Genetic, virulence, and antimicrobial resistance characteristics associated with distinct morphotypes in ST11 carbapenem-resistant Klebsiella pneumoniae.

ST11 is the most common lineage among carbapenem-resistant Klebsiella pneumoniae (CRKP) infections in Asia. Diverse morphotypes resulting from genetic mutations are associated with significant differences in microbial characteristics among K. pneumoniae isolates. Here, we investigated the genetic determinants and critical characteristics associated with distinct morphotypes of ST11 CRKP. An ST11-KL47 CRKP isolate carrying a pLVPK-like virulence plasmid was isolated from a patient with a bloodstream infection; the isolate had the "mcsw" morphotype. Two distinct morphotypes ("ntrd" and "msdw") were derived from this strain during in vitro passage. Whole genome sequencing was used to identify mutations that cause the distinct morphotypes of ST11 CRKP. Transmission electron microscopy, antimicrobial susceptibility tests, growth assays, biofilm formation, virulence assays, membrane permeability assays, and RNA-seq analysis were used to investigate the specific characteristics associated with different morphotypes of ST11 CRKP. Compared with the parental mcsw morphotype, the ntrd morphotype resulted from mutation of genes involved in capsular polysaccharide biosynthesis (wza, wzc, and wbaP), a result validated by gene knockout experiments. This morphotype showed capsule deficiency and lower virulence potential, but higher biofilm production. By contrast, the msdw morphotype displayed competition deficiency and increased susceptibility to chlorhexidine and polymyxin B. Further analyses indicated that these characteristics were caused by interruption of the sigma factor gene rpoN by insertion mutations and deletion of the rpoN gene, which attenuated membrane integrity presumably by downregulating the phage shock protein operon. These data expand current understanding of genetic, virulence, and antimicrobial resistance characteristics associated with distinct morphotypes in ST11 CRKP.

Comparison of in vitro synergy between polymyxin B or colistin in combination with 16 antimicrobial agents against multidrug-resistant Acinetobacter baumannii isolates.

PURPOSES: This study determined the synergy of polymyxin B (POLB) and colistin (COL) with 16 other tested antimicrobial agents in the inhibition of multidrug-resistant Acinetobacter baumannii (MDR-AB). METHODS: We used chequerboard assays to determine synergy between the drugs against 50 clinical MDR-AB from a tertiary hospital in the Zhejiang province in 2019, classifying combinations as either antagonistic, independent, additive, or synergistic. The efficacy of hit combinations which showed highest synergistic rate were confirmed using time-kill assays. RESULTS: Both POLB and COL displayed similar bactericidal effects when used in combination with these 16 tested drugs. Antagonism was only observed for a few strains (2%) exposed to a combination of POLB and cefoperazone/sulbactam (CSL). A higher percentage of synergistic combinations with POLB and COL were observed with rifabutin (RFB; 90%/96%), rifampicin (RIF; 60%/78%) and rifapentine (RFP; 56%/76%). Time-kill assays also confirmed the synergistic effect of POLB and rifamycin class combinations. 1/2 MIC rifamycin exposure can achieve bacterial clearance when combined with 1/2 MIC POLB or COL. CONCLUSION: Nearly no antagonism was observed when combining polymyxins with other drugs by both chequerboard and time-kill assays, suggesting that polymyxins may be effective in combination therapy. The combinations of POLB/COL with RFB, RIF, and RFP displayed neat synergy, with RFB showing the greatest effect.

ESKAPE in China: epidemiology and characteristics of antibiotic resistance.

The escalation of antibiotic resistance and the diminishing antimicrobial pipeline have emerged as significant threats to public health. The ESKAPE pathogens - Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter spp. - were initially identified as critical multidrug-resistant bacteria, demanding urgently effective therapies. Despite the introduction of various new antibiotics and antibiotic adjuvants, such as innovative ß-lactamase inhibitors, these organisms continue to pose substantial therapeutic challenges. People's Republic of China, as a country facing a severe bacterial resistance situation, has undergone a series of changes and findings in recent years in terms of the prevalence, transmission characteristics and resistance mechanisms of antibiotic resistant bacteria. The increasing levels of population mobility have not only shaped the unique characteristics of antibiotic resistance prevalence and transmission within People's Republic of China but have also indirectly reflected global patterns of antibiotic-resistant dissemination. What's more, as a vast nation, People's Republic of China exhibits significant variations in the levels of antibiotic resistance and the prevalence characteristics of antibiotic resistant bacteria across different provinces and regions. In this review, we examine the current epidemiology and characteristics of this important group of bacterial pathogens, delving into relevant mechanisms of resistance to recently introduced antibiotics that impact their clinical utility in China.

