Platelet membrane-camouflaged silver metal-organic framework drug system against infections caused by methicillin-resistant Staphylococcus aureus.

BACKGROUND: Due to the intelligent survival strategy and self-preservation of methicillin-resistant Staphylococcus aureus (MRSA), many antibiotics are ineffective in treating MRSA infections. Nano-drug delivery systems have emerged as a new method to overcome this barrier. The aim of this study was to construct a novel nano-drug delivery system for the treatment of MRSA infection, and to evaluate the therapeutic effect and biotoxicity of this system. We prepared a nano silver metal-organic framework using 2-methylimidazole as ligand and silver nitrate as ion provider. Vancomycin (Vanc) was loaded with Ag-MOF, and nano-sized platelet vesicles were prepared to encapsulate Ag-MOF-Vanc, thus forming the novel platelet membrane-camouflaged nanoparticles PLT@Ag-MOF-Vanc. RESULTS: The synthesized Ag-MOF particles had uniform size and shape of radiating corona. The mean nanoparticle size and zeta potential of PLT@Ag-MOF-Vanc were 148 nm and - 25.6 mV, respectively. The encapsulation efficiency (EE) and loading efficiency (LE) of vancomycin were 81.0 and 64.7 %, respectively. PLT@Ag-MOF-Vanc was shown to be a pH-responsive nano-drug delivery system with good biocompatibility. Ag-MOF had a good inhibitory effect on the growth of three common clinical strains (Escherichia coli, Pseudomonas aeruginosa, and S. aureus). PLT@Ag-MOF-Vanc showed better antibacterial activity against common clinical strains in vitro than free vancomycin. PLT@Ag-MOF-Vanc killed MRSA through multiple approaches, including interfering with the metabolism of bacteria, catalyzing reactive oxygen species production, destroying the integrity of cell membrane, and inhibiting biofilm formation. Due to the encapsulation of the platelet membrane, PLT@Ag-MOF-Vanc can bind to the surface of the MRSA bacteria and the sites of MRSA infection. PLT@Ag-MOF-Vanc had a good anti-infective effect in mouse MRSA pneumonia model, which was significantly superior to free vancomycin, and has no obvious toxicity. CONCLUSIONS: PLT@Ag-MOF-Vanc is a novel effective targeted drug delivery system, which is expected to be used safely in anti-infective therapy of MRSA.

[Analysis of antibiotics treatment in 86 cases of liver transplant recipients].

OBJECTIVE: To analyze the characteristic of bacterial infections, and the relationship between antibiotics treatment and bacterial infections after liver transplantation, and to prevent antibiotic-resistant bacterial infections. METHODS: 86 liver transplant recipients were retrospected. Different indexes including limited daily dose, the frequency of medication, drug use index were used to evaluate the rationality of the use of antibiotics, three-dimensional test was used to explore extended-spectrum beta-lactamase and AmpC enzyme of Gram-negative bacteria. RESULTS: The major pathogens of infection after liver transplantation were Enterococcus faecalis, Enterobacter cloacae, fungi and E. coli. Pre-operative antibiotic utilization rate was 83.7%, it was mainly a single use of antibiotics; After- operative antibiotic usage was 100.0%, it was mainly joint use of two or three antibiotics; The top 3 antibiotics used were cephalosporins, the combined enzyme inhibitors and penicillin. Antibiotics with drug utilization index (DUI) more than 1.1 included ampicillin and Lalin proxy. 43.3% and 31.8% of Gram -Negative bacteria produced ESBLs and AmpC, respectively, while 21.3% Gram -Negative bacteria produced two enzymes. CONCLUSION: There is high incidence of bacterial infections after liver transplantation. The use of antibiotics is high dose, high-frequency and reasonable; High resistance of bacterial infections was prone to develop and the prevention of the high resistance of bacterial infections is very important.

[Antibiotic resistance of Helicobacter pylori].

