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SalmonellaCorvallis ST1541 has recently emerged as a globally disseminated pathogenic strain that often causes severe food-borne infections. Unlike most pandemic serotypes of Salmonella, the ST1541 strains harbored ColRNA1 plasmids that contain qnr-like determinants known to be responsible for the increasing incidence of ciprofloxacin-resistant food-borne Salmonellainfections. In this study, we conducted a genomic analysis of a global collection of 388 S.Corvallis ST1541 strains collected within a twenty-year period. We investigated the genetic characteristics of plasmid-mediated quinolone resistance (PMQR) plasmids harbored by these S.Corvallis strains, established a minimum spanning tree (MST) to determine the temporal and spatial distribution of the top 10 MST clusters, inferred a time-phylogenies for the major sub-lineages and traced the routes of international dissemination of this serotype strains. Bayesian algorithm predicted that UK might be the origin of S.Corvallis strains currently prevalent in various countries. This idea is supported by the observation of the emergence of intercontinental-disseminated clonal strains and extensive transmission of the extensive-drug resistance (XDR)-encoding plasmid pSA663. This study therefore provides valuable insight into the evolution of globally transmitted S.Corvallis strains and suggests a need to strengthen cooperation between different countries to control the dissemination of these drug-resistant bacteria.

•The study investigated the effects on antibiotic treatment on antibiotic resistant sub-population organisms in animal GI tract.•Antibiotic resistant organisms constituted a varied but significant proportion of the gut flora regardless of the degree of previous exposure to antibiotics.•The proportion of sub-population of resistant organisms varied according to the presence of antibiotic pressure.•Increase of ceftiofur-resistant subpopulation was mainly attributed to transmission of blaCTX-M-borne plasmids.

ABSTRACTThis report describes the first detection of a blaVEB-2gene in a Vibrio parahaemolyticusstrain isolated from a shrimp sample. The blaVEB-2gene was carried on a novel Inc-type plasmid that was likely to have originated from aquatic organisms, as indicated by a comparison with other known genetic elements in the GenBank database. However, the plasmid contains resistance elements usually harbored by members of the family Enterobacteriaceae, suggesting that gene transfer events occurred and contributed to the formation of this multidrug resistance-encoding plasmid.

ABSTRACTThis study reported and analyzed the complete sequences of two oqxAB-bearing IncHI2 plasmids harbored by a clinical Salmonella entericaserovar Typhimurium strain and an S. Indiana strain of animal origin, respectively. In particular, pA3T recovered from S. Indiana comprised the resistance determinants oqxAB, aac(6′)Ib-cr, fosA3, and blaCTX-M-14. Further genetic screening of 63 oqxAB-positive Salmonellaisolates revealed that the majority carried IncHI2 plasmids, confirming that such plasmids play a pivotal role in dissemination of oqxABin Salmonellaspp.

ABSTRACTThis study reports the increasing prevalence of clinical Escherichia coliof sequence type 167 (ST167) carrying both blaNDM-1and blaNDM-5on the conjugative IncX3 plasmid in various parts of China. Close surveillance is needed to monitor the future dissemination of ST167 strains that harbor blaNDM-5or other blaNDM-like genes.

ABSTRACTA total of 55 cefotaxime-resistant Escherichia coliisolates were obtained from retail meat products purchased in Shenzhen, China, during the period November 2012 to May 2013. Thirty-seven of these 55 isolates were found to harbor a blaCTX-Mgene, with the blaCTX-M-1group being the most common type. blaCMY-2was detected in 16 isolates, alone or in combination with other extended-spectrum β-lactamase (ESBL) determinants. Importantly, the fosA3gene, which encodes fosfomycin resistance, was detected in 12 isolates, with several being found to reside in the conjugative plasmid that harbored the blaCTX-Mgene. The insertion sequence IS26was observed upstream of some of the blaCTX-M-55and fosA3genes. Conjugation experiments showed that blaCTX-Mgenes from 15 isolates were transferrable, with Inc I1 and Inc FII being the most prevalent replicons. High clonal diversity was observed among the blaCTX-Mproducers, suggesting that horizontal transfer of the blaCTX-Mgenes among E. colistrains in retail meats is a common event and that such strains may constitute an important reservoir of blaCTX-Mgenes, which may be readily disseminated to other potential human pathogens.