Clinical relevance, mechanisms, and evolution of polymyxin B heteroresistance carbapenem-resistant Klebsiella pneumoniae: A genomic, retrospective cohort study.

OBJECTIVES: To study the clinical relevance, mechanisms, and evolution of polymyxin B (POLB) heteroresistance (PHR) in carbapenem-resistant Klebsiella pneumoniae (CRKP), potentially leading to a significant rise in POLB full resistant (FR) CRKP. METHODS: Total of 544 CRKP isolates from 154 patients treated with POLB were categorized into PHR and POLB non-heteroresistance (NHR) groups. We performed statistical analysis to compare clinical implications and treatment responses. We employed whole-genome sequencing, bioinformatics, and PCR to study the molecular epidemiology, mechanisms behind PHR, and its evolution into FR. RESULTS: We observed a considerable proportion (118 of 154, 76.62%) of clinically undetected PHR strains before POLB exposure, with a significant subset of them (33 of 118, 27.97%) evolving into FR after POLB treatment. We investigated the clinical implications, epidemiological characteristics, mechanisms, and evolutionary patterns of PHR strains in the context of POLB treatment. About 92.86% (39 of 42) of patients had PHR isolates before FR, highlighting the clinical importance of PHR. the ST15 exhibited a notably lower PHR rate (1 of 8, 12.5% vs. 117 of 144, 81.25%; p < 0.01). The ST11 PHR strains showing significantly higher rate of mgrB mutations by endogenous insertion sequences in their resistant subpopulation (RS) compared with other STs (78 of 106, 73.58% vs. 4 of 12, 33.33%; p < 0.01). The mgrB insertional inactivation rate was lower in FR isolates than in the RS of PHR isolates (15 of 42, 35.71% vs. 84 of 112, 75%; p < 0.01), whereas the pmrAB mutation rate was higher in FR isolates than in the RS of PHR isolates (8 of 42, 19.05% vs. 2 of 112, 1.79%; p < 0.01). The evolution from PHR to FR was influenced by subpopulation dynamics and genetic adaptability because of hypermutability. DISCUSSION: We highlight significant genetic changes as the primary driver of PHR to FR in CRKP, underscoring polymyxin complexity.

Comparative analysis of genomic characteristics, virulence and fitness of community-associated Staphylococcus aureus ST121 clone causing fatal diseases in China and other CA-MRSA clones.

The increasing rate of community-associated Staphylococcus aureus (CA-SA) worldwide has aroused global public concern for decades. Although ST121 clone is one of the prevalent CA-SA in China, there is still limited knowledge about it. In this study, we conducted a genomic analysis of 28 CA-SA ST121 isolates from severe bloodstream infection cases and 175 ST121 isolates from the public database. Phylogenetic analysis revealed the consistency and the complexity of global ST121 lineages, and suggested potential cross-country even cross-continental transmission of ST121 isolates. By investigating the virulence and fitness between ST121-CA-methicillin-resistant SA (CA-MRSA) and other CA-MRSA clones, we found that ST121-MRSA exhibits virulence comparable to the highly virulent USA300 clone, exceeding that of the predominant CA-MRSA lineage ST59 in China and the other American CA-MRSA clone MW2. Notably, based on analyses of virulence genes, eta, etb, edin-C and egc were only found in ST121, suggesting that the high virulence of ST121 may be attributed to the combination of these virulence factors encoded by mobile genetic elements. However, results of experiments in mice nasal and human alveolar epithelial cells showed that the colonization capacity of ST121 is much lower than that of other clones. Moreover, ST121-MRSA displayed much lower acid tolerance, suggesting that ST121-MRSA may not have such capacity to achieve the epidemiological success of other CA-MRSA clones and become the dominant lineage. Our findings expand current understanding of the epidemiology and pathogenicity of the hypervirulent ST121 clone, and highlight the importance of colonization capacity and environmental adaption in MRSA epidemiological success.

Clinical, biological and genome-wide comparison of carbapenem-resistant Klebsiella pneumoniae with susceptibility transformation to polymyxin B during therapy.

