Epidemiology and molecular characterization of carbapenem-resistant Klebsiella pneumoniae isolated from neonatal intensive care units in General Hospital of Ningxia Medical University, China, 2017-2021

OBJECTIVES

This study aimed to retrospectively investigate the epidemiology and molecular characteristics of carbapenem-resistant Klebsiella pneumoniae (CRKP) isolates from neonatal intensive care units (NICU) between 2017 and 2021.

METHODS

The antibacterial susceptibility of all strains was assessed using the VITEK 2 compact system. The presence of antibiotic resistance, virulence genes, sequence types (STs), capsular (K) types, and the wzi genes was determined through polymerase chain reaction (PCR). Molecular typing was performed by pulsed-field gel electrophoresis (PFGE) using the restriction enzyme XbaI. Additionally, the virulence potential of peg344-positive strains was evaluated using the string test and mouse intraperitoneal infection models. Whole-genome sequencing was conducted on the DNB system and PacBio platforms.

RESULTS

A total of 46 CRKP isolates were collected during the study period. Out of these, 93.47% (43/46) were identified as CRKP strains belonging to the ST76-K10 type carrying blaNDM-5. It was observed that CRKP infection resulted in more severe clinical symptoms compared to CRKP colonization. Among the CRKP strains, a hypervirulent CRKP strain called KP-63, belonging to the ST23 type, was identified. This strain exhibited high mortality in the mouse infection model and was found to possess virulence genes. Genomic alignment analysis revealed a significant similarity between the virulence plasmid from KP-63 strain (pKP-63) and pK2044 from the hypervirulent K. pneumoniae strain NTUH-2044.

CONCLUSIONS

There has been a potential dissemination of ST76-K10 type CRKP carrying blaNDM-5 in the NICU at Ningxia Hospital. Neonatal CRKP infection has been found to cause more severe clinical symptoms than colonization. Furthermore, we have discovered a CR-hvKP strain of ST23 with serotype K1, which exhibits a significant resemblance in its virulent plasmid to pK2044. Therefore, it is crucial to enforce effective measures to restrict the spread and hinder the evolution of CRKP within the hospital.

Genomic epidemiology of hypervirulent carbapenem-resistant Klebsiella pneumoniae at Jinshan local hospital, Shanghai, during 2014-2018

BACKGROUND

Hypervirulent carbapenem-resistant Klebsiella pneumoniae (Hv-CRKP) triggered a significant public health challenge. This study explored the prevalence trends and key genetic characteristics of Hv-CRKP in one Shanghai suburbs hospital during 2014-2018.

METHODS

During five years, Hv-CRKP strains identified from 2579 CRKP by specific PCR, were subjected to performed short- and long-read sequencing technology; epidemiological characteristics, antimicrobial-resistance genes (ARGs), virulence determinants, detailed plasmid profiles and conjugation efficiency were comprehensively investigated.

RESULTS

155 Hv-CRKP and 31 non-Hv-CRKP strains were sequenced. Hv-CRKP strains exhibited significant resistance to six common antibiotic classes (>92%). ST11 steadily increased and became the most prevalent ST (85.2%), followed by ST15 (8.5%), ST65 (2.6%), ST23 (1.9%), and ST86 (0.6%). ST11-KL64 (65.2%) rapidly increased from 0 in 2014 to 93.9% in 2018. blaKPC-2 was the primary carbapenemase gene (97.4%). Other ARGs switched from aac(3)-IId to aadA2 in aminoglycoside and from sul1 to sul2 in sulfanilamide. The time-dated phylogenetic tree was divided into four independent evolutionary clades. Clade 1 and 3 strains were mostly limited in the ICU, whereas Clade 2 strains were distributed among multiple departments. Compared to ybt14 in ICEKp12 in Clade 1, Clade 3 strains harbored ybt9 in ICEKp3 and blaCTX-M-65. Hv-CRKP infected more wards than non-Hv-CRKP and showed greater transmission capacity. Three plasmids containing crucial carbapenemase genes demonstrated their early transmission across China.

