Wenqiang He

In Vitro Activities of Ceftazidime-Avibactam and Aztreonam-Avibactam against 372 Gram-Negative Bacilli Collected in 2011 and 2012 from 11 Teaching Hospitals in China

ABSTRACT Ceftazidime-avibactam, aztreonam-avibactam, and comparators were tested by reference broth microdilution against 372 nonrepetitive Gram-negative bacilli (346 unselected plus 26 selected meropenem-nonsusceptible Enterobacteriaceae isolates) collected from 11 teaching hospitals in China in 2011 and 2012. Meropenem-nonsusceptible isolates produced extended-spectrum β-lactamases (ESBLs; e.g., CTX-M-14/3), AmpCs (e.g., CMY-2), and/or carbapenemases (e.g., KPC-2 and NDM-1). Avibactam potentiated the activity of ceftazidime against organisms with combinations of ESBLs, AmpCs, and KPC-2. Aztreonam-avibactam was active against all β-lactamase producers (including producers of NDM-1 and IMP-4/8) except blaOXA-containing Acinetobacter baumannii and some Pseudomonas aeruginosa isolates.

Population structure and characterisation of Staphylococcus aureus from bacteraemia at multiple hospitals in China: association between antimicrobial resistance, toxin genes and genotypes

Staphylococcus aureus from bacteraemia at multiple hospitals in China were genetically characterised to improve understanding of its epidemiology. A total of 236 consecutive, non-duplicate S. aureus bacteraemia isolates were collected at 16 Chinese hospitals. Isolates were characterised by antimicrobial resistance, 19 toxin genes, agr alleles, multilocus sequence typing and spa typing. The prevalence of meticillin-resistant S. aureus (MRSA) was 47.5% (112/236). Forty-two sequence types (STs) and 63 spa types were identified, including 14 STs and 14 spa types for MRSA. Clonal complex (CC) 8, CC5, ST7 and CC188 accounted for 67.4% of the isolates. ST239-t030/t037-SCCmecIII-agrI was the predominant MRSA genotype (50%), followed by ST5-t002/t570-SCCmecII-agrII (8%). A vancomycin MIC ≥ 1mg/L was detected significantly more often in ST5-SCCmecII and ST239-t037-SCCmecIII, whereas rifampicin resistance was overwhelmingly associated with ST239-t030-SCCmecIII (P<0.001). Oxacillin MICs were relatively low for ST59-MRSA. Major genotypes of meticillin-susceptible S. aureus (MSSA) were ST7-t091/t796-agrI (16.1%), ST188-t189-agrI (12.1%) and ST398-t571/t034-agrI (5.6%). Toxin genes were identified in 95.8% of isolates and formed 89 toxin gene profiles. The toxin genes sea, selk, selq and sell were significantly more common in MRSA, whilst tsst-1, seb, sed, selm, seln, selp and selj were more prevalent in MSSA (P<0.001). The pvl gene was more commonly detected in CC59, whereas tsst-1 was more frequent in CC15, CC188 and ST398 (P<0.001). The major genotypes were associated with specific antimicrobial resistance and toxin gene profiles.

Linezolid-resistant clinical isolates of enterococci and Staphylococcus cohnii from a multicentre study in China: molecular epidemiology and resistance mechanisms

Genetic characterisation of linezolid-resistant Gram-positive cocci in a multicentre study in China has not been reported previously. To study the mechanism underlying the resistance of linezolid-resistant isolates, nine Enterococcus faecalis, one Enterococcus faecium and three Staphylococcus cohnii isolates with various levels of resistance were collected from five hospitals across China in 2009-2012. The nine E. faecalis isolates were classified into seven sequence types, indicating that these linezolid-resistant E. faecalis isolates were polyclonal. Enterococci isolates had reduced susceptibility to linezolid (MICs of 4-8 mg/L) and had mutation of ribosomal protein L3, with three also having mutation of L4, but without the multidrug resistance gene cfr or the 23S rRNA mutation G2576T. The three S. cohnii isolates were highly resistant to linezolid (MICs of 64 mg/L to >256 mg/L), harboured the cfr gene and had the 23S rRNA mutation G2576T. Southern blotting indicated that the cfr gene of these three isolates resided on different plasmids (pHK01, pRM01 and pRA01). In plasmid pHK01, IS21-558 and the cfr gene were integrated into transposon Tn558. In plasmids pRM01 and pRA01, the cfr gene was flanked by two copies of an IS256-like insertion sequence, indicating that the transferable form of linezolid resistance is conferred by the cfr gene. In conclusion, the emergence of linezolid-resistant Gram-positive cocci in different regions of China is of concern. The cfr gene and the 23S rRNA mutation contribute to high-level linezolid resistance in S. cohnii, and the L3 and L4 mutations are associated with low-level linezolid resistance in enterococci.

