Distribution and spread of tigecycline resistance gene tet(X4) in Escherichia coli from different sources.

Tigecycline serves as a last-resort antimicrobial agent against severe infections caused by multidrug-resistant bacteria. Tet(X) and its numerous variants encoding flavin-dependent monooxygenase can confer resistance to tigecycline, with tet(X4) being the most prevalent variant. This study aims to investigate the prevalence and characterize tigecycline resistance gene tet(X) in E. coli isolates from various origins in Yangzhou, China, to provide insights into tet(X) dissemination in this region. In 2022, we tested the presence of tet(X) in 618 E. coli isolates collected from diverse sources, including patients, pig-related samples, chicken-related samples, and vegetables in Yangzhou, China. The antimicrobial susceptibility of tet(X)-positive E. coli isolates was conducted using the agar dilution method or the broth microdilution method. Whole genome sequencing was performed on tet(X)-positive strains using Illumina and Oxford Nanopore platforms. Four isolates from pig or pork samples carried tet(X4) and exhibited resistance to multiple antimicrobial agents, including tigecycline. They were classified as ST542, ST10, ST761, and ST48, respectively. The tet(X4) gene was located on IncFIA8-IncHI1/ST17 (n=2), IncFIA18-IncFIB(K)-IncX1 (n=1), and IncX1 (n=1) plasmids, respectively. These tet(X4)-carrying plasmids exhibited high similarity to other tet(X4)-bearing plasmids with the same incompatible types found in diverse sources in China. They shared related genetic environments of tet(X4) associated with ISCR2, as observed in the first identified tet(X4)-bearing plasmid p47EC. In conclusion, although a low prevalence (0.65%) of tet(X) in E. coli strains was observed in this study, the horizontal transfer of tet(X4) among E. coli isolates mediated by pandemic plasmids and the mobile element ISCR2 raises great concerns. Thus, heightened surveillance and immediate action are imperative to curb this clinically significant resistance gene and preserve the efficacy of tigecycline.

The active ingredients in Chinese peony pods synergize with antibiotics to inhibit MRSA growth and biofilm formation.

Staphylococcus aureus (S. aureus) is a zoonotic pathogen that infects both humans and animals. The rapid spread of methicillin-resistant S. aureus (MRSA) and its resistance to antibiotics, along with its ability to form biofilms, poses a serious challenge to the clinical application of traditional antibiotics. Peony (Paeonia lactiflora Pall.) is a traditional Chinese medicine with multiple pharmacological effects. This study observed the strong antibacterial and antibiofilm activity of the water extract (WE) and ethyl acetate extract (EA) of Chinese peony pods against MRSA. The combination of EA and vancomycin, cefotaxime, penicillin G or methicillin showed a synergistic or additive antibacterial and antibiofilm effects on MRSA, which is closely related to the interaction of 1,2,3,4,6-penta-O-galloyl-ß-D-glucose (PG) and methyl gallate (MG). The active ingredients in peony pods have been found to increase the sensitivity of MRSA to antibiotics and demonstrate antibiofilm activity, which is mainly related to the down-regulation of global regulatory factors sarA and sigB, extracellular PIA and eDNA encoding genes icaA and cdiA, quorum sensing related genes agrA, luxS, rnaIII, hld, biofilm virulence genes psma and sspA, and genes encoding clotting factors coa and vwb, but is not related to genes that inhibit cell wall anchoring. In vivo test showed that both WE and EA were non-toxic and significantly prolonged the lifespan of G. mellonella larvae infected with MRSA. This study provides a theoretical basis for further exploration of the combined use of PG, MG and antibiotics to combat MRSA infections.

Prevalence and genetic characteristics of Salmonella enterica serovar Meleagridis from animals and humans.

