Y.H. Yang

The prevalence of plasmid-mediated AmpC β-lactamases among clinical isolates of Escherichia coli and Klebsiella pneumoniae from five children’s hospitals in China

The purpose of this study was to investigate the prevalence of plasmid-mediated AmpC β-lactamases in Escherichia coli and Klebsiella pneumoniae from five children’s hospitals in China. A total of 494 E. coli and 637 K. pneumoniae isolates were collected from five children’s hospitals in China from 2005 to 2006. The isolates with decreased susceptibility to cefoxitin were subjected to confirmation test with 3-aminophenyl boronic acid. Polymerase chain reaction (PCR) amplification of the blaAmpC, blaTEM, blaCTXM, and blaSHV genes and their gene sequencing were performed. Transconjugants were achieved by conjugation experiments. Plasmid-mediated AmpC β-lactamases were found in 10.1% of K. pneumoniae (64/637) and in 2.0% of E. coli (10/494) strains. The proportion of plasmid-mediated AmpC-producing strains significantly increased from 2005 (2.6%) to 2006 (9.3%) (p<0.001). The DHA-1-producing isolates were the most prevalent type (93.2%, 69/74). The sequences of blaDHA-1 genes were all identical to those from the GenBank. Strains of blaCMY-2 were isolated from five isolates (6.8%), which were all from E. coli. One sequence of blaCMY-2 differs from blaCMY-2 in the GenBank. Eighteen of the 74 (24.3%) AmpC-producing K. pneumoniae and E. coli isolates coproduced an extended-spectrum β-lactamase (ESBL). Cefoxitin resistance was transferred to 15 of the 74 positive strains (20.3%). Our study has demonstrated the occurrence of plasmid-mediated AmpC β-lactamases in E. coli and K. pneumoniae in Chinese pediatric patients and DHA-1 type AmpC enzymes had the highest prevalent rate. The CMY-2 AmpC β-lactamases from the children’s hospitals in China in this study are the first reported. Hence, continuous surveillance of the prevalence and evolution of AmpC β-lactamase is important.

Molecular and clinical characteristics of clonal complex 59 methicillin-resistant Staphylococcus aureus infections in Mainland China.

Detailed molecular analyses of Clonal Complex 59 (CC59) methicillin-resistant Staphylococcus aureus (MRSA) isolates from children in seven major cities across Mainland China were examined. A total of 110 CC59 isolates from invasive and non-invasive diseases were analyzed by multilocus sequence typing (MLST), Staphylococcus cassette chromosome mec (SCCmec) typing, staphylococcal protein A (spa) typing and pulsed-field gel electrophoresis (PFGE). Antibiotics susceptibilities, carriage of plasmids and 42 virulence genes and the expression of virulence factors were examined. ST59 (101/110, 91.8%) was the predominant sequence type (ST), while single locus variants (SLVs) belonging to ST338 (8/110, 7.3%) and ST375 (1/110, 0.9%) were obtained. Three SCCmec types were found, namely type III (2.7%), type IV (74.5%) and type V (22.7%). Seven spa types including t437, which accounted for 87.3%, were determined. Thirteen PFGE types were obtained. PFGE types A and B were the major types totally accounting for 81.8%. The dominant clone was ST59-t437-IVa (65.5%), followed by ST59-t437-V (14.5%). The positive rate of luks-PV and lukF-PV PVL encoding (pvl) gene was 55.5%. Plasmids were detected in 83.6% (92/110) of the strains. The plasmid size ranging from 23.4 kb to 50 kb was most prevalent which accounted for 83.7% (77/92). A significantly lower expression of hla was found in ST59-t437-IVa compared with ST59-t437-V. Among the 110 cases, 61.8% of the patients were less than 1 year old. A total of 90 cases (81.8%) were community-associated (CA) infections whereas 20 cases (18.2%) were hospital-associated (HA) infections. Out of the 110 patients, 36.4% (40/110) were diagnosed with invasive infectious diseases in which ST59-t437-IVa accounted for 67.5% (27/40). In brief, ST59-t437-IVa was proved as the dominant clone in CC59 MRSA strains. The carriage rate of pvl gene was high. CC59 MRSA could result in CA and HA infections. The majortiy of MRSA infection children were in young age.

Characterization of emm types and superantigens of Streptococcus pyogenes isolates from children during two sampling periods.