OBJECTIVE: To examine the infection and bacteria resistance of Helicobacter pylori (H.pylori) to clarithromycin and furazolidone,to determine whether the antibiotic resistance is primary or secondary, and to decide if a new H.pylori infection plays a role in eradication failures. METHODS: Twenty one H.pylori had been isolated from human biopsy specimens, and antimicrobial susceptibility testing was performed. DNA fingerprints were generated using random amplification polymorphic DNA (RAPD) to determine the identity of H.pylori before and after the eradication therapy. RESULTS: Eight bacteria resisted against clarithromycin, and one against furazolidone, with the resistant rates 38.1% and 4.8% respectively. The number of primary antibiotic resistance, secondary resistance and new infection was 1 for each. CONCLUSION: Resistance to clarithromycin is more common compared with that to furazolidone. Development of primary and secondary resistance to clarithromycin occurs as a rule in eradication failures. New H.pylori infection plays a role in eradication failures.

[Cefoxitin disk diffusion test in the detection of MRS heterogenic drug-resistant strains].

OBJECTIVE: To evaluate the reliability and clinical practicability of cefoxitin disk diffusion test in the detection of methicillin-resistant staphylococcus (MRS) heterogenic drug-resistant strains. METHODS: Three hundred and ten strains of staphylococcus isolated from clinics were detected by the oxacillin disk diffusion test, the cefoxitin disk diffusion test as well as the oxacillin agar dilution test according to the standard operation procedures of NCCLS, and the detection of mecA gene of staphylococcus was used as a criterion. The sensitivities and specitivities of the 4 methods were compared. RESULTS: By the detection of mecA gene, the ratio for MRSA was 57.1%(113/198) and the ratio for MRCNS was 62.5%(70/112). Both the sensitivity and specificity of cefoxitin disk diffusion test in the detection of MRS were 100%, and those in the detection of MRCNS were 98.6% and 100%. CONCLUSION: Cefoxitin disk diffusion test is reliable, simple and convenient, and it can be used as a conventional method for the detection of MRS in clinical laboratories.

[Effect of CagA(+) helicobacter pylori strain on the expression of connexin 43 and cell proliferation in BGC-823 cells].

OBJECTIVE: To determine the effect of CagA(+) Helicobacter pylori(H.pylori)strain and anti-H.pylori drugs on the expression of connexin 43(Cx43) and cell proliferation of BGC-823 cells in vitro,and to investigate the relation between the changes of Cx43 expression, cell proliferation of BGC-823 cells and CagA(+)H.pylori. METHODS: BGC-823 cells were co-cultured with CagA(+) H.pylori strain(NCTC J99) or CagA(-) H.pylori strain(NCTC 12908)at bacteria/cells ratio of 20:1,100:1 and 500:1 for 24 hours and 48 hours respectively. anti-H.pylori drugs was given in the group co-cultured at bacteria/cells ratio of 100:1 after 16 hours. In the control group, BGC-823 cells were cultured for 24 hours and 48 hours respectively,but without H.pylori or antij H.pylori drugs. Immunocytochemical SABC method and the image analysis of the computer were applied to detect the changes of Cx43 expression in BGC-823 cells. The cell proliferation was examined by methyl tetrazolium (MTT) method. RESULTS: (1)The expression of Cx43 in the control group after cultivation for 48 hours was higher than that for 24 hours (P< 0.05). The expression of Cx43 in the groups co-cultured with CagA(+) H.pylori strain after cultivation for 48 hours was lower than that co-cultured for only 24 hours, and that of the groups co-cultured with CagA(+) H.pylori strain was lower than that of the control group for both 24 hours and 48 hours (P< 0.05). The expression of Cx43 in the groups at bacteria/cells ratio of 500:1 was lower than that at bacteria/cells ratio of 20:1 and 100:1 for both 24 and 48 hours (P< 0.05),and that at bacteria/cells ratio of 100:1 was lower than that at bacteria/cells ratio of 20:1 for 48 hours (P< 0.05).However, there was no significant difference in Cx43 expression between 24 and 48 hours in the groups co-cultured with CagA(-) H.pylori strain (P>0.05). Cx43 expression in the groups co-cultured with CagA(-) H.pylori strain at the ratio of 100:1 and 500:1 was lower than that in the control group, and Cx43 expression at the ratio of 500:1 was lower than that at the ratio of 20:1 for 24 hours and 48 hours. Cx43 expression increased after the intervention with anti-H.pylori drugs for 48 hours. (2) In the groups co-cultured with CagA(+)H.pylori strain, the optical density value of MTT indicated that the cell proliferation at the bacteria/cells ratio of 100:1 was higher than that in the control group, but no significant difference was found in other two groups co-cultured for 24 hours. After co-culturing for 48 hours, the cell proliferation at the bacteria/cells ratio of 20:1 and 100:1 was significantly accelerated, while the cell proliferation at 500:1 was inhibited. In the groups co-cultured with CagA(-) H.pylori strain,there was no change in the cell proliferation. Intervention with anti-H.pylori drugs could suppress the cell proliferation. CONCLUSION: CagA(+) H.pylori can down-regulate the expression of Cx43 in BGC-823 cells,which is related to the reaction time and the density of H.pylori. Low density of CagA(+)H.pylori suspensions can accelerate the proliferation of BGC-823 cells, while high density can suppress the cell proliferation. The CagA(-) H.pylori has no effect on the cell proliferation. Intervention with anti-H.pylori drugs can up-regulate the expression of Cx43,and suppress the cell proliferation of BGC-823 cells.