CONCLUSION

The Hv-CRKP ST11-KL64 has rapidly replaced ST11-KL47 and emerged as the predominant epidemic subtype in various hospital wards, highlighting the importance of conducting comprehensive early surveillance for Hv-CRKP, especially in respiratory infections.

Short review: Geographical distribution of equine-associated pVAPA plasmids in Rhodococcus equi in the world

Virulent Rhodococcus equi strains expressing virulence-associated 15-17 kDa protein (VapA) and having a large virulence plasmid (pVAPA) of 85-90 kb containing vapA gene are pathogenic for horses. In the last two decades, following pVAPA, two host-associated virulence plasmid types of R. equi have been discovered: a circular plasmid, pVAPB, associated with porcine isolates in 1995, and a recently detected linear plasmid, pVAPN, related to bovine and caprine isolates. Molecular epidemiological studies of R. equi infection in foals on horse-breeding farms in Japan and many countries around the world have been conducted in the last three decades, and the epidemiological studies using restriction enzyme digestion patterns of plasmid DNAs from virulent isolates have shown 14 distinct pVAPA subtypes and their geographical preference. This short review summarizes previous reports regarding equine-associated pVAPA subtypes in the world and discusses their geographic distribution from the standpoint of horse movements.

Whole genome sequence of carbapenem-resistant hypermucoviscous Klebsiella pneumoniae K2-ST375 with blaNDM-harbouring conjugative IncX3 and pLVPK-like virulence plasmids from a patient in China

OBJECTIVES

Carbapenem-resistant hypermucoviscous Klebsiella pneumoniae (CR-HMKP) poses unprecedented public health challenges. However, genomic information regarding the CR-HMKP K2-ST375 strain is scarce. The aim of this study was to characterize the whole genome sequence of the CR-HMKP K2-ST375 strain Kp0179 isolated from a male patient in China.

METHODS

The whole genome of Kp0179 was sequenced using the DNBSEQ and Pacific Biosciences RSII platforms. The capsular serotype, multilocus sequence typing (MLST), antimicrobial resistance genes, and virulence factors were determined using available databases and bioinformatics tools. Conjugation experiments were performed using rifampicin-resistant Escherichia coli C600 as the recipient.

RESULTS

The Kp0179 strain with hypermucoviscous phenotype was resistant to almost all β-lactams, including ertapenem and imipenem. Whole genome sequencing revealed that Kp0179 belonged to K2-ST375 and contained blaNDM-IncX3 and a virulence plasmid ca. 121 kb. Kp0179 contained 5146 coding genes, 88 tRNAs, 25 rRNAs and 38 non-coding RNA genes. Among the six acquired antibiotic resistance genes, blaSHV-99, fosA, oqxAB were located on the chromosome, whereas blaNDM-1, qnrS1 and blaSHV-12 were located on the conjugative plasmid pNDM-Kp0179 (IncX3 type). Virulence gene analysis indicated that pLVPK-Kp0179 carried multiple virulence-encoding genes, such as iroBCDN, iucABCDiutA, rmpA and rmpA2. In addition to carrying a virulence plasmid, capsule formation (kvgA) and the type 3 fimbriae operon (mrkABCDFHIJ) were located on the chromosome of Kp0179.

CONCLUSION

To our knowledge, this is the first report of a CR-HMKP K2-ST375 strain with a blaNDM-harboured conjugative IncX3 plasmid and a pLVPK-like virulence plasmid from a patient in China. Therefore, the spread of CR-HMKP K2-ST375 isolates in China should be closely monitored.

