Molecular characterization and epidemiology of carbapenem non-susceptible Enterobacteriaceae isolated from the Eastern region of Heilongjiang Province, China

A large-scale surveillance revealed that KPC variants mediated ceftazidime-avibactam resistance in clinically isolated Klebsiella pneumoniae

To monitor the resistance rate and gain a deeper understanding of the resistance mechanisms, we conducted over a 2-year surveillance focusing on the Klebsiella pneumoniae associated with the clinical usage of ceftazidime-avibactam (CZA) in a teaching hospital. A total of 4,641 K. pneumoniae isolates were screened to identify the CZA resistance through antimicrobial susceptibility testing. Comprehensive analyses, including homology analysis, conjugation experiments, clone assays, and whole genome sequencing, were furtherly performed on the CZA-resistant strains. In total, four CZA-resistant K. pneumoniae (CZA-R-Kp) strains were separated from four patients, in which three of them received CZA treatment during the hospitalization, accounting for a 4% (3/75) resistance development rate of K. pneumoniae under CZA stress. All CZA-R-Kp isolates were found to possess variants of blaKPC-2. The identified mutations included blaKPC-33, blaKPC-86, and a novel variant designated as blaKPC-129, all of which were located in the Ω loop of the KPC enzyme. These mutations were found to impact the amino acid sequence and spatial structure of the enzyme's active center, consequently affecting KPC carbapenemase activity. This study underscores the importance of active surveillance to monitor the emergence of resistance to CZA, highlighting the need for ongoing research to develop effective strategies for combating antimicrobial resistance. Understanding the mechanisms behind resistance is crucial in maintaining the efficacy of CZA, a vital tool in the battle against multidrug-resistant infections.IMPORTANCEAs an effective drug for the treatment of carbapenem-resistant Klebsiella pneumoniae, ceftazidime-avibactam (CZA) began to develop resistance in recent years and showed an increasing trend. In order to effectively monitor the resistance rate of CZA and understand its resistance mechanism, we monitored K. pneumoniae for more than 2 years to find CZA-resistant strains. Through comprehensive analysis of the selected CZA-resistant strains, it was found that all the CZA-resistant strains had mutation, which could affect the activity of KPC carbapenemase. This study highlights the importance of proactive surveillance to monitor the emergence of CZA resistance, which highlights the need for ongoing research to develop effective strategies to combat antimicrobial resistance. Understanding the mechanisms behind resistance is critical to maintaining the effectiveness of CZA, an important tool in the fight against multidrug-resistant infections.

Carbapenem-resistant Enterobacteriaceae in the livestock, humans and environmental samples around the globe: a systematic review and meta-analysis

Carbapenem-resistant Enterobacteriaceae (CRE) have diminished treatment options causing serious morbidities and mortalities. This systematic review and meta-analysis assessed the prevalence and associated factors of Enterobacteriaceae infections in clinical, livestock and environmental settings globally. The population intervention comparison and outcome strategy was used to enroll studies using the preferred reporting system for systematic review and meta-analysis to include only cross-sectional studies. Search engines used to retrieve articles included journal author name estimator, PubMed, Google Scholar and African Journals Online (AJOL). The Newcastle-Ottawa scale was used to assess the quality of studies. Sixteen articles from 2013 to 2023 in Africa, Asia, Europe and South America were studied. The pooled prevalence of CRE was 43.06% (95% CI 21.57-66.03). Klebsiella pneumoniae (49.40%), Escherichia coli (26.42%), and Enterobacter cloacae (14.24%) were predominant. Klebsiella pneumoniae had the highest resistance with the blaKPC-2 in addition to blaNDM, blaOXA-48, blaIMP and blaVIM. The blaKPC-2 genes occurrence was associated with environmental (P-value < 0.0001) and South American studies (P-value < 0.0001), but there was no difference in the trends over time (P-value = 0.745). This study highlights the high rates of CRE infections, particularly within blaKPC production. Monitoring and surveillance programs, research and infection control measures should be strengthened. Additionally, further studies are needed to explore the mechanisms driving the predominance of specific bacterial species and the distribution of resistance genes within this bacterial family.

In vitro and in vivo activity of ceftazidime/avibactam and aztreonam alone or in combination against mcr-9, serine- and metallo-β-lactamases-co-producing carbapenem-resistant Enterobacter cloacae complex

PURPOSE

Enterobacteriaceae carrying mcr-9, in particularly those also co-containing metallo-β-lactamase (MBL) and TEM type β-lactamase, present potential transmission risks and lack adequate clinical response methods, thereby posing a major threat to global public health. The aim of this study was to assess the antimicrobial efficacy of a combined ceftazidime/avibactam (CZA) and aztreonam (ATM) regimen against carbapenem-resistant Enterobacter cloacae complex (CRECC) co-producing mcr-9, MBL and TEM.

METHODS

The in vitro antibacterial activity of CZA plus ATM was evaluated using a time-kill curve assay. Furthermore, the in vivo interaction between CZA plus ATM was confirmed using a Galleria mellonella (G. mellonella) infection model.

RESULTS

All eight clinical strains of CRECC, co-carrying mcr-9, MBL and TEM, exhibited high resistance to CZA and ATM. In vitro time-kill curve analysis demonstrated that the combination therapy of CZA + ATM exerted significant bactericidal activity against mcr-9, MBL and TEM-co-producing Enterobacter cloacae complex (ECC) isolates with a 100% synergy rate observed in our study. Furthermore, in vivo survival assay using Galleria mellonella larvae infected with CRECC strains co-harboring mcr-9, MBL and TEM revealed that the CZA + ATM combination significantly improved the survival rate compared to the drug-treatment alone and untreated control groups.

CONCLUSION

To our knowledge, this study represents the first report on the in vitro and in vivo antibacterial activity of CZA plus ATM against CRECC isolates co-harboring mcr-9, MBL and TEM. Our findings suggest that the combination regimen of CZA + ATM provides a valuable reference for clinicians to address the increasingly complex antibiotic resistance situation observed in clinical microorganisms.

Transcriptomic analysis of induced resistance to polymyxin in carbapenem-resistant Enterobacter cloacae complex isolate carrying mcr-9

OBJECTIVES

Polymyxins are currently the last-resort treatment against multi-drug resistant Gram-negative bacterial infections, but plasmid-mediated mobile polymyxin resistance genes (mcr) threaten its efficacy, especially in carbapenem-resistant Enterobacter cloacae complex (CRECC). The objective of this study was to provide insights into the mechanism of polymyxin-induced bacterial resistance and the effect of overexpression of mcr-9.

