mg/kg, and the ED50 for Escherichia coli was 2.02 mg/kg. These results demonstrate potent in vivo efficacy including activity against strains containing common resistance determinants. Omadacycline demonstrated in vitro activity against a broad range of Gram-positive and select Gram-negative pathogens, including resistance determinant-containing strains, and this activity translated to potent efficacy in vivo.

Red wine prevents the postprandial increase in plasma cholesterol oxidation products: a pilot study.

Moderate wine consumption has been shown to lower cardiovascular risk. One of the mechanisms could involve the control of postprandial hyperlipaemia, a well-defined risk factor for atherosclerosis, reasonably by reducing the absorption of lipid oxidised species from the meal. The objective of the present study was to investigate whether wine consumption with the meal is able to reduce the postprandial increase in plasma lipid hydroperoxides and cholesterol oxidation products, in human subjects. In two different study sessions, twelve healthy volunteers consumed the same test meal rich in oxidised and oxidisable lipids (a double cheeseburger), with 300 ml of water (control) or with 300 ml of red wine (wine). The postprandial plasma concentration of cholesterol oxidation products was measured by GC-MS. The control meal induced a significant increase in the plasma concentration of lipid hydroperoxides and of two cholesterol oxidation products, 7-ß-hydroxycholesterol and 7-ketocholesterol. The postprandial increase in lipid hydroperoxides and cholesterol oxidation products was fully prevented by wine when consumed with the meal. In conclusion, the present study provides evidence that consumption of wine with the meal could prevent the postprandial increase in plasma cholesterol oxidation products.

Chlamydia pneumoniae induces T cell apoptosis through glutathione redox imbalance and secretion of TNF-alpha.

Chlamydia pneumoniae persistent infection has been implicated in the pathogenesis of several chronic inflammatory diseases including atherosclerosis, and we hypothesized that modulation of the apoptosis of macrophages and/or T cells by C. pneumoniae infection may contribute to the development of such diseases. We therefore evaluated apoptosis, cytokine response, and redox status in human primary T cells and macrophages infected with C. pneumoniae. In addition, co-cultures of T cells and macrophages infected with C. pneumoniae were also carried out. Apoptosis, and levels of glutathione (GSH), glutathione disulfide (GSSG), and tumour necrosis factor (TNF)-alpha were measured by flow cytometry, high performance liquid chromatography and enzyme-linked immunosorbent assay. C. pneumoniae induced apoptosis in T cells as well as in co-cultures of T cells and infected macrophages by marked decrease in GSH/GSSG ratio and increased production of TNF-alpha, respectively. The results demonstrate that interaction of C. pneumoniae with T cells and/or macrophages characterized by interference with redox status, and secretion of tumour necrosis factor-alpha culminates in the induction of T cell apoptosis and survival of infected macrophages. In conclusion, the inappropriate T cell response against C. pneumoniae and survival of infected macrophages could explain the persistence of this intracellular obligate pathogen in the host-organism; it may contribute to the development of chronic inflammatory diseases, although further studies are needed to clarify such a complex mechanism.

Vanin-1-/- mice exhibit a glutathione-mediated tissue resistance to oxidative stress.

Vanin-1 is an epithelial ectoenzyme with pantetheinase activity and generating the amino-thiol cysteamine through the metabolism of pantothenic acid (vitamin B(5)). Here we show that Vanin-1(-/-) mice, which lack cysteamine in tissues, exhibit resistance to oxidative injury induced by whole-body gamma-irradiation or paraquat. This protection is correlated with reduced apoptosis and inflammation and is reversed by treating mutant animals with cystamine. The better tolerance of the Vanin-1(-/-) mice is associated with an enhanced gamma-glutamylcysteine synthetase activity in liver, probably due to the absence of cysteamine and leading to elevated stores of glutathione (GSH), the most potent cellular antioxidant. Consequently, Vanin-1(-/-) mice maintain a more reducing environment in tissue after exposure to irradiation. In normal mice, we found a stress-induced biphasic expression of Vanin-1 regulated via antioxidant response elements in its promoter region. This process should finely tune the redox environment and thus change an early inflammatory process into a late tissue repair process. We propose Vanin-1 as a key molecule to regulate the GSH-dependent response to oxidative injury in tissue at the epithelial level. Therefore, Vanin/pantetheinase inhibitors could be useful for treatment of damage due to irradiation and pro-oxidant inducers.