Modeling gastrointestinal anthrax disease

Bacillus anthracis is a spore-forming microbe that persists in soil and causes anthrax disease. The most natural route of infection is ingestion by grazing animals. Gastrointestinal (GI) anthrax also occurs in their monogastric predators, including humans. Exposure of carcasses to oxygen triggers sporulation and contamination of the surrounding soil completing the unusual life cycle of this microbe. The pathogenesis of GI anthrax is poorly characterized. Here, we use B. anthracis carrying the virulence plasmids pXO1 and pXO2, to model gastrointestinal disease in Guinea pigs and mice. We find that spores germinate in the GI tract and precipitate disease in a dose-dependent manner. Inoculation of vegetative bacilli also results in GI anthrax. Virulence is impacted severely by the loss of capsule (pXO2-encoded) but only moderately in absence of toxins (pXO1-encoded). Nonetheless, the lack of toxins leads to reduced bacterial replication in infected hosts. B. cereus Elc4, a strain isolated from a fatal case of inhalational anthrax-like disease, was also found to cause GI anthrax. Because transmission to new hosts depends on the release of large numbers of spores in the environment, we propose that the acquisition of pXO1- and pXO2-like plasmids may promote the successful expansion of members of the Bacillus cereus sensu lato group able to cause anthrax-like disease.

Characterization difference of typical KL1, KL2 and ST11-KL64 hypervirulent and carbapenem-resistant Klebsiella pneumoniae

Almost all the formation of hypervirulent and carbapenem-resistant Klebsiella pneumoniae follow two major patterns: KL1/KL2 hvKP strains acquire carbapenem-resistance plasmids (CR-hvKP), and carbapenem-resistant Klebsiella pneumoniae (CRKP) strains obtain virulence plasmids (hv-CRKP). These two patterns may pose different phenotypes. In this study, three typical resistance and hypervirulent K. pneumoniae (KL1, KL2, and ST11-KL64), isolating from poor prognosis patients, were selected. Compared with ST11-KL64 hv-CRKP, KL1/KL2 hypervirulent lineages harbor significantly fewer resistance determinants and exhibited lower-level resistance to antibiotics. Notably, though the bla_KPC gene could be detected in all these isolates, KL1/KL2 hvKP strain did not exhibit corresponding high-level carbapenem resistance. Unlike the resistance features, we did not observe significant virulence differences between the three strains. The ST11-KL64 hv-CRKP (1403) in this study, showed similar mucoviscosity, siderophores production, and biofilm production compared with KL1 and KL2 hvKP. Moreover, the hypervirulent of ST11-KL64 hvKP also verified with the human lung epithelial cells infection and G. mellonella infection models. Moreover, we found the pLVPK-like virulence plasmid and IncF bla_KPC-2 plasmid was crucial for the formation of hypervirulent and carbapenem-resistant K. pneumoniae. The conservation of origin of transfer site (oriT) in these virulence and bla_KPC-2 plasmids, indicated the virulence plasmids could transfer to CRKP with the help of bla_KPC-2 plasmids. The co-existence of virulence plasmid and bla_KPC-2 plasmid facilitate the formation of ST11-KL64 hv-CPKP, which then become nosocomial epidemic under the antibiotic stress. The ST11-KL64 hv-CPKP may poses a substantial threat to healthcare networks, urgent measures were needed to prevent further dissemination in nosocomial settings.

Opposite evolution of pathogenicity driven by in vivo wzc and wcaJ mutations in ST11-KL64 carbapenem-resistant Klebsiella pneumoniae

AIMS

To investigate the in vivo evolution of the mucoid-phenotype of ST11-KL64 carbapenem-resistant Klebsiella pneumoniae (CRKP) isolated from the same patients and gain insights into diverse evolution and biology of these strains.

METHODS

Whole genome sequencing and bioinformatic analysis were used to determine the mutation involved in the mucoid phenotype of ST11-KL64 CRKP. Gene knockout, bacterial morphology and capsular polysaccharides (CPS) extraction were used to verify the role of wzc and wcaJ in the mucoid phenotypes. Antimicrobial susceptibility, growth assay, biofilm formation, host cell adhesion and virulence assay were used to investigate the pleiotropic role of CPS changes in ST11-KL64 CRKP strains.