Drug resistance of infectious pathogens after liver transplantation.

BACKGROUND: Infection in liver recipients is related to high risk of transplantation failure and mortality. Infectious agents isolated from 55 liver recipients from January 2003 through June 2005 were studied to improve the anti-infectious therapy. METHODS: Pathogens were isolated from routine culture. K-B method was used to examine the drug susceptibility. Extended spectrum beta-lactamase, AmpC beta-lactamase and Van gene in E.coli were examined by the agar-dilution susceptibility test and Nitrocefin test. RESULTS: Thirty-nine of the 55 recipients got infection. The 513 strains of pathogens isolated from 1861 specimens were predominantly Gram negative bacteria and over 40% of them showed resistance to more than 4 drugs. The positive rates of extended spectrum beta-lactamse and AmpC beta-lactamse production in E.cloacae were 32.4% and 36.8%, in E.coli were 33.8% and 10.5%, but the rates of these 2 bacteria producing both lactamses were 24.3% and 7.0%. The beta-lactamse production rates of Enterococcus faecalis and Enterococcus faecium were 8.8% and 11.1%, and the resistance rates to vancomycin were 11.2% and 18.5%, respectively. CONCLUSIONS: Infectious pathogens isolated from liver recipients are potent and multiple drug resistant. ESBLs and AmpC beta-lactamases are the major factors associated with Gram negative drug resistance. The infection of Enterococcal species presents as a particular challenge.

[Distribution of pathogen and resistance of nosocomial infections in the intensive care units].

OBJECTIVE: To determine the distribution of pathogens and their characteristics of drug susceptibility originating from nosocomial infections in the intensive care units (ICU), and to provide evidence for clinical anti-infection treatments. METHODS: Retrospective analysis to the pathogens and their drug susceptibility characteristics was carried out. These pathogens were isolated from the samples that came from patients infected in the ICU from 2002 to 2004. RESULTS: The main nosocomial infective pathogens in the ICU were gram negative bacilli (48.2%), and the next ones were gram positive bacteria (43.3%) and fungus (8.5%). The most common gram negative bacilli were Pseudomonas aeruginosa and Escherichia coli; while for gram positive bacteria, the main bacterin were Staphylococcus aureus. The gram negative bacilli could resist 4 or more than 4 antibiotics, and the rate for resistance exceeded 40%. Similarly, oxacillin resistance staphylococcus could resist 7 antibiotics, and the rate was over 50%. The detective rates of ESBLs and AmpC enzymes produced by Escherichia coli and K. peumoniae were 34.0% & 30.7% and 13.2% & 23.1%, respectively. The rate for oxacillin resistance staphylococcus was 66.3%, and there was relative high resistance rate ( > 55%) for most antibiotics: There was statistical difference, compared with that of non-resistant strains. CONCLUSION: Though gram positive coccus still play an important role, most infections are caused by gram negative bacilli of nosocomial infections in the ICU. The antibiotics resistant rate of all bacteria has been rising gradually. It shows strong resistance and multi-drug resistance. The most importment cause for resistance of gram negative bacilli is that the bacteria can produce ESBLs and AmpC enzymes. The antibiotic resistant rate for oxacillin resistance staphylococcus is really high.