The characteristics of 359 group A streptococcal (GAS) isolates collected from Chinese paediatric patients in two periods (1993-1994, 2005-2006) were studied. Isolates were assigned to emm types and assayed for eight superantigen (SAg) genes (speA, speC, speH, speI, speG, speJ, ssa, SMEZ). Types emm1 and emm12 were consistently the most prevalent during the two periods, while others varied in frequency. GAS isolates carrying six or more SAg genes increased from 46.53% (1993-1994) to 78.39% (2005-2006); ssa, speH and speJ genes (P<0.05) increased but speA declined (P<0.05). SAg gene profiles were closely associated with the emm type, but strains of the same emm type sometimes carried different SAg genes in the two periods. No significant difference in emm-type distribution and SAg gene profile was noted between isolates from different diseases. These data may contribute towards the development of a GAS vaccine in China.

Serogroup distribution and antimicrobial resistance of nasopharyngeal isolates of Streptococcus pneumoniae among Beijing children with upper respiratory infections (2000–2005)

The aims of this study were to estimate pneumococcal carriage rate, antimicrobial resistance and serogroup distribution of nasopharyngeal isolates of Streptococcus pneumoniae among children with acute upper respiratory infections (AURIs) aged 1xa0month to 5xa0years attending outpatient department of the Beijing Children’s Hospital between 2000 and 2005. Susceptibilities to penicillin, amoxicillin-clavulanic acid, ceftriaxone, cefuroxime, cefaclor, erythromycin, tetracycline, sulfamethoxazole-trimethoprim and chloramphenicol were assessed using the E-test and disc diffusion. We also analyzed the correlation between antibiotic consumption and rates of resistance. The prevalence of penicillin-nonsusceptible pneumococci increased from 26% during 2000–2001 and 21% during 2002–2003 to 31.5% in 2004–2005. The percentage of S. pneumoniae resistant to cefaclor and cefuroxime increased from about 6% during 2000–2001 to about 23% during 2004–2005 (P<0.01). The frequency of resistance to erythromycin ranged from 87% to 94%. Tetracycline and co-trimoxazole resistance rates were greater than 80%. We conclude that resistance rates for most antibiotics are increasing, possibly due to misues of antibiotics in the hospital setting. However, chloramphenicol resistance was found to decrease, which correlated with the cessation of chloramphenicol administration in 1999. Pneumococcal strains (n=519) were analyzed by serogroup, and only 296 were found to be seven-valent pneumococcal conjugate vaccine-related serotype isolates. This serotype distribution is important for surveillance of the new conjugate vaccine.

Type distribution of serogroup 6 Streptococcus pneumoniae and molecular epidemiology of newly identified serotypes 6C and 6D in China

The recently determined serotypes 6C and 6D Streptococcus pneumoniae, as well as subtypes 6B-I and 6B-II, were not reported in China. Among the 171 invasive isolates, 19 were identified as serogroup 6. There were equal distribution (42.1%) of 6B-I and 6B-II, 15.8% of 6A and lack of 6C and 6D. Among 1662 noninvasive isolates, 210 were identified as serogroup 6. The rates of types 6A, 6B-I, 6B-II, 6C, and 6D were 42.4%, 21.0%, 29.1%, 4.8%, and 2.9%, respectively. Subtype 6B-II was more resistant to antibiotics than others. The main sequence types (STs) of serotype 6C and 6D isolates were ST2912 and ST982, respectively. These results suggested that all recognized types of serogroup 6 can be found in China and that subtype 6B-II was more drug resistant. The epidemic STs of serotype 6C and 6D did not show genetic association with the STs spreading in other countries.

Skin and soft tissue infections caused by community‐associated methicillin‐resistant staphylococcus aureus among children in China

Aim:u2002 To investigate the characteristic of community‐associated methicillin‐resistant staphylococcus aureus (CA‐MRSA) skin and soft tissue infections (SSTIs) among children in China.

