Dissemination of Multidrug-Resistant Shigella flexneri and Shigella sonnei with Class 1, Class 2, and Atypical Class 1 Integrons in China.

Background: Emergence of multidrug-resistant Shigella, a major causative agent of bacterial dysentery, has generated many concerns not only in China but also worldwide. However, the prevalence of Shigella resistance caused by integron in the nonpopular season of diarrhea is not clear. Materials and Methods: Thirty-one Shigella flexneri and 22 Shigella sonnei samples collected in December 2010 from 10 cities of China were characterized for antimicrobial susceptibility, gene cassettes, widespread of integrons, and pulsed-field gel electrophoresis (PFGE) profile. Results: Multidrug resistance (MDR) was detected in 29 (93.5%) S. flexneri and 20 (90.9%) S. sonnei isolates. Class 1 integrons were detected in 25 (80.6%) S. flexneri and in 13 (59.1%) S. sonnei isolates; class 2 integrons were detected in 26 (83.9%) S. flexneri and in 19 (86.4%) S. sonnei isolates. Interestingly, the atypical class 1 integrons were mostly detected in S. flexneri (45.2%) isolates, whereas in only 1 (4.5%) S. sonnei isolate. DNA sequencing revealed two novel cassette arrays, dfrA5 and aacA4-cmlA, of class 1 integrons in S. flexneri, and dfrA17-aadA5 in S. sonnei isolates. The cassette arrays, dfrA1-sat1-aadA1 of class 2 integron and blaoxa-30-aadA1 of atypical class 1 integron, were also identified. PFGE profiles demonstrated A6 subtype of S. flexneri strains prevalent in Shanghai, Changchun, Jinan, and Changsha; and F6 subtype of S. sonnei prevalent in Jinan, Changchun, and Shanghai. Conclusion: The dissemination of MDR Shigella strains with integrons makes it an increasing public health problem in China. Increased surveillance and the development of adequate prevention strategies are warranted.

Clonal dissemination of KPC-2-producing Klebsiella pneumoniae ST11 and ST48 clone among multiple departments in a tertiary teaching hospital in Jiangsu Province, China.

BACKGROUND: The world-wide prevalence of carbapenem-resistant Klebsiella pneumoniae (CRKP) poses a threat to the public health. The objective of this study was to determine the epidemiological and molecular patterns of KPC-producing Klebsiella pneumoniae (K. pneumoniae) clinical isolates. METHODS: In this study, a total of 82 non-duplicated CRKP isolates were analyzed for the prevalence of resistant determinants including carbapenemase, extended spectrum ß-lactamase (ESBLs), and AmpC as well as integrons and cassette regions by polymerase chain reaction (PCR) and DNA sequencing. The genetic relatedness was investigated by pulsed field gel electrophoresis (PFGE) and multi-locus sequencing typing (MLST). RESULTS: Overall, bla KPC-2 (n=75) was the predominant carbapenemase gene, followed by high prevalence of bla SHV (92.7%) and bla CTX-M (90.2%). PFGE and MLST analysis revealed that 65 out of 68 KPC-2-producing CRKP belonged to the ST11 clone and were distributed mainly in the department of neurology ICU. Moreover, first report on clonal dissemination of KPC-2-producing CRKP ST48 clone and NDM-5-producing CRKP ST337 clone was also identified. Class I integron were detected in 17 (20.7%) of 82 isolates with aadA2 being the most common cassette. And a novel cassette array of integron, aac(6')-II-bla CARB/PSE-1 was identified. CONCLUSIONS: All in all, KPC-2-producing CRKP ST11 and ST48 clone were widely disseminated in multiple departments of our hospital, which triggers the need for active surveillance and implementation of infection control measures.

High Prevalence of bla NDM Variants Among Carbapenem-Resistant Escherichia coli in Northern Jiangsu Province, China.

The continuous emergence of carbapenem-resistant Escherichia coli (CRECO) presents a great challenge to public health. New Delhi metallo-lactamase (NDM) variants are widely disseminated in China, so the research on the prevalence and transmission of diverse bla NDM variants is urgently needed. In the present study, 54 CRECO isolates were collected from 1,185 Escherichia coli isolates in five hospitals in Northern Jiangsu Province, China from September 2015 to August 2016. Antimicrobial susceptibility tests, PCR detection of resistance determinants, multi-locus sequence typing (MLST) and pulsed-field gel electrophoresis (PFGE) were performed to characterize these strains. Plasmid conjugation experiments were carried out to determine the transferability of resistant genes from selected isolates. PCR-based replicon typing (PBRT), S1 nuclease-PFGE, and Southern blotting were conducted for plasmid profiling. Carbapenemase genes were detectable in all CRECO isolates, among which thirty-one CRECO isolates were found to carry bla NDM-5 (54.7%), while, bla NDM-1, bla NDM-7, bla NDM-4, bla NDM-9, and bla KPC-2 were identified in 14, five, two, one, and one isolates, respectively. MLST results revealed 15 different STs and four new STs were first reported to be linked with NDM-producing isolates. PFGE typing showed that no more than two isolates with the same ST appeared to the same band pattern except three ST410 isolates. Twenty-six selected NDM-producing isolates were successfully transferred to E. coli J53 by conjugation experiments. Notably, 50.0% (13/26) of blaNDM variants were found to be carried by ~55 kb IncX3 plasmid. Our study reported a high prevalence of blaNDM variants, especially bla NDM-5, in Northern Jiangsu province, China. Diverse bla NDM variants were mainly carried by ~55 kb IncX3 plasmids, suggesting that the fast evolution and high transferability of this kind of plasmid promote the high prevalence of bla NDM variants. Therefore, large-scale surveillance and effective infection control measures are also urgently needed to prevent diverse bla NDM variants from becoming epidemic in the future.

