Two novel plasmids harbouring the multiresistance gene cfr in porcine Staphylococcus equorum.

BACKGROUND: The emergence and transmission of the multidrug resistance gene cfr have raised public health concerns worldwide. OBJECTIVES: Multidrug-resistant Staphylococcus equorum isolates can pose a threat to public health. In this study, we have characterised the whole-genome of one Staphylococcus equorum isolate harbouring two distinct cfr-carrying plasmids. METHODS: Antimicrobial susceptibility testing was performed by broth microdilution. Genomic DNA was sequenced using both the Illumina HiSeq X Ten and Nanopore MinION platforms. De novo hybrid assembly was performed by Unicycler. Genomic data were assessed by in silico prediction and bioinformatic tools. RESULTS: Staphylococcus equorum isolate SN42 exhibited resistance or high MICs to linezolid, erythromycin, tetracycline, oxacillin, clindamycin, virginiamycin, tiamulin, chloramphenicol and florfenicol. It carried two cfr-harbouring plasmids: the RepA N-family plasmid pSN42-51 K and the Inc18-family plasmid pSN42-50 K. These two plasmids exhibited low structural similarities to the so far reported cfr-carrying plasmids. Both plasmids harboured an arsenic resistance operon, copper and cadmium resistance genes as well as the lincosamide-pleuromutilin-streptogramin A resistance gene lsa(B). In addition, plasmid pSN42-51 K carried two erm(B) genes for macrolide-lincosamide-streptogramin B resistance, the streptomycin resistance gene ant(6)-Ia as well as mercury resistance genes while pSN42-50 K was associated with the heavy metal translocating P-type ATPase gene hmtp. The co-carriage and co-existence of these antimicrobial resistance and heavy metal resistance genes increases the likelihood of co-selection of the cfr-carrying plasmids. CONCLUSION: This is the first report of S. equorum carrying two distinct cfr-carrying plasmids, underscoring the need for ongoing surveillance to address the potential dissemination of multi-drug resistance in bacteria from food-producing animals to ensure food safety and public health.

Anticancer agent 5-fluorouracil reverses meropenem resistance in carbapenem-resistant Gram-negative pathogens.

The global increasing incidence of clinical infections caused by carbapenem-resistant Gram-negative pathogens requires urgent and effective treatment strategies. Antibiotic adjuvants represent a promising approach to enhance the efficacy of meropenem against carbapenem-resistant bacteria. This study shows that the anticancer agent 5-fluorouracil (5-FU, 50 µM) significantly reduced the minimum inhibitory concentration of meropenem against blaNDM-5 positive Escherichia coli by 32-fold through cell-based high-throughput screening. Further pharmacological studies indicated that 5-FU exhibited potentiation effects on carbapenem antibiotics against 42 Gram-negative bacteria producing either metallo-ß-lactamases (MBLs), such as NDM and IMP, or serine ß-lactamases (Ser-BLs), like KPC and OXA. These bacteria included E. coli, Klebsiella pneumoniae, Pseudomonas aeruginosa and Acinetobacter spp., 32 of which were obtained from human clinical samples. Mechanistic investigations revealed that 5-FU inhibited the transcription and expression of the blaNDM-5 gene. In addition, 5-FU combined with meropenem enhanced bacterial metabolism, and stimulated the production of reactive oxygen species (ROS), thereby rendering bacteria more susceptible to meropenem. In a mouse systemic infection model, 5-FU combined with meropenem reduced bacterial loads and effectively elevated the survival rate of 83.3%, compared with 16.7% with meropenem monotherapy. Collectively, these findings indicate the potential of 5-FU as a novel meropenem adjuvant to improve treatment outcomes against infections caused by carbapenem-resistant bacteria.

Adaptive evolution of carbapenem-resistant hypervirulent Klebsiella pneumoniae in the urinary tract of a single patient.

