In vitro activity of ceftolozane/tazobactam against Gram-negative bacilli isolated from pediatric patients: results from the Study for Monitoring Antimicrobial Resistance Trends (SMART) 2017-2021, China.

OBJECTIVES: Ceftolozane-tazobactam (C/T) is a combination of a cephalosporin and a ß-lactamase inhibitor with activity against Gram-negative bacilli (GNB). The study aims were to evaluate the activity of C/T in vitro vs. comparators against clinical GNB isolated from Chinese pediatric patients. METHODS: From 2017-2021, 660 GNB isolates were collected from 20 hospitals across China. The minimum inhibitory concentrations were tested using a Trek Diagnostic System (Thermo Fisher Scientific). Susceptibility was determined by CLSI broth microdilution and the results were interpreted according to CLSI M100 (2021) breakpoints. RESULTS: GNB isolates were obtained from pediatric patients < 18 years old, mainly from the bloodstream (n=146), intraperitoneal cavity (n=138), lower respiratory (n=278) and urinary tract (n=96). Overall, C/T was active against 76.6% of 436 Enterobacterales, with a descending susceptibility rate of 100.0% to S. marcescens, 92.2% to E. coli, 83.3% to K. oxytoca, 66.7% to K. aerogenes, 66.7% to P. mirabilis, 58.6% to K. pneumoniae and 57.1% to E. cloacae. The susceptibility of P. aeruginosa to C/T was 89.4%, which was the highest among the ß-lactams and was second only to amikacin (92.9%). Isolates of respiratory tract infection (RTI) derived P. aeruginosa were highly susceptible (93.8%) to C/T, while < 75% of isolates of RTI derived P. aeruginosa were susceptible to the other ß-lactams tested, except for ceftazidime-avibactam (91.2%). CONCLUSION: GNBs collected from pediatric patients in China showed a high susceptibility to C/T making this drug combination an effective choice for treating the pediatric population, especially those infected with P. aeruginosa.

Emergence and plasmid cointegration-based evolution of NDM-1-producing ST107 Citrobacter freundii high-risk resistant clone in China.

Carbapenem-resistant Citrobacter freundii (CRCF) poses an enormous challenge in the health care setting. However, the epidemiology and plasmid dynamic evolution of this species have not been well studied, especially for the novel high-risk resistant clones in the intensive care units (ICUs). Here, we characterised the cointegration-based plasmid dynamic evolution of the emerging ST107 CRCF clone in China. Twenty CRCF strains were identified, including ST22 (30%), ST107 (25%), ST396 (10%) and ST116 (10%). Interestingly, the tigecycline (TGC) resistance gene cluster tmexCD2-toprJ2 and blaNDM-1 and blaKPC-2 were simultaneously found in one ST107 strain. Epidemiological analysis showed that ST107 clone contained human- and environment-derived strains from five countries. Notably, 93.75% (15/16) of the isolates harboured blaNDM-1 or blaKPC-2. Plasmid fusion among various ST107 strains of two patients occurred in the same ICU, mediated by Tn5403 and IS26-based insertion and deletion events. pCF1807-2 carried blaNDM-1 while pCF1807-3 carried both tmexCD2-toprJ2 and blaKPC-2 in the CF1807 strain. Importantly, the cointegrate plasmid pCF1807-2 exhibited higher transfer efficiency and could remain stable after serial passage. Notably, no fitness cost was observed for the host. In conclusion, ST107 CRCF is a high-risk resistant clone due to its ability to integrate resistant plasmids. Our findings elucidated the potential threat and global transmission of the ST107 lineage, and reasonable monitoring should be performed to prevent its further spread in hospitals.

Genome Analysis of ST1 Bartonella henselae, a Zoonotic Pathogen Causing Endocarditis in an Elderly Patient in China.

Infective endocarditis (IE) is a rare disease but with high associated mortality. Currently, the mainstays of diagnosis are still echocardiography and blood cultures. Here, we reported a case of infective endocarditis with negative blood cultures, and blood and aortic valve tissue metagenomic next-generation sequencing (mNGS) results suggested Bartonella henselae. In addition, we obtained the whole genomic sequence of B. henselae ZJBH strain. To our knowledge, this is the first report of B. henselae genomic analysis isolated from clinic in China. Furthermore, we described the whole genome sequencing (WGS) data incorporating all B. henselae from diverse sources worldwide and shed light on underlying risk of B. henselae transmitted between cats and humans.