Determination of aminoethylcysteine ketimine decarboxylated dimer in human plasma and cultured cells by high-performance liquid chromatography with electrochemical detection.

Aminoethylcysteine ketimine decarboxylated dimer (AECK-DD) is a natural compound with antioxidant properties of a new family of sulfur-containing amino acids. It has been detected in human urine and plasma, in mammalian cerebellum and, more recently, in dietary vegetables. In the present study, a simple, highly sensitive method using a high-performance liquid chromatography system with electrochemical detection (ECD) has been developed. The method showed excellent precision and accuracy. It has been found to be about 100-fold more sensitive than gas chromatographic method and 2000-fold more sensitive in respect to the liquid chromatography method with UV detection. The method showed the required features of specificity and sensitivity to detect aminoethylcysteine ketimine decarboxylated dimer in human plasma and in cultured cells after in vitro supplementation.

Enhancement of neonatal innate defense: effects of adding an N-terminal recombinant fragment of bactericidal/permeability-increasing protein on growth and tumor necrosis factor-inducing activity of gram-negative bacteria tested in neonatal cord blood ex vivo.

Innate defense against microbial infection requires the action of neutrophils, which have cytoplasmic granules replete with antibiotic proteins and peptides. Bactericidal/permeability-increasing protein (BPI) is found in the primary granules of adult neutrophils, has a high affinity for lipopolysaccharides (or "endotoxins"), and exerts selective cytotoxic, antiendotoxic, and opsonic activity against gram-negative bacteria. We have previously reported that neutrophils derived from newborn cord blood are deficient in BPI (O. Levy et al., Pediatrics 104:1327-1333, 1999). The relative deficiency in BPI of newborns raised the possibility that supplementing the levels of BPI in plasma might enhance newborn antibacterial defense. Here we determined the effects of addition of recombinant 21-kDa N-terminal BPI fragment (rBPI(21)) on the growth and tumor necrosis factor (TNF)-inducing activity of representative gram-negative clinical isolates. Bacteria were tested in citrated newborn cord blood or adult peripheral blood. Bacterial viability was assessed by plating assay, and TNF-alpha release was measured by enzyme-linked immunosorbent assay. Whereas adult blood limited the growth of all isolates except Klebsiella pneumoniae, cord blood also allowed logarithmic growth of Escherichia coli K1/r and Citrobacter koseri. Bacteria varied in their susceptibility to rBPI(21)'s bactericidal action: E. coli K1/r was relatively susceptible (50% inhibitory concentration [IC(50)], approximately 10 nM), C. koseri was intermediate (IC(50), approximately 1,000 nM), Klebsiella pneumoniae was resistant (IC(50), approximately 10,000 nM), and Enterobacter cloacae and Serratia marcescens were highly resistant (IC(50), >10,000 nM). All isolates were potent inducers of TNF-alpha activity in both adult and newborn cord blood. In contrast to its variable antibacterial activity, rBPI(21) consistently inhibited the TNF-inducing activity of all strains tested (IC(50), 1 to 1,000 nM). The antibacterial effects of rBPI(21) were additive with those of a combination of conventional antibiotics typically used to treat bacteremic newborns (ampicillin and gentamicin). Whereas ampicillin and gentamicin demonstrated little inhibition of bacterially induced TNF release, addition of rBPI(21) either alone or together with ampicillin and gentamicin profoundly inhibited release of this cytokine. Thus, supplementing newborn cord blood with rBPI(21) potently inhibited the TNF-inducing activity of a variety of gram-negative bacterial clinical pathogens and, in some cases, enhanced bactericidal activity. These results suggest that administration of rBPI(21) may be of clinical benefit to neonates suffering from gram-negative bacterial infection and/or endotoxemia.