Salmonella enterica serovar Meleagridis (S. Meleagridis) is a non-typhoidal Salmonella serotype commonly found in food and humans. In this study, we investigated 61 Chinese S. Meleagridis isolates from various sources, predominantly from pigs and pig products. Additionally, the serotype was also identified in samples from human infections. Whole-genome sequencing analysis of these isolates, combined with 10 isolates from other countries, demonstrated that the Chinese isolates formed a distinct Cluster C, further divided into two subclusters (Cluster C-1 and Cluster C-2) based on cgMLST analysis. CRISPR typing divided the 61 isolates into three CRISPR types (MCT1, MCT2, MCT3), belonging to Cluster I (96.7%, 59/61) and Cluster II (3.3%, 2/61), which corresponded to Cluster C-2 and Cluster C-1, respectively. Among the 48 identified spacers, the spacer SoeB5 was the only target differentiating MCT1 and MCT2 isolates of Cluster I. MelB12 and MelB13, identified in US and Denmark isolates, were not found among the 61 Chinese isolates. Examination of antimicrobial resistance gene profiles and their genetic contexts uncovered the presence of IncR plasmids in 43 (70.5%, 43/61) isolates within Cluster C, conferring resistance to tetracycline and trimethoprim/sulfamethoxazole. Homology analysis of spacers showed that 12 spacers exhibited similarity to sequences in phages or plasmids. Additionally, five spacers showed homology to sequences in plasmids from other Salmonella serotypes, suggesting their potential role in helping S. Meleagridis resist against Salmonella isolates carrying similar plasmids. The comprehensive analysis of CRISPR, cgMLST, and antimicrobial resistance in S. Meleagridis highlights the pig reservoir as a crucial factor in the evolution and transmission of this serotype to humans.

Microevolution of Salmonella 4,[5],12:i:- derived from Salmonella enterica serovar Typhimurium through complicated transpositions.

Salmonella enterica subsp. enterica serovar 4,[5],12:i:- (Salmonella 4,[5],12:i:-), derived from S. Typhimurium, has become the dominant serotype causing human salmonellosis. In this study, we define the genetic mechanism of the generation of Salmonella 4,[5],12:i:- from S. Typhimurium through complicated transpositions and demonstrate that Salmonella 4,[5],12:i:- displays more efficient colonization and survival abilities in mice than its parent S. Typhimurium strain. We identified intermediate strains carrying both resistance regions (RRs) and the fljAB operon for the generation of Salmonella 4,[5],12:i:-. The insertion of RR3 into the chromosomal hin-iroB site of S. Typhimurium produced RR3-S. Typhimurium as a primary intermediate. Salmonella 4,[5],12:i:- was then produced by replacing the fljAB operon and/or its flanking sequences through intramolecular transpositions mediated by IS26 and/or IS1R elements in RR3-S. Typhimurium, which was further confirmed both in vitro and in vivo. Overall, we demonstrate the molecular mechanism underlying the origin, generation, and advantage of RRs-Salmonella 4,[5],12:i:- from S. Typhimurium.

Poultry production as the main reservoir of ciprofloxacin- and tigecycline-resistant extended-spectrum ß-lactamase (ESBL)-producing Salmonella enterica serovar Kentucky ST198.2-2 causing human infections in China.