OBJECTIVES: The emergence of carbapenem-resistant Klebsiella pneumoniae (CRKP) is a major clinical concern, and polymyxin B (PMB) is a 'last resort' antibiotic for its treatment. Understanding the effects of drug susceptibility transformation in CRKP-infected patients undergoing PMB treatment would be beneficial to optimize PMB treatment strategies. METHODS: We retrospectively collected data from patients infected with CRKP and treated with PMB from January 2018 to December 2020. CRKPs were collected before and after PMB therapy, and patients were classified into the 'transformation' group (TG) and 'non-transformation' group (NTG) by the shift of susceptibility to PMB. We compared clinical characteristics between these groups, and further analysed the phenotypic and genome variation of CRKP after PMB susceptibility transformation. RESULTS: A total of 160 patients (37 in the TG and 123 in the NTG) were included in this study. The duration of PMB treatment before PMB-resistant K. pneumoniae (PRKP) appearance in TG was even longer than the whole duration of PMB treatment in NTG (8 [8] vs. 7 [6] days; p 0.0496). Compared with isogenic PMB-susceptible K. pneumoniae (PSKP), most PRKP strains had missense mutations in mgrB (12 isolates), yciC (10 isolates) and pmrB (7 isolates). The competition index of 82.4% (28/34) of PRKP/PSKP pairs was <67.6% (23/34), and 73.5% (25/34) of PRKP strains showed a higher 7-day lethality in Galleria mellonella and a greater ability to resist complement-dependent killing than their corresponding PSKP, respectively. CONCLUSION: Low dose with longer PMB treatment durations may be associated with the emergence of polymyxin resistance. The evolution of PRKP is predominantly mediated by an accumulation of mutations, including those in mgrB, yciC, and pmrB. Lastly, PRKP exhibited reduced growth and increased virulence compared with parental PSKP.

Genomic epidemiology of mcr carrying multidrug-resistant ST34 Salmonella enterica serovar Typhimurium in a one health context: The evolution of a global menace.

The rapid global dissemination of Salmonella enterica sequence type 34 (ST34) has sparked significant concern due to its resistance to critical antimicrobials and its ability to spread across various sectors. In order to investigate the evolution and transmission dynamics of this epidemic clonal lineage, as well as the horizontal transfer of mcr-carrying plasmids within the One Health framework, we conducted a comprehensive genomic epidemiological study. This study focused on the 11 mcr-carrying S. enterica isolates obtained from clinical settings in China, while also considering 2337 publicly available genomes of mcr-carrying S. enterica collected from 20 countries and diverse sources spanning over a 22-year period. Among the mcr-positive Salmonella isolates, ST34 was found to be the predominant lineage, comprising 30.12 % (704/2337) of the total collection. These isolates were identified as either serovar Typhimurium or its monophasic variant, which were obtained from both clinical and non-clinical sources. Phylogeographic analyses traced the global spread of the mcr-carrying ST34 lineage, which was divided into three distinct clusters, with 83.10 % of them carrying mcr-1 or/and mcr-9 genes. Notably, the mcr-1 positive ST34 isolates were primarily found in China (190/298, 63.76 %), with only four from the United States. Conversely, mcr-9 positive ST34 isolates were predominantly identified in the United States (261/293, 89.08 %), while none were observed in China. The mcr-1 positive ST34 isolates was predicted to have originated from clinical sources in United Kingdom, whereas mcr-9 positive ST34 isolates was likely derived from environmental sources in Germany. The most recent common ancestor for mcr-1 and mcr-9 carrying ST34 S. enterica was estimated to have emerged around 1983 and 1951. These findings provided thorough and intuitive insights into the intercontinental spread of mcr-carrying S. enterica ST34 lineage in a One Health context. Ongoing surveillance is crucial for effectively monitoring the worldwide dissemination of this multidrug-resistant high-risk clone.

The variants of polymyxin susceptibility in different species of genus Aeromonas.