METHODS

The clinical strain CRECC414 carrying the mcr-9 gene was treated with a gradient concentration of polymyxin. Subsequently, the broth microdilution was used to determine the minimum inhibitory concentration (MIC) and RT-qPCR was utilized to assess mcr-9 expression. Transcriptome sequencing and whole genome sequencing (WGS) was utilized to identify alterations in strains resulting from increased polymyxin resistance, and significant transcriptomic differences were analysed alongside a comprehensive examination of metabolic networks at the genomic level.

RESULTS

Polymyxin treatment induced the upregulation of mcr-9 expression and significantly elevated the MIC of the strain. Furthermore, the WGS and transcriptomic results revealed a remarkable up-regulation of arnBCADTEF gene cassette, indicating that the Arn/PhoPQ system-mediated L-Ara4N modification is the preferred mechanism for achieving high levels of resistance. Additionally, significant alterations in bacterial gene expression were observed with regards to multidrug efflux pumps, oxidative stress and repair mechanisms, cell membrane biosynthesis, as well as carbohydrate metabolic pathways.

CONCLUSION

Polymyxin greatly disrupts the transcription of vital cellular pathways. A complete PhoPQ two-component system is a prerequisite for polymyxin resistance of Enterobacter cloacae, even though mcr-9 is highly expressed. These findings provide novel and important information for further investigation of polymyxin resistance of CRECC.

Activities of aztreonam in combination with several novel β-lactam-β-lactamase inhibitor combinations against carbapenem-resistant Klebsiella pneumoniae strains coproducing KPC and NDM

Isolates coproducing serine/metallo-carbapenems are a serious emerging public health threat, given their rapid dissemination and the limited number of treatment options. The purposes of this study were to evaluate the in vitro antibacterial activity of novel β-lactam-β-lactamase inhibitor combinations (BLBLIs) against carbapenem-resistant Klebsiella pneumoniae (CRKP) coproducing metallo-β-lactamase and serine-β-lactamase, and to explore their effects in combination with aztreonam, meropenem, or polymyxin in order to identify the best therapeutic options. Four CRKP isolates coproducing K. pneumoniae carbapenemase (KPC) and New Delhi metallo-β-lactamase (NDM) were selected, and a microdilution broth method was used to determine their susceptibility to antibiotics. Time-kill assay was used to detect the bactericidal effects of the combinations of antibiotics. The minimum inhibitory concentration (MIC) values for imipenem and meropenem in three isolates did not decrease after the addition of relebactam or varbobactam, but the addition of avibactam to aztreonam reduced the MIC by more than 64-fold. Time-kill assay demonstrated that imipenem-cilastatin/relebactam (ICR) alone exerted a bacteriostatic effect against three isolates (average reduction: 1.88 log10 CFU/mL) and ICR combined with aztreonam exerted an additive effect. Aztreonam combined with meropenem/varbobactam (MEV) or ceftazidime/avibactam (CZA) showed synergistic effects, while the effect of aztreonam combined with CZA was inferior to that of MEV. Compared with the same concentration of aztreonam plus CZA combination, aztreonam/avibactam had a better bactericidal effect (24 h bacterial count reduction >3 log10CFU/mL). These data indicate that the combination of ATM with several new BLBLIs exerts powerful bactericidal activity, which suggests that these double β-lactam combinations might provide potential alternative treatments for infections caused by pathogens coproducing-serine/metallo-carbapenems.

Mechanism for transmission and pathogenesis of carbapenem-resistant Enterobacterales harboring the carbapenemase IMP and clinical countermeasures

Carbapenem-resistant Enterobacterales (CRE) are some of the most important pathogens causing infections, which can be challenging to treat. We identified four blaIMP-carrying CRE isolates and collected clinical data. The transferability and stability of the plasmid were verified by conjugation, successive passaging, and plasmid elimination assays. The IncC blaIMP-4-carrying pIMP4-ECL42 plasmid was successfully transferred into the recipient strain, and the high expression of traD may have facilitated the conjugation transfer of the plasmid. Interestingly, the plasmid showed strong stability in clinical isolates. Whole-genome sequencing was performed on all isolates. We assessed the sequence similarity of blaIMP -harboring plasmid from our institution and compared it to plasmids for which sequence data are publicly available. We found that four blaIMP-carrying CRE belonged to four different sequence types. The checkerboard technique and time-kill assays were used to investigate the best antimicrobial therapies for blaIMP-carrying CRE. The time-kill assay showed that the imipenem of 1× minimum inhibitory concentration (MIC) alone had the bactericidal or bacteriostatic effect against IMP-producing strains at 4-12 h in vitro. Moreover, the combination of tigecycline (0.5/1/2 × MIC) and imipenem (0.5/1 × MIC) showed a bactericidal effect against the blaIMP-26-carrying CRECL60 strain.IMPORTANCECarbapenem-resistant Enterobacterales (CRE) are an urgent public health threat, and infections caused by these microorganisms are often associated with high mortality and limited treatment options. This study aimed to determine the clinical features, molecular characteristics, and plasmid transmissible mechanisms of blaIMP carriage as well as to provide a potential treatment option. Here, we demonstrated that conjugated transfer of the IncC blaIMP-4-carrying plasmid promotes plasmid stability, so inhibition of conjugated transfer and enhanced plasmid loss may be potential ways to suppress the persistence of this plasmid. The imipenem alone or tigecycline-imipenem combination showed a good bactericidal effect against IMP-producing strains. In particular, our study revealed that imipenem alone or tigecycline-imipenem combination may be a potential therapeutic option for patients who are infected with IMP-producing strains. Our study supports further trials of appropriate antibiotics to determine optimal treatment and emphasizes the importance of continued monitoring of IMP-producing strains in the future.

Molecular Epidemiology of Carbapenem-Resistant Klebsiella pneumoniae in a Tertiary Hospital in Northern China

Background

In recent years, carbapenem-resistant Klebsiella pneumoniae (CRKP) has emerged rapidly in China with the abuse and overuse of antibiotics, and infections caused by CRKP pose a serious threat to global public health safety. The present study aimed to explore the epidemiological characteristics of CRKP isolates in Northern China and to elucidate their drug resistance mechanisms.