Study on Effects of Refining Slag on Properties and Hydration of Cemented Solid Waste-Based Backfill.

This study used refining slag (RS), ground granulated blast furnace slag (GGBS), steel slag (SS), and desulfurized gypsum (DG) to prepare a mine-filling cementitious material. The developed cementitious material and tailings sand were mixed to prepare a novel mine backfill material with better performance and a lower cost. The macroscopic properties and hydration mechanism of the cemented solid waste-based backfill were investigated when RS content was 0, 5%, 10%, 15%, 20%, 30% and 40%. The results showed that introducing RS could reduce the bleeding rate and shorten the setting time of backfill slurry while significantly enhancing the 3-day compressive strength of backfill. Compared to JL-0, the bleeding rate decreased by 50.3% as the RS content was raised to 15%, while the setting time was shortened by 36.5%, and the 3-day compressive strength increased by 4.3 times. As the RS content did not exceed 20%, the 28-day compressive strength of the backfill was not lower than that of the cement backfill (4.3 MPa). The results of microanalysis (including XRD, FT-IR, SEM, TG-DSC, and heat of hydration) revealed that the hydration products of the RS-GGBS-SS-DG quaternary material are primarily C-(A)-S-H gels and AFt. The main effect of RS is to improve the content of aluminates, accelerating and increasing the production of AFt, thus leading to faster overall hydration. This research can provide data support for the application of RS in the mine-filling field. Applying quaternary solid waste-based cementitious materials in the mine-filling field has good economic benefits.

Invasive Infection With emm3/ST15 Streptococcus pyogenes: The First Case Report From China and Complete Genome Analysis.

Streptococcus pyogenes (GAS) may cause severe invasive disease with a high fatality rate, especially M3-type strains, which are less common in China. Here, we report the first emm3/ST15 invasive GAS infection case in China. The patient was diagnosed with severe skin and soft tissue infection (SSTI) and septicaemia caused by one GAS strain. Antibiotic susceptibility tests showed that the isolate was susceptible to all tested drugs. Antimicrobial therapy was then applied, and the patient fully recovered and was discharged from the hospital on Day 43. Whole-genome sequencing was carried out using the Illumina and Oxford Nanopore platforms and revealed this to be the first emm3/ST15-type GAS invasive infection in China. The closely related emm3/ST15-type GAS strains are MGAS315 from the United States and M3-b from Japan. Our finding is a warning that we should pay attention to invasive M3-type GAS infections in China and indicates the global spread of the highly virulent emm3/ST15 GAS strain.

Complete Genome Sequence of a Rare Pigment-Producing Strain of Acinetobacter johnsonii, Isolated from the Bile of a Patient in Hangzhou, China.

Here, we report the complete genome sequence of a rare pigment-producing strain of Acinetobacter johnsonii. The genome consists of a 3,360,823-bp circular chromosome (G+C content, 41.56%) and an 8,887-bp plasmid (G+C content, 33.71%). It possesses 3,038 coding gene sequences, 19 rRNA genes, 87 tRNA genes, and 4 noncoding RNA (ncRNA) genes.

Mechanism of eravacycline resistance in Acinetobacter baumannii mediated by a deletion mutation in the sensor kinase adeS, leading to elevated expression of the efflux pump AdeABC.

Acinetobacter baumannii is an important pathogen and presents a major burden in healthcare as strains frequently cause hospital associated opportunistic infections with high mortality rates. Due to increasing numbers of drug resistant A. baumannii strains, newly developed antibiotics are being used to treat infections caused by such strains. One novel synthetic antibiotic of the tetracycline class with activity against A. baumannii is eravacycline. To investigate possible mechanisms of eravacycline resistance, we performed an in vitro evolution experiment to select for an eravacycline resistant strain, with the clinical isolate MDR-ZJ06 as parental strain. We obtained a strain designated MDR-ZJ06-E6 that was able to grow in 64-fold MIC. Genomic mutations were identified by whole genome sequencing, where we found a deletion mutation in the gene adeS. Using complementation experiments, including growth rate determination and antibiotics susceptibility testing, we could confirm that this mutation was responsible for eravacycline resistance of strain MDR-ZJ06-E6. As a mechanism of resistance, we identified a significant overexpression of the efflux pump AdeABC which seems to be regulated by the mutation in adeS in A. baumannii.