The aquatic environment is an important medium for the accumulation and dissemination of antibiotic-resistant bacteria as it is often closely related to human activities. Previous studies paid little attention to the prevalence and mechanism of polymyxin-resistant bacteria in the aquatic environment. As a Gram-negative opportunistic pathogen widely distributed in aquatic ecosystems, the antibiotic-resistant profile of Aeromonas spp. deserves much attention. In this study, we identified 61 Aeromonas spp. isolates from water samples in the section of the Yangtze River. The total polymyxin B (PMB) resistance rate of these strains was 49.18% (30/61), showing a high level of polymyxin resistance in Aeromonas spp. The MIC50 and MIC90 for PMB exhibited a significant discrepancy among different species (p < 0.001). The MIC50 and MIC90 for PMB in the Aeromonas hydrophila were 128 mg/L and above 128 mg/L while in Aeromonas caviae and Aeromonas veronii, the MIC50 and MIC90 value were both 2 mg/L. Only two A. veronii strains (MIC = 2 mg/L) and one A. caviae strain (MIC = 0.5 mg/L) were identified as carrying mobilized polymyxin resistant gene mcr-3.42, and mcr-3.16. All mcr genes were located in the chromosome. This is the first report that the downstream region of mcr-3.42 was the truncated mcr-3-like gene separated by the insertion sequences of ISAs20 (1,674 bp) and ISAs2 (1,084 bp). Analysis of epidemiology of mcr-positive Aeromonas genomes from GenBank database showed that the genus Aeromonas and the aquatic environment might be the potential container and reservoir of mcr-3. By the whole-genome sequencing and qRT-PCR, we inferred that the sequence differences in the AAA domain of MlaF protein and its expression level among these three species might be involved in the development of polymyxin resistance. Our study provided evidences of the possible mechanism for the variety of polymyxin susceptibility in different species of the genus Aeromonas and a theoretical basis for the surveillance of the aquatic environment.

Efficacy and safety of novel carbapenem-ß-lactamase inhibitor combinations: Results from phase II and III trials.

Objectives: The addition of novel ß-lactamase inhibitors to carbapenems restores the activity against multidrug-resistant Gram-negative bacteria. The aim of this study was to summarize the evidence on the efficacy and safety of novel carbapenem-ß-lactamase inhibitor combinations. Methods: We conducted a meta-analysis of clinical trials comparing novel carbapenem-ß-lactamase inhibitor combinations with comparators to assess the clinical and microbiological responses, mortality, and adverse events (AEs). Results: A total of 1,984 patients were included. The pooled risk ratios (RRs) of clinical cure, microbiological eradication, all-cause mortality, and 28-day mortality were 1.11 (95% CI: 0.98-1.26), 0.98 (95% CI: 0.82-1.16), 0.90 (95% CI: 0.49-0.94), and 0.68 (95% CI: 0.49-0.94) between the novel carbapenem-ß-lactamase inhibitor combinations and control groups. Sensitivity analysis revealed that the phase II trial of imipenem-cilastatin/relebactam (ICR) against complicated urinary tract infections could be the most important factor of heterogeneity for the microbiological response. The therapeutic effect of novel carbapenem-ß-lactamase inhibitor combinations was better in meropenem-vaborbactam (MEV), phase III trials, and number of patients less than 200. The RRs of AEs from any cause and serious adverse events (SAEs) for patients receiving novel carbapenem-ß-lactamase inhibitor combinations were 0.98 (95% CI: 0.93-1.04) and 1.01 (95% CI: 0.75-1.36), respectively. Conclusions: ICR and MEV were superior to comparators for clinical cure and survival rate in the treatment of complicated infections, and both were as tolerable as the comparators.

Corrigendum: Comparative respiratory tract microbiome between carbapenem-resistant Acinetobacter baumannii colonization and ventilator associated pneumonia.

[This corrects the article DOI: 10.3389/fmicb.2022.782210.].

Emergence of Colistin Resistance Gene mcr-10 in Enterobacterales Isolates Recovered from Fecal Samples of Chickens, Slaughterhouse Workers, and a Nearby Resident.