The emergence of carbapenem-resistant hypervirulent Klebsiella pneumoniae (CR-hvKp) is a growing concern due to its high mortality and limited treatment options. Although hypermucoviscosity is crucial for CR-hvKp infection, the role of changes in bacterial mucoviscosity in the host colonization and persistence of CR-hvKp is not clearly defined. Herein, we observed a phenotypic switch of CR-hvKp from a hypermucoviscous to a hypomucoviscous state in a patient with scrotal abscess and urinary tract infection (UTI). This switch was attributed to decreased expression of rmpADC, the regulator of mucoid phenotype, caused by deletion of the upstream insertion sequence ISKpn26. Postswitching, the hypomucoid variant showed a 9.0-fold decrease in mice sepsis mortality, a >170.0-fold reduction in the ability to evade macrophage phagocytosis in vitro, and an 11.2- to 40.9-fold drop in growth rate in normal mouse serum. Conversely, it exhibited an increased residence time in the mouse urinary tract (21 vs. 6 d), as well as a 216.4-fold boost in adhesion to bladder epithelial cells and a 48.7% enhancement in biofilm production. Notably, the CR-hvKp mucoid switch was reproduced in an antibiotic-free mouse UTI model. The in vivo generation of hypomucoid variants was primarily associated with defective or low expression of rmpADC or capsule synthesis gene wcaJ, mediated by ISKpn26 insertion/deletion or base-pair insertion. The spontaneous hypomucoid variants also outcompeted hypermucoid bacteria in the mouse urinary tract. Collectively, the ISKpn26-associated mucoid switch in CR-hvKp signifies the antibiotic-independent host adaptive evolution, providing insights into the role of mucoid switch in the persistence of CR-hvKp.

Limited transmission of carbapenem-resistant Klebsiella pneumoniae between animals and humans: a study in Qingdao.

ABSTRACTDespite no carbapenem use in food animals, carbapenem-resistant Klebsiella pneumoniae (CRKP) perseveres within food animals, rising significant concerns regarding public health risks originating from these non-clinical reservoirs. To investigate the potential link between CRKP in food animals and its infections in humans, we conducted a cross-sectional study encompassing human clinical, meat products, and farm animals, in Qingdao city, Shandong province, China. We observed a relatively higher presence of CRKP among hospital inpatients (7.3%) compared to that in the meat products (2.7%) and farm animals (pig, 4.6%; chicken, 0.63%). Multilocus sequence typing and core-genome phylogenetic analyses confirm there is no evidence of farm animals and meat products in the clinical acquisition of K. pneumoniae isolates and carbapenem-resistant genes. However, potential transmission of K. pneumoniae of ST659 and IncX3 plasmid harbouring blaNDM-5 gene from pigs to pork and farm workers was observed. Our findings suggest a limited role of farm animals and meat products in the human clinical acquisition of K. pneumoniae, and the transmission of K. pneumoniae is more common within settings, than between them.

VirBR, a transcription regulator, promotes IncX3 plasmid transmission, and persistence of blaNDM-5 in zoonotic bacteria.

IncX3 plasmids carrying the New Delhi metallo-ß-lactamase-encoding gene, blaNDM-5, are rapidly spreading globally in both humans and animals. Given that carbapenems are listed on the WHO AWaRe watch group and are prohibited for use in animals, the drivers for the successful dissemination of Carbapenem-Resistant Enterobacterales (CRE) carrying blaNDM-5-IncX3 plasmids still remain unknown. We observe that E. coli carrying blaNDM-5-IncX3 can persist in chicken intestines either under the administration of amoxicillin, one of the largest veterinary ß-lactams used in livestock, or without any antibiotic pressure. We therefore characterise the blaNDM-5-IncX3 plasmid and identify a transcription regulator, VirBR, that binds to the promoter of the regulator gene actX enhancing the transcription of Type IV secretion systems (T4SS); thereby, promoting conjugation of IncX3 plasmids, increasing pili adhesion capacity and enhancing the colonisation of blaNDM-5-IncX3 transconjugants in animal digestive tracts. Our mechanistic and in-vivo studies identify VirBR as a major factor in the successful spread of blaNDM-5-IncX3 across one-health AMR sectors. Furthermore, VirBR enhances the plasmid conjugation and T4SS expression by the presence of copper and zinc ions, thereby having profound ramifications on the use of universal animal feeds.

Halicin: A New Horizon in Antibacterial Therapy against Veterinary Pathogens.