Methods

45 CRKP strains were consecutively collected at a teaching hospital from March 1st, 2018 to June 30th, 2018. Antimicrobial susceptibility was determined by the VITEK2 compact system and microbroth dilution method. Polymerase chain reaction (PCR) and sequencing were used to analyze multilocus sequence typing (MLST), drug resistance determinants, and plasmid types. The transfer of resistance genes was determined by conjugation. All statistical analysis was performed using SPSS 22.0 software.

Results

All 45 isolates showed multidrug resistance (MDR). MLST analysis showed ST11 (48.9%, 22/45) was the most frequent type. All of the 45 CRKP isolates contained carbapenemase genes, extended-spectrum β-lactamase (ESBL) genes, and plasmid-mediated quinolone resistance (PMQR) genes. For carbapenemase genes, KPC-2 (93.3%, 42/45) was the main genotype, and followed by GES (37.8%, 17/45) and NDM-1 (11.1%, 5/45). Plasmid typing analysis showed that IncFII and IncFIB were the most prevalent plasmids. The carbapenem resistance rate of K.pneumoniae was 11.4% and ICU was the main CRKP infection source.

Conclusions

ST11 is the most frequent sequence type and KPC-2 is the predominant carbapenemase of CRKP strains in Northern China. KPC-2-ST11 are representative clonal lineages.

Molecular antibiotic resistance mechanisms and co-transmission of the mcr-9 and metallo-β-lactamase genes in carbapenem-resistant Enterobacter cloacae complex

Carbapenem-resistant Enterobacter cloacae complex (CRECC) has increasingly emerged as a major cause of healthcare-associated infections, with colistin being one of the last-resort antibiotics of treatment. Mobile colistin resistance (mcr)-9 is a member of a growing family of mcr genes and has been reported to be an inducible gene encoding an acquired phosphoethanolamine transferase. Here, we collected 24 ECC strains from Chongqing, China from 2018 to 2021. Subsequently, antibiotic resistance genes and the transmission dynamics of the strains were determined by PCR, whole-genome sequencing, and bioinformatic analysis. The mcr-9 was identified in IncHI2/2A or IncHI2/2A + IncN plasmids from six CRECC strains and was co-located with bla NDM-1 or bla IMP-4 in 2/6 plasmids. The genetic environment of mcr-9.1 was composed of IS903B-mcr-9.1-wbuC-IS26 in the five mcr-9.1-harboring-plasmid, but IS1B was located downstream of mcr-9.2 in the pECL414-1 sequence. We also found that the pNDM-068001 plasmid carrying mcr-9.1 could be a hybrid plasmid, formed by a Tn6360-like bla NDM-1 region inserted into an mcr-9.1-positive IncHI2/2A plasmid. A conjugation assay showed that plasmids mediated the co-dissemination of mcr-9 and metallo-β-lactamase (MBL) genes. In addition, we performed induction assays with sub-inhibitory concentrations of colistin and found an increase in the relative expression levels of the mcr-9.2, qseC, and qseB genes, as well as an increase in the minimum inhibitory concentration values of colistin in the CRECC414 strain. These findings provide a basis for studying the regulatory mechanisms of mcr-9 expression and highlight the importance of effective monitoring to assess the prevalence of MBL and mcr-9 co-existing plasmids.

Increased Expression and Amplification of blaKPC-2 Contributes to Resistance to Ceftazidime/Avibactam in a Sequence Type 11 Carbapenem-Resistant Klebsiella pneumoniae Strain

Ceftazidime/avibactam (CAZ/AVI) is regarded as an effective alternative antibiotic for the clinical treatment of Klebsiella pneumoniae carbapenemase (KPC)-producing isolates. As resistance has been reported in some strains, it is critical to understand the key mechanisms contributing to the acquired resistance to CAZ/AVI. From January 2018 to April 2020, 127 KPC-producing carbapenem-resistant Klebsiella pneumoniae strains (CRKPs) were isolated at a university hospital in Chongqing, China, and 25 strains showed reduced susceptibility to CAZ/AVI. All reduced-susceptibility CRKPs were deficient in Ompk35 and Ompk36 porins, and 24 strains had a premature termination at amino acid position 63 in Ompk35 and 134 to 135 glycine and aspartic acid (GD) insertion in OmpK36, while the blaKPC-2 expression level showed no significant difference compared to that of strain BAA-1705. Four reduced-susceptibility strains evolved resistance under selective pressure of CAZ/AVI with the blaKPC-2 expression level increased, and two of these strains had mutations in the Ω-loop. The study found a strain of CRKP55 with changes in the resistance phenotype during conjugation, evolving from reduced sensitivity to high-level resistance to CAZ/AVI. Through plasmid sequencing and reverse transcription-quantitative PCR, it was speculated that insertion sequence (IS)26-mediated blaKPC-2 gene amplification caused the MIC value change in the conjugant JKP55. Our findings illustrated the potential of CAZ/AVI resistance under antibiotic stress and demonstrated that IS26 may mediate blaKPC-2 replication transposition, leading to high-level resistance during horizontal gene transfer. Investigation of CAZ/AVI resistance mechanisms may offer a unique opportunity to study the horizontal evolutionary trajectories of K. pneumoniae high-risk clones. IMPORTANCE Klebsiella pneumoniae carbapenemase (KPC) production is the most common mechanism of K. pneumoniae resistance to carbapenems in China. Currently, CAZ/AVI is considered a potential alternative therapeutic option for infections caused by these isolates. However, there have been increasing reports of resistant or reduced-sensitivity strains since the approval of this agent. In this study, resistance to CAZ/AVI was induced under drug-selective pressure and was caused by blaKPC-2 overexpression and/or substitutions in the Ω-loop of KPC. Additionally, it was demonstrated that a conjugative plasmid carrying blaKPC-2 could transfer horizontally between species, and perhaps, IS26-derived tandem amplification of blaKPC-2 during this period led to high-level resistance to CAZ/AVI. Our research suggests that IS26-mediated resistance evolution may have important implications in guiding clinical antibiotic use.

Molecular characterization of NDM-1-producing carbapenem-resistant E. cloacae complex from a tertiary hospital in Chongqing, China

Background

The aim of this study was to clarify the molecular characterization of NDM-1-producing carbapenem-resistant Enterobacter cloacae complex (CREL) at a teaching hospital in Chongqing, China.