Effects of traditional and ultrasonic liposuction on adipose tissue: a biochemical approach.

Little is known about the interaction of ultrasonic liposculpture with fat tissue. The surgical technique is well established and its clinical effects are satisfactory. However, the in vivo effects on adipose tissue remain to be determined. Previous studies have shown that ultrasound waves break fat cells. The purpose of this study was to ascertain whether ultrasound waves can cause the release of fatty acids from the molecular structure of triglycerides. A double-blind study was designed with samples obtained from traditional and ultrasonic liposuction of an equivalent area in the same patient. Samples were checked for triglycerides and for free fatty acids. Triglyceride values were always higher in the sample that had undergone ultrasonic procedure. No significant differences were observed between the free fatty acid chromatograms of the two kinds of samples analyzed. Data showed that no changes occurred in the triglyceride molecule when using ultrasound waves in the experimental conditions.

Time to detection of positive cultures in 28- to 90-day-old febrile infants.

OBJECTIVE: To determine the time to detection of positive blood, urine, and cerebrospinal fluid (CSF) cultures among febrile 28- to 90-day-old infants. STUDY DESIGN: Retrospective cohort of consecutive 28- to 90-day-old infants presenting with a temperature of >/=38 degrees C to an urban pediatric emergency department. Positive cultures and times to detection were noted. Patients were categorized as being at high risk for serious bacterial illness (SBI) based on clinical and laboratory criteria. RESULTS: Of the 3166 febrile infants seen in the emergency department during the study, 2733 had blood (86%), 2517 had urine (80%), and 2361 had CSF (75%) specimens obtained for culture, and 2190 had all 3 cultures (69%) sent. There were 224 positive cultures in 214 patients; of these, 191 had all 3 cultures (89%) sent. Subsequent analyses were confined to those who had all 3 cultures sent. The detected rate of SBI was 8.7% (191/2190). There were 28 positive blood cultures (1. 3%), 165 positive urine cultures (7.5%), and 8 positive CSF cultures (.4%). Median time to detection of positive cultures was 16 hours for blood, 16 hours for urine, and 18 hours for CSF. Four blood cultures (.1%), 20 urine cultures (.9%), and 0 CSF cultures were noted to have growth of a pathogen >24 hours after the specimen was obtained. All 4 blood cultures and 17 of 20 urine cultures with growth noted after 24 hours occurred among high-risk patients. CONCLUSIONS: The risk of identifying SBI after 24 hours is 1.1% among all 28- to 90-day-old febrile infants and.3% in low-risk infants.

Identification of aminoethylcysteine ketimine decarboxylated dimer in human plasma.

Aminoethylcysteine ketimine decarboxylated dimer (AECK-DD) is a natural sulfur-containing tricyclic compound detected, until now, in human urine and bovine cerebellum. Recently, the antioxidant properties of this compound, and particularly its protective effect on the in vitro oxidation of low-density lipoproteins, have been demonstrated. In this paper, the identification of AECK-DD in human plasma by means of gas chromatography, high-performance liquid chromatography and gas chromatography-mass spectrometry, performed after a simple and fast purification procedure, is reported.

Impact of simple screening criteria on utilization of low-yield bacterial stool cultures in a Children's Hospital.