Emergence of a Clinical Escherichia coli Sequence Type 131 Strain Carrying a Chromosomal bla KPC-2 Gene.

Objectives: Bacteria carrying the Klebsiella pneumoniae carbapenemase genes have rapidly spread worldwide and have become a great threat to public health. The bla KPC-2 gene has been primarily located on plasmids cocirculating in various strains. However, chromosomal integration of the bla KPC -2 gene in Escherichia coli has not been reported. In the present study, we report the detection of the first clinical strain of E. coli ST131 with a bla KPC -2 gene, which integrated in the chromosome. E. coli strain EC3385 was identified and subjected to susceptibility testing and genotyping. The complete genome sequences of this strain and four Proteus mirabilis strains were obtained. Chromosomal integration of the bla KPC-2 gene was confirmed using a combination of short- and long-read sequencing. Comparative genetic analyses were performed and the origin of the chromosomal location of the bla KPC-2 gene was further analyzed. Whole-genome sequencing revealed that strain EC3385 belonged to the ST131 type and possessed various resistance and virulence genes. Sequence analysis showed that the bla KPC-2 gene was carried in a 24-kb insertion sequence on the chromosome. This insertion sequence possessed high sequence similarity to previously reported bla KPC-2 -habouring plasmids of P. mirabilis in China. To the best of our knowledge, this is the first report of a clinical ST131 E. coli strain carrying bla KPC-2 on the chromosome. The bla KPC-2 gene was probably horizontally transferred from the P. mirabilis plasmid to the E. coli chromosome by the IS26 element, indicating that P. mirabilis might be an important reservoir of bla KPC-2 gene for E. coli. Furthermore, the E. coli ST131 strain carrying the chromosomal bla KPC -2 gene could be further spread due to its carbapenem resistance and high virulence. It is imperative to perform active surveillance to prevent further dissemination of KPC-2 type carbapenemase-producing isolates.

Detection and characterization of a clinical Escherichia coli ST3204 strain coproducing NDM-16 and MCR-1.

OBJECTIVES: A plasmid-mediated colistin resistance gene, mcr-1, has been reported worldwide and has caused concern regarding a major therapeutic challenge. Alarmingly, mcr-1 has spread into clinical carbapenem-resistant Enterobacteriaceae isolates, resulting in extensively drug-resistant and even pan drug-resistant isolates that can cause untreatable infections. In this study, we report isolation of an extensively drug-resistant Escherichia coli strain EC1188 that coproduces NDM-16 and MCR-1 from a urine sample taken from a patient with craniocerebral injury. MATERIALS AND METHODS: E. coli strain EC1188 was identified and subjected to genotyping, susceptibility testing and conjugation experiments. The genetic locations of blaNDM-16 and mcr-1 were established with southern blot hybridization. The complete genome sequence of this strain was obtained and the genetic characteristics of the mcr-1- and blaNDM-16-harboring plasmids were analyzed. In addition, comparative genetic analyses of mcr-1 and blaNDM-16 with closely related plasmids were also carried out. RESULTS: Whole-genome sequencing revealed that strain EC1188 possess various resistance genes and virulence genes. S1-pulsed-field gel electrophoresis and southern blot suggested that the blaNDM-16 and mcr-1 genes were located on an ~65 kb plasmid and an ~80 kb plasmid, respectively. Moreover, the two genes could successfully transfer their resistance phenotype to E. coli strain C600. Sequence analysis showed that these two plasmids possessed high sequence similarity to previously reported blaNDM-5-harboring and mcr-1-harboring plasmids in China. CONCLUSION: To the best of our knowledge, this is the first report to isolate an E. coli strain that coproduces NDM-16 and MCR-1. In addition, we characterized the blaNDM-16-harboring plasmid for the first time. Our study further emphasizes that the co-occurrence of the two prevalent transferrable resistance plasmids in a single isolate is highly significant because infections caused by MCR-1-producing carbapenem-resistant Enterobacteriaceae isolates are increasing each year. It is imperative to perform active surveillance to prevent further dissemination of MCR-1-producing CRE isolates.