The wide spread of plasmid-borne mobilized colistin resistance (mcr) genes from animals to humans broadly challenges the clinical use of polymyxins. Here, we evaluated the incidence of a recently reported mcr variant, mcr-10, in animals and humans in the same area. Our results revealed the presence of novel mcr-10-carrying plasmids in two Klebsiella pneumoniae isolates from chickens, one Escherichia coli isolate from slaughterhouse workers, and a chromosome-borne mcr-10 gene in Enterobacter kobei from a healthy resident in the same region. It is worth mentioning that the multidrug-resistant ST11 K. pneumoniae isolates coharboring mcr-10 and mcr-8 genes in two separate plasmids not only were resistant to polymyxins (MIC = 8 mg/L) but also showed reduced susceptibility to tigecycline (MIC ≥ 2 mg/L) due to the tet(A) mutation or the tmexCD1-toprJ1 gene cluster. The structure xerC-mcr10-insCinsD-like was found in genetic environments of both the plasmid and chromosome carrying mcr-10. We compared genomic epidemiological characteristics of mcr-10-harboring bacteria available in 941,449 genomes in the NCBI database (including strains of K. pneumoniae, E. coli, and E. kobei) with isolates in this study. The results indicated a sporadic distribution of mcr-10 all around the world and in a variety of sources, including humans, environments, and animals, which confirms that mcr-10 has spread among various hosts and warrants close monitoring and further future studies. IMPORTANCE We discovered mcr-10-harboring isolates in the "one health" approach and reported for the first time multidrug-resistant clinically threatening ST11 K. pneumoniae isolates coharboring mcr-10 and mcr-8 genes that are resistant to polymyxins and show reduced susceptibility to tigecycline. The exhaustive screening of 941,449 bacterial genomes in the GenBank database discovered a sporadic distribution of mcr-10-harboring isolates all around the world in a variety of sources, especially humans, which warrants close monitoring and a particular concern in clinical settings.

Comparative Respiratory Tract Microbiome Between Carbapenem-Resistant Acinetobacter baumannii Colonization and Ventilator Associated Pneumonia.

Background: Carbapenem-resistant Acinetobacter baumannii (CRAB) is a common cause of ventilator-associated pneumonia (VAP) in intensive care unit (ICU) patients, but its infection and colonization state are difficult to distinguish. If the judgment is wrong, it may aggravate the abuse of antibiotics and further accelerate the evolution of drug resistance. We sought to provide new clues for the diagnosis, pathogenesis and treatment of CRAB VAP based on lower respiratory tract (LRT) microbiota. Methods: A prospective study was conducted on patients with mechanical ventilation from July 2018 to December 2019 in a tertiary hospital. Multi-genomics studies (16S rRNA amplicon, metagenomics, and whole-genome sequencing [WGS]) of endotracheal deep aspirate (ETA) were performed. Results: Fifty-two ICU patients were enrolled, including 24 with CRAB VAP (CRAB-I), 22 with CRAB colonization (CRAB-C), and six CRAB-negative patients (infection-free) (CRAB-N). Diversity of pulmonary microbiota was significantly lower in CRAB-I than in CRAB-C or CRAB-N (mean Shannon index, 1.79 vs. 2.73 vs. 4.81, P < 0.05). Abundances of 11 key genera differed between the groups. Acinetobacter was most abundant in CRAB-I (76.19%), moderately abundant in CRAB-C (59.14%), and least abundant in CRAB-N (11.25%), but its interactions with other genera increased in turn. Metagenomics and WGS analysis showed that virulence genes were more abundant in CRAB-I than in CRAB-C. Multi-locus sequence typing (MLST) of 46 CRAB isolates revealed that the main types were ST208 (30.43%) and ST938 (15.22%), with no difference between CRAB-I and CRAB-C. Conclusion: Lower respiratory tract microbiota dysbiosis including elevated relative abundance of Acinetobacter and reduced bacterial interactions, and virulence enrichment may lead to CRAB VAP.

Genomic epidemiology and characterisation of penicillin-sensitive Staphylococcus aureus isolates from invasive bloodstream infections in China: an increasing prevalence and higher diversity in genetic typing be revealed.

Many countries have reported increasing rates of penicillin-susceptible methicillin-sensitive Staphylococcus aureus (MSSA-PENS). To date, there is relatively little known about the current situation and molecular characteristics of MSSA-PENS in China. In this study, we carried out a laboratory-based multi-region retrospective study to investigate the genomic epidemiology and characterisation of MSSA-PENS isolated from invasive bloodstream infections (BSIs) across 17 provinces. The prevalence of MSSA-PENS isolates increased significantly over the 6-year period, with the proportion increasing from 3.51% in 2014-8.80% in 2019, an average relative increase of 22.14% per year (95% confidence interval 9.67%-34.61%, P for trend <0.001), suggesting that China is experiencing a resurgence of MSSA-PENS. Phylogenetic analysis showed a higher strain diversity occurred; the most frequent clonal complexes (CCs) identified were CC188 (17.14%), CC398 (15.71%) and CC5 (15.71%). Over half of MSSA-PENS strains were pan-susceptible, with erythromycin the most frequent resistance observed. Moreover, 25 isolates were identified as immune evasion cluster negative, including CC15, CC188 and CC1, and 6 strains encoded the Panton-Valentine leucocidin gene. Importantly, virulence assays showed that MSSA-PENS exhibited a level of virulence comparable to that of penicillin-resistant MSSA (MSSA-PENR), indicating that more-sensitive strains should not be mistaken for lacking aggressiveness in vivo. Furthermore, 11 of these isolates were confirmed as blaZ positive but phenotype sensitive, with different amino acid changes in blaZ. Our data support the recommendation to clinicians regarding the usage of penicillin in invasive BSIs caused by MSSA-PENS, which might create a novel opportunity for better antimicrobial stewardship in the future.