RESULTS

Mutation of wzc S682N led to hypermucoid phenotype, which had negative impact on bacterial fitness and resulted in reduced biofilm formation and epithelial cell adhesion; while enhanced resistance to macrophage phagocytosis and virulence. Mutations of wcaJ gene led to non-mucoid phenotype with increased biofilm formation and epithelial cell adhesion, but reduced resistance of macrophage phagocytosis and virulence. Using virulence gene knockout, we demonstrated that CPS, rather than the pLVPK-like virulence plasmid, has a greater effect on mucoid phenotypic changes. CPS could be used as a surrogate marker of virulence in ST11-KL64 CRKP strains.

CONCLUSIONS

ST11-KL64 CRKP strains sacrifice certain advantages to develop pathogenicity by changing CPS with two opposite in vivo evolution strategies.

Detection and Molecular Identification of Salmonella Pathogenic Islands and Virulence Plasmid Genes of Salmonella in Xuzhou Raw Meat Products

ABSTRACT

Virulence genes expressed in Salmonella are a primary contributing factor leading to the high morbidity and mortality of salmonellosis in humans. The pathogenicity of Salmonella is mainly determined by the specific virulence factors that it carries. These factors also confer greater virulence and play a role in infection of a host and transmission of disease, and most Salmonella enterica can cause cross-infections between humans and animals. In this study, 265 samples in total were collected from a farmer's market and two supermarkets in Xuzhou, Jiangsu province, China, including 205 pork samples and 60 chicken samples. The suspected Salmonella isolates were isolated and identified using microbiological and molecular methods, and the confirmed isolates were used for serovar analysis and antimicrobial susceptibility testing. The virulence genes of Salmonella pathogenic islands (SPIs) and Salmonella virulence plasmids (Spv) in Salmonella-positive isolates were subsequently detected. Salmonella was isolated from 29.0% of samples, and all isolates were confirmed by PCR targeting the stn gene. Among the Salmonella isolates, resistance was most frequently observed against ciprofloxacin (84.4%), followed by tetracycline (71.4%) and streptomycin (68.8%). Resistance to amoxicillin-clavulanic acid (6.3%) and aztreonam (5%) was less commonly detected. The presence of the following virulence genes was determined by specific PCRs: hilA (SPI-1), sifA (SPI-2), misL (SPI-3), siiE (SPI-4), sopB (SPI-5), and spvC. The detection rate for SPI-1 to SPI-5 was 93.5, 87.0, 97.4, 97.4, and 97.4%, respectively. In addition, the detection rate of the spvC gene was 96.1%. Except for sopB (94.7%), all isolates of the dominant serovar S. enterica subsp.. enterica serovar Enteritidis contained all virulence genes from SPI-1 to SPI-5. This study demonstrated the epidemiological status of Salmonella in raw meat products in Xuzhou, and the complex antibiotic resistance and high isolation rate of virulence genes observed reveal many potential risks of which the findings presented herein will provide orientation to improve public health safeguards.

HIGHLIGHTS

An IncB/O/K/Z conjugative plasmid encodes resistance to azithromycin and mediates transmission of virulence plasmid in Klebsiella pneumoniae

INTRODUCTION

Azithromycin resistance in bacterial pathogens has increased worldwide, and Klebsiella pneumoniae (K. pneumoniae) carries a variety of azithromycin resistance encoding genes.

METHODS

Genomic DNA of K. pneumoniae strain 16HN-12 was subjected to whole-plasmid sequencing using both the 150-bp paired-end Illumina NextSeq 500 platform and the long-read Oxford Nanopore Technologies MinION platform. Transferability of the azithromycin-resistance plasmid and the virulence plasmid was assessed by performing the conjugation assay.

