Prevalence of Escherichia coli ST1193 Causing Intracranial Infection in Changsha, China

ST1193 is an emerging new virulent and resistant clone among Escherichia coli with a tendency to spread rapidly across the globe. However, the prevalence of intracranial infection-causing E. coli ST1193 is rarely reported. This study aimed at determining the prevalence of E. coli ST1193 isolates, causing intracranial infections in Changsha, central China. A total of 28 E. coli isolates were collected from the cerebrospinal fluid of patients with intracranial infection over a four-year period. All isolates were differentiated using multilocus sequence typing (MLST), and phylogenetic grouping, and tested for antibiotic resistance. MLST analysis showed 11 sequence types (ST) among the 28 E. coli isolates. The most prevalent ST was B2-ST1193 (28.6%, 8/28), followed by B2-ST131 (21.4%, 6/28) and F-ST648 (10.7%, 3/28). Of the eight ST1193 isolates, three carried CTX-M-55, and one carried CTX-M-27. All eight ST1193 isolates were resistant to Ciprofloxacin, showing gyrA1AB/parC4A mutations. Two ST1193 isolates carried the aac(6′)-Ib-cr gene. All ST1193 isolates were recovered from infants with meningitis, with a fatal outcome for one three-month-old infant. ST1193 has emerged as the predominant type of E. coli strain causing intracranial infections in Changsha, China. This study highlights the importance of implementing appropriate surveillance measures to prevent the spread of this emerging public health threat.

Fructose-coated Ångstrom silver prevents sepsis by killing bacteria and attenuating bacterial toxin-induced injuries

Serious infection caused by multi-drug-resistant bacteria is a major threat to human health. Bacteria can invade the host tissue and produce various toxins to damage or kill host cells, which may induce life-threatening sepsis. Here, we aimed to explore whether fructose-coated Ångstrom-scale silver particles (F-AgÅPs), which were prepared by our self-developed evaporation-condensation system and optimized coating approach, could kill bacteria and sequester bacterial toxins to attenuate fatal bacterial infections.

Methods: A series of in vitro assays were conducted to test the anti-bacterial efficacy of F-AgÅPs, and to investigate whether F-AgÅPs could protect against multi-drug resistant Staphylococcus aureus (S. aureus)- and Escherichia coli (E. coli)-induced cell death, and suppress their toxins (S. aureus hemolysin and E. coli lipopolysaccharide)-induced cell injury or inflammation. The mouse models of cecal ligation and puncture (CLP)- or E. coli bloodstream infection-induced lethal sepsis were established to assess whether the intravenous administration of F-AgÅPs could decrease bacterial burden, inhibit inflammation, and improve the survival rates of mice. The levels of silver in urine and feces of mice were examined to evaluate the excretion of F-AgÅPs.

Results: F-AgÅPs efficiently killed various bacteria that can cause lethal infections and also competed with host cells to bind with S. aureus α-hemolysin, thus blocking its cytotoxic activity. F-AgÅPs inhibited E. coli lipopolysaccharide-induced endothelial injury and macrophage inflammation, but not by directly binding to lipopolysaccharide. F-AgÅPs potently reduced bacterial burden, reversed dysregulated inflammation, and enhanced survival in mice with CLP- or E. coli bloodstream infection-induced sepsis, either alone or combined with antibiotic therapy. After three times injections within 48 h, 79.18% of F-AgÅPs were excreted via feces at the end of the 14-day observation period.

Conclusion: This study suggests the prospect of F-AgÅPs as a promising intravenous agent for treating severe bacterial infections.

Comparative Evaluation of Seven Tigecycline Susceptibility Testing Methods for Carbapenem-Resistant Enterobacteriaceae

Purpose

Carbapenem-resistant Enterobacteriaceae (CRE) strains are extensively resistant to most antibiotics. Tigecycline is one of the few effective drugs that can be used to treat infections caused by CRE. The aim of this study was to evaluate the accuracy of different methods for detecting the susceptibility of CRE to tigecycline.

Methods

Seven commonly used drug susceptibility testing methods were compared and evaluated for the ability to determine CRE tigecycline susceptibility: broth microdilution (BMD), agar dilution method (ADM), disk diffusion method, Etest, MicroScan, Vitek2 COMPACT, and BD Phoenix 100.

Results

The minimum inhibitory concentration (MIC) of tigecycline to inhibit 50% and 90% of CRE growth (MIC₅₀ and MIC₉₀, respectively) assessed by ADM and BD Phoenix 100 was the same as that determined by the reference method, BMD. The MIC₅₀ was 2 µg/mL, and the MIC₉₀ was 4 µg/mL. The highest number of susceptible strains was detected by MicroScan, followed by BMD, Etest, ADM, BD Phoenix 100, Vitek2 COMPACT, and disk diffusion method, in descending order. No significant differences were observed among the tigecycline susceptibility results (P > 0.05) obtained from MicroScan, Etest, BD Phoenix 100, and BMD. BMD confirmed that 82.0% of strains were susceptible to tigecycline. ADM, MicroScan, and BD Phoenix 100 yielded the categorical agreement of 96%, 92%, and 93%, respectively. No method was found to present any very major errors (VMEs), and only the Vitek2 COMPACT yielded major errors (MEs) greater than 3%.

Conclusion

Among the seven methods tested, the ADM, MicroScan, and BD Phoenix 100 methods were accurate for determining the tigecycline susceptibility of CRE. MicroScan was acceptable with better performance than other methods.