Methods

Antimicrobial susceptibility and resistance genes were analyzed. Epidemiological relationship was analyzed by pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing (MLST). Conjugation experiments were performed to determine the transferability of plasmids. Whole-genome sequencing (WGS) of strains was implemented, and the genetic environment of the blaNDM-1- and mcr-9-carrying plasmids was analyzed.

Results

A total of 10 blaNDM-1-positive CREL isolates were identified. All isolates harbored multiple resistance genes. ECL68 and ECL78 co-produce blaNDM-1 and mcr-9. Among the four different sequence types (STs) detected, ST1466 was assigned as a novel ST. Six isolates exhibited highly similar PFGE patterns. Conjugation assay proved that all plasmids containing blaNDM-1 or mcr-9 could be transferred to the recipient Escherichia coli. WGS indicated that blaNDM-1 genes were carried by diverse plasmids, including IncHI2/IncN, IncX3, and one unclassified plasmid type. The backbone structure of these plasmids is involved in replication initiation (repAB), partitioning (parABM), and conjugation/type IV secretion (tra/virB). Analysis of the genetic environment showed that blaNDM-1 in three plasmids exhibited a highly similar structure to protype Tn125. Co-existence of blaNDM-1 and the colistin resistance gene mcr-9 was detected in the two isolates, ECL68 and ECL78. In ECL68, blaNDM-1 and mcr-9 were present on the same plasmid while located in two separate plasmids in ECL78. The genetic environment of mcr-9 was organized as IS26-wbuC-mcr-9-IS903-pcoS-pcoE-rcnA-rcnR, and the two-component system encoding genes qseC and qseB was not found in two plasmids, which could explain mcr-9-harboring strains’ colistin susceptibility.

Conclusions

We first report a nosocomial outbreak of NDM-1-producing E. cloacae complex ST177 in China. Conjugative plasmids contributed to the horizontal transfer of antibiotic resistance genes. The prevalence and even coexistence of blaNDM-1 and mcr-9 may further threaten public health. Our results highlight further surveillance for blaNDM-1, and mcr-9 is essential to prevent its dissemination.

A Longitudinal Survey of Antibiotic-Resistant Enterobacterales in the Irish Environment, 2019-2020

The natural environment represents a complex reservoir of antibiotic-resistant bacteria as a consequence of different wastewater discharges including anthropogenic and agricultural. Therefore, the aim of this study was to examine sewage and waters across Ireland for the presence of antibiotic-resistant Enterobacterales. Samples were collected from the West, East and South of Ireland. Two periods of sampling took place between July 2019 and November 2020, during which 118 water (30 L) and 36 sewage samples (200 mL) were collected. Waters were filtered using the CapE method, followed by enrichment and culturing. Sewage samples were directly cultured on selective agars. Isolates were identified by MALDI-TOF and antibiotic susceptibility testing was performed in accordance with EUCAST criteria. Selected isolates were examined for bla_CTX-M, bla_VIM, bla_IMP, bla_OXA-48, bla_NDM, and bla_KPC by real time PCR and whole genome sequencing (n = 146). A total of 419 Enterobacterales (348 water, 71 sewage) were isolated from all samples. Hospital sewage isolates displayed the highest percentage resistance to many beta-lactam and aminoglycoside antibiotics. Extended-spectrum beta-lactamase-producers were identified in 78% of water and 50% of sewage samples. One or more carbapenemase-producing Enterobacterales were identified at 23 individual sampling sites (18 water, 5 sewage). This included the detection of bla_OXA-48 (n = 18), bla_NDM (n = 14), bla_KPC (n = 4) and bla_OXA-484 (n = 1). All NDM-producing isolates harbored the ble-MBL bleomycin resistance gene. Commonly detected sequence types included Klebsiella ST323, ST17, and ST405 as well as E. coli ST131, ST38 and ST10. Core genome MLST comparisons detected identical E. coli isolates from wastewater treatment plant (WWTP) influent and nursing home sewage, and the surrounding waters. Similarly, one Klebsiella pneumoniae isolated from WWTP influent and the surrounding estuarine water were identical. These results highlight the need for regular monitoring of the aquatic environment for the presence of antibiotic-resistant organisms to adequately inform public health policies.

Carbapenemase Production and Epidemiological Characteristics of Carbapenem-Resistant Klebsiella pneumoniae in Western Chongqing, China

Background

This study aimed to determine the molecular characteristics of carbapenem-resistant Klebsiella pneumoniae (CRKP) isolates in a hospital in western Chongqing, southwestern China.

Methods

A total of 127 unique CRKP isolates were collected from the Yongchuan Hospital of Chongqing Medical University, identified using a VITEK-2 compact system, and subjected to microbroth dilution to determine the minimal inhibitory concentration. Enterobacteriaceae intergenic repeat consensus polymerase chain reaction and multilocus sequence typing were used to analyze the homology among the isolates. Genetic information, including resistance and virulence genes, was assessed using polymerase chain reaction. The genomic features of the CRKP carrying gene bla_KPC-2 were detected using whole-genome sequencing.

Results

ST11 was the dominant sequence type in the homology comparison. The resistance rate to ceftazidime-avibactam in children was much higher than that in adults as was the detection rate of the resistance gene bla_NDM (p < 0.0001). Virulence genes such as mrkD (97.6%), uge (96.9%), kpn (96.9%), and fim-H (84.3%) had high detection rates. IncF (57.5%) was the major replicon plasmid detected, and sequencing showed that the CRKP063 genome contained two plasmids. The plasmid carrying bla_KPC-2, which mediates carbapenem resistance, was located on the 359,625 base pair plasmid IncFII, together with virulence factors, plasmid replication protein (rep B), stabilizing protein (par A), and type IV secretion system (T4SS) proteins that mediate plasmid conjugation transfer.

Conclusion

Our study aids in understanding the prevalence of CRKP in this hospital and the significant differences between children and adults, thus providing new ideas for clinical empirical use of antibiotics.

Microbial Characteristics and Genomic Analysis of an ST11 Carbapenem-Resistant Klebsiella pneumoniae Strain Carrying blaKPC−2 Conjugative Drug-Resistant Plasmid

Background

The sequence type 11 (ST11) carbapenem-resistant Klebsiella pneumoniae (CRKP) carrying blaKPC−2 has been widespread all over the world, and it has been reported frequently in China. The blaKPC−2 located on the mobile genetic element brings tremendous pressure to control the spread and outbreak of resistant bacteria. Whole-genome sequencing (WGS) technology can comprehensively and in-depth display the molecular characteristics of drug-resistant bacteria, providing a basis for evaluating the genetic diversity within the CRKP genome.