It is crucial to discover novel antimicrobial drugs to combat resistance. This study investigated the antibacterial properties of halicin (SU3327), an AI-identified anti-diabetic drug, against 13 kinds of common clinical pathogens of animal origin, including multidrug-resistant strains. Employing minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) assessments, halicin demonstrated a broad-spectrum antibacterial effect. Time-killing assays revealed its concentration-dependent bactericidal activity against Escherichia coli ATCC 25922 (E. coli ATCC 25922), Staphylococcus aureus ATCC 29213 (S. aureus ATCC 29213), and Actinobacillus pleuropneumoniae S6 (APP S6) after 4 h of treatment at concentrations above the MIC. Halicin exhibited longer post-antibiotic effects (PAEs) and sub-MIC effects (PA-SMEs) for E. coli 25922, S. aureus 29213, and APP S6 compared to ceftiofur and ciprofloxacin, the commonly used veterinary antimicrobial agents, indicating sustained antibacterial action. Additionally, the results of consecutive passaging experiments over 40 d at sub-inhibitory concentrations showed that bacteria exhibited difficulty in developing resistance to halicin. Toxicology studies confirmed that halicin exhibited low acute toxicity, being non-mutagenic, non-reproductive-toxic, and non-genotoxic. Blood biochemical results suggested that halicin has no significant impact on hematological parameters, liver function, and kidney function. Furthermore, halicin effectively treated respiratory A. pleuropneumoniae infections in murine models. These results underscore the potential of halicin as a new antibacterial agent with applications against clinically relevant pathogens in veterinary medicine.

Fate of florfenicol and linezolid resistance genes and their bacterial hosts during two waste treatment models in swine feedlots.

Florfenicol resistance genes (FRGs) are widely present in livestock farms. The aim of this study was to evaluate the removal efficiencies of FRGs as well as the relationships between FRGs, mobile genetic elements (MGEs) and bacterial communities during the natural drying (ND) and anaerobic digestion (AD) processes of manure treatment in swine farms by combining bacterial isolation, quantitative PCR and metagenomic approaches. Solid manure showed a higher abundance of FRGs than fresh manure and was the main contamination source of fexA and fexB in ND farms, whilst biogas slurry displayed a lower abundance of FRGs than the wastewater in AD farms. Moreover, fresh manure and wastewater showed a high abundance of optrA, and wastewater was the main contamination source of cfr in both ND and AD farms. Both optrA/fexA-positive enterococci and cfr/fexA-positive staphylococci were mainly isolated along the farms' treatment processes. The cfr-positive staphylococci were highly prevalent in wastewater (57.14 % - 100 %) and may be associated with nasal-derived cfr-positive porcine staphylococci. An increased abundance of Enterococcus, Jeotgalibaca and Vagococcus in the bacterial community structures may account for the high optrA abundance in wastewater and Jeotgalibaca may be another potential host of optrA. Furthermore, the abundance of FRG-related MGEs increased by 22.63 % after the ND process and decreased by 66.96 % in AD farms. A significant correlation was observed between cfr and ISEnfa4, whereas no significance was found between optrA and IS1216E, although IS1216E is the predominant insertion sequence involved in the transfer of optrA. In conclusion, manure and wastewater represented independent pollution sources of FRGs in swine farms. Associated MGEs might play a key role in the transfer and persistence of FRGs. The AD process was more efficient in the removal of FRGs than the ND method, nevertheless a longer storage of slurry may be required for a complete removal.

Antimicrobial resistance profiles of common mastitis pathogens on large Chinese dairy farms.