RESULTS

This study identified an IncB/O/K/Z conjugative plasmid that harboured erm(B) and mph(A) genes from a clinical K. pneumoniae strain. The plasmid was readily able to conjugate to Escherichia coli (E. coli) strain J53 and Salmonella enterica subsp. enterica serovar Typhimurium strain PY1 and promoted phenotypic resistance to azithromycin. Furthermore, the virulence plasmid harboured by this K. pneumoniae strain could be conjugated to E. coli strain EC600 and K. pneumoniae strain WZ1-2 via the help of this resistance plasmid through formation of a fusion plasmid. The fusion process was generated by homologous recombination through a homologous region located in both the virulence plasmid and resistance plasmid.

CONCLUSIONS

Generation of this kind of conjugative plasmid simultaneously carrying virulence and resistance determinants could accelerate dissemination of these determinants and generate bacterial pathogens encoding these phenotypes. These data provide more information about transmission of azithromycin resistance and virulence determinants and call for action to further investigate and prevent such an evolutionary trend.

Mobilization of the nonconjugative virulence plasmid from hypervirulent Klebsiella pneumoniae

Background

Klebsiella pneumoniae, as a global priority pathogen, is well known for its capability of acquiring mobile genetic elements that carry resistance and/or virulence genes. Its virulence plasmid, previously deemed nonconjugative and restricted within hypervirulent K. pneumoniae (hvKP), has disseminated into classic K. pneumoniae (cKP), particularly carbapenem-resistant K. pneumoniae (CRKP), which poses alarming challenges to public health. However, the mechanism underlying its transfer from hvKP to CRKP is unclear.

Methods

A total of 28 sequence type (ST) 11 bloodstream infection-causing CRKP strains were collected from Ruijin Hospital in Shanghai, China, and used as recipients in conjugation assays. Transconjugants obtained from conjugation assays were confirmed by XbaI and S1 nuclease pulsed-field gel electrophoresis, PCR detection and/or whole-genome sequencing. The plasmid stability of the transconjugants was evaluated by serial culture. Genetically modified strains and constructed mimic virulence plasmids were employed to investigate the mechanisms underlying mobilization. The level of extracellular polysaccharides was measured by mucoviscosity assays and uronic acid quantification. An in silico analysis of 2608 plasmids derived from 814 completely sequenced K. pneumoniae strains available in GenBank was performed to investigate the distribution of putative helper plasmids and mobilizable virulence plasmids.

Results

A nonconjugative virulence plasmid was mobilized by the conjugative plasmid belonging to incompatibility group F (IncF) from the hvKP strain into ST11 CRKP strains under low extracellular polysaccharide-producing conditions or by employing intermediate E. coli strains. The virulence plasmid was mobilized via four modes: transfer alone, cotransfer with the conjugative IncF plasmid, hybrid plasmid formation due to two rounds of single-strand exchanges at specific 28-bp fusion sites or homologous recombination. According to the in silico analysis, 31.8% (242) of the putative helper plasmids and 98.8% (84/85) of the virulence plasmids carry the 28-bp fusion site. All virulence plasmids carry the origin of the transfer site.

Conclusions

The nonconjugative virulence plasmid in ST11 CRKP strains is putatively mobilized from hvKP or E. coli intermediates with the help of conjugative IncF plasmids. Our findings emphasize the importance of raising public awareness of the rapid dissemination of virulence plasmids and the consistent emergence of hypervirulent carbapenem-resistant K. pneumoniae (hv-CRKP) strains.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13073-021-00936-5.