[Analysis of pathogen spectrum and antimicrobial resistance of pathogens associated with hospital-acquired infections collected from 11 teaching hospitals in 2018]

Objective: To investigate the spectrum and antimicrobial resistance of major pathogens causing nosocomial infections in China, 2018. Methods: Non-duplicated nosocomial cases as well as pathogens causing bloodstream infections (BSI), hospital-acquired pneumonia (HAP) and intra-abdominal infections (IAI) from 11 teaching hospitals across China were collected. The minimum inhibitory concentrations (MICs) of clinically significant strains were determined by agar dilution method or broth microdilution method. The Clinical and Laboratory Standards Institute (CLSI) M100-S29 criteria were used for interpretation, and the WHONET-5.6 software was used in data analysis. Results: A total of 1 590 cases were collected, including 831 cases from BSI, 450 cases from HAP and 309 cases from IAI. The most prevalent pathogens causing BSI were Escherichia coli (29.2%, 243/831), Klebsiella pneumoniae (16.2%, 135/831) and Staphylococcus aureus (10.1%, 84/831); the most prevalent pathogens causing IAI were E. coli (26.2%, 81/309), Enterococcus faecium (15.5%, 48/309) and K. pneumoniae (13.3%, 41/309); while Acinetobacter baumanii (24.7%, 111/450), Pseudomonas aeruginosa (20.7%, 93/450) and K. pneumoniae (16.2%, 73/450) were dominated in HAP. All S. aureus were susceptible to tigecycline, linezolid, daptomycin and glycopeptides; 77.8% (105/135) of S. aureus strains were susceptible to ceftaroline. Methicillin-resistant S. aureus (MRSA) accounted for 29.6% (40/135) of all the S. aureus, and was lower than the accounted rate of methicillin-resistant coagulase-negative Staphylococcus (MRCNS) (83.7%, 41/49). One E. faecium strain (1.1%, 1/95) resistant to vacomycin and teicoplanin and one E. faecalis strain (2.3%, 1/43) resistant to linezolid was found. The prevalence of extended-spectrum β-lactamase (ESBL) was 56.1% (193/344) in E. coli and 22.1% (55/249) in K. pneumonia; the rate of carbapenem resistant E. coli and K. pneumonia was 4.1% (14/344) and 22.9% (57/249), respectively; the percentage of ceftazidime/avibactam resistant E. coli and K. pneumonia was 2.3% (8/344) and 2.0% (5/249), respectively; the percentage of colistin resistant E. coli and K. pneumonia was 1.5% (5/344) and 7.6% (19/249), respectively; no E. coli and K. pneumonia strains were found resistant to tigecycline. The rate of carbapenem resistant A. baumanii and P. aeruginosa were 78.9% (146/185) and 36.7% (66/180), respectively. A. baumanii showed low susceptibility to the antimicrobial agents except colistin (99.5%, 184/185) and tigecycline (91.4%, 169/185). Colistin, amikacin and ceftazidime/avibactam demonstrated high antibacterial activity against P. aeruginosa with susceptility rate of 100% (180/180), 93.3% (168/180) and 85.6% (154/180), respectively. Conclusions: Nosocomial Gram-negative pathogens show high susceptibilities to tigecycline, colistin and ceftazidime/avibactam in vitro. Antimicrobial resistance in A. baumannii is a serious problem. The prevalence of carbapenem-resistant Enterobacteriaceae has increased, which should be monitored continuously in China.

Ångstrom-scale silver particle-embedded carbomer gel promotes wound healing by inhibiting bacterial colonization and inflammation

Poor wound healing after diabetes or extensive burn remains a challenging problem. Recently, we presented a physical approach to fabricate ultrasmall silver particles from Ångstrom scale to nanoscale and determined the antitumor efficacy of Ångstrom-scale silver particles (AgÅPs) in the smallest size range. Here we used the medium-sized AgÅPs (65.9 ± 31.6 Å) to prepare carbomer gel incorporated with these larger AgÅPs (L-AgÅPs-gel) and demonstrated the potent broad-spectrum antibacterial activity of L-AgÅPs-gel without obvious toxicity on wound healing-related cells. Induction of reactive oxygen species contributed to L-AgÅPs-gel-induced bacterial death. Topical application of L-AgÅPs-gel to mouse skin triggered much stronger effects than the commercial silver nanoparticles (AgNPs)-gel to prevent bacterial colonization, reduce inflammation, and accelerate diabetic and burn wound healing. L-AgÅPs were distributed locally in skin without inducing systemic toxicities. This study suggests that L-AgÅPs-gel represents an effective and safe antibacterial and anti-inflammatory material for wound therapy.

Risk Factors for Subsequential Carbapenem-Resistant Klebsiella pneumoniae Clinical Infection Among Rectal Carriers with Carbapenem-Resistant Klebsiella pneumoniae

Purpose

Carbapenem-resistant Klebsiella pneumoniae (CRKP) infection has become a critical clinical concern for its high mortality. Rectal carriage of CRKP has been reported playing an important role in CRKP infection; however, the extent to which carrier develops clinical CRKP infection is unclear. This study aimed to identify risk factors for developing subsequential CRKP clinical infection in rectal carriers with CRKP.