Biomimetic hybrid hydrogel for hemostasis, adhesion prevention and promoting regeneration after partial liver resection.

Partial liver resection is an established treatment for hepatic disorders. However, surgical bleeding, intra-abdominal adhesion and rapid liver regeneration are still major challenges after partial liver resection, associated with morbidity and mortality. Herein, a biomimetic hybrid hydrogel, composed of oxidized hyaluronic acid, glycol chitosan and MenSCs-derived conditioned medium (CM), is presented to address these issues. The hybrid hydrogel is formed through reversible Schiff base, and possesses injectability and self-healing capability. Moreover, hybrid hydrogel exhibits the capabilities of hemostasis, anti-infection, tissue adhesion and controllable release of cargoes. Based on in vivo studies of the multifunctional hybrid hydrogel, it is demonstrated that acute bleeding in partial liver resection can be ceased immediately by virtue of the hemostasis features of hybrid hydrogel. Also, a significant reduction of intra-abdominal adhesion is confirmed in hybrid hydrogel-treated resection surface. Furthermore, upon the treatment of hybrid hydrogel, hepatic cell proliferation and tissue regeneration can be significantly improved due to the controllably released cytokines from MenSCs-derived CM, exerting the effects of mitogenesis and anti-inflammation in vivo. Thus, the biomimetic hybrid hydrogel can be a promising candidate with great potential for application in partial liver resection.

In Vitro Activity Comparison of Ceftazidime-Avibactam and Aztreonam-Avibactam Against Bloodstream Infections With Carbapenem-Resistant Organisms in China.

Objectives: The aim of this work was to investigate the activity of ceftazidime-avibactam (CZA) and aztreonam-avibactam (AZA) against bloodstream infections caused by carbapenem-resistant organisms (CROs). Methods: Non-duplicate CROs, including 56 carbapenem-resistant Escherichia coli (CR-Eco), 318 carbapenem-resistant Klebsiella pneumoniae (CR-Kpn), and 65 carbapenem-resistant Pseudomonas aeruginosa (CR-Pae), were collected using the Blood Bacterial Resistant Investigation Collaborative System (BRICS) program in China. The minimum inhibitory concentrations (MICs) of 24 antibiotics were tested. Carbapenemase genes were amplified for CZA-resistant CROs by PCR. The MICs of CZA and AZA were further determined with avibactam at 8 and 16 mg/L, respectively. Results: The resistance rate of polymyxin B against CROs was less than 5%. Only one CR-Kpn was resistant to tigecycline. The resistance rates of CZA against CR-Eco, CR-Kpn, and CR-Pae were 75.0%, 12.6%, and 18.5%, respectively. The MIC90 values of AZA against CR-Eco, CR-Kpn, and CR-Pae were 2/4, 1/4, and 64/4 mg/L, respectively. Among the CZA-resistant CROs, 42 (100%) CR-Eco, 24 (60%) CR-Kpn, and 1 (8.3%) CR-Pae isolates harbored metallo-ß-lactamase genes. The increase of avibactam concentration enhanced the susceptibility of CZA and AZA against CROs, especially for CR-Eco and CR-Kpn. Conclusions: The in vitro activity of AZA was superior to that of CZA against CR-Eco and CR-Kpn, whereas CZA showed better effect against CR-Pae.

Socioeconomic Burden of Bloodstream Infections Caused by Carbapenem-Resistant Enterobacteriaceae.