The primary objective of this study was to determine the antimicrobial resistance (AMR) profile of common mastitis pathogens on large Chinese dairy farms. A total of 673 isolates, including Staphylococcus aureus (14.41%, 97/673), coagulase-negative staphylococci (CNS, 52.30%, 352/673), Streptococcus agalactiae (5.64%, 38/673), non-agalactiae streptococci (7.42%, 50/673), Acinetobacter spp. (7.72%, 52/673), Escherichia spp. (6.39%, 43/673), and Klebsiella spp. (6.09%, 41/673), were collected from 15 large Chinese dairy farms in 12 provinces. The AMR profiles were measured using a microdilution method. Our results showed that more than 75% of Staph. aureus (87/97) and CNS (291/352) were resistant to penicillin (PEN). More than 30% of Escherichia spp. (15/43) showed resistance to ampicillin (AMP). However, less than 10% CNS and non-agalactiae streptococci showed resistance to amoxicillin/clavulanate (AMC; 1/352; 0/50), cephalexin (LEX; 1/352; 0/50), ceftiofur (EFT; 10/352; 0/50), and rifaximin (RIX; 21/352; 2/50); less than 10% Staph. aureus showed resistance to AMC (1/97), oxacillin (OX; 3/97), LEX (1/97), EFT (2/97), and RIX (2/97); less than 10% Strep. agalactiae showed resistance to PEN (3/38), AMC (0/38), LEX (0/38), EFT (0/38), and RIX (0/38); and less than 10% Escherichia spp. showed resistance to AMC (1/43) and EFT (4/43). These results suggested that most mastitis pathogens were susceptible to most antimicrobials with exceptions of Staph. aureus tested against penicillin or ampicillin and CNS against penicillin or oxacillin. To control the AMR threat in Chinese dairy farms, a nationwide surveillance program for AMR of bovine mastitis pathogens is needed.

Transmission of blaNDM in Enterobacteriaceae among animals, food and human.

Despite carbapenems not being used in animals, carbapenem-resistant Enterobacterales (CRE), particularly New Delhi metallo-ß-lactamase-producing CRE (NDM-CRE), are prevalent in livestock. Concurrently, the incidence of human infections caused by NDM-CRE is rising, particularly in children. Although a positive association between livestock production and human NDM-CRE infections at the national level was identified, the evidence of direct transmission of NDM originating from livestock to humans remains largely unknown. Here, we conducted a cross-sectional study in Chengdu, Sichuan Province, to examine the prevalence of NDM-CRE in chickens and pigs along the breeding-slaughtering-retail chains, in pork in cafeterias of schools, and in colonizations and infections from children's hospital and examined the correlation of NDM-CRE among animals, foods and humans. Overall, the blaNDM increases gradually along the chicken and pig breeding (4.70%/2.0%) -slaughtering (7.60%/22.40%) -retail (65.56%/34.26%) chains. The slaughterhouse has become a hotspot for cross-contamination and amplifier of blaNDM. Notably, 63.11% of pork from the school cafeteria was positive for blaNDM. The prevalence of blaNDM in intestinal and infection samples from children's hospitals was 21.68% and 19.80%, respectively. whole genome sequencing (WGS) analysis revealed the sporadic, not large-scale, clonal spread of NDM-CRE along the chicken and pig breeding-slaughtering-retail chain, with further spreading via IncX3-blaNDM plasmid within each stage of whole chains. Clonal transmission of NDM-CRE is predominant in children's hospitals. The IncX3-blaNDM plasmid was highly prevalent among animals and humans and accounted for 57.7% of Escherichia coli and 91.3% of Klebsiella pneumoniae. Attention should be directed towards the IncX3 plasmid to control the transmission of blaNDM between animals and humans.

Tigecycline Sensitivity Reduction in Escherichia coli Due to Widely Distributed tet(A) Variants.

Despite scattered studies that have reported mutations in the tet(A) gene potentially linked to tigecycline resistance in clinical pathogens, the detailed function and epidemiology of these tet(A) variants remains limited. In this study, we analyzed 64 Escherichia coli isolates derived from MacConkey plates supplemented with tigecycline (2 µg/mL) and identified five distinct tet(A) variants that account for reduced sensitivity to tigecycline. In contrast to varied tigecycline MICs (0.25 to 16 µg/mL) of the 64 tet(A)-variant-positive E. coli isolates, gene function analysis confirmed that the five tet(A) variants exhibited a similar capacity to reduce tigecycline sensitivity in DH5α carrying pUC19. Among the observed seven non-synonymous mutations, the V55M mutation was unequivocally validated for its positive role in conferring tigecycline resistance. Interestingly, the variability in tigecycline MICs among the E. coli strains did not correlate with tet(A) gene expression. Instead, a statistically significant reduction in intracellular tigecycline concentrations was noted in strains displaying higher MICs. Genomic analysis of 30 representative E. coli isolates revealed that tet(A) variants predominantly resided on plasmids (n = 14) and circular intermediates (n = 13). Within China, analysis of a well-characterized E. coli collection isolated from pigs and chickens in 2018 revealed the presence of eight tet(A) variants in 103 (4.2%, 95% CI: 3.4-5.0%) isolates across 13 out of 17 tested Chinese provinces or municipalities. Globally, BLASTN analysis identified 21 tet(A) variants in approximately 20.19% (49,423/244,764) of E. coli genomes in the Pathogen Detection database. These mutant tet(A) genes have been widely disseminated among E. coli isolates from humans, food animals, and the environment sectors, exhibiting a growing trend in tet(A) variants over five decades. Our findings underscore the urgency of addressing tigecycline resistance and the underestimated role of tet(A) mutations in this context.