Patients and Methods

Patients were screened for rectal carriage of CRKP in a tertiary university hospital; then, rectal CRKP carriers were divided into case group (those who developed subsequential clinical infection) and control group. Demographics, comorbid conditions, invasive procedures, antimicrobial exposure and other clinical parameters of those two groups were compared and analyzed using univariate and multivariate logistic regression analyses. Antimicrobial susceptibility profile and carbapenemase phenotype/genotype of those CRKP isolates were determined. MLST was applied to elucidate the molecular epidemiology of rectal CRKP isolates and clinical infection ones.

Results

Eight hundred and thirty-five patients were screened for rectal CRKP carriage. A total of 62 CRKP rectal carriers were identified; among them, 37.1% (23/62) developed CRKP clinical infection. CRKP isolates were resistant to most of the tested antimicrobial agents. ST11 was the dominant MLST type in rectal CRKP isolates (71.0%), and all the 23 clinical infection isolates were ST11. Multivariate analysis revealed that admission to the intensive care unit (ICU) (OR, 6.753; P=0.006), being in coma condition (OR, 11.085; P=0.015) and receiving central venous catheter (OR, 8.628; P=0.003) were independent risk factors for progressing to subsequential CRKP infection among those rectal carriers.

Conclusion

This study identified independent risk factors for developing subsequential CRKP clinical infection among CRKP rectal carriers, with being in coma condition as a new finding. It would help clinician target those high-risk rectal CRKP-colonized patients for prevention of subsequential clinical infection.

Fecal Carriage and Epidemiology of Carbapenem-Resistant Enterobacteriaceae Among Hospitalized Patients in a University Hospital

Purpose

To determine the prevalence and epidemiology of fecal carriage of carbapenem-resistant Enterobacteriaceae (CRE), antimicrobial susceptibility, carbapenemase phenotype/genotype, and the colistin-resistance gene mcr-1 in a university hospital in China.

Methods

A comprehensive study of the fecal carriage of CRE in 704 patients was performed. Multilocus sequence typing (MLST) and pulsed-field gel electrophoresis (PFGE) were applied to elucidate the molecular epidemiology of the isolates.

Results

In total, 60 CRE were detected in the 704 stool samples (8.5%), including 42 Klebsiella pneumoniae, 7 Escherichia coli, 3 Citrobacter freundii, 3 Klebsiella oxytoca, 3 Enterobacter cloacae, 1 Enterobacter aerogenes, and 1 Raoultella planticola. Fifty-five CRE isolates were positive for the carbapenemase phenotype, of which 39 were Klebsiella pneumoniae carbapenemase (KPC) producers. Thirty KPC-producing K. pneumoniae sequence type (ST) 11 isolates were identified and 28 were grouped into one cluster with a similarity of ≥85%, of predominately intensive care unit (ICU) strains. Three KPC-producing ST1889 strains were isolated from the pediatric ward, all indistinguishable and resistant to tigecycline. All CRE were susceptible to colistin and negative for mcr-1.

Conclusion

This study revealed a predominant fecal carriage of the KPC-producing K. pneumoniae ST11 clone, with several indistinguishable strain clusters, and the emergence of ST1889 in a Chinese university hospital. This evidence of cross-infection supports the urgent need for the implementation of infection control measures to prevent CRE dissemination.

Escherichia coli O25b-ST131 and O16-ST131 causing urinary tract infection in women in Changsha, China: molecular epidemiology and clinical characteristics

Objective

This study aimed to investigate the prevalence of Escherichia coli ST131 and molecularly characterize the O25b-ST131 and O16-ST131 subgroups among urinary tract infection (UTI) E. coli isolates from women in central China. We also assessed the clinical characteristics and outcomes of infections caused by E. coli ST131.

Methods

Between January 2014 and December 2015, a total of 216 consecutive, non-repetitive E. coli isolates were recovered from UTI urine samples from women in Changsha, China. All isolates were analyzed for phylogenetic groups, antimicrobial resistance and virulence genotypes. ST131 clonal groups were identified using PCR and characterized using O serotyping, CTX-M genotypes, fimH, gyrA, and parC alleles, fluoroquinolone resistance genes and pulsed-field gel electrophoresis (PFGE). Clinical data were obtained from medical records.

Results

Overall, 41 (19.0%) of 216 E. coli isolates were identified to contain ST131 strains, among which 27 were O25b-ST131 strains and 14 were O16-ST131 strains. The clinical characteristics and outcomes of the ST131 group did not differ significantly from those of the non-ST131 group, except for the presence of urinary stones (43.9% vs 27.4%, P=0.039). Ciprofloxacin resistance was found to be significantly higher in O25b-ST131 isolates than O16-ST131 isolates (96.3% vs 14.3%, P<0.001). The majority of O25b-ST131 isolates belonged to fimH30 (92.6%), followed by fimH41 (3.7%) and fimH27 (3.7%). O25b-H30 and O25b-H41 isolates were resistant to ciprofloxacin, and possessed gyrA1AB/parC1aAB combination. All of the O16-S131 isolates were found to belong to fimH41, and of which, two of the ciprofloxacin-resistant strains harbored gyrA1AB/parC3A combination. Three PFGE clusters, consisting of 38 (92.7%) isolates, with more than 70% similarity were identified.

Conclusion

The O25b and O16 sub-lineages have emerged as an important group of E. coli ST131 in UTI isolates from women in China. UTI patients with a history of urinary stones may need to be particularly vigilant against ST131 infection.