ABSTRACTResistance to extended-spectrum β-lactams in Salmonella, in particular, in serotypes such as Salmonella entericaserovar Enteritidis that are frequently associated with clinical infections, is a serious public health concern. In this study, phenotypic characterization of 433 clinical S. Enteritidis strains obtained from a nationwide collection of the Chinese Center for Disease Control and Prevention during the period from 2005 to 2010 depicted a trend of increasing resistance to ceftriaxone from 2008 onwards. Seventeen (4%) of the strains were found to be resistant to ceftriaxone, 7% were found to be resistant to ciprofloxacin, and 0.7% were found to be resistant to both ciprofloxacin and ceftriaxone. Most of the ceftriaxone-resistant S. Enteritidis strains (15/17) were genetically unrelated and originated from Henan Province. The complete sequence of an IncI1 plasmid, pSE115, which belonged to a novel sequence type, was obtained. This 87,255-bp IncI1 plasmid was found to harbor a blaCTX-M-14gene in a novel multidrug resistance region (MRR) within the tralocus. Although the majority of strains were also found to contain conjugative IncI1 plasmids with a size similar to that of pSE115 (∼90 kb) and harbor a variety of blaCTX-Mgroup 1 and group 9 elements, the novel MRR site at the tralocus in pSE115 was not detectable in the other IncI1 plasmids. The findings from this study show that cephalosporin resistance in S. Enteritidis strains collected in China was mainly due to the dissemination of IncI1 plasmids carrying blaCTX-M, resembling the situation in which IncI1 plasmids serve as major vectors of blaCTX-Mvariants in other members of the Enterobacteriaceae.

•Carbapenem-resistant Pseudomonas aeruginosa, Pseudomonas putidaand Pseudomonas otitidiswere isolated from retail meats.•No acquired carbapenemase genes were detectable in these isolates.•Overexpression of efflux pumps was responsible for carbapenem resistance.•Loss of porins also played a role in carbapenem resistance.•The intrinsic metallo-β-lactamase blaPOMalso contributed to the decreased carbapenem susceptibility in P. otitidis.

ABSTRACTSalmonellainfection is an important public health issue for which the needs of antimicrobial treatment are increasing. A total of 546 human clinical S. entericaserovar Typhimurium isolates were recovered from patients in hospitals in China during the period of 2005 to ∼2011. Twenty percent of the isolates exhibited resistance to ciprofloxacin, and 4% were resistant to ceftriaxone. Importantly, for the first time, 12 (2%) S. Typhimurium isolates resistant to both ciprofloxacin and ceftriaxone were recovered; among these 12 isolates, two were also resistant to azithromycin, and one was resistant to all other drugs tested. The combined effects of various transferrable extended-spectrum β-lactamase determinants and a novel efflux-based ciprofloxacin resistance mechanism encoded by the mobile efflux gene oqxABwere responsible for the emergence of these extremely (highly) drug-resistant (XDR) S. Typhimurium isolates. The dissemination of resistance genes, such as those encoding ESBLs and the OqxAB pump, among Salmonellaorganisms will speed up the selection of XDR Salmonella, posing a huge threat to public health and Salmonellainfection control.

ABSTRACTWe report the emergence of five carbapenem-resistant K1 hypervirulent Klebsiella pneumoniae(hvKP) strains which caused fatal infections in hospital patients in Zhejiang Province, China, upon entry through surgical wounds. Genotyping results revealed the existence of three genetically related strains which exhibited a new sequence type, ST1797, and revealed that all strains harbored the magAand wcaGvirulence genes and a plasmid-borne blaKPC-2gene. These findings indicate that K1 hvKP is simultaneously hypervirulent, multidrug resistant, and transmissible.