High prevalence of fluoroquinolone-resistant group B streptococci among clinical isolates in China and predominance of sequence type 19 with serotype III.

ABSTRACT A total of 146 group B streptococcus isolates from 8 cities across China belonged to four serotypes. Serotype Ia was more common in children. A high prevalence of resistance was observed for levofloxacin (37.7%), erythromycin (71.2%), clindamycin, (53.4%), and tetracycline (81.5%). The levofloxacin and clindamycin resistances among the 4 serotypes differed significantly. Eighty percent of fluoroquinolone-resistant isolates belonged to the sequence type 19 (ST19)/serotype III clone, with GyrA-ParC-ParE triple substitutions. This clone carried the erm(B), mef(E), and tet(M) genes.

Genetic characterisation of clinical Klebsiella pneumoniae isolates with reduced susceptibility to tigecycline: Role of the global regulator RamA and its local repressor RamR.

Laboratory-derived Klebsiella pneumoniae mutants demonstrated that the ramA locus mediated low-level tigecycline resistance. The aim of this study was to elucidate the underlying mechanisms of tigecycline resistance in clinical K. pneumoniae isolates. In total, 106 isolates with tigecycline MICs ranging from 0.125 mg/L to 16 mg/L were collected to determine the correlations between expression of the global regulon ramA, marA, soxS, the acrB pump gene and tigecycline MICs. PCR was used to determine whether mutations in ramR, acrR or the rpsJ gene encoding 30S ribosomal protein S10 were responsible for tigecycline resistance. ramA or ramR inactivation and corresponding trans-complemented strains were used to characterise the contribution of RamA and RamR to tigecycline resistance. Tigecycline MICs were correlated with transcriptional levels of ramA and acrB, but were negatively correlated with marA and soxS. Disrupting ramA strikingly reduced the tigecycline MIC by 16-fold, accompanied by a 0.5-fold downregulation of acrB expression and 3.14- and 3.80-fold upregulation of marA and soxS, respectively. Complementation with plasmid-borne ramA restored the original parental phenotype of decreased tigecycline susceptibility. Of 34 tigecycline-non-susceptible isolates, 21 harbouring diverse mutations in RamR led to ramA overexpression. Disrupting the mutated ramR gene and complementing the mutated ramR gene with a wild-type gene downregulated expression of ramA but maintained the same tigecycline-resistant phenotype as the parental strain; the complemented strain exhibited 4.21- and 27.51-fold increased expression of acrB and marA, respectively. In conclusion, for the majority of tigecycline-resistant K. pneumoniae, ramA, depressed by ramR, was the major factor accounting for tigecycline resistance.

Efficacy and safety of daptomycin for the treatment of infectious disease: a meta-analysis based on randomized controlled trials

OBJECTIVES A systematic review and meta-analysis based on randomized controlled trials (RCTs) of the efficacy and safety of daptomycin versus comparators. METHODS Electronic databases (PubMed, Embase, Cochrane Central Register of Controlled Trials and clinical registered trials) were searched to identify RCTs that assessed the efficacy and safety of daptomycin versus therapy with comparators. Two reviewers independently applied selection criteria, performed a quality assessment and extracted the data. The I(2) statistic was calculated for heterogeneity, and a random-effects or fixed-effects model was used for estimates of risk ratio (RR). The primary outcome assessed was clinical treatment success among the intention-to-treat (ITT) population. RESULTS Thirteen trials fulfilled the inclusion criteria. Daptomycin was as efficacious as comparator regimens among the ITT population (RR = 0.98, 95% CI 0.93-1.03) but had a lower efficacy among the clinically evaluable (CE) population (RR = 0.96, 95% CI 0.93-1.00). Subgroup analyses according to the quality of the trial, the type of antibiotic and the type of infection did not alter the outcomes. No significant difference was identified for all-cause mortality between the daptomycin and comparator groups (RR = 1.17, 95% CI 0.76-1.79) but daptomycin therapy did reduce the duration of treatment. Daptomycin caused a significantly lower incidence of renal impairment, nausea and headache but caused a reversible increase in creatine phosphokinase (CPK). Subgroup analysis indicated that daptomycin was significantly associated with a higher incidence of CPK elevation and fewer renal impairments among the population with a mean age ≤60 years and a dose of daptomycin ≥6 mg/kg/24 h. CONCLUSIONS Daptomycin showed efficacy similar to the comparator regimens among the ITT population but lower efficacy among the CE population. Fewer adverse effects in total, but more CPK elevation effects, were observed in patients treated with daptomycin.