Methods

The ST11 CRKP in this study was collected in the intensive care unit of a major teaching hospital. PCR and Sanger sequencing confirmed the existence of blaKPC−2. The AST-GN card and the microbroth dilution test were used for antimicrobial susceptibility testing. The transferability of plasmid was verified by a conjugation test. The whole genome is sequenced using the Illumina HiSeq short-read and Oxford Nanopore long-read sequencing technology.

Results

The studied strain was named CRKP63, which is a multi-drug resistance bacteria, which carries blaKPC−2 and blaSHV−182. Its genome consists of a circular chromosome of 5,374,207 bp and an IncFII plasmid named pKPC-063001 of 359,625 bp. In the drug-resistant plasmid pKPC-063001, the key carbapenem resistance gene blaKPC−2 was located in the genetic context with insertion sequence ISKpn27 upstream and ISKpn6 downstream and bracketed by IS26. The three copies of the IS26–ISKpn27–blaKPC−2–ISKpn6–IS26 unit were present in tandem. blaKPC−2 can be transferred horizontally between other species by conjugation, the complete type IV secretion system (T4SS) structure helps to improve the adaptability of bacteria to the external environment, strengthen the existence of drug-resistant bacteria, and accelerate the spread of drug resistance.

Conclusion

High-throughput sequencing has discovered the different surrounding environments of blaKPC−2, which provides a new idea for further revealing the transmission and inheritance of blaKPC−2 at the molecular level. In order to control the further spread and prevalence of drug-resistant bacteria, we should pay close attention to the changes in the genetic environment of blaKPC−2 and further study the transcription and expression of T4SS.

Prevalence and characterisation of carbapenemase encoding genes in multidrug-resistant Gram-negative bacilli

Background

Emerging worldwide in the past decade, there has been a significant increase in multidrug-resistant bacteria from serious nosocomial infections, especially carbapenemase-producing Gram-negative bacilli that have emerged worldwide. The objective of this study is to investigate carbapenem resistance in Gram-negative bacilli bacteria using phenotypic detection, antimicrobial resistance profiles and genotypic characterisation methods.

Methods

200 Gram-negative bacilli isolates were collected from different clinical specimens. All clinical samples were exposed to isolation and identification of significant pathogens applying bacteriological examination and an automated Vitek-2 system. The isolates were subjected to susceptibility tests by the Vitek-2 automated system and those isolates that were resistant to beta-lactam drugs, including carbapenems, third-generation cephalosporines or cefoxitin, were selected for phenotyping using Carba plus disc system assay for detection of carbapenemase-producing isolates. These isolates were further confirmed by molecular detection. PCR was used for the detection carbapenem-resistant genes (OXA-48, IMP, NDM, VIM, and KPC).

Results

110 (55%) of 200 Gram-negative bacilli were identified as beta-lactam-resistant isolates. The frequency of carbapenem-resistant isolates was calculated to be 30.9% (n = 34/110). A collection totalling 65/110 (59%) isolates were identified as carbapenemase producers by phenotypic method. Moreover, among the 65 carbapenemase-producing Gram-negative isolates with a positive phenotype-based result, 30 (46%), 20 (30%) and 18 (27%) isolates were positive for OXA-48, KPC and MBL enzymes, respectively, as well as the production of 27% of AmpC with porin loss. Tigecycline was the most effective antibiotic that affected 70% of MDR isolates, but high rates of resistance were detected to other tested antimicrobials. Of interest, a high incidence of MDR, XDR and PDR profiles were observed among all carbapenemase-producing isolates. 36% (24/65) of the tested isolates were MDR to 3 to 5 antimicrobial classes. 29% (17/65) of the recovered isolates were XDR to 6 to 7 antimicrobial classes. Alarmingly, 24% (16/65) of isolates displayed PDR to all the tested 8 antimicrobial classes. Genotype assay, including 53 phenotypically confirmed carbapenemase-producing isolates of Gram-negative bacilli, found 51(96%) isolates were harbouring one or more genes. The most common carbapenemase gene was bla_NDM 83% (44/53) followed by bla_OXA-48 75% (40/53), bla_VIM 49% (26/53) and bla_IMP 43% (23/53), while the gene bla_KPC was least frequent 7% (4/53). 92% (46/51) of isolates were involved in the production of more than one carbapenemase gene.

Conclusion

This study demonstrated the emergence of carbapenemase-producing Gram-negative pathogens implicated in healthcare-related infections. Accurate identification of carbapenem-resistant bacterial pathogens is essential for patient treatment, as well as the development of appropriate contamination control measures to limit the rapid spread of pathogens. Tigecycline exhibited potent antimicrobial activity against MDR, XDR and PDR-producing strains that establish a threatening alert which indicates the complex therapy of infections caused by these pathogens.

Plasmids Shape the Current Prevalence of tmexCD1-toprJ1 among Klebsiella pneumoniae in Food Production Chains

