Feifei Zhang

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.

Emergence of a hypervirulent carbapenem-resistant Klebsiella pneumoniae isolate from clinical infections in China

OBJECTIVESnHypervirulent Klebsiella pneumoniae (hvKP) infections occur worldwide, but carbapenem-resistant hvKP strain has rarely been observed.nnnMETHODSnA retrospective study was conducted in 28 cases of carbapenem-resistant K. pneumoniae (CRKP) infections from 9 cities in China. Clinical data were collected from medical records. All the isolates were characterized by antimicrobial susceptibility testing, string test, multilocus sequence typing, and capsular genotyping. All the hypermucoviscous CRKP strains were analyzed by virulence gene profiles, serum killing assay, and mouse lethality assay.nnnRESULTSnOf 28 CRKP isolates, five were positive for string test. Importantly, one of the hypermucoviscous strains isolated from blood sample was identified as hvKP. The hypervirulent CRKP strain showed highly resistant to carbapenems (MICxa0>xa032xa0μg/mL), decreased expression of ompK35/36, and ESBLs production. Significantly increased resistance to serum killing and mice mortality were found in the hypervirulent CRKP strain compared to the other CRKPs. Capsular polysaccharide synthesis genotyping revealed that the hypervirulent strain belongs to K2 serotype, while others belong to K-nontypable serotype. The K2 hypervirulent CRKP strain carried rmpA, aerobactin, entB, and mrkD genes.nnnCONCLUSIONSnThe newly emerged hypervirulent carbapenem-resistant K. pneumoniae might cause a serious threat to public health, suggesting an urgent need to enhance clinical awareness and epidemiologic surveillance.

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.

High prevalence of hypervirulent Klebsiella pneumoniae infection in China: geographic distribution, clinical characteristics and antimicrobial resistance

ABSTRACT Hypervirulent Klebsiella pneumoniae (hvKP) is traditionally defined by hypermucoviscosity, but data based on genetic background are limited. Antimicrobial-resistant hvKP has been increasingly reported but has not yet been systematically studied. K. pneumoniae isolates from bloodstream infections, hospital-acquired pneumonia, and intra-abdominal infections were collected from 10 cities in China during February to July 2013. Clinical data were collected from medical records. All K. pneumoniae isolates were investigated by antimicrobial susceptibility testing, string test, extended-spectrum β-lactamase (ESBL) gene detection, capsular serotypes, virulence gene profiles, and multilocus sequence typing. hvKP was defined by aerobactin detection. Of 230 K. pneumoniae isolates, 37.8% were hvKP. The prevalence of hvKP varied among different cities, with the highest rate in Wuhan (73.9%) and the lowest in Zhejiang (8.3%). Hypermucoviscosity and the presence of K1, K2, K20, and rmpA genes were strongly associated with hvKP (P < 0.001). A significantly higher incidence of liver abscess (P = 0.026), sepsis (P = 0.038), and invasive infections (P = 0.043) was caused by hvKP. Cancer (odds ratio [OR], 2.285) and diabetes mellitus (OR, 2.256) appeared to be independent variables associated with hvKP infections by multivariate analysis. Importantly, 12.6% of hvKP isolates produced ESBLs, and most of them carried blaCTX-M genes. Patients with neutropenia (37.5% versus 5.6%; P = 0.020), history of systemic steroid therapy (37.5% versus 5.6%; P = 0.020), and combination therapy (62.5% versus 16.7%; P = 0.009) were more likely to be infected with ESBL-producing hvKP. The prevalence of hvKP is high in China and has a varied geographic distribution. ESBL-producing hvKP is emerging, suggesting an urgent need to enhance clinical awareness, especially for immunocompromised patients receiving combination therapy.

Phenotypic and Genotypic Characteristic of Invasive Pneumococcal Isolates from Both Children and Adult Patients from a Multicenter Surveillance in China 2005–2011

