Genetic factors related to the widespread dissemination of ST11 extensively drug-resistant carbapenemase-producing Klebsiella pneumoniae strains within hospital / 中华医学杂志(英文版)

BACKGROUND@#Carbapenemase-producing Klebsiella pneumoniae (CP-Kp) poses distinct clinical challenges due to extensively drug resistant (XDR) phenotype, and sequence type (ST) 11 is the most dominant blaKPC-2-bearing CP-Kp clone in China. The purpose of this current retrospective study was to explore the genetic factors associated with the success of XDR CP-Kp ST11 strains circulated in the intensive care unit (ICU) of a Chinese tertiary hospital.@*METHODS@#Six ST11 XDR CP-Kp strains were identified between May and December 2014 and validated by minimum inhibitory concentration examination, polymerase chain reaction, and pyrosequencing. The six ST11 XDR CP-Kp, as well as three multi-drug resistant (MDR) and four susceptible strains, were sequenced using single-molecule real-time method. Comprehensively structural and functional analysis based on comparative genomics was performed to identify genomic characteristics of the XDR ST11 CP-Kp strains.@*RESULTS@#We found that ST11 XDR blaKPC-2-bearing CP-Kp strains isolated from inpatients spread in the ICU of the hospital. Functionally, genes associated with information storage and processing of the ST11 XDR CP-Kp strains were more abundant than those of MDR and susceptible strains, especially genes correlative with mobile genetic elements (MGEs) such as transposons and prophages. Structurally, eleven large-scale genetic regions taken for the unique genome in these ST11 XDR CP-Kp strains were identified as MGEs including transposons, integrons, prophages, genomic islands, and integrative and conjugative elements. Three of them were located on plasmids and eight on chromosomes; five of them were with antimicrobial resistance genes and eight with adaptation associated genes. Notably, a new blaKPC-2-bearing ΔΔTn1721-blaKPC-2 transposon, probably transposed and truncated from ΔTn1721-blaKPC-2 by IS903D and ISKpn8, was identified in all six ST11 XDR CP-Kp strains.@*CONCLUSION@#Our findings suggested that together with clonal spread, MGEs identified uniquely in the ST11 XDR CP-Kp strains might contribute to their formidable adaptability, which facilitated their widespread dissemination in hospital.

Serological and molecular capsular typing, antibiotic susceptibility and multilocus sequence typing of Streptococcus pneumoniae isolates from invasive and non-invasive infections / 中华医学杂志(英文版)

<p><b>BACKGROUND</b>Streptococcus pneumoniae (S. pneumoniae) is a major causative agent of severe infections, including sepsis, pneumonia, meningitis, and otitis media, and has become a major public health concern. We report the pneumococcal serotype and sequence type (ST) distribution, and antimicrobial resistance of 39 S. pneumoniae strains from seven hospitals in China.</p><p><b>METHODS</b>Blood/cerebrospinal fluid (CSF) and sputum isolates from patients were analyzed to determine S. pneumoniae serotypes by polymerase chain reaction (PCR) and the Neufeld Quellung reaction, the multilocus sequence types (MLST) by PCR and sequencing, and susceptibility to antimicrobial agents by the VITEK Gram Positive Susceptibility Card.</p><p><b>RESULTS</b>A total of 39 isolates were collected including 21 blood/CSF and 18 sputum isolates. Conventional serotyping by the Quellung reaction required 749 reactions. In contrast, PCR based typing needed only 106 PCR reactions. The most frequent serotypes from the blood/CSF isolates were 14 (38.1%), 19A (14.3%), 23F (9.5%), and 18C (9.5%). In the sputum isolates the most frequent serotypes were 19F (33.3%), 23F (16.7%), 19A (11.1%), and 3 (11.1%). The incidence of penicillin resistance in the blood/CSF and sputum isolates was 66.7% and 55.6%, respectively. Statistical analysis showed that patients = 5 years old had a higher resistance to penicillin when they compared with the patients = 65 years old (P = 0.011). Serotypes 14, 19A and 19F were significantly associated with penicillin resistance (P < 0.001). ST320, ST271, and ST876 isolates showed high resistant rates to several antibiotics including penicillin (P = 0.006). All of the isolates of serotype 19A were resistant to both penicillin and erythromycin, and they were all multi-drug resistant (MDR) isolates.</p><p><b>CONCLUSIONS</b>The specificity and sensitivity of multiplex-PCR are good, and this method represents a substantial savings of time and money, and can be widely used in the laboratory and clinical practice. Data from this research showed an extremely high prevalence of penicillin resistance and an increasing prevalence of multi-drug resistant (MDR) rate in S. pneumoniae. A distinctive emergence of serotype 19A was observed which was also associated with the increasing prevalence of antimicrobial resistance. Therefore, nationwide surveillance of pneumococcal resistance and serotypes is strongly warranted.</p>

Drug-resistant genes carried by Acinetobacter baumanii isolated from patients with lower respiratory tract infection / 中华医学杂志(英文版)

<p><b>BACKGROUND</b>Acinetobacter baumanii (A. baumanii ) remains an important microbial pathogen resulting in nosocomial acquired infections with significant morbidity and mortality. The mechanism by which nosocomial bacteria, like A. baumanii, attain multidrug resistance to antibiotics is of considerable interest. The aim in this study was to investigate the spread status of antibiotic resistance genes, such as multiple β-lactamase genes and aminoglycoside-modifying enzyme genes, from A. baumanii strains isolated from patients with lower respiratory tract infections (LRTIs).</p><p><b>METHODS</b>Two thousand six hundred and ninety-eight sputum or the bronchoalveolar lavage samples from inpatients with LRTIs were collected in 21 hospitals in the mainland of China from November 2007 to February 2009. All samples were routinely inoculated. The isolated bacterial strains and their susceptibility were analyzed via VITEK-2 expert system. Several kinds of antibiotic resistant genes were further differentiated via polymerase chain reaction and sequencing methods.</p><p><b>RESULTS</b>Totally, 39 A. baumanii strains were isolated from 2698 sputum or bronchoalveolar lavage samples. There was not only a high resistant rate of the isolated A. baumanii strains to ampicillin and first- and second-generation cephalosporins (94.87%, 100% and 97.44%, respectively), but also to the third-generation cephalosporins (ceftriaxone at 92.31%, ceftazidine at 51.28%) and imipenem (43.59%) as well. The lowest antibiotic resistance rate of 20.51% was found to amikacin. The OXA-23 gene was identified in 17 strains of A. baumanii, and the AmpC gene in 23 strains. The TEM-1 gene was carried in 15 strains. PER-1 and SHV-2 genes were detected in two different strains. Aminoglycoside-modifying enzyme gene aac-3-Ia was found in 23 strains, and the aac-6'-Ib gene in 19 strains. aac-3-Ia and aac-6'-Ib genes hibernated in three A. baumanii strains that showed no drug-resistant phenotype.</p><p><b>CONCLUSIONS</b>A. baumanii can carry multiple drug-resistant genes at the same time and result in multi-drug resistance. Aminoglycoside-modifying enzyme genes could be hibernating in aminoglycoside sensitive strains without expressing their phenotype.</p>