The emergence of novel antimicrobial resistance genes conferring resistance to last-resort antimicrobials poses a serious challenge to global public health security. Recently, one plasmid-mediated RND family multidrug resistance efflux pump gene cluster named tmexCD1-toprJ1, which confers resistance to tigecycline, was identified in bacteria of animal and human origins. However, the comprehensive landscape of the genomic epidemiology of this novel resistance determinant remained unclear. To fill this knowledge gap, we isolated 25 tmexCD1-toprJ1-positive bacteria from 682 samples collected along the pork production chain, including swine farms, slaughterhouses, and retail pork, and characterized the positive strains systematically using antimicrobial susceptibility testing, conjugation assays, single-molecule sequencing, and genomic analyses. We found that tmexCD1-toprJ1-positive bacteria were most prevalent in slaughterhouses (7.32%), followed by retail pork (0.72%). Most of the positive strains were Klebsiella pneumoniae (23/25), followed by Proteus mirabilis (2/25). IncFIB(Mar)/IncHI1B hybrid plasmids were mainly vectors for tmexCD1-toprJ1 and dominated the horizontal dissemination of tmexCD1-toprJ1 among K. pneumoniae isolates. However, in this study, we identified the IncR plasmid as a tmexCD1-toprJ1-positive plasmid with a broad host range, which evidenced that the widespread prevalence of tmexCD1-toprJ1 is possible due to such kinds of plasmids in the future. In addition, we found diversity and heterogeneity of translocatable units containing tmexCD1-toprJ1 in the plasmids. We also investigated the genetic features of tmexCD1-toprJ1 in online databases, which led to the proposal of the umuC gene as the potential insertion site of tmexCD1-toprJ1. Collectively, this study enriches the epidemiological and genomic characterization of tmexCD1-toprJ1 and provides a theoretical basis for preventing an increase in tmexCD1-toprJ1 prevalence. IMPORTANCE Tigecycline, the first member of the glycylcycline class of antibacterial agents, is frequently used to treat complicated infections caused by multidrug-resistant Gram-positive and Gram-negative bacteria. The emergence of a novel plasmid-mediated efflux pump, TmexCD1-ToprJ1, conferring resistance to multiple antimicrobials, including tigecycline, poses a huge risk to human health. In this study, we investigated the prevalence of tmexCD1-toprJ1-positive strains along the food production chain and found that tmexCD1-toprJ1 was mainly distributed in IncFIB(Mar)/HI1B hybrid plasmids of K. pneumoniae. We also observed a potential risk of transmission of such plasmids along the pork processing chain, which finally may incur a threat to humans. Furthermore, the IncFIB(Mar)/HI1B tmexCD1-toprJ1-positive plasmids with a limited host range and specific insertion sites of tmexCD1-toprJ1 are strong evidence to prevent a fulminant epidemic of tmexCD1-toprJ1 among diverse pathogens. The mobilization and dissemination of tmexCD1-toprJ1, especially when driven by plasmids, deserve sustained attention and investigations.

An Outbreak of Carbapenem-Resistant Klebsiella pneumoniae in an Intensive Care Unit of a Major Teaching Hospital in Chongqing, China

Background

Due to the critical condition and poor immunity of patients, the intensive care unit (ICU) has always been the main hospital source of multidrug-resistant bacteria. In recent years, with the large-scale use of antibiotics, the detection rate and mortality of carbapenem-resistant Klebsiella pneumoniae (CRKP) have gradually increased. This study explores the molecular characteristics and prevalence of CRKP isolated from the ICU ward of a tertiary hospital in China.

Methods

A total of 51 non-duplicated CRKP samples isolated from the ICU were collected from July 2018-July 2020. The enzyme production of the strains was preliminarily screened by carbapenemase phenotypic test, and drug-resistant and virulence genes were detected by PCR. The transferability of plasmid was verified by conjugation test. The minimal inhibitory concentration (MIC) was determined by microbroth dilution method and genetic diversity was detected by multilocus sequence typing and pulsed-field gel electrophoresis.

Results

bla_KPC-2 was the only carbapenemase detected. The major virulence genes were uge (100%), mrkD (94.1%), kpn (94.1%), and fim-H (72.5%), while wcag, ironB, alls and magA genes were not detected. One sequence type ST1373 strain, hypervirulent K. pneumoniae (hvKP), was detected. CRKP strains were highly resistant to quinolones, cephalosporins, aminoglycosides, and polymyxin, but susceptive to tigecycline and ceftazidime-avibactam. The success rate of conjugation was 12.2%, indicating the horizontal transfer of bla_KPC-2 . Homology analysis showed that there was a clonal transmission of ST11 CRKP in the ICU of our hospital.

Conclusion

The present study showed the outbreak and dissemination in ICU were caused by ST11 CRKP, which were KPC-2 producers, and simultaneously, also carried some virulence genes. ST11 CRKP persisted in the ward for a long time and spread among different areas. Due to the widespread dispersal of the transferable bla_KPC-2 plasmid, the hospital should promptly adopt effective surveillance and strict infection control strategies to prevent the further spread of CRKP. Ceftazidime-avibactam showed high effectiveness against CRKP and could be used for the treatment of ICU infections.

Does an Antibiotic Stewardship Applied in a Pig Farm Lead to Low ESBL Prevalence?

Background. The aim of the present study was to prospectively evaluate the prevalence of intestinal carriage of colistin-resistant and extended-spectrum β-lactamase (ESBL)-producing Enterobacterales among pigs from a Swiss farm attending an animal health and antibiotic stewardship program and to determine the associated mechanisms of resistance. Materials/Methods. Eighty-one fecal samples were recovered and screened for either β-lactam-resistant, colistin-resistant, or aminoglycoside-resistant Enterobacterales, using respective screening media. All recovered isolates were tested for antimicrobial susceptibility and their clonal relationship (PFGE and MLST). Plasmid typing was performed by plasmid-based replicon typing (PBRT). Resistance genes were searched by PCR and sequencing. Results. A total of 38 ESBL-producing Escherichia coli and a single ESBL-producing Enterobacter cloacae were recovered from 81 pigs, corresponding to a prevalence of 50%, no other β-lactamase producer being identified. Among the 38 ESBL-producing E. coli, all belonged to sequence type (ST) ST10, except two ST34 and ST744 isolates. Among the ST10-bla_CTX-M-1 isolates, three subclones (n = 22, n = 13, and n = 1, respectively) were identified according to the PFGE analysis. The most commonly identified IncI1 plasmid harboring the bla_CTX-M-1 gene was 143 kb in size and coharbored other resistance genes. Only three colistin-resistant Enterobacterales isolates were recovered, namely two Klebsiella pneumoniae isolates and a single E. cloacae isolate. Screening for the plasmid-borne mcr-1 to mcr-9 genes in these three isolates gave negative results. The two K. pneumoniae isolates were clonally related, belonged to ST76, and harbored a truncated mgrB chromosomal gene being the source of colistin resistance. Conclusion. A high prevalence of fecal carriage of ESBL-producing E. coli was found, being mainly caused by the spread of a clonal lineage within the farm. By contrast, a low prevalence of colistin-resistant Enterobacterales was found.