Salmonella enterica serovar Kentucky (S. Kentucky) has been regarded as a common serotype causing human nontyphoidal salmonellosis, frequently associated with the consumption of contaminated poultry products. Recently, multidrug-resistant (MDR) S. Kentucky ST198 with strong resistance to cefotaxime, ciprofloxacin, and tigecycline has emerged and been frequently detected in both poultry and humans in Europe and Asia. In this study, whole-genome sequencing (WGS) analysis divided 327 S. Kentucky ST198 isolates into two clades, of which ST198.2 is more prevalent than ST198.1 worldwide. We further compared the genomic characteristics of 70 ST198 isolates from animals and humans during 2019-2022 plus previously reported 38 isolates from 2013 to 2019 in China. One hundred five of the 108 isolates were ST198.2, which could be differentiated into two subclades. ST198.2-1 was prevalent in isolates during 2013-2019, while ST198.2-2 has increased to be the predominant subclade in isolates since 2019. CRISPR typing can differentiate the clade ST198.1 isolates from clade ST198.2 ones but cannot differentiate the two subclade isolates. The acquisition of a large multi-drug resistant region in ST198.2-2 enhanced bacterial resistance to ß-lactam, aminoglycoside, amphenicol, and fosfomycin. In addition, compared with the extended-spectrum ß-lactamase (ESBL)-encoding gene blaCTX-M-14b in ST198.2-1, co-existence of blaCTX-M-55 and blaTEM-1B was detected in most of the ST198.2-2 isolates. The emergence of ciprofloxacin- and tigecycline-resistant ESBL-producing S. Kentucky ST198.2-2 strains highlight the necessity for Salmonella surveillance. It is imperative to implement more effective measures to prevent and control transmission of these strains from poultry to humans. IMPORTANCE Salmonella enterica serovar Kentucky (S. Kentucky) can cause human infections through consumption of contaminated food of animal origin, and the emergence of multidrug-resistant (MDR) ST198-S. Kentucky strains are of concern for human and animal health. Based on whole-genome sequencing (WGS) analysis, this study revealed that the clade ST198.2-2 S. Kentucky has increased to the predominant group in both chickens and humans in China since 2019, which is different to previous studies of the prevalent ST198.2-1 S. Kentucky before 2019. Acquirement of a multidrug resistance region (MRR) makes the ST198.2-2 S. Kentucky to be extensively drug-resistant (XDR) isolate compared with ST198.2-1 S. Kentucky. Besides, the ST198.2-2 S. Kentucky was mainly detected in chickens (chicken meat, intestinal contents, and slaughterhouse) and humans, indicating chicken is the main reservoir for these XDR S. Kentucky isolates. Therefore, it is necessary to implement continuous Salmonella surveillance and effective measures, such as the development of phages and novel antibiotics/compounds, to prevent the transmission of XDR ST198.2-2 S. Kentucky from chickens to humans across China.

An Endogenous Staphylococcus aureus CRISPR-Cas System Limits Phage Proliferation and Is Efficiently Excised from the Genome as Part of the SCCmec Cassette.

CRISPR-Cas is an adaptive immune system that allows bacteria to inactivate mobile genetic elements. Approximately 50% of bacteria harbor CRISPR-Cas; however, in the human pathogen Staphylococcus aureus, CRISPR-Cas loci are less common and often studied in heterologous systems. We analyzed the prevalence of CRISPR-Cas in genomes of methicillin-resistant Staphylococcus aureus (MRSA) strains isolated in Denmark. Only 2.9% of the strains carried CRISPR-Cas systems, but for strains of sequence type ST630, over half were positive. All CRISPR-Cas loci were type III-A and located within the staphylococcal cassette chromosome mec (SCCmec) type V(5C2&5), conferring ß-lactam resistance. Curiously, only 23 different CRISPR spacers were identified in 69 CRISPR-Cas positive strains, and almost identical SCCmec cassettes, CRISPR arrays, and cas genes are present in staphylococcal species other than S. aureus, suggesting that these were transferred horizontally. For the ST630 strain 110900, we demonstrate that the SCCmec cassette containing CRISPR-Cas is excised from the chromosome at high frequency. However, the cassette was not transferable under the conditions investigated. One of the CRISPR spacers targets a late gene in the lytic bacteriophage phiIPLA-RODI, and we show that the system protects against phage infection by reducing phage burst size. However, CRISPR-Cas can be overloaded or circumvented by CRISPR escape mutants. Our results imply that the endogenous type III-A CRISPR-Cas system in S. aureus is active against targeted phages, albeit with low efficacy. This suggests that native S. aureus CRISPR-Cas offers only partial immunity and in nature may work in tandem with other defense systems. IMPORTANCE CRISPR-Cas is an adaptive immune system protecting bacteria and archaea against mobile genetic elements such as phages. In strains of Staphylococcus aureus, CRISPR-Cas is rare, but when present, it is located within the SCCmec element, which encodes resistance to methicillin and other ß-lactam antibiotics. We show that the element is excisable, suggesting that the CRISPR-Cas locus is transferable. In support of this, we found almost identical CRISPR-Cas-carrying SCCmec elements in different species of non-S. aureus staphylococci, indicating that the system is mobile but only rarely acquires new spacers in S. aureus. Additionally, we show that in its endogenous form, the S. aureus CRISPR-Cas is active but inefficient against lytic phages that can overload the system or form escape mutants. Thus, we propose that CRISPR-Cas in S. aureus offers only partial immunity in native systems and so may work with other defense systems to prevent phage-mediated killing.