Dihydroartemisinin inhibits plasmid transfer in drug-resistant Escherichia coli via limiting energy supply.

Conjugative transfer of antibiotic resistance genes (ARGs) by plasmids is an important route for ARG dissemination. An increasing number of antibiotic and nonantibiotic compounds have been reported to aid the spread of ARGs, highlighting potential challenges for controlling this type of horizontal transfer. Development of conjugation inhibitors that block or delay the transfer of ARG-bearing plasmids is a promising strategy to control the propagation of antibiotic resistance. Although such inhibitors are rare, they typically exhibit relatively high toxicity and low efficacy in vivo and their mechanisms of action are inadequately understood. Here, we studied the effects of dihydroartemisinin (DHA), an artemisinin derivative used to treat malaria, on conjugation. DHA inhibited the conjugation of the IncI2 and IncX4 plasmids carrying the mobile colistin resistance gene ( mcr-1) by more than 160-fold in vitro in Escherichia coli, and more than two-fold (IncI2 plasmid) in vivo in a mouse model. It also suppressed the transfer of the IncX3 plasmid carrying the carbapenem resistance gene bla NDM-5 by more than two-fold in vitro. Detection of intracellular adenosine triphosphate (ATP) and proton motive force (PMF), in combination with transcriptomic and metabolomic analyses, revealed that DHA impaired the function of the electron transport chain (ETC) by inhibiting the tricarboxylic acid (TCA) cycle pathway, thereby disrupting PMF and limiting the availability of intracellular ATP for plasmid conjugative transfer. Furthermore, expression levels of genes related to conjugation and pilus generation were significantly down-regulated during DHA exposure, indicating that the transfer apparatus for conjugation may be inhibited. Our findings provide new insights into the control of antibiotic resistance and the potential use of DHA.

In Situ Neutralization and Detoxification of LPS to Attenuate Hyperinflammation.

Hyperinflammation elicited by lipopolysaccharide (LPS) that derives from multidrug-resistant Gram-negative pathogens, leads to a sharp increase in mortality globally. However, monotherapies aiming to neutralize LPS often fail to improve the prognosis. Here, an all-in-one drug delivery strategy equipped with bactericidal activity, LPS neutralization, and detoxification is shown to recognize, kill pathogens, and attenuate hyperinflammation by abolishing the activation of LPS-triggered acute inflammatory responses. First, bactericidal colistin results in rapid bacterial killing, and the released LPS is subsequently sequestered. The neutralized LPS is further cleared by acyloxyacyl hydrolase to remove secondary fatty chains and detoxify LPS in situ. Last, such a system shows high efficacy in two mouse infection models challenged with Pseudomonas aeruginosa. This approach integrates direct antibacterial activity with in situ LPS neutralizing and detoxifying properties, shedding light on the development of alternative interventions to treat sepsis-associated infections.

[Synergistic effect of ß-thujaplicin and tigecycline against tet(X4)-positive Escherichia coli in vitro].