Virulence-associated genes and molecular characteristics of non-O1/non-O139 Vibrio cholerae isolated from hepatitis B cirrhosis patients in China.

OBJECTIVES: We aimed to report virulence-associated genes and molecular characteristics of non-O1/non-O139 Vibrio cholerae isolated from hepatitis B cirrhosis patients in China. METHODS: Patient clinical data including course of disease, laboratory tests, antibiotic treatment and outcomes were collected. Antimicrobial susceptibility testing was performed and virulence-associated genes were detected by PCR. Genetic relatedness among non-O1/non-O139 V. cholerae strains was investigated by pulsed field gel electrophoresis (PFGE) and multilocus sequence typing (MLST). RESULTS: All three strains in this study harbored pathogenicity related genes like rtxA, rtxC, toxR, hapA, hlyA and ompW whereas they lacked ctxA, ctxB, tcpA, ompU and zot genes. None of them showed resistance to any antibiotic detected. A new allele of gyrB was submitted to the MLST database and designated as 97. Two novel sequence types (ST518 and ST519) and ST271 were identified by multilocus sequence typing (MLST). PFGE indicated considerable diversity among three non-O1/non-O139 V. cholerae strains. CONCLUSIONS: Three sporadic cases highlight that non-O1/non-O139 V. cholerae can cause opportunistic invasiveness infection in cirrhosis patients. Pathogenicity may be related to virulence-associated genes. Timely detection and antibiotic therapy should be paid more attention to in clinic.

The emerging problem of linezolid-resistant enterococci.

Enterococcus is a significant pathogen in numerous infections, particularly in nosocomial infections, and is thus a great challenge to clinicians. Linezolid (LNZ), an oxazolidinone antibiotic, is an important therapeutic option for infections caused by Gram-positive bacterial pathogens, especially vancomycin-resistant enterococci. A systematic review was performed of the available literature on LNZ-resistant enterococci (LRE) to characterise these infections with respect to epidemiological, microbiological and clinical features. The results validated the potency of LNZ against enterococcal infections, with a sustained susceptibility rate of 99.8% in ZAAPS and 99.2% in LEADER surveillance programmes. Patients with LRE had been predominantly exposed to LNZ prior to isolation of LRE, with a mean treatment duration of 29.8±48.8days for Enterococcus faecalis and 23.1±21.4days for Enterococcus faecium. Paradoxically, LRE could also develop in patients without prior LNZ exposure. LNZ resistance was attributed to 23S rRNA (G2576T) mutations (51.2% of E. faecalis and 80.5% of E. faecium) as well as presence of the cfr gene (4.7% and 4.8%, respectively), which could transfer horizontally among the strains. In addition to the cfr gene, 32 cases of optrA-positive LRE were identified. Further study is required to determine the prevalence of novel resistance genes. The emergence of LRE thus hampers the treatment of such infections, which warrants worldwide surveillance.

Novel mutations in gyrA and parC among Shigella sonnei strains from Jiangsu Province of China, 2002-2011.

BACKGROUND: To investigate fluoroquinolone resistance and associated mechanisms of Shigella sonnei isolates in Jiangsu Province of China between 2002 and 2011. METHODS: All 337 unduplicated S. sonnei isolates were collected from hospitals in Jiangsu Province from January 2002 to December 2011. Fluoroquinolone susceptibility was characterized by Kirby-Bauer disk diffusion method, and direct nucleotide sequencing of genes of the quinolone resistance determining regions were conducted. Also, the transferable quinolone resistance determinants, including qnrA, qnrB, qnrC, qnrD, qnrS, aac-(6')-Ib-cr and qepA were amplified by PCR. RESULTS: Among 950 Shigella isolates, 337 (35.5%) were identified as S. sonnei, of which 76.6% displayed nalidixic acid resistance and norfloxacin-resistant isolates appeared in 2005-2009, with an average resistance rate of 21.8%. Commonly reported point mutations of Ser83Leu and Asp87Asn/Gly in gyrA and Ser80Ile in parC were detected, with mutation rates of 78.0%, 9.5% and 30.3%, respectively, while no alteration in gyrB or parE were detected. Besides, His211Tyr mutation in gyrA was first reported in a S. sonnei strain in 2009 and two novel mutations in parC were found, of which Met86Trp occurred in another strain in 2009 and Ser129Pro appeared every year except 2011 (28.8%). Plasmid-mediated quinolone resistance determinants were found in 23 isolates and 19 of these isolates were resistant to both nalidixic acid and norfloxacin. qnrB, qnrS, aac-(6')-Ib-cr and qepA were detected in 1, 7, 14 and 2 S. sonnei strains, relatively, and the most abundant PMQR gene found in this work was aac-(6')-Ib-cr (4.2%). INTERPRETATION & CONCLUSIONS: S. sonnei became increasingly important as fluoroquinolone-resistant isolates emerged, and further detection on the resistant genes would be useful in the treatment and control of this infection.