Advancement in Understanding Immune Responses against Zoonotic Infections.

This Special Issue focuses on the recent advancements in our understanding of immune responses against zoonoses, which include viral, bacterial, parasitic and fungal diseases [...].

Prevalence and molecular characterization of mcr-1-positive foodborne ST34-Salmonella isolates in China.

Salmonella enterica serovar Typhimurium (S. Typhimurium) and S. 4,[5],12:i:- have become the most common serovars associated with human salmonellosis worldwide. Moreover, the emergence of mcr-carrying S. Typhimurium and S. 4,[5],12:i:- with multidrug resistance (MDR) patterns has posed a threat to public health. In this study, we retrospectively screened 2009-2022 laboratory-preserved strains for the presence of mcr genes. We obtained 16 mcr-1-positive S. Typhimurium and S. 4,[5],12:i:- strains with MDR that belonged to sequence type 34 (ST34). Whole-genome sequencing analysis revealed that the mcr-1 was located on the IncI2 or IncHI2 plasmids. The ISApl1 element downstream of mcr-1 was present in all pig-derived strains. Conjugation experiments confirmed that nine mcr-1-carrying IncHI2 plasmids could not be transferred to Escherichia coli due to loss of the conjugation region. Finally, core genome single nucleotide polymorphism (cgSNP) analyses of the 16 mcr-1-carrying strains and 77 mcr-carrying ST34-Salmonella genome sequences from the NCBI and ENA databases showed that five out of eight clusters contained strains from pig and pig products, revealing pigs and pig products as key reservoirs of mcr-1-positive ST34-Salmonella strains. The transmission of mcr-carrying ST34 Salmonella strains to humans via the pig food chain is a potential cause for public health concern in controlling human salmonellosis.

Identification of Salmonella Pullorum Factors Affecting Immune Reaction in Macrophages from the Avian Host.

The host-specific Salmonella serovar S. Pullorum (SP) modulates the chicken immune response to a Th2-biased response associated with persistent infection. This is different from the Th1-biased immune response induced by the genetically close serovar, S. Enteritidis (SE). Based on core genome differences between SP and SE, we used three complementary bioinformatics approaches to identify SP genes, which may be important for stimulation of the immune response. Defined mutants were constructed in selected genes, and the infection potential and ability of mutants to stimulate cytokine production in avian derived HD11 macrophages were determined. Deletion of large genomic regions unique to SP did not change infection potential nor immune stimulation significantly. Mutants in genes with conserved single nucleotide polymorphisms (SNPs) between the two serovars in the region 100 bp upstream of the start codon (conserved upstream SNPs [CuSNPs]) such as sseE, osmB, tolQ, a putative immune antigen, and a putative persistent infection factor, exhibited differences in induction of inflammatory cytokines compared to wild-type SP, suggesting a possible role of these CuSNPs in immune regulation. Single nucleotide SP mutants correcting for the CuSNP difference were constructed in the upstream region of sifA and pipA. The SNP corrected pipA mutant expressed pipA at a higher level than the wild-type SP strain, and the mutant differentially caused upregulation of proinflammatory cytokines. It suggests that this CuSNP is important for the suppression of proinflammatory responses. In conclusion, this study has identified putative immune stimulating factors of relevance to the difference in infection dynamics between SP and SE in avian macrophages. IMPORTANCE Salmonella Pullorum is host specific to avian species, where it causes life-threatening infection in young birds. It is unknown why it is host restricted and causes systemic disease, rather than gastroenteritis normally seen with Salmonella. In the present study, we identified genes and single nucleotide polymorphisms (SNPs; relative to the broad-host-range type Salmonella Enteritidis), which affected survival and immune induction in macrophages from hens suggesting a role in development of the host specific infection. Further studies of such genes may enable understanding of which genetic factors determine the development of host specific infection by S. Pullorum. In this study, we developed an in silico approach to predict candidate genes and SNPs for development of the host-specific infection and the specific induction of immunity associated with this infection. This study flow can be used in similar studies in other clades of bacteria.