A global perspective on the convergence of hypervirulence and carbapenem resistance in Klebsiella pneumoniae

Hypervirulence and carbapenem resistance have emerged as two distinct evolutionary directions for Klebsiella pneumoniae, which pose a great threat in clinical settings. Multiple virulence factors contribute to hypervirulence, and the mechanisms of carbapenem resistance are complicated. However, more and more K. pneumoniae strains have been identified in recent years integrating both phenotypes, resulting in devastating clinical outcomes. Hypervirulent and carbapenem-resistant K. pneumoniae (CR-hvKP) emerged in the early 2010s and thereafter have become increasingly prevalent. CR-hvKP are primarily prevalent in Asia, especially China, but are reported all over the world. Mechanisms for the emergence of CR-hvKP can be summarised by three patterns: (i) carbapenem-resistant K. pneumoniae (CRKP) acquiring a hypervirulent phenotype; (ii) hypervirulent K. pneumoniae (hvKP) acquiring a carbapenem-resistant phenotype; and (iii) K. pneumoniae acquiring both a carbapenem resistance and hypervirulence hybrid plasmid. With their global dissemination, continued surveillance of the emergence of CR-hvKP should be more highly prioritised.

Gene Assembly in Agrobacterium via Nucleic Acid Transfer Using Recombinase Technology (GAANTRY)

Plant biotechnology provides a means for the rapid genetic improvement of crops including the enhancement of complex traits like yield and nutritional quality through the introduction and coordinated expression of multiple genes. GAANTRY (gene assembly in Agrobacterium by nucleic acid transfer using recombinase technology) is a flexible and effective system for stably stacking multiple genes within an Agrobacterium virulence plasmid transfer DNA (T-DNA) region. The system provides a simple and efficient method for assembling and stably maintaining large stacked constructs within the GAANTRY ArPORT1 Agrobacterium rhizogenes strain. The assembly process utilizes unidirectional site-specific recombinases in vivo and an alternating bacterial selection scheme to sequentially assemble multiple genes into a single transformation construct. A detailed description of the procedures used for bacterial transformation, selection, counter selection, and genomic PCR validation with the GAANTRY system are presented. The methods described facilitate the efficient assembly and validation of large GAANTRY T-DNA constructs. This powerful, yet simple to use, technology will be a convenient tool for transgene stacking and plant genetic engineering of rice and other crop plants.

Complete genome sequence and annotation of the laboratory reference strain Shigella flexneri serotype 5a M90T and genome-wide transcriptional start site determination

Background

Shigella is a Gram-negative facultative intracellular bacterium that causes bacillary dysentery in humans. Shigella invades cells of the colonic mucosa owing to its virulence plasmid-encoded Type 3 Secretion System (T3SS), and multiplies in the target cell cytosol. Although the laboratory reference strain S. flexneri serotype 5a M90T has been extensively used to understand the molecular mechanisms of pathogenesis, its complete genome sequence is not available, thereby greatly limiting studies employing high-throughput sequencing and systems biology approaches.

Results

We have sequenced, assembled, annotated and manually curated the full genome of S. flexneri 5a M90T. This yielded two complete circular contigs, the chromosome and the virulence plasmid (pWR100). To obtain the genome sequence, we have employed long-read PacBio DNA sequencing followed by polishing with Illumina RNA-seq data. This provides a new hybrid strategy to prepare gapless, highly accurate genome sequences, which also cover AT-rich tracks or repetitive sequences that are transcribed. Furthermore, we have performed genome-wide analysis of transcriptional start sites (TSS) and determined the length of 5′ untranslated regions (5′-UTRs) at typical culture conditions for the inoculum of in vitro infection experiments. We identified 6723 primary TSS (pTSS) and 7328 secondary TSS (sTSS). The S. flexneri 5a M90T annotated genome sequence and the transcriptional start sites are integrated into RegulonDB (http://regulondb.ccg.unam.mx) and RSAT (http://embnet.ccg.unam.mx/rsat/) databases to use their analysis tools in the S. flexneri 5a M90T genome.