OBJECTIVE: To determine diagnostic yield of stool cultures for Salmonella, Shigella, Campylobacter jejuni, Yersinia enterocolitica, and Escherichia coli O157:H7 (SSCYE) among hospitalized children and to develop guidelines for appropriate use of these tests. Setting. Tertiary care pediatric hospital. DESIGN: Computerized records from the Microbiology Laboratory from January 1992 to December 1996 were reviewed retrospectively to collect data on the number of stool cultures performed in inpatients and outpatients, the length of hospital stay at the time cultures were sent, and diagnostic yield of cultures in hospitalized patients. A detailed review of medical records of all patients with a stool pathogen isolated after 3 days of hospitalization was also undertaken. The results from this retrospective analysis were used to develop guidelines to reduce unwarranted stool cultures and to educate medical care providers in the appropriate use of these tests. The impact of these guidelines on reduction in the volume of stool cultures performed on hospitalized patients was measured prospectively from January 1998 to June 1998. RESULTS: A total of 27 110 stool cultures for SSCYE were performed in the 5-year study period. Of the 14 125 cultures from inpatients, 174 (1.2%) were positive. Among the cultures from inpatients, 9378 (66%) were from patients hospitalized for >3 days. Only 13 (.14%) were positive. Of these 13 cultures, 4 represented nosocomial infections, whereas the remaining 9 cultures either were sent to document clearance from a patient known previously to be infected with an enteric pathogen (7), or were attributed to delayed testing in individuals admitted with a diarrheal illness (2). Introduction of guidelines to reject all SSCYE cultures from patients hospitalized for >3 days who did not meet specified criteria was associated with an overall reduction of 689 (43%) in the volume of tests performed in the 6-month period evaluated. This included 497 fewer cultures ordered and 192 cultures that were ordered but rejected because screening criteria were not met. Only 11 (5.4%) of 203 cultures sent >3 days after admission were processed because they met clinical criteria for testing. None were positive. Estimated cost savings were $50 163/year. CONCLUSIONS: Stool cultures for SSCYE among hospitalized patients have very low diagnostic yield and are extremely overutilized. Simple guidelines, such as rejecting (with few exceptions) cultures from patients hospitalized for >3 days, can reduce substantially such unnecessary testing.

Antioxidant activity of aminoethylcysteine ketimine decarboxylated dimer on copper-induced LDL oxidation.

Aminoethylcysteine ketimine decarboxylated dimer (AECK-DD), a member of a family of natural cyclic sulfur-containing aminoacids, recently detected in biological samples, protects low density lipoprotein (LDL) against copper-mediated oxidation, as assessed by monitoring the kinetics of conjugated diene formation, thiobarbituric acid-reactive substances production and LDL-tryptophan fluorescence quenching. Moreover, AECK-DD exerts a protective effect also against metal-independent, peroxyl radical-induced lipoprotein oxidation. It is of note that the concentrations exerting a protective effect against LDL oxidation are similar to those found in biological samples.

Detection of a decarboxylated dimer of aminoethylcysteine ketimine in bovine cerebellum.

Aminoethylcysteine ketimine is a sulfur-containing cyclic compound produced by the enzymatic alpha-deamination of the parent aminoethylcysteine that has been detected in bovine brain and cerebellum. Aminoethylcysteine ketimine is known to dimerize spontaneously and easily lose one carboxyl group. This decarboxylated compound, simply named the dimer, has been recently detected in normal human urine. In this article we provide evidence on the occurrence of the dimer in the bovine cerebellum.

Antioxidant properties of the decarboxylated dimer of aminoethylcysteine ketimine: assessment of its ability to scavenge peroxynitrite.

The natural sulfur compound aminoethylcysteine ketimine decarboxylated dimer (AECK dimer) has been investigated for its ability to act as peroxynitrite scavenger. It has been found that the product efficiently protects against the nitration of tyrosine and the inactivation of alpha1-antiproteinase by peroxynitrite. The tyrosine nitration can be completely prevented by 100 microM AECK dimer which appears as effective as the antioxidants glutathione and N-acetylcysteine. The AECK dimer was also found to limit surface charge alteration of low density lipoprotein induced by peroxynitrite. These findings indicate that the AECK dimer is a strong protective agent against peroxynitrite damage and that it could play an important role in the defence against oxidative stress in human diseases.

Aminoethylcysteine ketimine decarboxylated dimer detected in normal human urine by gas-liquid chromatography, selected-ion monitoring and mass spectrometry.

Aminoethylcysteine ketimine is a biochemical product known to be converted spontaneously in the decarboxylated dimer. Since the ketimine has been detected in a mammalian brain, it was assumed that also the dimer could be present in the mammalian body and eventually excreted in the urine. Using human urine as the biological source, an extract was prepared which, submitted to gas-liquid chromatography, selected-ion monitoring and mass spectrometry, indicated the presence of the dimer.