Prevalence and molecular characteristics of community-associated methicillin-resistant Staphylococcus aureus in the respiratory tracts of Chinese adults with community-acquired pneumonia.

BACKGROUND: Community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) is an important pathogen causing healthcare-associated infections. In recent years, an increasing number of CA-MRSA clones have emerged and rapidly spread in the community and hospital settings in China. OBJECTIVES: To investigate the molecular epidemiology and resistance of CA-MRSA in the respiratory tracts of Chinese adults with community-acquired pneumonia (CAP). METHODS: A total of 243 sputum samples were collected from adult patients with CAP at the Nantong Hospital in China between 2018 and 2021. S. aureus was identified using PCR, and its susceptibility to 14 antimicrobials was tested using the broth dilution method. Genomic characterization of respiratory CA-MRSA and our previously collected intestinal CA-MRSA isolates was performed using whole-genome sequencing, and the evolutionary relationships of these isolates were assessed using phylogenetic analysis. RESULTS: The CA-MRSA colonization rate among adults with CAP in China was 7.8 % (19/243). Antimicrobial resistance analysis revealed that the proportion of multidrug-resistant respiratory CA-MRSA isolates (100 %) was higher than that of intestinal CA-MRSA isolates (6.3 %). Among the 35 CA-MRSA isolates, 10 MLST types were identified and clustered into five clone complexes (CCs). CC5 (48.6 %) and CC88 (20 %) were predominant CA-MRSA clones. Notably, the CC5 clone ST764/ST6292-MRSA-II-t002 was identified as the major lineage causing respiratory tract infections in Chinese adults with CAP. CONCLUSIONS: The prevalence of CA-MRSA among Chinese adults with CAP is high and often involves ST764/ST6292-MRSA-II-t002 as the causal pathogen.

Characterization of Extensively Drug-Resistant Salmonella enterica Serovar Kentucky Sequence Type 198 Isolates from Chicken Meat Products in Xuancheng, China.