A Polyclonal Spread Emerged: Characteristics of Carbapenem-Resistant Klebsiella pneumoniae Isolates from the Intensive Care Unit in a Chinese Tertiary Hospital

Carbapenem-resistant Klebsiella pneumoniae (CRKP) isolates often cause nosocomial infections with limited therapeutic options and spread rapidly worldwide. In this study, we revealed a polyclonal emergence of CRKP isolates from the intensive care unit in a Chinese tertiary hospital. We applied a series of methods including automated screening, antimicrobial susceptibility testing, the modified carbapenem inacti vation method (mCIM), PCR amplification, DNA sequencing, and multilocus sequence typing (MLST) to characterize 30 non-duplicated CRKP isolates along with the collection of the related medical records. The results showed the polyclonal spread of CRKP isolates belonged to ST722, ST1446, ST111, ST896, ST290, and ST11. Among them, ST722 and ST1446 were two novel types of K. pneumoniae, and ST896 isolate harboring bla_KPC-2 was also found for the first time. Since the polyclonal spread of CRKP in the same ward is rare, the silent clonal evolution with the switching genotypes prompts us to stay alert for outbreaks caused by novel subclones.

Molecular Characterization of Carbapenemase-Producing Klebsiella pneumoniae Isolated from Egyptian Pediatric Cancer Patients Including a Strain with a Rare Gene-Combination of β-Lactamases

PURPOSE

Healthcare-associated infections caused by multi-drug-resistant (MDR) pathogens are a global threat. We aim to assess the clonal relatedness among carbapenemase-producing Klebsiella pneumoniae (CPKP) strains infecting Egyptian pediatric cancer patients.

MATERIALS AND METHODS

Identification and antimicrobial susceptibility testing of 149 Gram-negative isolates obtained from pediatric cancer patients were performed by VITEK 2. Genes encoding carbapenemases and extended-spectrum β-lactamases were detected by PCR and verified by DNA sequencing of representative samples. The transferability of the plasmids harboring bla OXA-48, from representative clinical samples, was evaluated by performing a conjugation experiment followed by PCR and MIC shift determination. Clonal relationships among the bla OXA-48-harboring K. pneumoniae isolates were determined by enterobacterial repetitive intergenic consensus (ERIC)-PCR and pulsed-field gel electrophoresis (PFGE).

RESULTS

Carbapenem resistance was observed in 59% of the isolates. The most prevalent species was K. pneumoniae (45.6%) and 57% of them were isolated from ICU. Fifty-nine % of the K. pneumoniae isolates were carbapenemase-producers and bla OXA-48 was detected in (58%) of them. One isolate co-harbored bla OXA-48, bla NDM-1, and bla IMP-1 genes for the first time in Egypt. PCR and meropenem MIC shift confirmed the success of the transferability of representative plasmids to E. coli K12. ERIC and PFGE identified 93% and 100% of the K. pneumoniae with a similarity coefficient ≥85%, respectively, including strains with indistinguishable patterns, suggesting possible clonal dissemination.

CONCLUSION

Our findings underline the dissemination of diverse clones of MDR CPKP among Egyptian pediatric cancer patients. Hence, routine molecular characterizations followed by strict implementation of infection control measures are crucial to tackling this threat.

Outbreak of KPC-2 Carbapenem-resistant Klebsiella pneumoniae ST76 and Carbapenem-resistant K2 Hypervirulent Klebsiella pneumoniae ST375 strains in Northeast China: molecular and virulent characteristics

BACKGROUND

Carbapenem-resistant hypervirulent Klebsiella pneumoniae strains have recently come into existence worldwide; however, researchers in northeast China are not aware of their clinical features and molecular characteristics.

METHODS

Here, the molecular and virulent characteristics of 44 carbapenem-resistant K. pneumoniae (CRKP) isolates collected from January 2015 to December 2017 were studied. Multilocus sequence typing (MLST) and pulsed-field gel electrophoresis (PFGE) were carried out to define the clonal relatedness among the isolates. PCR and capsular serotyping of the virulence-associated genes, as well as biofilm formation and serum complement-mediated killing assays, were employed to determine the virulent potential. The genomic features and associated mobile genetic elements of JmsCRE57 were detected by whole genome sequencing.

RESULTS

The only positive isolate was JmsCRE57, which belonged to the ST375 serotype K2 that expressed uge, mrkD, fimH, kpn, aerobactin and rmpA virulence-associated genes and showed strong biofilm formation and serum sensitivity. Sequencing results showed that the JmsCRE57 genome mainly consisted of a circular chromosome, three antimicrobial resistant plasmids and a virulent plasmid. The antimicrobial resistant plasmid expressing bla_KPC-2, bla_CTX-M-15, aph(3″)-Ib, aph(6)-Id, qnrB1, aac(3)-IIa, aac(6')-Ib-cr, bla_OXA-1, bla_TEM-1B, catB4, sul2, dfrA14 and bla_SHV-99. The virulent plasmid belonged to the IncHI1B group, which is mainly composed of mucoid phenotype genes and siderophore-associated genes. The remaining CRKP strains that expressed uge, fimH, mrkD and kpn virulence-associated genes were not successfully typed.

CONCLUSION

Our results provide new insights on the epidemiology of carbapenem-resistant K2 hypervirulent K. pneumoniae ST375 and CRKP ST76 strains in northeast China, which may help control their future outbreaks.

The determination of gyrA and parC mutations and the prevalence of plasmid-mediated quinolone resistance genes in carbapenem resistant Klebsiella pneumonia ST11 and ST76 strains isolated from patients in Heilongjiang Province, China

BACKGROUND

There is increasing resistance to carbapenems among Klebsiella pneumoniae,and fluoroquinolones (FQ) are increasingly used to treat infections from extended-spectrum β- lactamase(ESBLs) and carbapenemase-producing Klebsiella pneumoniae. However, the acquisition of plasmid-mediated quinolone resistance (PMQR) or the spontaneous mutation of the quinolone resistance-determining regions (QRDR) of the gyrA and parC genes can severely affect the therapeutic effect of quinolones. The goal of this study was to investigate the molecular determinants of FQ resistance(FQ-R) in carbapenem-resistant Klebsiella pneumoniae (CRKP) isolates from Heilongjiang Province,China.

MATERIALS AND METHODS

We isolated 40 strains of CRKP from a treatment center in the eastern part of Heilongjiang Province from January 2016 to December 2018. The VITEK2 Compact analyzer was used to identify and detect drug sensitivity. Different types of drug resistance genes were detected by polymerase chain reaction (PCR). PCR and DNA sequencing were used to assess the presence of qnrA, qnrB, qnrS,qepA and acc(6') Ib-cr genes,which are plasmid-encode genes that can contribute to resistance. The sequences of gyrA and parC genes were sequenced and compared with the sequences of standard strains to determine if mutations were present.Multi-site sequence typing (MLST) and pulsed-field gel electrophoresis (PFGE) were performed on the strains to assess homology.