ABSTRACTThe extended-spectrum-β-lactamase (ESBL) determinant CTX-M-55 is increasingly prevalent in Escherichia colibut remains extremely rare in Salmonella. This study reports the isolation of a plasmid harboring the blaCTX-M-55element in a clinical Salmonella entericaserotype Typhimurium strain resistant to multiple antibiotics. This plasmid is genetically identical to several known IncI2-type elements harbored by E. colistrains recovered from animals. This finding indicates that IncI2 plasmids harboring the blaCTX-Mgenes may undergo cross-species migration among potential bacterial pathogens, with E. colias the major source of such elements.

ABSTRACTThe nucleotide sequence of a self-transmissible plasmid pVPH1 harboring blaPER-1from Vibrio parahaemolyticuswas determined. pVPH1 was 183,730 bp in size and shared a backbone similar to pAQU1 and pAQU2, differing mainly in an ∼40-kb multidrug resistance (MDR) region. A complex class 1 integron was identified together with ISCR1and blaPER-1(ISCR1-blaPER-1-gst-abct-qacEΔ1-sul1), which was shown to form a circular intermediate playing an important role in the dissemination of blaPER-1.

This study reported the clonal dissemination of OXA-232-producing sequence type 15 (ST15) carbapenem-resistant Klebsiella pneumoniaeamong elderly patients in China. All patients were immunocompromised, suffered from multiple underlying diseases, and were hospitalized for a prolonged period; however, they slowly recovered on antimicrobial therapy.

Completed sequences of three plasmids from a carbapenem-resistant hypervirulent Klebsiella pneumoniaeisolate, SH9, were obtained. In addition to the pLVPK-like virulence-conferring plasmid (pVir-CR-HvKP_SH9), the two multidrug-resistant plasmids (pKPC-CR-HvKP4_SH9 and pCTX-M-CR-HvKP4_SH9) were predicted to originate from a single pKPC-CR-HvKP4-like multireplicon plasmid through homologous recombination.

ABSTRACTThis study reports the prevalences of qnrVCgenes in 74 ciprofloxacin-resistant Vibriosp. isolates. Two novel functional qnrVCalleles, qnrVC8and qnrVC9, sharing 98% and 99% nucleotide similarity with qnrVC6and qnrVC7, respectively, were identified. Our findings suggested that carriage of qnrVCalleles, together with target mutations in gyrAand parCgenes, may contribute to the development of fluoroquinolone resistance in Vibriospecies, posing a serious threat to public health.

ABSTRACTThis work investigated the molecular events driving the evolution of the CTX-M-type β-lactamases by the use of DNA shuffling of fragments of the blaCTX-M-14and blaCTX-M-15genes. Analysis of a total of 51 hybrid enzymes showed that enzymatic activity could be maintained in most cases, yet hybrids that were active possessed fewer amino acid substitutions than those that were inactive, suggesting that point mutations in the constructs rather than reshuffling of the fragments of the two target genes would more likely cause disruption of CTX-M activity. For example, the P67L and L261P changes in a CTX-M-14 fragment could completely abolish the activity of the enzyme on all antibiotics tested. Structural analysis showed that L216was located in the active-site β sheet and might interact with the adjacent hydrophobic residues to stabilize the active-site β sheet and maintain the integrity of the enzyme active site. Likewise, a single amino acid substitution, E64K, was found to exhibit a significant suppressive effect on CTX-M-15 activity. Structural analysis showed that E64might form a salt bridge with R44, disruption of which might affect CTX-M-15 activity. Further analysis of the structure-function relationship of a range of mutant enzymes confirmed that, as can be expected, unstable enzymes lose their activity and avoid selective events. These findings suggest that the distal pockets could also contribute to the activity of the enzymes and may be regarded as alternative targets for inhibitor development.