The purpose of this study was to characterize extensively drug-resistant Salmonella enterica serovar Kentucky sequence type 198 (ST198) isolates from chicken meat products. Ten S. Kentucky strains obtained from chicken meat products in Xuancheng, China, carried 12 to 17 resistance genes, such as blaCTX-M-55, rmtB, tet(A), floR, and fosA3, combined with mutations within gyrA (S83F and D87N) and parC (S80I), resulting in resistance to numerous antimicrobial agents, including the clinically important antibiotics cephalosporin, ciprofloxacin, tigecycline, and fosfomycin. These S. Kentucky isolates shared a close phylogenetic relationship (21 to 36 single-nucleotide polymorphisms [SNPs]) and showed close genetic relatedness to two human clinical isolates from China. Three S. Kentucky strains were subjected to whole-genome sequencing using Pacific Biosciences (PacBio) single-molecule real-time (SMRT) technology. All antimicrobial resistance genes were located on their chromosomes and clustered in one multiresistance region (MRR) and Salmonella genomic island (SGI) SGI1-K. The MRRs in three S. Kentucky strains were bounded by IS26 at both ends and were inserted downstream of the bcfABCDEFG cluster with 8-bp direct repeats. The MRRs were related to those of IncHI2 plasmids but differed by insertions, deletions, and rearrangements of multiple segments involving resistance genes and plasmid backbones. This finding suggests that the MRR fragment possibly originates from IncHI2 plasmids. Four SGI1-K variants with slight differences were identified in 10 S. Kentucky strains. Mobile elements, particularly IS26, play an essential role in forming distinct MRRs and SGI1-K structures. In conclusion, the emergence of extensively drug-resistant S. Kentucky ST198 strains containing numerous chromosomally located resistance genes is alarming and needs continued surveillance. IMPORTANCE Salmonella spp. are important foodborne pathogens, and multidrug-resistant (MDR) Salmonella strains have become a serious threat to clinical therapy. MDR S. Kentucky ST198 strains have been increasingly reported from various sources and have become a global risk. In this study, we described extensively drug-resistant S. Kentucky ST198 strains from chicken meat products from a city in China. Numerous resistance genes are clustered in the chromosomes of S. Kentucky ST198 strains, possibly acquired with the help of mobile elements. This would facilitate the spread of numerous resistance genes as intrinsic chromosomal genes within this global epidemic clone, with the potential to capture more resistance genes. The emergence and dissemination of extensively drug-resistant S. Kentucky ST198 pose a severe clinical and public health threat; therefore, continuous surveillance is warranted.

Development and application of a multiplex PCR method to differentiate Salmonella enterica serovar Typhimurium from its monophasic variants in pig farms.

Salmonella enterica serovar Typhimurium monophasic variants (Salmonella 4,[5],12:i:-) has increased dramatically, causing human salmonellosis and colonization in pigs. With a difference to S. Typhimurium, the monophasic variants of S. Typhimurium lose the gene cassettes encoding the second phase flagellin. To establish a rapid method to detect and differentiate the two serotypes, we analyzed the published 679 genomes of S. Typhimurium and its monophasic variants and found that no Salmonella 4,[5],12:i:- strains carry both fljB and hin genes. Therefore, we established a novel multiplex PCR method using the fljB-hin region and mdh gene as target sequences to detect and differentiate both serotypes. This method can be used to specifically detect both serotypes with a detection limit for DNA concentration at 10 pg/µL. In addition, the PCR assay successfully differentiated 36 S. Typhimurium isolates from 62 isolates of monophasic variants preserved in our laboratory from 2009 to 2017, which corresponds to the whole-genome-based serotyping results. Application of the multiplex PCR method to 60 fecal samples from a pig farm identified 11.7% (7/60) of S. Typhimurium monophasic variants, which is consistent with the whole-genome-based serotyping results. The multiplex PCR assay is a rapid and precise method for the detection of S. Typhimurium monophasic variants from samples across food production chains.

The prevalence of Staphylococcus aureus and the emergence of livestock-associated MRSA CC398 in pig production in eastern China.