Conclusions

We provide the first complete genome for S. flexneri serotype 5a, specifically the laboratory reference strain M90T. Our work opens the possibility of employing S. flexneri M90T in high-quality systems biology studies such as transcriptomic and differential expression analyses or in genome evolution studies. Moreover, the catalogue of TSS that we report here can be used in molecular pathogenesis studies as a resource to know which genes are transcribed before infection of host cells. The genome sequence, together with the analysis of transcriptional start sites, is also a valuable tool for precise genetic manipulation of S. flexneri 5a M90T. Further, we present a new hybrid strategy to prepare gapless, highly accurate genome sequences. Unlike currently used hybrid strategies combining long- and short-read DNA sequencing technologies to maximize accuracy, our workflow using long-read DNA sequencing and short-read RNA sequencing provides the added value of using non-redundant technologies, which yield distinct, exploitable datasets.

Differences in immune responses of pigs vaccinated with Salmonella Typhimurium and S. Choleraesuis strains and challenged with S. Choleraesuis

S. Choleraesuis (Choleraesuis) and S. Typhimurium (Typhimurium) cause salmonellosis in pigs and humans. The effects of vaccine strains pSV-less Typhimurium OU5048 and Choleraesuis OU7266 and SPI-2-mutant Choleraesuis SC2284 on the immune responses of pigs against Typhimurium, Choleraesuis, and S. Enteritidis (Enteritidis) with or without the virulence plasmid (pSV) were determined. After oral vaccination of three vaccine groups and challenge with Choleraesuis CN36, the level of Salmonella-specific IgG in sera and the bactericidal effects and superoxide generation of peripheral blood mononuclear cells (PBMCs) and polymorphonuclear leukocytes (PMNs) against the above strains were determined using ELISA and NBT assay, respectively. Among three vaccine strains tested, OU7266 stimulated the highest Salmonella-specific IgG levels. Complement inactivation increased IgG concentration, while E. coli absorption reduced IgG levels. The pSV-containing strains were less resistant to serum killing than the pSV-less strains, and Enteritidis exhibited the lowest resistance to serum killing. Serovars tested, vaccine strains, and timeline periods postvaccination and challenge were important factors affecting superoxide production. The two Choleraesuis vaccine strains stimulated greater levels of superoxide from PMNs and PBMCs than the Typhimurium strains. The PMNs and PBMCs in challenged and vaccinated pigs reduced more superoxide than those in challenged hosts. In vaccinated hosts, pSV-less Salmonella strains triggered lower levels of PMN/PBMC-generated superoxide upon challenge than strains with pSV against Enteritidis and Choleraesuis. Overall, Choleraesuis OU7266 may be better than the other vaccine strains in generating the greatest IgG levels, serum bactericidal activity and superoxide levels. The pSV likely influences the immune responses.

Choleraesuis strains with large plasmids to the human THP-1 cell death

Salmonella is a common foodborne and zoonotic pathogen. Only a few serovars carry a virulence plasmid (pSV), which enhances the pathogenicity of the host. Here, we investigated the pathogenicity roles of the pSVs among wild-type, plasmid-less, and complemented S. Typhimurium, S. Enteritidis S. Choleraesuis in invasion, phagocytosis, and intracellular bacterial survival in human THP-1 cells and cell death patterns by flow cytometry and difference in cell death patterns between pig and human S. Choleraesuis isolates with large pSCVs. Virulence plasmid (pSTV) led to slightly increasing cellular apoptosis for S. Typhimurium; virulence plasmid (pSEV) enhanced apoptosis and necrosis significantly for S. Enteritidis; and pSCV reduced apoptosis significantly for S. Choleraesuis. After complementation, pSTV increased the intracellular survival of pSCV-less Choleraesuis and the cytotoxicity against human THP-1 cells. Using the Cytochalasin D to differentiate the invasion of S. Choleraaesuis and phagocytosis of THP-1 cells determined that pSCV were responsible for invasion and phagocytosis at 0 h and inhibited intracellular replication in THP-1 cells, and pSTV were responsible for invasion and increased intracellular survival for S. Choleraesuis in THP-1 cells. The human isolates with large pSCV induced more cellular apoptosis and necrosis than the pig isolates. In conclusion, human S. Choleraesuis isolates carrying large pSCVs were more adapted to human THP-1 cells for more cell death than pig isolates with large pSCV. The role of pSVs in invasion, phagocytosis, intracellular survival and apoptosis differed among hosted serovars.