Hypervalinemia and hyperleucine-isoleucinemia caused by mutations in the branched-chain-amino-acid aminotransferase gene

Valine, leucine, and isoleucine are essential branched chain amino acids (BCAAs). When BCAA metabolism is genetically impaired in human, serum levels of BCAA and/or their metabolites rise considerably, causing severe neurological dysfunction. The first step in BCAA catabolism is catalyzed by branched chain aminotransferase (BCAT). Hypervalinemia and hyperleucine-isoleucinemia caused by BCAT gene mutation in human have not been reported previously. A 25-year-old man presented with headache complaints and mild memory impairment for about six years. Brain MRI showed symmetric white matter abnormal signals. Metabolic studies revealed remarkably elevated plasma valine and leucine concentrations. Maple syrup urine disease (MSUD) diagnosis was not supported since all genes for the branched-chain α-keto acid dehydrogenase complex (BCKD) gene were normal. Interestingly, two heterogeneous BCAT2 gene mutations were found in the patient, including c.509Gu2009>u2009A (p.Arg170Gln) and c.790Gu2009>u2009A (p.Glu264Lys). In addition, c.509Gu2009>u2009A (p.Arg170Gln) and c.790Gu2009>u2009A (p.Glu264Lys) were found in his father and mother, respectively, suggesting an autosomal recessive disorder. BCAT2 functional studies demonstrated that the two BCAT2 gene mutations resulted in decreased BCAT2 enzyme activity. After treatment with vitamin B6, the levels of BCAA, especially valine were remarkably decreased and brain MRI lesions were improved. These findings suggest a new type of branched chain amino acid metabolism disorder. This rare case provides great insight into the further understanding of BCAA metabolism and its defect in human. BCAT2 gene mutations can cause hypervalinemia and hyperleucine-isoleucinemia, which are associated with brain white matter lesions.

Genotype replacement within serotype 23F Streptococcus pneumoniae in Beijing, China: characterization of serotype 23F.

We investigated the genetic structure of 99 isolates of serotype 23F Streptococcus pneumoniae from children with acute respiratory infections collected over two periods from 1997 to 2006, and 2010. All isolates were susceptible to vancomycin and amoxicillin-clavulanic acid; 97 were resistant to erythromycin, 95 of which carried the ermB gene and two carried both mefA/E and ermB genes. Multidrug resistance to three or more classes of antibiotics was exhibited by 90 isolates. Sequence types ST342 and ST81 were the most frequent in 1997-2006 and 2010, respectively. All CC81 isolates were non-susceptible to β-lactam antibiotics and had higher minimum inhibitory concentration values for penicillin than other clone complexes and sequence types. The increased β-lactam antibiotic resistance may have resulted from the replacement of multidrug-resistant clones related to ST81. Long-term studies on S. pneumoniae serotype 23F, especially the ST81 clone, should be conducted to better understand the epidemiological picture of this pathogen in China.

Spread of multidrug-resistant clonal complex 271 of serotype 19F Streptococcus pneumoniae in Beijing, China: characterization of serotype 19F.

We investigated the genetic structure of 120 isolates of serotype 19F Streptococcus pneumoniae from Chinese children with acute respiratory infections collected from 1997 to 2006, and 2010. All strains were susceptible to vancomycin and levofloxacin, and only five strains were not susceptible to penicillin. The non-susceptibility rate to cephalosporins increased from 1997 to 2010. Of 119 erythromycin-resistant strains, 60 carried both ermB and mefA genes. The percentage of clonal complex 271 (CC271) increased from 14.3% in 1997-1998 to 92% in 2010, whereas that of CC983 decreased from 64.3% to 0%. CC271 had a higher non-susceptibility rate to β-lactam antibiotics than CC983 and other CCs. The increased non-susceptibility rate to β-lactam antibiotics in serotype 19F pneumococci was found to be associated with the spread of the international resistant clone CC271 presumably caused by antibiotic pressure. Long-term surveys of serotype 19F S. pneumoniae are required to monitor CC prevalence and trends in antimicrobial resistance.

OL-049 Epidemiology and molecular characteristics of community-associated methicillin-resistant and methicillin-susceptible Staphylococcus aureus from skin/soft tissue infections in Beijing Children's Hospital, China

or intermediate to ertapenem and the emergence of P. mirabilis isolates resistant to imipenem. Acinetobacter baumannii showed a worryingly high level of resistance: 9/10 strains resistant to cefepime, 8/10 to carbapenems. Conclusions: Over 40% of skin and soft tissue infections are produced by Gram-negative bacteria with increased antibiotic resistance. The level of MRSA was over 30%, higher that what we found in former studies performed in this clinic.