Epidemiology and molecular characterization of mcr-1 in Escherichia coli recovered from patients with bloodstream infections in Changsha, central China

Objectives

The main aim of this study was to investigate the prevalence and molecular characteristics of the mcr-1 gene in Escherichia coli isolates obtained from all patients with bloodstream infections over a year in a Chinese teaching hospital. We also assessed the susceptibility profiles of the mcr-1-positive strains and prognostic impact of this gene on the patients.

Methods

A total of 144 consecutive, non-repetitive E. coli isolates causing bloodstream infections were collected at a teaching hospital in Changsha, China from January to December 2016. The presence of the mcr-1 gene was assessed by PCR. All mcr-1-positive E coli isolates were characterized by antimicrobial susceptibility testing, multilocus sequence typing (MLST), a conjugation experiment, and plasmid replicon typing. Clinical data were obtained from medical records.

Results

The mcr-1 gene was detected in three (2.1%) of the 144 E. coli isolates. The three mcr-1-positive E. coli isolates were resistant to colistin. All three isolates showed a lower resistance to other classes of antibacterials, with all three being susceptible to carbapenems. The MLST results indicated that the three E. coli isolates were assigned to three different sequence types: ST457, ST101, and ST1413, respectively. The conjugation experiment showed that the mcr-1 gene was successfully transferred to the recipient (E. coli EC600) from two isolates, one of which possessed IncI1 replicons and the other of which carried IncHI2 and IncN replicons. The patients with bloodstream infections caused by mcr-1-positive isolates had severe underlying diseases and were cured after antibacterial treatment.

Conclusion

The prevalence of the mcr-1 gene in patients with E. coli bloodstream infection was 2.1% in Changsha, China. The mcr-1-positive E. coli isolates had varied susceptibility profiles, although all three were susceptible to carbapenems. This therapeutic window is crucial given the risk of rapid deterioration in high-incidence areas worldwide.

[Emergence of methicillin-resistant Staphylococcus aureus SCCmec type IV/V epidemic clones in a large teaching hospital in China]

OBJECTIVE

To investigate the staphylococcal cassette chromosome mec (SCCmec) genotype and molecular epidemiological characteristics of healthcare-associated methicillin-resistant Staphylococcus aureus (HA-MRSA) in a large teaching hospital in China.

METHODS

From January 2012 to December 2012, a total of 71 nonduplicate HA-MRSA were collected in a teaching hospital in Changsha, China. SCCmec types were determined by multiplex PCR, and Panton-Valentine leukocidin (PVL) gene was detected by PCR. The homology among the tested isolates was determined using pulsed-field gel electrophoresis (PFGE).

RESULTS

Of the 71 HA-MRSA isolates, 49 (69.0%) carried SCCmec Ⅲ, 10 (14.1%) carried SCCmec Ⅳ, 3 (4.2%) carried SCCmec Ⅴ and 3 (4.2%) carried SCCmec Ⅱ; the remaining 6 isolates were not typeable by PCR. Compared with patients having SCCmec Ⅰ/Ⅱ/Ⅲ MRSA infections, those with SCCmec Ⅳ/Ⅴ MRSA infections had a significantly younger age and a similar duration of hospital stay before the first MRSA-positive culture and total hospital stay. PVL genes were strongly associated with SCCmec type Ⅳ/Ⅴ MRSA infections. HA-SCCmec Ⅳ/Ⅴ MRSA strains showed a greater susceptibility to rifampicin, gentamicin, levofloxacin, ciprofloxacin, and tetracycline than HA-SCCmec Ⅰ/Ⅱ/Ⅲ MRSA strains. The 13 HA-SCCmec Ⅳ/Ⅴ MRSA isolates formed one large group at the 55% similarity level. Three PFGE clusters with a similarity index of 85% or more were identified, and unique PFGE profiles were observed in 4 isolates.

CONCLUSIONS

This is the first report of HA-MRSA isolates carrying SCCmec Ⅴ in Chinese hospitals. SCCmec types Ⅳ and Ⅴ MRSA clones have emerged in Chinese hospitals, which urges more rigorous surveillance of their spread in healthcare facilities in China.

An Outbreak of Infections Caused by a Klebsiella pneumoniae ST11 Clone Coproducing Klebsiella pneumoniae Carbapenemase-2 and RmtB in a Chinese Teaching Hospital

Background:

Klebsiella pneumoniae carbapenemase (KPC)-producing K. pneumoniae bacteria, which cause serious disease outbreaks worldwide, was rarely detected in Xiangya Hospital, prior to an outbreak that occurred from August 4, 2014, to March 17, 2015. The aim of this study was to analyze the epidemiology and molecular characteristics of the K. pneumoniae strains isolated during the outbreak.

Methods:

Nonduplicate carbapenem-resistant K. pneumoniae isolates were screened for bla_KPC-2 and multiple other resistance determinants using polymerase chain reaction. Subsequent studies included pulsed-field gel electrophoresis (PFGE), multilocus sequence typing, analysis of plasmids, and genetic organization of bla_KPC-2 locus.