Genomic analysis of multidrug-resistant Escherichia coli ST58 causing urosepsis

Sequence type 58 (ST58) phylogroup B1 Escherichia coli have been isolated from a wide variety of mammalian and avian hosts but are not noted for their ability to cause serious disease in humans or animals. Here we determined the genome sequences of two multidrug-resistant E. coli ST58 strains from urine and blood of one patient using a combination of Illumina and Single Molecule, Real-Time (SMRT) sequencing. Both ST58 strains were clonal and were characterised as serotype O8:H25, phylogroup B1 and carried a complex resistance locus/loci (CRL) that featured an atypical class 1 integron with a dfrA5 (trimethoprim resistance) gene cassette followed by only 24 bp of the 3'-CS. CRL that carry this particular integron have been described previously in E. coli from cattle, pigs and humans in Australia. The integron abuts a copy of Tn6029, an IS26-flanked composite transposon encoding bla_TEM, sul2 and strAB genes that confer resistance to ampicillin, sulfathiazole and streptomycin, respectively. The CRL resides within a novel Tn2610-like hybrid Tn1721/Tn21 transposon on an IncF, ColV plasmid (pSDJ2009-52F) of 138 553 bp that encodes virulence associated genes implicated in life-threatening extraintestinal pathogenic E. coli (ExPEC) infections. Notably, pSDJ2009-52F shares high sequence identity with pSF-088-1, a plasmid reported in an E. coli ST95 strain from a patient with blood sepsis from a hospital in San Francisco. These data suggest that extraintestinal infections caused by E. coli carrying ColV-like plasmids, irrespective of their phylogroup or ST, may pose a potential threat to human health, particularly to the elderly and immunocompromised.

Genetic analysis of virulence and antimicrobial-resistant plasmid pOU7519 in Salmonella enterica serovar Choleraesuis

BACKGROUND

Zoonotic Salmonella enterica serovar Choleraesuis (S. Choleraesuis), causing paratyphoid in pigs and bacteremia in humans, commonly carry a virulence plasmid and sometimes a separate antimicrobial-resistant plasmid or merging together. This study aimed to analyze the likely mechanism of how to form a virulence-resistance chimera of plasmid in S. Choleraesuis.

METHODS

Whole plasmid sequence of pOU7519 in S. Choleraesuis strain OU7519 was determined using shotgun cloning and sequencing. Sequence annotation and comparison were performed to determine the sequence responsible for the formation of a chimeric virulence-resistance pOU7519. Other chimeric plasmids among the collected strains of S. Choleraesuis were also confirmed.

RESULTS

The sequence of pOU719, 127,212 bp long, was identified to be a chimera of the virulence plasmid pSCV50 and a multidrug-resistant plasmid pSC138 that have been found in S. Choleraesuis strain SC-B67. The pOU7519 is a conjugative plasmid carrying various mobile DNAs, including prophages, insertion sequences, integrons and transposons, especially a Tn6088-like transposon. By dissecting the junction site of the pSCV50-pSC138 chimera in pOU7519, defective sequences at integrase gene scv50 (int) and its attachment site (att) were found, and that likely resulted in a stable chimera plasmid due to the failure of excision from the pSCV50-pSC138 chimera. Similar structure of chimera was also found in other large plasmids.

CONCLUSION

The deletion of both the int and att sties could likely block chimera excision, and result in an irreversible, stable pSCV50-pSC138 chimera. The emergence of conjugative virulence and antimicrobial-resistant plasmids in S. Choleraesuis could pose a threat to health public.