Livestock-associated Staphylococcus aureus (LA-MRSA) has been of increasing concern due to its potential risk to humans. This study investigated the prevalence of MRSA in pig production in Eastern China and determined the genomic characteristics of pig-associated MRSA isolates by whole-genome sequencing (WGS). A total of 1,318 samples were collected from pig farms and pig slaughterhouses, and 150 S. aureus were identified, including 63 MRSA isolates and 87 MSSA isolates. MRSA was detected in all pig farms and pig slaughterhouses. The antimicrobial susceptibility test revealed that all MRSA isolates were multidrug-resistant. The WGS and MLST analysis demonstrated that 56 MRSA isolates belonged to clonal complex (CC) 398, and seven MRSA isolates belonged to CC9. All LA-MRSA isolates were absent of phiSa3 phage containing immune evasion cluster (IEC) and possessed an intact hlb gene. In addition, genes associated with Panton-Valentine leukocidin, typically indicative of human adaptation, were not detected. The analysis of antibiotic resistance genes (ARGs) demonstrated that all MRSA isolates contained multiple ARGs. All MRSA isolates had Plthe mecA gene and at least one tetracycline resistance gene. Both tetM and tetK were detected in all MRSA CC398 isolates, while tetL was detected in all MRSA CC9 isolates. The phenicol resistance gene fexA was detected in 51 MRSA isolates, while the linezolid resistance gene cfr was detected in 60 MRSA isolates. The emergence of LA-MRSA CC398 in four pig farms and one slaughterhouse in this study indicates the spread of this clonal complex in the pig production sector in Eastern China. Further investigations are required to understand the potential transmission routes of LA-MRSA CC398 within the pork production chain in China and to assess the potential risks to humans.

The Salmonella T3SS1 effector IpaJ is regulated by ItrA and inhibits the MAPK signaling pathway.

Invasion plasmid antigen J (IpaJ) is a protein with cysteine protease activity that is present in Salmonella and Shigella species. Salmonella enterica serovar Pullorum uses IpaJ to inhibit the NF-κB pathway and the subsequent inflammatory response, resulting in bacterial survival in host macrophages. In the present study, we performed a DNA pull-down assay and EMSA and identified ItrA, a new DeoR family transcriptional regulator that could control the expression of IpaJ by directly binding to the promoter of ipaJ. The deletion of itrA inhibited the transcription of ipaJ in Salmonella. Tn-Seq revealed that two regulators of Salmonella pathogenicity island 1 (SPI-1), namely HilA and HilD, regulated the secretion of IpaJ. The deletion of hilA, hilD or SPI-1 inhibited the secretion of IpaJ in both cultured medium and Salmonella-infected cells. In contrast, the strain with the deletion of ssrB (an SPI-2 regulator-encoding gene) displayed normal IpaJ secretion, indicating that IpaJ is an effector of the SPI-1-encoded type III secretion system (T3SS1). To further demonstrate the role of IpaJ in host cells, we performed quantitative phosphoproteomics and compared the fold changes in signaling molecules in HeLa cells infected with wild-type S. Pullorum C79-13 with those in HeLa cells infected with the ipaJ-deleted strain C79-13ΔpSPI12. Both phosphoproteomics and Western blot analyses revealed that p-MEK and p-ERK molecules were increased in C79-13ΔpSPI12- and C79-13ΔpSPI12-pipaJ(C45A)-infected cells; and Co-IP assays demonstrated that IpaJ interacts with Ras to reduce its ubiquitination, indicating that IpaJ can inhibit the activation of the MAPK signaling pathway.

Preclinical evaluation of OMVs as potential vaccine candidates against Salmonella enterica serovar Enteritidis infection.

Salmonella enterica serovar Enteritidis is the most prevalent serotype that causes human infections worldwide. Consumption of S. Enteritidis-contaminated animal foods is a major source of human infections; however, eradicating bacteria from animals remains difficult. Therefore, it is necessary to develop new measures to prevent and control salmonellosis. Here, we used the outer-membrane vesicles (OMVs) of S. Enteritidis and assessed their protective efficacy and immune response in mice. Deletion of tolR in S. Enteritidis increased the production and size of OMVs compared to those in the wild type (WT) and ΔrfaQ strains. Intramuscular immunization with OMVs conferred greater protection than intraperitoneal and intranasal immunization. Moreover, OMVs extracted from both WT and ΔtolR strains provided an 83.3% protective rate in mice challenged with S. Enteritidis, which was higher than that provided by OMVs extracted from the ΔrfaQ strain. However, compared with OMVs from the ΔtolR strain, OMVs from WT and ΔrfaQ strains rapidly eradicated S. Enteritidis colonizing the liver, spleen, ileum, and cecum of BALB/c mice after immunization. Immunization with OMVs from each of the three strains induced humoral immune responses and showed no side effects on the growth of mice. Our study revealed that OMVs from various S. Enteritidis strains could be developed for use as subunit vaccine candidates against nontyphoidal Salmonella infections in mammals.