Results:

Seventeen bla_KPC-2-positive K. pneumoniae were identified. A wide range of resistant determinants was detected. Most isolates (88.2%) coharbored bla_KPC-2 and rmtB in addition to other resistance genes, including bla_SHV-1, bla_TEM-1, and aac(3)-IIa. The bla_KPC-2 and rmtB genes were located on the conjugative IncFIB-type plasmid. Genetic organization of bla_KPC-2 locusin most strains was consistent with that of the plasmid pKP048. Four types (A1, A2, A3, and B) were detected by PFGE, and Type A1, an ST11, was the predominant PFGE type. A novel K. pneumoniae sequence type (ST1883) related to ST11 was discovered.

Conclusions:

These isolates in our study appeared to be clonal and ST11 K. pneumoniae was the predominant clone attributed to the outbreak. Coharbing of bla_KPC-2 and rmtB, which were located on a transferable plasmid, in clinical K. pneumoniae isolates may lead to the emergence of a new pattern of drug resistance.

Evaluation of our self-designed nanometer silicon membrane sandwich cup system for diagnosing tuberculosis

BACKGROUND AND AIMS

A nanometer silicon membrane sandwich cup system was self-designed. It could concentrate the bacilli via 0.45-μm microporous filter membrane and semi-automate the acid-fast bacilli (AFB) by a bacteria-staining machine. The aim of the study was to assess the clinical value of our self-designed system for diagnosing tuberculosis (TB).

METHODS

A total of 1993 sputum specimens obtained from patients with confirmed or suspected TB were subjected to direct or concentrated specimens smear at XiangYa Hospital, Central South University between May 2012 and February 2013. In addition, all the specimens were also inoculated into Lowenstein-Jensen (L-J) media, and culture results were considered as the gold standard for calculating sensitivity and specificity.

RESULTS

Compared with direct smear examination, an increased density of red stained bacilli was observed in the self-designed nanometer silicon membrane sandwich cup analysis under the microscope. The positive rate of the self-designed analysis was significantly higher than that of direct AFB smear [10.9% (217/1993) vs 6.2% (123/1993), P < 0.05]. The sensitivity of the self-designed system increased (97.3% vs 55.2%, P < 0.05) without a loss of specificity (100% vs 100%) for identifying positive TB cases compared with the direct smear method.

CONCLUSION

The self-designed nanometer silicon membrane sandwich cup and semi-automatic bacteria-staining machine could more efficiently and rapidly detect the AFB in respiratory specimens than direct microscopy. This is a novel and safe examination, and it may replace direct smear examination for the diagnosis of patients with TB.

Preparation and preliminary application of monoclonal antibodies to the receptor binding region of Clostridium difficile toxin B

A previous nationwide Chinese epidemiological study revealed through isolation of A‑B+ Clostridium difficile strains, which produce toxin B (TcdB), but not toxin A TcdA, that the strains are widespread and more frequent in east Asian countries,. The development of a process capable of detecting TcdB is required in microbiological laboratories in order to facilitate the control of the A‑B+ C. difficile strains, however, no diagnostic reagents have been developed to date. The aim of the present study was to prepare monoclonal antibodies (mAbs) targeting the receptor binding region of TcdB (CDB3), and to establish a double‑antibody sandwich enzyme-linked immunosorbent assay (ds‑ELISA), which can be used for the diagnosis of C. difficile infection. The recombinant protein, glutathione S transferase (GST)‑CDB3 was expressed and purified using an Escherichia coli system. BALB/c mice were immunized with GST‑CDB3 recombinant protein. A hybridoma technique was used for the production of anti‑CDB3 mAb. The hybridoma clones were then screened using indirect ELISA, and anti‑CDB3 mAb was produced in the ascites of the BALB/c mice. Isotyping of anti‑CDB3 mAb was performed using an SBA Clonotyping system/horseradish peroxidase (HRP) ELISA kit. Protein G affinity chromatography was used for purification of anti‑CDB3 mAbs, and the titer and specificity of the anti‑CDB3 mAbs were assessed using indirect ELISA and western blot analysis, respectively. The ds‑ELISA was established using HRP‑labeled anti‑CDB3 mAbd, which were used to detect TcdB clinically in diarrhea stools. A total of five stable hybridoma cell clones (1E7B, 1F8D3, 2F8A6, 3B6F1 and 4A4G2) producing anti‑CDB3 mAb were established. The results of the present study indicated that the immunoglobulin (Ig)G isotype was predominant, as 1E7B2 IgG1 (λ), 2F8A6 IgG2a (κ) and 4A4G2 IgG1 (κ). In addition, the highest titer of anti‑CDB3 mAb (2F8A6 and 4A4G2) was 1:51,200. Western blotting revealed that the 2F8A6 and 4A4G2 mAbs recognized the CDB3 protein specifically. Following anti‑CDB3 mAb (4A4G2) HRP‑labeling, the optimal working concentration was confirmed to be 1:400, and the concentration of coated antibody (2F8A6) was 20 µg/ml. The sensitivity of the ds‑ELISA was 73.33% for the A+B+ toxigenic C. difficile strains, and 86.67% for the A‑B+ toxigenic C. difficile strains, with a specificity of 100% for all. In conclusion, the present study successfully developed novel mAbs specific to CDB3, and developed a ds-ELISA kit with high specificity and sensitivity for the rapid detection of TcdB. This offers a useful tool for the diagnostic assessment of TcdB.

Emergence and spread of O16-ST131 and O25b-ST131 clones among faecal CTX-M-producing Escherichia coli in healthy individuals in Hunan Province, China

Objectives

The objectives of this study were to determine CTX-M-producing Escherichia coli ST131 strain prevalence in stool specimens from healthy subjects in central China and to molecularly characterize clonal groups.

