ObjectiveTo investigate CTX-M genotypes among extended-spectrum β-lactamase-producing Escherichia coli (ESBL-EC) isolated from patients with community-onset and hospital-onset infections in China, their clonality and the distribution of CTX-M variants in different specimens of community-onset and hospital-onset infections.MethodsESBL-EC isolates were collected from general hospitals from 2011 to 2012 in China. Broth microdilution method antimicrobial susceptibility testing of 16 antibiotics was performed. Clinical data from community-onset and hospital-onset infections due to ESBL-EC were analyzed. ESBL-encoding genes were amplified by PCR and sequenced, and multilocus sequence typing (MLST) was performed for a random selection of predominant CTX-M type strains identified.ResultsA total of 1,168 ESBL-EC isolates were obtained from various clinical specimens, 41.7% of which were responsible for causing community-onset infections. The presence of urinary calculi was higher in community-onset infections, whereas malignancy, cardiovascular and cerebrovascular diseases, dementia, chronic renal disease, diabetes mellitus and surgical treatment were found to have higher proportions in hospital-onset infections. There was no significant difference in trauma between community-onset and hospital-onset infections. 96.2% of the isolates were detected to harbor bla CTX-M genes. bla CTX-M-1 group and bla CTX-M-9 group were detected at 40.7% and 48.7% respectively, and both positive group accounted for 10.6%. bla CTX-M-55 (24.8%) and bla CTX-M-15 (18.2%) were the major genotypes in bla CTX-M-1 group while bla CTX-M-14 (46.8%) was predominant in bla CTX-M-9 group. A comparison of bla CTX-M distribution in different specimens between ESBL-EC causing community-onset and hospital-onset infection showed no significant difference. A total of 229 isolates were tested for MLST. ST131 (14%) was the predominant type. ST648, ST405 and ST1193 were also detected.ConclusionsCommunity-onset ESBL-EC has emerged as a common pathogen in China. CTX-M-14 is the most commonly encountered, CTX-M-55 and CTX-M-15 have spread rapidly. ST131 is the predominant clonal group, and the great diversity of CTX-M-producing isolates of E. coli has emerged in China.

Methicillin-resistant Staphylococcus aureus (MRSA) is a significant cause of hospital-associated pneumonia (HAP). The rapid identification of MRSA would be beneficial for early diagnosis. The study aimed to evaluate a multilocus, fluorescence-based PCR assay based on the detection of mecA and nuc genes for identification of S. aureusin lower respiratory tract (LRT) specimens. Sensitivity and specificity of the PCR assay were analyzed. Clinical evaluation for the assay was performed using LRT specimens from patients with HAP, and the sensitivity, specificity, positive and negative predictive values (PPV and NPV) were evaluated in comparison with semi-quantitative culture methods. The result showed the assay provided positive identification of all MRSA reference strains with a limit of detection for MRSA of 4 × 103 CFU/mL. Compared with semi-quantitative culture, the sensitivity, specificity, PPV and NPV were 100%, 89.6%, 75.0%, and 100%, respectively. A positive correlation between MRSA bacterial colonies and PCR copy number was found. The specificity and PPV reached 96.6% and 89.7% respectively, if the PCR copy number reached a definite positive threshold of 5.96 × 105. It suggested that this novel multilocus, fluorescence-based PCR assay proved to be a fast, sensitive and specific tool for direct detection of MRSA from LRT specimens.