Molecular Characterization of Methicillin-Sensitive Staphylococcus aureus from the Intestinal Tracts of Adult Patients in China.

Intestinal infections caused by methicillin-sensitive Staphylococcus aureus (MSSA) have posed a great challenge for clinical treatments. In recent years, the intestinal carriage rates of MSSA have risen steadily in hospital settings in China. However, the epidemiology and molecular characteristics of MSSA from the intestinal tracts of Chinese adult patients remain unknown. In the present study, a total of 80 S. aureus isolates, including 64 MSSA and 16 methicillin-resistant Staphylococcus aureus (MRSA), were recovered from 466 fecal swabs in adult patients between 2019 and 2021 in China. The MSSA isolates exhibited high resistance to penicillin (92.2%) and erythromycin (45.3%). In addition, a higher proportion of MSSA isolates (14.1%) were multidrug-resistant (MDR) strains than that of MRSA isolates (1.3%). Among the 64 MSSA isolates, we identified 17 MLST types, of which ST398 and ST15 were the most predominant types. The most frequently detected resistance genes were blaZ (87.5%) and erm(C) (21.9%). The hemolysin genes (hla, hld, hlgA, hlgB, hlgC) were detected in all the MSSA isolates, but the Panton-Valentine leucocidin (pvl) gene was identified in 1.7% of the MSSA isolates. Our findings indicated that the prevalence and antimicrobial resistance of intestinal MSSA was a serious concern among adult patients in China.

Nasal carriage of CTX-M-55-producing Escherichia coli ST8369 in a healthy cohort in the city of Yangzhou, China.

This study aimed to investigate the prevalence and diversity of extended-spectrum ß-lactamases (ESBL)-producing Escherichia coli isolates from healthy individuals in a community and to elucidate their dissemination mechanism. Cefotaxime-resistant E. coli were isolated from 95 samples of healthy persons from one community in Yangzhou, China, and were tested for minimal inhibitory concentrations of 14 antimicrobial agents. The isolates were subjected to whole genome sequencing by Illumina Hiseq or PacBio single-molecule real-time sequencing. A total of 30 cefotaxime-resistant E. coli isolates were obtained, carrying bla CTX-M (n=29) or bla DHA (n=1), of which the bla CTX-M-55 (n=19) was the most predominant genotype. One novel bla CTX-M variant bla CTX-M-252 was identified. Thirteen CTX-M-55-producing E. coli isolates belonged to ST8369 from nasal (n=12) or faecal (n=1) samples shared the identical cgMLST type, resistance profiles, resistance genes, plasmid replicons, and a 5,053-bp bla CTX-M-55 structure ΔIS26-ΔISEcp1-bla CTX-M-55-Δorf477-ΔTn2. The bla CTX-M-55 gene was located on IncHI2/ST3 plasmid in E. coli ST8369. The lengths of bla CTX-M/bla DHA-carrying contigs in the remaining 17 E. coli strains ranged from 1,663 to 382,836 bp, located on chromosome (n=4) or plasmids (n=5); the location of the other eight contigs could not be determined due to incomplete assembly. The bla CTX-M was associated with ISEcp1 as previously reported. Nasal colonization of CTX-M-55-producing ST8369 E. coli strains has occurred among healthy individuals in one community. There is a potential risk of antimicrobial resistance dissemination between humans within one community through close contact or environment via aerosols or dust. Therefore, surveillance of nasal carriage of bla CTX-M in communities is warranted to further monitor the spread of the antimicrobial resistance genes in China.

The Immunology of Zoonotic Infection.

Zoonotic infection can threaten public health locally and globally [...].