The Effect of Colistin Resistance-Associated Mutations on the Fitness of Acinetobacter baumannii.

Acinetobacter baumannii had emerged as an important nosocomial and opportunistic pathogen worldwide. To assess the evolution of colistin resistance in A. baumannii and its effect on bacterial fitness, we exposed five independent colonies of A. baumannii ATCC 17978 to increasing concentrations of colistin in agar (4/5) and liquid media (1/5). Stable resistant isolates were analyzed using whole genome sequencing. All strains were colistin resistant after exposure to colistin. In addition to the previously reported lpxCAD and pmrAB mutations, we identified four novel putative colistin resistance genes: A1S_1983. hepA. A1S_3026, and rsfS. Lipopolysaccharide (LPS) loss mutants exhibited higher fitness costs than those of the pmrB mutant in nutrient-rich medium. The colistin-resistant mutants had a higher inhibition ratio in the serum growth experiment than that of the wild type strain in 100% serum. Minimum inhibitory concentration (MIC) results showed that the LPS-deficient but not the pmrB mutant had an altered antibiotic resistance profile. The compensatory mutations partially or completely rescued the LPS-deficient's fitness, suggesting that compensatory mutations play an important role in the emergence and spread of colistin resistance in A. baumannii.

Rapid emergence of high-level tigecycline resistance in Escherichia coli strains harbouring blaNDM-5 in vivo.

Tigecycline (TIG) resistance is a growing concern because this antibiotic is regarded as one of the last resorts to treat infections caused by multidrug-resistant and extensively drug-resistant (XDR) bacteria. Information regarding TIG-resistant Escherichia coli isolates is scarce. In this study, we report the emergence of high-level TIG resistance in a longitudinal series of XDR E. coli isolates collected during TIG treatment. Whole-genome sequencing was performed for six E. coli strains harbouring bla(NDM-5) and genomic comparison revealed two amino acid substitutions. Mutation in rpsJ could be a significant factor conferring TIG resistance in these isolates. The fitness cost of TIG resistance in resistant strains was evaluated by determining the relative growth rate, indicating that TIG resistance reduced fitness by ca. 7%. This study is the first report to demonstrate high-level TIG resistance in E. coli in vivo. In addition, we report the first treatment-emergent minimum inhibitory concentration (MIC) development of TIG from 1mg/L to 64 mg/L in E. coli. Clinicians should be aware of the risk of an increase in the MIC of TIG under therapy.

Cefepime combined with amoxicillin/clavulanic acid: a new choice for the KPC-producing K. pneumoniae infection.

OBJECTIVE: Clinical treatment for blaKPC-positive Klebsiella pneumoniae isolates is challenging because the recommended antibiotic options are limited and are extraordinarily expensive. This study aimed to explore a new therapy for infection caused by KPC-producing K. pneumoniae. METHODS: Patients with blaKPC-positive K. pneumoniae infection, were prospectively screened and were categorised into two groups: patients in the study group received a combination-based therapy of cefepime and amoxicillin/clavulanic acid and the control group received tigecycline-based therapy. The pathogen clearance rate, 28-day mortality and cost of the antibiotic treatment were compared between the two groups. Moreover, the checkerboard microdilution method was performed to determine the synergy between cefepime and amoxicillin/clavulanic acid in vitro. RESULTS: Twenty-six and 25 cases were enrolled in the study and control groups. The mortality and the overall pathogen clearance rate showed no significant differences (P=0.311 and P=0.447). Both the total cost and the portion of the cost not covered by insurance were higher for the control group compared to the study group (both P<0.001). Consistently, synergy (65.4%) and partial synergy (26.9%) were the main effects. CONCLUSIONS: In contrast to the currently recommended tigecycline-based therapy, cefepime and amoxicillin/clavulanic acid combination was an effective and economical option to KPC-KP infection in China.