Methods

From November 2013 to January 2014, stool specimens from healthy individuals in Hunan Province were screened for ESBL-producing E. coli using chromogenic medium and CTX-M genotypes and phylogenetic groups were determined. ST131 clonal groups were detected by PCR and characterized for antibiotic resistance, fimH, gyrA and parC alleles, plasmid-mediated quinolone resistance determinants, virulence genotypes and PFGE patterns.

Results

Among 563 subjects, 287 (51.0%) exhibited the presence of faecal ESBL-producing E. coli, all of which produced CTX-M enzymes. The most common CTX-M genotypes were CTX-M-14 (48.4%), CTX-M-15 (27.5%) and CTX-M-27 (15.0%). Of the 287 CTX-M-producing isolates, 32 (11.1%) belonged to the ST131 clone. O16-ST131 isolates were dominant (75%) and contained the fimH41 allele. The remaining eight (25%) ST131 isolates were of the O25b subgroup and contained fimH30 or fimH41. Ciprofloxacin resistance was found in 100% of the O25b-ST131 isolates, whereas only 8% of the O16-ST131 isolates were resistant. All of the O25b-ST131 isolates except one showed gyrA1AB and parC1aAB mutations; most of the O16-ST131 isolates had gyrA1A and parC1b mutations. The virulence genotypes of O16-ST131 resembled those of the O25b-ST131 isolates. The 32 ST131 isolates formed one large group at the 64% similarity level. They comprised 15 PFGE groups (defined at ≥85% similarity).

Conclusions

O16-ST131 isolates have emerged as the predominant type of ST131 isolate in faecal CTX-M-producing E. coli in healthy individuals in China.

Methylation of PRDM2, PRDM5 and PRDM16 genes in lung cancer cells

AIMS

To investigate the changes of expression and methylation status of PRDM2, PRDM5, PRDM16 in lung cancer cells after treatment with demethylation agent.

METHODS

A549 (lung adenocarcinoma cell line), HTB-182 (lung squamous cell carcinoma cell line) and HBE (normal bronchial cell line) were treated with 5-aza-2dC. The methylation state of PRDM2, PRDM5, PRDM16 was detected by MSP. The expression of PRDM2, PRDM5, PRDM16 was detected by RT-PCR and Western blot analysis. Cell growth was detected by MTT assay.

RESULTS

5-aza-2-dC reduced the methylation of PRDM2, PRDM5, PRDM16 gene in A549 and HTB-182 cells but not in HBE cells. Consistently, 5-aza-2dC increased mRNA and protein expression of PRDM2, PRDM5, PRDM16 in A549 and HTB-182 cells but not in HBE cells. Furthermore, 5-aza-2dC inhibited the growth of A549 and HTB-182 cells but not HBE cells.

CONCLUSIONS

PRDM2, PRDM5, PRDM16 promoters are methylated and their expression is suppressed in lung cancer cells. Demethylation drug 5-aza-2dC could upregulate the expression of PRDM2, PRDM5, PRDM16 and suppress lung cancer cell growth. 5-aza-2dC has potential to be used for lung cancer therapy by epigenetic mechanism.

Promoter methylation-mediated downregulation of PRDM5 contributes to the development of lung squamous cell carcinoma

PRDM5 has been proposed as a tumor suppressor frequently downregualted in tumor. In this study, lung squamous cell carcinoma tissues and adjacent nontumorous normal tissues were collected from 30 patients. PRDM5 expression was detected by reverse transcription polymerase chain reaction and Western blot analysis, DNA methylation of PRDM5 promoter was analyzed by methylation-specific PCR. SK-MES-1 cells or xenografts in nude mice were treated with 5-aza-2'-deoxycitydine, and cell proliferation and tumor growth in nude mice were examined. We found that PRDM5 promoter was methylated and PRDM5 expression at both mRNA and protein levels was reduced in lung squamous cell carcinoma tissues. Furthermore, PRDM5 promoter methylation was significantly correlated with tumor differentiation and lymph node metastasis of lung squamous cell carcinoma, but not with age, gender, smoking, or tumor grade. 5-aza-2'-deoxycitydine inhibited the proliferation of SK-MES-1 cells and the growth of xenografts in nude mice, accompanied by reduced methylation of PRDM5 promoter and increased expression of PRDM5. Taken together, our data suggest that PRDM5 is a tumor suppressor in lung cancer and is a promising target for the diagnosis, prognosis, and therapy of lung squamous cell carcinoma.

[NDM-1-producing Klebsiella pneumoniae in mainland China]

OBJECTIVE

To investigate the characteristics of New Delhi metallo-beta-lactamase-1 (NDM-1) gene of Klebsiella pneumoniae (K. pneumoniae) emerging in Hunan, and its relationship to antibiotic resistance.

METHODS

The clinical strain was isolated from a sputum sample of a child with severe pnemonia and toxic myocarditis who was admitted into a general hospital of Hunan Province. VITEK-2 compact instrument was used for bacterial identification and antibiotic susceptibility test. Modified Hodge test was used for the screening of carbapenemase. EDTA-synergy test and combination disk diffusion test were used for detection of metallo-β-lactamase (MBL). PCR was performed for amplification of NDM-1 genes and the positive products were sequenced and analyzed with BLAST. Conjugation was also performed to analyze mechanisms of antibiotic resistance. The results of antibiotic susceptibility tests were compared before and after conjugation.

