Molecular epidemiology of bla OXA-23 -producing carbapenem-resistant Acinetobacter baumannii in a single institution over a 65-month period in north China.

BACKGROUND: Carbapenem-resistant Acinetobacter baumannii poses a significant threat to hospitalized patients, as few therapeutic options remain. Thus, we investigated the molecular epidemiology and mechanism of resistance of carbapenem-resistant A.baumannii isolates in Beijing, China. METHODS: Carbapenem-resistant A.baumannii isolates (n = 101) obtained between June 2009 and November 2014 were used. Multilocus sequence typing (MLST) and PCR assays for class C and D ß-lactamase were performed on all isolates. S1 nuclease pulsed-field gel electrophoresis (PFGE) and Southern blot hybridization were performed to identify the resistance gene location. RESULTS: All 101 A.baumannii isolates were highly resistant to frequently used antimicrobials, and were considered multidrug resistant. A total of 12 sequence types (STs) were identified, including 10 reported STs and 2 novel STs. Eighty-seven isolates were classified to clonal complex 92 (CC92), among which ST191 and ST195 were the most common STs. The bla OXA-23 gene was positive in most (n = 95) of the A.baumannii isolates. Using S1-nuclease digestion PFGE and Southern blot hybridization, 3 patterns of plasmids carrying bla OXA-23 were confirmed. ST191 and ST195 (both harboring bla OXA-23 ) caused outbreaks during the study period, and this is the first report of outbreaks caused by ST191 and ST195 in north China. CONCLUSION: bla OXA-23 -producing A.baumannii ST191 and ST 195 isolates can disseminate in a hospital and are potential nosocomial outbreak strains. Surveillance of imipenem-resistant A.baumannii and antimicrobial stewardship should be strengthened.

Clinical features, microbial spectrum, and antibiotic susceptibility patterns of spontaneous bacterial peritonitis in cirrhotic patients.

BACKGROUND AND AIMS: The microbial spectrum and antimicrobial resistance patterns change over time and vary across regions in patients with spontaneous bacterial peritonitis (SBP). There is an urgent need to clarify the factors associated with in-hospital mortality in these patients. METHODS: In this study, 377 patients with SBP and 794 patients with bacterascites were analyzed for the microbial spectrum, antimicrobial resistance profiles, and laboratory findings. RESULTS: The most common pathogens were Escherichia coli (96, 25.5%), Staphylococcus epidermidis (55, 14.6%), and Enterococcus faecium (42, 11.1%). Multidrug-resistant (MDR) bacteria comprised 49.7% of gram-positive bacteria (GPB) and 48.8% of gram-negative bacteria (GNB). The most sensitive antibiotics were amikacin (91.5%), meropenem (89.8%) and piperacillin/tazobactam (87.6%). Extensively drug-resistant (XDR) (OR=51.457, p < 0.001), neutrophil count (OR=1.088, p < 0.001), and the model for end-stage liver disease (MELD) score (OR=1.124, p < 0.001) were independent predictive factors of in-hospital mortality in patients with SBP. CONCLUSION: MDR represented nearly half of the bacteria isolated from patients with SBP, of which the high prevalence of extended-spectrum ß-lactamase-producing and Carbapenem-resistant bacteria is concerning. The presence of XDR, higher MELD score, and neutrophil count were independent predictive factors associated with higher in-hospital mortality in patients with SBP, indicating that intensive care should be provided to these patients.

Quenching effect of nickel ions on fluorescent gold nanoparticles.

Herein, we reported the quenching effect of Ni(2+) on bovine serum albumin protected fluorescent gold nanoparticles (BSA-GNPs). The quenching mechanism was discussed and a static quenching mechanism was proposed. The number of binding sites (n), apparent stability constants (K) and corresponding thermodynamic parameters of BSA-GNPs-Ni(2+) complex were measured at different temperatures. Under optimum conditions, the fluorescence intensity of BSA-GNPs is linearly proportional to nickel concentration from 6.0x10(-8)mol/L to 8.0x10(-6)mol/L with a detection limit of 1.0x10(-8)mol/L. The result indicated that BSA-GNP was a potential Ni(2+) probe.

Photoluminescence from water-soluble BSA-protected gold nanoparticles.

The photoluminescence from water-soluble gold nanoparticles, each composed of a 5.1 nm gold core and a bovine serum albumin (BSA)-protected layer, has been observed. The maximal excitation and the maximal emission wavelength are at 320 and 404 nm, respectively. The photoluminescence quantum yield is estimated as 0.053+/-0.0070, at room temperature. The mechanism of the luminescence is hypothesized to be associated with interband transitions between the filled 5d(10) band and 6(sp)(1) conduction band. The photoluminescence is sensitive to pH, organic solvents and metal ions. These observations suggest that this nanoparticles are a viable alternative to organic fluorophores or semiconductor nanoparticles for biological labeling and imaging.

A cresyl violet-based fluorescent off-on probe for the detection and imaging of hypoxia and nitroreductase in living organisms.

A new cresyl violet-based fluorescent off-on probe has been developed through a one-step synthesis for the detection of nitroreductase (NTR) and hypoxia. The detection mechanism is based on the NTR-catalyzed reduction of the probe to cresyl violet, accompanied with a large fluorescence enhancement at a long wavelength of 625 nm. The probe can detect NTR in aqueous solution with high selectivity and sensitivity, and the detection limit is 1 ng mL(-1) NTR. Most importantly, the probe has been successfully used to image not only NTR and hypoxia in living cells, but also the distribution of NTR in zebrafish in vivo.

Isolation and Identification of Listeria monocytogenes from Retail Meats in Beijing.

To determine the contamination of retail meats by Listeria monocytogenes in Beijing, 70 meat samples (25 pork, 10 beef, 14 lamb, and 21 chicken) were analyzed between January and March in 1990. Eight (11%) samples were positive for L. monocytogenes , and 39 (56%) samples were found to contain other Listeria spp. Seven pork and one chicken sample contained L. monocytogenes , whereas all beef and lamb were free of L. monocytogenes . Meanwhile, 15 (60%) pork, 11 (52%) chicken, 7 (70%) beef, and 6 (43%) lamb samples were positive for other Listeria spp. The eight confirmed isolates of L. monocytogenes were serologically typed. Six (5 from pork and 1 from chicken) were serotype l/2a, and the other two isolates (2 pork) were serotype l/2c and l/2b. No isolates were of serotypes 3 and 4. All positive samples for L. monocytogenes were frozen meats, and the incidence of Listeria spp. was greater for frozen samples than for fresh. Sixty of 70 samples (22 pork, 8 beef, 11 lamb, and 19 chicken) were used to compare the effectiveness of Oxford medium and Palcam medium for the isolation of L. monocytogenes from meat samples. L. monocytogenes was isolated from seven samples by Palcam medium, while five samples were positive by Oxford medium, indicating that Palcam medium was more effective for recovering L. monocytogenes than Oxford medium.