[Pathogenic characters of infected bacteria after liver transplantation].

OBJECTIVE: To analyze the main pathogens of infection after the liver transplantation and their antibiotic resistant patterns. METHODS: The main pathogens of infection after the liver transplantation were retrospectively analyzed. Using 3-dimensional tests, ESBLs (extended-spectrum beta-lactamase), and AmpC were detected among the Gram negative bacilli. beta-Lactamase and Van gene in Enterococcus were determined by the standard agar dilution susceptibility tests and Nitrocefin respectively. RESULTS: The main infected strains were Enterococcus faecalis (15.0%), Enterobacter cloacae (13.9%), fungus (13.3%), and Escherichia coli (10.7%) after the liver transplantation. Among them, 32.4% of Enterobacter cloacae and 36.8% of Escherichia coli produced ESBLs; 33.8% of Enterobacter cloacae and 10.5% of Escherichia coli. produced AmpC beta-lactamases. The detectable rate of VanA gene in Enterococcusfaecalis and Enterococcus faecium was 7.5% and 11.1%; VanB was 3.8% and 7.4%; VanC was 1.3% and 0, respectively. CONCLUSION: The infection mainly occurs in the intestinal tract after the liver transplantation. The production of ESBLs and AmpC beta-lactamases is the main mechanism of antibiotic resistance. The increased detectable rate of vancomycin-resistant Enterococcus should be paid attention to.

Correlation of tumor necrosis factor-ß and interleukin-1 gene cluster polymorphism with susceptibility to bacteremia in patients undergoing kidney transplantation.

BACKGROUND: Bacteremia remains a significant cause of morbidity and mortality after kidney transplantation. This study was conducted to investigate whether the polymorphisms of tumor necrosis factor (TNF)-ß, interleukin (IL)-1ß, and IL-1 receptor antagonist (IL-1ra) gene predicted the susceptibility to bacteremia within the first 6 months after kidney transplantation. METHODS: Subjects comprised 82 infected kidney transplant recipients and 60 non-infected kidney transplant recipients. Bacteremia was diagnosed in 16 of the 82 infected recipients. Genomic DNA from these 142 kidney transplant recipients was extracted from peripheral blood leukocytes. Regions containing the NcoI polymorphic site at position +252 of TNF-ß gene and the AvaI polymorphic site at position -511 of IL-1ß gene were amplified by polymerase chain reaction (PCR) and subsequently digested with NcoI and AvaI restriction enzymes, respectively. The polymorphic regions within intron 2 of IL-1ra gene containing variable numbers of a tandem repeat (VNTR) of 86 base pairs were amplified by PCR. RESULTS: Genotypic and allelic frequencies were similar between infected recipients and non-infected ones. Individual locus analysis showed that recipient TNF-ß and IL-1ra gene polymorphisms were not associated with the presence of bacteremia (P = 0.684 and P = 0.567, respectively). However, genotype analysis revealed that recipient IL-1ß-511CC genotype was strongly associated with susceptibility to develop bacteremia (P = 0.003). Recipient IL-1ß-511CC genotype (odds ratio 5.242, 95% confidence intervals 1.645-16.706, P = 0.005) independently predicted the risk for bacteremia within the first 6 months after kidney transplantation. CONCLUSIONS: These findings indicate a critical role of IL-1ß gene polymorphisms in susceptibility to bacteremia after kidney transplantation, which may be useful to screen for patients at higher risk for post-transplant bacteremias. Thus, the identified individuals can benefit from preventive treatment and a less potent immunosuppressive regimen.