RESULTS

The isolated strain was identified as K.pneumoniae. Modified Hodge test, EDTA-synergy test and combination disk diffusion test were all positive for the strain. The homology between gene sequence of PCR amplification products and NDM-1 gene FN396876.1 in the GenBank was 100%. Transconjugant DNA was used as template for the amplification of NDM-1 gene. The amplification products were sequenced and found to be the same as the NDM-1 gene amplification product of the donor strain. The MIC of transconjugant E.coli J53 (NDM-1) to all the β-lactams increased significantly compared with the recipient strain E.coli J53. The MIC of ertapenem and imipenem increased by more than 8 times, while the MIC of ceftazidime and ceftriaxone increased by more than 64 times.

CONCLUSIONS

This study first identified a strain of K. pneumoniae carrying NDM-1 in mainland China. NDM-1 gene can be transmitted among different strains and causes extensively drug-resistance to β-lactams.

The use of pleural fluid procalcitonin and C-reactive protein in the diagnosis of parapneumonic pleural effusions: a systemic review and meta-analysis

BACKGROUND

We aimed to perform a systematic review and meta-analysis of the diagnostic performance of pleural fluid procalcitonin (PCT) or C-reactive protein (CRP) in differentiating parapneumonic effusion in patients with pleural effusion.

METHODS

We searched the EMBASE, MEDLINE, and Cochrane database in December 2011. Original studies that reported the diagnostic performance of PCT alone or compared with that of other biomarkers for differentiating the characteristics of pleural effusion were included.

RESULTS

We found 6 qualifying studies including 780 patients with suspected parapneumonic effusion and 306 confirmed cases of parapneumonic effusion. Six studies examined the diagnostic performance of pleural fluid PCT, 3 also tested for serum PCT, and another 3 tested for serum CRP. The bivariate pooled sensitivity and specificity were as follows 0.67 (95% confidence interval [CI], 0.54-0.78) and 0.70 (95% CI, 0.63-0.76), respectively, for pleural fluid PCT; 0.65 (95% CI, 0.55-0.74) and 0.68 (95% CI, 0.62-0.74), respectively, for serum PCT; and 0.54 (95% CI, 0.47-0.61) and 0.77 (95% CI, 0.72-0.81), respectively, for serum CRP. There was evidence of significant heterogeneity (I(2)=55.0%) for pleural fluid or serum PCT but not for CRP (I(2)=0.0%).

CONCLUSION

The existing literature suggests that both pleural fluid and serum PCT tests have low sensitivity and specificity for differentiating parapneumonic effusion from other etiologies of pleural effusion. Compared with PCT, serum CRP has higher specificity and a higher positive likelihood ratio, and thus, it has a higher rule-in value than PCT.

Antimicrobial resistance and molecular epidemiological characteristics of clinical isolates of Staphylococcus aureus in Changsha area

BACKGROUND

Increasing prevalence of Staphylococcus aureus (S. aureus), particularly methicillin-resistant S. aureus (MRSA) has been reported in China. In this study, we investigated the drug resistance characteristic, genetic background, and molecular epidemiological characteristic of S. aureus in Changsha.

METHODS

Between January 2006 and December 2008, 293 clinical isolates of S. aureus were collected from 11 hospitals in Changsha and identified by the Vitek-2 system. All the isolates were verified as MRSA by PCR amplification of both femA and mecA genes. K-B disk method was used to test drug sensitivity of S. aureus to antibiotics. Pulsed-field gel electrophoresis (PFGE) was performed for genotypic and homologous analysis of 115 isolates randomly selected from the original 293 clinical S. aureus isolates.

RESULTS

S. aureus was highly resistant to penicillin, ampicillin, erythromycin, and clindamycin with resistant rates of 96.6%, 96.6%, 77.1%, and 67.2% respectively. All the isolates were susceptible to tecoplanin, vancomycin, and linezolid. MRSA accounted for 64.8% (190/293) of all the S. aureus strains. The 115 S. aureus isolates were clustered into 39 PFGE types by PFGE typing, with 13 predominant patterns (designated types A to M) accounting for 89 isolates. The most prevalent PFGE type was type A (n = 56, 48.7%) and 100.0% of type A strains were MRSA. PFGE type A included 13 subtypes, and the most prevalent subtype was subtype A1 (46.4%, 26/56). Strains with PFGE type A were isolated from eight hospitals (8/11), and both subtypes A1 and A4 strains were isolated in a university hospital.

CONCLUSIONS

Clinical isolates of S. aureus in Changsha were resistant to multiple traditional antibiotics. There was an outbreak of PFGE type A MRSA in this area and the A1 subtype was the predominant epidemic clone. Dissemination of the same clone was an important reason for the wide spread of MRSA.