BACKGROUND: Although infection with carbapenem-resistant Enterobacteriaceae (CRE) has become an urgent public health threat worldwide, the socioeconomic burden of CRE bloodstream infection (BSI) remains to be clarified. METHODS: This retrospective study included all patients infected with Escherichia coli or Klebsiella pneumoniae who were hospitalized for BSI from 2013 to 2015. Socioeconomic burden, including direct and indirect economic burden, was compared in patients infected with carbapenem-sensitive Enterobacteriaceae (CSE) and CRE following 1:1 propensity score matching (PSM) to control for confounding variables. RESULTS: Data from 879 patients with Enterobacteriaceae BSI were evaluated, including 152 (17.3%) patients infected with CRE and 727 (82.7%) infected with CSE. PSM yielded 112 pairs of 224 patients. Median hospital length of stay did not differ significantly in the CRE and CSE groups (35 vs 29 days, P = 0.089), but in-hospital 28-day mortality rate was significantly higher in patients infected with CRE than with CSE (45.5% vs 32.1%, P = 0.040). Median direct economic burden was significantly greater in patients with CRE-BSI than with CSE-BSI during hospitalization ($24,940.1 vs 16,864.0, P = 0.017) but not during the period after infection ($10,403.4 vs 8498.0, P = 0.178). Drug expenditure accounted for the largest proportion of costs in both groups. The median disability-adjusted life year (DALY) was higher in CRE-BSI than in CSE-BSI patients, but the difference was not statistically significant (7.9 vs 6.7 years, P = 0.190). Median indirect economic burden did not differ significantly in these two groups ($3848.5 vs 1139.9, P = 0.304), although indirect economic burden increased significantly from 2013 to 2015 in patients with CRE-BSI. CONCLUSION: Carbapenem resistance had a major impact on the clinical and socioeconomic burden of patients with Enterobacteriaceae BSI. The higher mortality rate in patients with CRE-BSI was associated with increased direct healthcare burden and indirect socioeconomic loss.

Genomic Epidemiology and Characterization of Methicillin-Resistant Staphylococcus aureus from Bloodstream Infections in China.

Since 2010, methicillin-resistant Staphylococcus aureus (MRSA) ST59 began to increase in prevalence in China, gradually replacing ST239 and has become the dominant clone in most hospitals in China. Here, we investigated the changing epidemiology, phylogenetic reconstruction, and genomic characterization of MRSA clones in China to identify the genomic driving factors in the prevalence of ST59. Most MRSA isolates were identified as ST59 (36.98%; 277/749), which increased from 25.09% in 2014 to 35.53% in 2019. The phylogenetic analysis of the 749 MRSA isolates showed a high level of diversity and the copresence of hospital-associated, community-associated, livestock-associated, and hypervirulent clones. Furthermore, minimum spanning trees revealed that ST59 MRSA clones from different hospitals and regions were integrated, suggesting that frequent exchanges had occurred between regions and hospitals. ST59 clones displayed higher susceptibility to antimicrobials than did ST239 and ST5 MRSA clones, indicating that resistance to non-ß-lactam and fluoroquinolone antibiotics may be not critical for the epidemic success of ST59 clones. Virulence factors detection showed that sak and chp genes enriched in MRSA ST59 may be associated with the enhanced spreading success of ST59, whereas qacA may have contributed to the predominance of ST5 in East China. Our refined analysis of different clones among ST239, ST5, ST59, and ST398 demonstrated the existence of potential driving factors for the evolution of nosocomial MRSA populations and diversity of the evolutionary events surrounding clonal replacement. IMPORTANCE As a developing country, China has an unbalanced health care system due to regional differences in economic development. However, China is also a country worthy of study with regard to the population dynamics of MRSA within the more resource-rich health care systems. In this study, we carried out genomic analysis to investigate the genomic epidemiology and characterization of MRSA isolated from bloodstream infections over a timespan of 6 years. Our refined analysis of different MRSA clones among ST59, ST5, ST239, and ST398 demonstrated the existence of driving factors for the evolution of nosocomial MRSA populations and diversity of the evolutionary events surrounding clonal replacement.

New options for bloodstream infections caused by colistin- or ceftazidime/avibactam-resistant Klebsiella pneumoniae.

Concerns regarding carbapenem-resistant Klebsiella pneumoniae (CR-Kp), especially in bloodstream infections (BSIs), are continuing to increase worldwide. Several novel agents with activity against BSI CR-Kp have been approved or are in late-stage clinical development. In this study, the antibacterial effects of ceftazidime/avibactam (CZA), aztreonam/avibactam (AZA), meropenem/vaborbactam (MEV), imipenem-cilastatin/relebactam (ICR) and eravacycline (ERV) against three colistin-resistant CR-Kp (COLR-Kp) and four CZA-resistant CR-Kp (CZAR-Kp) were tested by time-kill assay. Klebsiella pneumoniae ATCC® BAA-1705TM was used as a control strain. Two COLR-Kp isolates carried the blaKPC-2 gene and four CAZR-Kp isolates carried metallo-ß-lactamase genes. The results revealed that ERV resulted in re-growth of seven tested isolates. CZA and MEV showed a bactericidal effect against isolates harbouring blaKPC-2. ICR reduced the population of six isolates to >5 log10 CFU/mL compared with the initial count. AZA showed a bactericidal effect (>5 log10 CFU/mL) against seven isolates and a bacteriostatic effect (<3 log10 CFU/mL) against one CZAR-Kp isolate. Therefore, AZA and ICR are effective therapeutic candidates for COLR-Kp and CZAR-Kp isolates.