Streptococcus pneumoniae is an important pathogen in both children and the elderly, but previous studies in China have provided limited information about invasive pneumococcal disease (IPD). A total of 240 IPD S. pneumoniae strains (from 105 children and 135 adults) were collected from 12 cities in China in 2005–2011. Their phenotypes and genetic characteristics were analyzed. Streptococcus pneumoniae remained highly resistant to macrolides, tetracycline, and cotrimoxazole each year. Serotypes were assigned to the 240 isolates, and 19A (22.1%), 19F (21.7%), 14 (7.5%), 3 (7.1%), and 23F (5.4%) were the most prevalent, accounting for 63.8% of all strains. Serogroup 19 strains were significantly more common among children than among adults (58.7% vs 32.4%, respectively; P < 0.001). Serotypes 19F and 19A demonstrated higher resistance to β-lactams and cephalosporins than the other serotypes. The coverage of PCV13 was superior to that calculated for PCV7 and PCV10 (77.9% vs 40.8% and 47.1%, respectively), and coverage was higher in children than in adults (85.6% vs 72.1%, respectively; P = 0.012). A multilocus sequence typing analysis revealed great diversity, with nine clonal complexes and 83 singletons among all the strains. Specifically, CC271 was more common in children, whereas singletons were more prevalent in adults. Among the serogroup 19 strains, 84.7% were ST271, ST320, or ST236, belonging to CC271. The homogeneous genetic background of 19F and 19A, together with the high resistance of these strains, suggests that clonal spread is responsible for the high prevalence of serogroup 19 in IPD. This is the first large study to investigate IPD strains in both children and adults in China.

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.

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).

Evolution of Carbapenem-Resistant Acinetobacter baumannii Revealed through Whole-Genome Sequencing and Comparative Genomic Analysis

ABSTRACT Acinetobacter baumannii is a globally important nosocomial pathogen characterized by an evolving multidrug resistance. A total of 35 representative clinical A. baumannii strains isolated from 13 hospitals in nine cities in China from 1999 to 2011, including 32 carbapenem-resistant and 3 carbapenem-susceptible A. baumannii strains, were selected for whole-genome sequencing and comparative genomic analysis. Phylogenetic analysis revealed that the earliest strain, strain 1999BJAB11, and two strains isolated in Zhejiang Province in 2004 were the founder strains of carbapenem-resistant A. baumannii. Ten types of AbaR resistance islands were identified, and a previously unreported AbaR island, which comprised a two-component response regulator, resistance-related proteins, and RND efflux system proteins, was identified in two strains isolated in Zhejiang in 2004. Multiple transposons or insertion sequences (ISs) existed in each strain, and these gradually tended to diversify with evolution. Some of these IS elements or transposons were the first to be reported, and most of them were mainly found in strains from two provinces. Genome feature analysis illustrated diversified resistance genes, surface polysaccharides, and a restriction-modification system, even in strains that were phylogenetically and epidemiologically very closely related. IS-mediated deletions were identified in the type VI secretion system region, the csuE region, and core lipooligosaccharide (LOS) loci. Recombination occurred in the heme utilization region, and intrinsic resistance genes (blaADC and blaOXA-51-like variants) and three novel blaOXA-51-like variants (blaOXA-424, blaOXA-425, and blaOXA-426) were identified. Our results could improve the understanding of the evolutionary processes that contribute to the emergence of carbapenem-resistant A. baumannii strains and help elucidate the molecular evolutionary mechanism in A. baumannii.

Comparative Proteomics-Based Identification of Genes Associated with Glycopeptide Resistance in Clinically Derived Heterogeneous Vancomycin-Intermediate Staphylococcus aureus Strains

Heterogeneous vancomycin-intermediate Staphylococcus aureus (hVISA) is associated with clinical treatment failure. However, the resistance mechanism of hVISA has not been fully clarified. In the present study, comparative proteomics analysis of two pairs of isogenic vancomycin-susceptible S. aureus (VSSA) and hVISA strains isolated from two patients identified five differentially expressed proteins, IsaA, MsrA2, Asp23, GpmA, and AhpC, present in both isolate pairs. All the proteins were up-regulated in the hVISA strains. These proteins were analyzed in six pairs of isogenic VSSA and hVISA strains, and unrelated VSSA (nu200a=u200a30) and hVISA (nu200a=u200a24) by real-time quantitative reverse transcriptase–PCR (qRT–PCR). Of the six pairs of isogenic strains, isaA, msrA2 and ahpC were up-regulated in all six hVISA strains; whereas asp23 and gpmA were up-regulated in five hVISA strains compared with the VSSA parental strains. In the unrelated strains, statistical analyses showed that only isaA was significantly up-regulated in the hVISA strains. Analysis of the five differentially expressed proteins in 15 pairs of persistent VSSA strains by qRT–PCR showed no differences in the expression of the five genes among the persistent strains, suggesting that these genes are not associated with persistence infection. Our results indicate that increased expression of isaA may be related to hVISA resistance.