The widespread of tigecycline resistance gene tet(X4) has a serious impact on the clinical efficacy of tigecycline. The development of effective antibiotic adjuvants to combat the looming tigecycline resistance is needed. The synergistic activity between the natural compound ß-thujaplicin and tigecycline in vitro was determined by the checkerboard broth microdilution assay and time-dependent killing curve. The mechanism underlining the synergistic effect between ß-thujaplicin and tigecycline against tet(X4)-positive Escherichia coli was investigated by determining cell membrane permeability, bacterial intracellular reactive oxygen species (ROS) content, iron content, and tigecycline content. ß-thujaplicin exhibited potentiation effect on tigecycline against tet(X4)-positive E. coli in vitro, and presented no significant hemolysis and cytotoxicity within the range of antibacterial concentrations. Mechanistic studies demonstrated that ß-thujaplicin significantly increased the permeability of bacterial cell membranes, chelated bacterial intracellular iron, disrupted the iron homeostasis and significantly increased intracellular ROS level. The synergistic effect of ß-thujaplicin and tigecycline was identified to be related to interfere with bacterial iron metabolism and facilitate bacterial cell membrane permeability. Our studies provided theoretical and practical data for the application of combined ß-thujaplicin with tigecycline in the treatment of tet(X4)-positive E. coli infection.

Genomic Diversity of Methicillin-Resistant Staphylococcus aureus CC398 Isolates Collected from Diseased Swine in the German National Resistance Monitoring Program GERM-Vet from 2007 to 2019.

Livestock-associated methicillin-resistant Staphylococcus aureus (LA-MRSA) clonal complex 398 (CC398) isolates (n = 178) collected in the national resistance monitoring program GERM-Vet from diseased swine in Germany from 2007 to 2019 were investigated for their genomic diversity with a focus on virulence and antimicrobial resistance (AMR) traits. Whole-genome sequencing was followed by molecular typing and sequence analysis. A minimum spanning tree based on core-genome multilocus sequence typing was constructed, and antimicrobial susceptibility testing was performed. Most isolates were assigned to nine clusters. They displayed close phylogenetic relationships but a wide molecular variety, including 13 spa types and 19 known and four novel dru types. Several toxin-encoding genes, including eta, seb, sek, sep, and seq, were detected. The isolates harbored a wide range of AMR properties mirroring the proportions of the classes of antimicrobial agents applied in veterinary medicine in Germany. Multiple novel or rare AMR genes were identified, including the phenicol-lincosamide-oxazolidinone-pleuromutilin-streptogramin A resistance gene cfr, the lincosamide-pleuromutilin-streptogramin A resistance gene vga(C), and the novel macrolide-lincosamide-streptogramin B resistance gene erm(54). Many AMR genes were part of small transposons or plasmids. Clonal and geographical correlations of molecular characteristics and resistance and virulence genes were more frequently observed than temporal relations. In conclusion, this study provides insight into population dynamics of the main epidemic porcine LA-MRSA lineage in Germany over a 13-year-period. The observed comprehensive AMR and virulence properties, most likely resulting from the exchange of genetic material between bacteria, highlighted the importance of LA-MRSA surveillance to prevent further dissemination among swine husbandry facilities and entry into the human community. IMPORTANCE The LA-MRSA-CC398 lineage is known for its low host specificity and frequent multiresistance to antimicrobial agents. Colonized swine and their related surroundings represent a considerable risk of LA-MRSA-CC398 colonization or infection for occupationally exposed people through which such isolates might be further disseminated within the human community. This study provides insight into the diversity of the porcine LA-MRSA-CC398 lineage in Germany. Clonal and geographical correlations of molecular characteristics and resistance and virulence traits were detected and may be associated with the spread of specific isolates through livestock trade, human occupational exposure, or dust emission. The demonstrated genetic variability underlines the lineage's ability to horizontally acquire foreign genetic material. Thus, LA-MRSA-CC398 isolates have the potential to become even more dangerous for various host species, including humans, due to increased virulence and/or limited therapeutic options for infection control. Full-scale LA-MRSA monitoring at the farm, community, and hospital level is therefore essential.

[Discovery, structure and function of plasmid mediated shufflon].