Comparative Genomic Analysis Provides Insights into the Evolution and Genetic Diversity of Community-Genotype Sequence Type 72 Staphylococcus aureus Isolates.

Staphylococcus aureus sequence type (ST) 72, the predominant community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) lineage in South Korea, has emerged as a major cause of bloodstream infection in hospital settings. However, relatively little information is available regarding the genomic characteristics and dissemination of ST72. Here, we characterized the whole-genome sequence of 24 ST72 isolates from China, along with 83 ST72 genomes from global sources. Of these 107 ST72 isolates, 63 were MRSA and 44 were methicillin-susceptible S. aureus (MSSA). Phylogenetic analysis revealed four distinct clades (A, B, C, and D), of which clade D contained only MSSA isolates. By characterizing the evolutionary dynamics of the ST72 lineage, we found that the MRSA from China might not have developed from the MSSA in China. Furthermore, we observed both international transmission of ST72 isolates and interregional transmission within China. The distributions of the SCCmec and spa types of isolates differed among clades. Additionally, in silico analyses revealed that the distributions of resistance genes, virulence genes, and mobile genetic elements (MGEs) also differed among isolates of the four clades. This was especially true for clade D isolates, which had the lowest level of antimicrobial resistance and had obtained specific virulence genes such as tsst-1 by acquisition of specific MGEs. Notably, ST72 MRSA isolates were more antibiotic resistant than ST72 MSSA isolates, but comparably virulent. Our findings provide insight into the potential transmission and genotypic features of ST72 clones across the globe. IMPORTANCE Understanding the evolution and dissemination of community-genotype ST72 Staphylococcus aureus isolates is important, as isolates of this lineage have rapidly spread into hospital settings and caused serious health issues. In this study, we first carried out genome-wide analysis of 107 global ST72 isolates to characterize the evolution and genetic diversity of the ST72 lineage. We found that the MSSA lineage in China might have evolved independently from the MRSA isolates from China, and that ST72 isolates have the potential to undergo both international transmission and interregional transmission within China. The diversity of isolates correlated with distinct acquisitions of SCCmec elements, antibiotic resistance genes, virulence genes, and mobile genetic elements. The comprehensive information on the ST72 lineage emerging from this study will enable improved therapeutic approaches and rapid molecular diagnosis.

Genomic and Transcriptomic Analysis of Colistin-Susceptible and Colistin-Resistant Isolates Identify Two-Component System EvgS/EvgA Associated with Colistin Resistance in Escherichia coli.

PURPOSE: Colistin is one of the last-resort antimicrobial agents that combat the increasing threat of multi-drug resistant (MDR) gram-negative bacteria. Based on the known mechanism of colistin resistance which contributes to chromosomal mutations involved in the synthesis and modification of lipopolysaccharide (LPS), we explored the regulatory genes mediate colistin resistance, by whole genome sequencing and transcriptome analysis. MATERIALS AND METHODS: In this study, a colistin-resistant (Colr) strain Escherichia coli ATCC 25922-R was generated from colistin-sensible (Cols) strain E. coli ATCC 25922 by colistin induction. We compared the genome and transcriptome sequencing result from Cols and Colr strain. MALDI-TOF mass spectrometry was used to detect LPS. RESULTS: Genomic analysis and complementation experiment demonstrated the PmrB amino acid substitution in ATCC 25922-R (L14R) conferred the colistin resistance phenotype. Results of RNA sequencing (RNA-Seq) and comparative transcriptome analysis indicated that the two-component system EvgS/EvgA is highly involved in the global regulation of colistin resistance. CONCLUSION: This study demonstrated that PmrB L14R amino acid substitution resulted in colistin resistance, and two-component system EvgS/EvgA might participate in colistin resistance in E. coli.