Prevalence and molecular typing of oxacillin-susceptible mecA-positive Staphylococcus aureus from multiple hospitals in China

Among 1588 non-duplicated Staphylococcus aureus isolates from 10 cities in China, 60 isolates were susceptible to oxacillin (MIC50: 1 μg/mL; MIC90: 2 μg/mL) but were mecA-positive. Twenty-one spa and 5 staphylococcal cassette chromosome mec (SCCmec) types were detected, and combined with multilocus sequence typing method, ST59-t437-SCCmecIV/V was the predominant clone (26.7%, 16/60).

Identification of Gene Clusters Associated with Host Adaptation and Antibiotic Resistance in Chinese Staphylococcus aureus Isolates by Microarray-Based Comparative Genomics

A comparative genomic microarray comprising 2,457 genes from two whole genomes of S. aureus was employed for the comparative genome hybridization analysis of 50 strains of divergent clonal lineages, including methicillin-resistant S. aureus (MRSA), methicillin-susceptible S. aureus (MSSA), and swine strains in China. Large-scale validation was confirmed via polymerase chain reaction in 160 representative clinical strains. All of the 50 strains were clustered into seven different complexes by phylogenetic tree analysis. Thirteen gene clusters were specific to different S. aureus clones. Ten gene clusters, including seven known (vSa3, vSa4, vSaα, vSaβ, Tn5801, and phage ϕSa3) and three novel (C8, C9, and C10) gene clusters, were specific to human MRSA. Notably, two global regulators, sarH2 and sarH3, at cluster C9 were specific to human MRSA, and plasmid pUB110 at cluster C10 was specific to swine MRSA. Three clusters known to be part of SCCmec, vSa4 or Tn5801, and vSaα as well as one novel gene cluster C12 with homology with Tn554 of S. epidermidis were identified as MRSA-specific gene clusters. The replacement of ST239-spa t037 with ST239-spa t030 in Beijing may be a result of its acquisition of vSa4, phage ϕSa1, and ϕSa3. In summary, thirteen critical gene clusters were identified to be contributors to the evolution of host specificity and antibiotic resistance in Chinese S. aureus.

Food-Animal Related Staphylococcus aureus Multidrug-Resistant ST9 Strains with Toxin Genes

To determine whether methicillin-susceptible S. aureus (MSSA) and methicillin-resistant Staphylococcus aureus (MRSA) are present in commercial pig farms and food products from supermarkets in China, we characterized S. aureus isolates from 250 samples associated with swine and animal-related food products in Shandong Province. The isolates were characterized by susceptibility testing, toxin gene detection, pulse-field gel electrophoresis (PFGE), multilocus sequence typing, and spa typing. MRSA were identified and typed by the staphylococcal cassette chromosome mec (SCCmec). The prevalence of S. aureus among all samples was 19.6% (49/250). MRSA and MSSA accounted for 16.7% (20/120) and 8.3% (10/120), respectively, of swine feces samples. Only MSSA was detected from swine carcass, pork, chicken, and raw milk, accounting for 15% (6/40), 10% (3/30), 20% (6/30), and 13.3% (4/30), respectively. The predominant MRSA clone was ST9-t899 SCCmecIVb/PFGE A (70.0%, 14/20). Among the MSSA isolates, ST9-t899/PFGE A was the most prevalent (27.6%), followed by ST15-t084 (17.2%), ST97-t2756 (10.3%), ST1-t127 (6.9%), and ST398-t899 (3.5%). Some lineages were found that are commonly detected in humans (e.g., ST1, ST5, ST7, ST59, ST88) or are human-specific (e.g., ST15). The toxin genes sec, seh, and enterotoxin gene cluster (egc) were significantly more prevalent among isolates of lineage ST9 (p<0.001) compared to other lineages, and the ST9 isolates were more resistant to erythromycin, clindamycin, ciprofloxacin, chloramphenicol, and gentamicin. The same lineage was identified from different sample types, indicating circulation of the related strains within the area of study. In conclusion, swine and food products of animal origin carried S. aureus, and the predominant ST9 clone possesses a multidrug-resistance profile and a high prevalence of sec, seh, and egc enterotoxin genes.

In vitro antimicrobial activity of the novel oxazolidinone tedizolid and comparator agents against Staphylococcus aureus and linezolid-resistant Gram-positive pathogens: a multicentre study in China

∗∗ Corresponding author. were recovered from lower respiratory tract infections. Of the 43 linezolid-resistant CoNS isolates, 42 (97.7%) were recovered ∗ Corresponding author. Present address: Room F816, IMCAS, 1st Beichen West Road, Chaoyang District, Beijing 100101, PR China. Tel.: +86 10 6480 7665; fax: +86 10 6480 7665. E-mail addresses: huanqindai@gmail.com (H. Dai), lzhang03@gmail.com (L. Zhang).