Antimicrobial resistance has become a major public health issue of global concern. Conjugation is an important way for fast spreading drug-resistant plasmids, during which the type Ⅳ pili plays an important role. Type Ⅳ pili can adhere on the surfaces of host cell and other medium, facilitating formation of bacterial biofilms, bacterial aggregations and microcolonies, and is also a critical factor in liquid conjugation. PilV is an adhesin-type protein found on the tip of type Ⅳ pili encoded by plasmid R64, and can recognize the lipopolysaccharid (LPS) molecules that locate on bacterial membrane. The shufflon is a clustered inversion region that diversifies the PilV protein, which consequently affects the recipient recognition and conjugation frequency in liquid mating. The shufflon was firstly discovered on an IncI1 plasmid R64 and has been identified subsequently in plasmids IncI2, IncK and IncZ, as well as the pathogenicity island of Salmonella typhi. The shufflon consists of four segments including A, B, C, and D, and a specific recombination site named sfx. The shufflon is regulated by its downstream-located recombinase-encoding gene rci, and different rearrangements of the shufflon region in different plasmids were observed. Mobile colistin resistance gene mcr-1, which has attracted substantial attentions recently, is mainly located in IncI2 plasmid. The shufflon may be one of the contributors to fast spread of mcr-1. Herein, we reviewed the discovery, structure, function and prevalence of plasmid mediated shufflon, aiming to provide a theoretical basis on transmission mechanism and control strategy of drug-resistant plasmids.

Genomic Shift in Population Dynamics of mcr-1-positive Escherichia coli in Human Carriage.

Emergence of the colistin resistance gene, mcr-1, has attracted worldwide attention. Despite the prevalence of mcr-1-positive Escherichia coli (MCRPEC) strains in human carriage showing a significant decrease between 2016 and 2019, genetic differences in MCRPEC strains remain largely unknown. We therefore conducted a comparative genomic study on MCRPEC strains from fecal samples of healthy human subjects in 2016 and 2019. We identified three major differences in MCRPEC strains between these two time points. First, the insertion sequence ISApl1 was often deleted and the percentage of mcr-1-carrying IncI2 plasmids was increased in MCRPEC strains in 2019. Second, the antibiotic resistance genes (ARGs), aac(3)-IVa and blaCTX-M-1, emerged and coexisted with mcr-1 in 2019. Third, MCRPEC strains in 2019 contained more virulence genes, resulting in an increased proportion of extraintestinal pathogenic E. coli (ExPEC) strains (36.1%) in MCRPEC strains in 2019 compared to that in 2016 (10.5%), implying that these strains could occupy intestinal ecological niches by competing with other commensal bacteria. Our results suggest that despite the significant reduction in the prevalence of MCRPEC strains in humans from 2016 to 2019, MCRPEC exhibits increased resistance to other clinically important ARGs and contains more virulence genes, which may pose a potential public health threat.

Spreading of cfr-Carrying Plasmids among Staphylococci from Humans and Animals.

The multidrug resistance gene cfr mediates resistance to multiple antimicrobial agents, including linezolid. Plasmids are the preferred vector for the dissemination of cfr. However, the presence and transmission of cfr-carrying plasmids among staphylococci from humans and animals have rarely been studied. Here, we investigated the presence of the cfr gene in 2,250 staphylococci of human clinical origin collected in Zhejiang, China, in 1998 to 2021 and in 3,329 porcine staphylococci preserved in our laboratories. The cfr gene was detected in 38 human isolates; its presence in Staphylococcus haemolyticus and Staphylococcus cohnii in 2003 was earlier than that identified in 2005, and Staphylococcus capitis (n = 30) was the predominant species. The cfr-carrying fragment in 38 isolates exhibited >99% nucleotide sequence similarity to plasmid pLRSA417 (39,504 bp), which was identified in 2015 and originated from a human clinical methicillin-resistant Staphylococcus aureus isolate from Zhejiang, China. The cfr-carrying plasmids in 18 MinION-sequenced staphylococci ranged in size from 32,697 bp to 43,457 bp. Fifteen plasmids were identical to pLRSA417, except for the inversion of an 8.4-kb segment comprising IS256-aacA/aphD-ISEnfa4_1-cfr-ISEnfa4_2, while the remaining 3 plasmids exhibited slightly different structures. Among the 114 cfr-positive staphylococci from pigs, pLRSA417-like plasmids were detected in 3 isolates. Intraspecies and interspecies conjugation occurred in human-derived pLRSA417-like plasmids. The presence of pLRSA417-like plasmids in staphylococci from multiple geographic regions and different hosts implied the possible transmission of the respective isolates between humans and animals. IMPORTANCE The therapeutic efficacy of the oxazolidinone antimicrobial linezolid is reduced by the emergence and dissemination of the multidrug resistance gene cfr. The cfr-carrying plasmid pLRSA417 was first identified in a clinical methicillin-resistant Staphylococcus aureus isolate, but its presence in staphylococci of human and animal origin has not been reported previously. This study showed that conjugative plasmids similar to pLRSA417 were detected mainly in Staphylococcus capitis and existed in different staphylococci in 2003 to 2021 in various clinical departments in the same hospital. pLRSA417-like plasmids were also present in staphylococci of food animal sources from different geographic regions, which suggested possible transmission among humans and animals.