[A study of the autoimmune pathogenesis of chronic HCV infection]

To explore the autoimmune pathogenesis of chronic hepatitis C virus(HCV) infection. Anti-GOR, antinuclear antibodies(ANA), thyroglobulin antibody(TGA), thyroid microsome antibody(TMA), serum levels of soluble Fas(sFas), and peripheral blood lymphocyte(PBMC) subsets and their apoptosis were measured in chronic HCV infection by using immunity assay and flow cytometry, respectively. The results showed that the positive rates of anti-GOR, ANA and TMA/TGA were significantly higher in chronic HCV-infected patients than those in normal controls(P < 0.01, respectively). In comparison with chronic HBV infected patients, anti-GOR and ANA were also significantly increased in chronic HCV infected patients(P < 0.01, P < 0.05, respectively). The serum levels of sFas were significantly higher in chronic HCV infection than those in healthy donors(P < 0.01). The apoptosis percentage of PBMCs and CD3+ cell was all increased in chronic HCV infection (vs normal controls P < 0.05). However, the apoptosis percentages of CD4+ T and CD19+ B cells in PBMCs were significantly decreased in patients with anti-GOR positive as compared with anti-GOR negative(P < 0.01, P < 0.05). The results indicate that autoimmune reactions and the imbalance of lymphocyte apoptosis exist during chronic HCV infection. Decreasing of the apoptosis of CD4+ T and CD19+ B lymphocytes may be the important reasons for the mechanism of autoimmune pathogenesis of chronic HCV infection. Increased serum levels of sFas may be responsible for the decrease of the apoptosis in a part of lymphocytes in chronic HCV infection.

Effect of IL-12 on T-cell immune responses in patients with chronic HCV infection

As the host's immune responses may determine the outcome of hepatitis C virus (HCV) infection, and interleukin (IL)-12 plays an essential role in host defense against infectious diseases, we studied the antigen-specific and non-specific cellular immune responses in patients with chronic HCV infection. A proliferative response to phytohemagglutinin (PHA) was found in all 20 patients. Of the 20, 8 (40%) displayed a lymphocyte proliferation in response to HCV antigen c22, 2 (10%) to c33, 6 (30%) to c100-3, and 1 (5%) to NS5. The addition of rhIL-12 to cultures of peripheral blood mononuclear cells (PBMC) stimulated with PHA significantly enhanced the proliferative responses in normal controls as well as in HCV-infected subjects. The increased proliferation was also observed in HCV-infected patients when PBMC were co-cultured with HCV antigens c22 and c100-3 in the presence of rhIL-12. The production of interferon gamma (IFNgamma), IL-2, IL-4 and IL-10 was observed in 7 (58.3%), 5 (41.7%), 3 (25.0%) and 5 (41.7%) HCV-infected individuals stimulated with c22, and in 4 (33.3%), 2 (16.7%), 2 (16.7%) and 2 (16.7%) with c100-3, respectively. All HCV-infected individuals had increased production of cytokines IFNgamma, IL-2, IL-4 and IL-10 in supernatants of PBMC after stimulation with PHA. IL-12 significantly augmented Th1 cytokine production in HCV-infected individuals stimulated with PHA and with HCV antigens. In conclusion, deficient cellular immune responses are present in HCV-infected patients and IL-12 can enhance the immune responses in these patients.

[Serum HBV DNA detected by polymerase chain reaction with dUTP/uracil-DNA glycosylase]

The ability of PCR reagent containing dUTP/uracil-DNA glycosylase for controlling carry-over contamination of PCR products was explored. All of 204 sera taken from hepatitis patients were used for HBV DNA detection by PCR with PCR-dUTP/UDG reagent in comparison with that without dUTP/UDG. The results showed that its efficiency of controlling contamination was excellent. At least, contamination of 100 ng PCR products was got rid of. The corresponding rate of HBV DNA detection by PCR-dUTP/UDG in combination with dot hybridization using digoxin-labeled HBV probe was as high as 89.32%, higher than that (81.45%) of PCR without dUTP/UDG plus dot hybridization(P < 0.05). It suggests that PCR-dUTP/UDG method could prevent PCR products from contaminating and increase accuracy and specificity of PCR amplification.

Circulating Th1 and Th2 cytokines in patients with hepatitis C virus infection

The imbalance of T-helper (Th) lymphocyte cytokine production may play an important role in immunopathogenesis of persistent hepatitis C virus (HCV) infection. To know whether an imbalance between Th1 and Th2 cytokines is present in chronic HCV infection, serum levels of Th1 cytokines, interferon gamma (IFN-gamma) and interleukin (IL)-2, and Th2 cytokines, IL-4 and IL-10, were measured using enzyme-linked immunosorbent assay in this study. Eighteen individuals with chronic HCV infection, 11 healthy subjects as normal controls and 10 chronic HBV infected patients as disease controls were observed. The results showed that the levels of Th2 cytokines (IL-4 and IL-10) were significantly increased in chronic HCV infected patients compared with normal controls (IL-4: 30.49+/-17.55 vs. 14.94+/-13.73, pg/ml, P<0.025; IL-10: 50.30+/-19.59 vs. 17.87+/-9.49, pg/ml, P<0.001). Similarly, the levels of Th1 cytokine, IL-2, was also elevated in individuals with chronic HCV infection when compared with normal controls (IL-2: 118.53+/-95.23 vs. 61.57+/-28.70, pg/ml, P<0.05). However, Th1 cytokine IFN-gamma level was not significantly changed during HCV infection (IFN-gamma: 28.09+/-15.65 vs. 24.10+/-15.61, pg/ml, P>0.05). Furthermore, the elevated levels of Th2 cytokines are greater than Th1 cytokines in HCV infection. Thus, the study indicates that an enhanced Th2 responses are present during chronic HCV infection, which may partly be responsible for the persistence of HCV infection.