Catheter infection caused by Methylobacterium in immunocompromised hosts: report of three cases and review of the literature.

Three cases of catheter infection due to Methylobacterium extorquens are reported. Each patient had a history of acute leukemia and was immunocompromised; two had undergone bone marrow transplantation, and the third was receiving consolidation chemotherapy. All three patients survived after removal of the central venous catheter and antibiotic treatment. The clinical features of these cases are compared with those of the 12 previously reported cases of infection due to Methylobacterium species.

Rapid detection of group A streptococci: comparative performance by nurses and laboratory technologists in pediatric satellite laboratories using three test kits.

Rapid tests for detecting group A streptococci in throat swabs are often performed outside hospitals or commercial laboratories by individuals with little or no technical training. We compared the abilities of nurses and technologists to perform and interpret three commercial kits (Directigen 1-2-3, ICON Strep A, and Culturette Brand 10-Minute Strep A ID) in three hospital satellite locations (the emergency department, a walk-in emergency clinic, and a general pediatric clinic). When the three tests were compared with culture, the sensitivities of the tests as performed by nurses and technologists, respectively, were 39 versus 44% for Directigen, 55 versus 51% for Culturette, and 72 versus 39% for ICON. A significant difference in sensitivity was found only with ICON tests. This result was largely explained by the tendency of technologists to test moist swabs, while nurses generally processed dry swabs; ICON test sensitivity was significantly greater with dry swabs. The specificities of Directigen and ICON tests performed by nurses and technologists were high (97 to 100%). The difference in the specificities of the Culturette test as determined from results obtained by nurses and technologists (80 versus 98%) was due to the tendency of one nurse to overinterpret the latex agglutination reaction. Analysis of the accuracies of the tests during practice periods compared with the accuracies of the tests during the study periods revealed statistically significant improvement in test performance. We conclude that these tests are specific but not sensitive when performed by nurses and technologists in satellite laboratories. With one exception, nurses and technologists performed the tests with comparable accuracy after brief training periods.

False resistance to imipenem with a microdilution susceptibility testing system.

Routine monitoring of antibiotic resistance at Children's Hospital, Boston, detected a dramatic increase in the prevalence of imipenem-resistant strains of Pseudomonas aeruginosa. Further studies documented that false resistance to imipenem was due, in part, to the loss of imipenem potency in customized MIC microdilution trays supplied by Sensititre Ltd. (West Sussex, United Kingdom). Recognition of the problem was delayed by use of the quality control standard recommended by the manufacturer, which were higher and broader than those suggested by the National Committee for Clinical Laboratory Standards.

Enzymatically labelled nucleic acid (NA) probe assays for detection of Campylobacter spp. in human faecal specimens and in culture.

Seventy-two stock clinical isolates of C. jejuni were tested with the SNAP Culture Identification Test Kit (Molecular Biosystems, Inc., San Diego, CA), an enzyme labelled nucleic acid probe colony blot assay, and with the Campyslide (BBL Microbiology Systems, Cockeysville, MD), a latex agglutination test. The sensitivity and overall agreement of both the SNAP and Campyslide tests were 100% in comparison with standard culture and identification tests. In addition, 14 C. jejuni, two C. laridis, and one 'C. upsaliensis', and one C. hyointestinalis, all fresh isolates from acutely ill patients, were detected with both tests. Ninety-eight faecal specimens from acutely ill patients were tested within 48 h using the probe based SNAP Diagnostic Test Kit (Molecular Biosystems, Inc.). Results were compared with standard culture. The probe test detected 4/6 specimens positive by culture; sensitivity was 66%. However, the two culture positive specimens, undetected by the probe test, had pathogens present at levels well below the probe test sensitivity (10(5) CFU g-1 stool). Specificity of the probe test was 98% (90/92 negative specimens) compared to culture. The results of this study demonstrate the accuracy of enzyme labelled oligonucleotide probes in the identification of C. jejuni isolated on culture and suggest a potential role for such probes in the direct detection of campylobacter in clinical faecal specimens.