Metabolic Characteristics of Porcine LA-MRSA CC398 and CC9 Isolates from Germany and China via Biolog Phenotype MicroArrayTM.

Livestock-associated methicillin-resistant Staphylococcus aureus (LA-MRSA) is an important zoonotic pathogen, often multi-resistant to antimicrobial agents. Among swine, LA-MRSA of clonal complex (CC) 398 dominates in Europe, Australia and the Americas, while LA-MRSA-CC9 is the main epidemic lineage in Asia. Here, we comparatively investigated the metabolic properties of rare and widespread porcine LA-MRSA isolates from Germany and China using Biolog Phenotype MicroArray technology to evaluate if metabolic variations could have played a role in the development of two different epidemic LA-MRSA clones in swine. Overall, we were able to characterize the isolates' metabolic profiles and show their tolerance to varying environmental conditions. Sparse partial least squares discriminant analysis (sPLS-DA) supported the detection of the most informative substrates and/or conditions that revealed metabolic differences between the LA-MRSA lineages. The Chinese LA-MRSA-CC9 isolates displayed unique characteristics, such as a consistently delayed onset of cellular respiration, and increased, reduced or absent usage of several nutrients. These possibly unfavorable metabolic properties might promote the ongoing gradual replacement of the current epidemic LA-MRSA-CC9 clone in China with the emerging LA-MRSA-CC398 lineage through livestock trade and occupational exposure. Due to the enhanced pathogenicity of the LA-MRSA-CC398 clone, the public health risk posed by LA-MRSA from swine might increase further.

Clonal relationship of tet(X4)-positive Escherichia coli ST761 isolates between animals and humans.

OBJECTIVES: To characterize the relationship of tet(X4)-positive isolates from different hosts and environments. METHODS: PCR and MALDI-TOF MS were used to identify the tet(X4)-positive isolates. The MICs of 13 antimicrobial agents were determined by broth microdilution. Illumina technology was used to sequence all of the isolates. One isolate was randomly selected from Escherichia coli ST761 clones for long-read sequencing to obtain plasmid sequences. Bioinformatics analysis was used to determine the phylogeny of 46 tet(X4)-positive E. coli ST761 strains. RESULTS: A total of 12 tet(X4)-positive isolates, 8 E. coli and 4 Aeromonas simiae, were obtained from six lairages of a slaughterhouse. These isolates exhibited resistance to at least three classes of antimicrobials, including tigecycline. The majority of them, seven E. coli and three A. simiae, represent separate clonal groups. Notably, the seven E. coli isolates belonged to ST761, a common ST carrying the tet(X4) gene that has been identified in 39 isolates from animals, meat, wastewater and humans from seven Chinese provinces. All 46 tet(X4)-positive E. coli ST761 strains from various sources have a close phylogenetic relationship (0-72 SNPs), with a high nucleotide sequence similarity of resistance genes and the tet(X4)-carrying IncX1-IncFIA(HI1)-IncFIB(K) hybrid plasmid, indicating a clonal relationship of tet(X4)-positive E. coli ST761 among animals, food, the environment and humans. CONCLUSIONS: The clonal relationship of tet(X4)-positive E. coli ST761 between humans and animals poses a previously underestimated threat to public health. To the best of our knowledge, this is the first description of tet(X4)-positive A. simiae.