RESULTS

The isolated CRKP strains showed rates of resistance to fluoroquinolones of 22.5% to 42.5%. The resistance rate of ciprofloxacin was significantly higher than that of levofloxacin.Nine CRKP strains (22.5%) showed co-resistance to ciprofloxacin and levofloxacin.The quinolone resistant strains were screened for plasmid-encoded genes that can contribute to resistance (PMQR genes).Among the 17 quinolone resistant strains,one strain contained no PMQR genes,twelve strains contained two PMQR genes,and four strains contained four PMQR genes.Acc (6') Ib-cr was the most frequently detected PMQR gene, detected in 95% of strains tested (38 of 40) and in 94.1% of the quinolone-resistant strains (16 of 17). The qepA gene encoding an efflux pump was not detected in any strains.No isolate carried five different PMQRs simultaneously.Changes of S83I and D87G changes in gyrA, and the S80I change in parC,which were mediated by QRDR,were identified in two isolates,which showed resistance to both ciprofloxacin and levofloxacin.Most of the FQ-R strains(58.8%,10/17) belong to ST(sequence type) 76, which is dominant in the local area, while all the mutant strains (100%,2/2),that differ in at least one site from standard bacteria, belong to the ST11 group. The strains were isolated from a hospital where there had been a recent outbreak of ST76 type CRKP in the neurosurgery ward and intensive care unit.

CONCLUSION

CRKP strains were identified that were insensitive or even resistant to quinolones,and this resistance is common in Heilongjiang Province of eastern China;fluoroquinolone-resistance in these clinical CRKP strains is a complex interplay between PMQR determinants and mutations in gyrA and parC.The resistance level caused by QRDR mutation is higher than that caused by PMQR, however, the high frequency of PMQR genes in the isolated CRKP strains suggests the potential for impact of these genes.PMQR determinants are often found in carbapenemase-producing or ESBLs-producing Klebsiella pneumoniae,and some resistance genes,such as:SHV,TEM, CTX-M-15,and OXA-1 are closely associated with FQ-R. Finally, geographical factors can affect the emergence and spread of PMQR and QRDR.Some genetic lineages have higher potential risks, and continuous close monitoring is required.

Molecular Mechanisms and Epidemiology of Carbapenem-Resistant Escherichia coli Isolated from Chinese Patients During 2002-2017

Background

The emergence and spread of carbapenem-resistant Escherichia coli (E. coli) pose a serious threat to human health worldwide. This study aimed to investigate the molecular mechanisms underlying carbapenem resistance and their prevalence among E. coli in China.

Methods

A collection of 5796 E. coli clinical isolates were collected from the First Affiliated Hospital of Wenzhou Medical University from 2002 to 2017. Sensitivity to antibiotics was determined using the agar dilution method. The detection of carbapenemases production and the prevalence of resistance-associated genes were investigated through modified carbapenem inactivation method (mCIM), PCR and sequencing. The mutations in outer membrane porins genes (ompC and ompF) were also analyzed by PCR and sequencing assays. The effect of efflux pump mechanism on carbapenem resistance was also tested. E. coli were typed by pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing (MLST).

Results

A total of 58 strains (1.0%) of carbapenem-resistant E. coli were identified. The strains carrying bla_KPC-2 and bla_NDM accounted for 22.4% (13/58) and 51.7% (30/58), respectively. Among bla_NDM- positive strains, 27 bla_NDM genes were assigned to bla_NDM-5, while the remaining three strains were bla_NDM-1, whereas bla_VIM, bla_IMP, bla_OXA-48, and bla_SHV were not found. The CTX-M-type β-lactamase genes accounted for 96.6% (56/58). In addition, bla_TEM-1 genes were identified in 58.6% of tested strains. In carbapenem-resistant isolates, mutations in OmpC (the majority of mutated sites were D192G and Q104_F141del, accounting for 54.5%) and OmpF (large deletions S75_V127del, W83_D135del and Q88_D135del) were detected. Of note, the antibiotic resistance was not associated with overexpression of efflux pump. Moreover, MLST categorized the 58 carbapenem-resistant isolates into 19 different sequence types. PFGE analysis revealed that homology among the carbapenem-resistant isolates was low and sporadic.

Conclusion

The bla_NDM was the principal resistance mechanism of carbapenem-resistant E. coli in the hospital. bla_NDM-5 is becoming a new threat to public health and the alteration of outer membrane porins might help further increase the MIC of carbapenem.

Molecular characterization of metallo-β-lactamase- producing carbapenem-resistant Enterobacter cloacae complex isolated in Heilongjiang Province of China

Background

Enterobacter cloacae complex (ECC) is one of the most common extended-spectrum β-lactamase and carbapenemase-producing pathogen that threatens millions of the elderly and vulnerable sick persons. The objective of this study was to perform the molecular characteristics of the carbapenem-resistant E. cloacae complex (CREC) emerged in Heilongjiang Province of China.

Methods

Six CREC strains were isolated from the patients with infectious diseases. The identities of ECC isolates were confirmed by sequencing the polymerase chain reaction (PCR) products of 16S rRNA gene. The characterization of the CREC isolates were analyzed by sequencing PCR products of the carbapenemase, ampC and fluoroquinolone resistance genes and performing multilocus sequence typing (MLST), pulsed-field gel electrophoresis (PFGE) and whole genome sequencing.

Results

All 6 isolates harbored multiple resistance genes. Of them, 5 carried metallo-β-lactamases and one was bla_KPC-2-positive. The levofloxacin and ciprofloxacin-resistant strains had substitutions of gyrA83, gyrA87, and parC80 in the quinolone-resistance determining regions. The MLST analyses revealed that 6 isolates belonged to five sequence types (ST520, ST528, ST1119, ST1120, and ST93) while the PFGE patterns of the isolates fallen into four clusters. The strain ST1120 was found to carry two separated plasmids that encode bla_NDM-1 and bla_IMP-4.

Conclusions

Our study, for the first time, identified a CREC strain that co-produces bla_NDM-1 and bla_IMP-4 in the Northeast China. Our finding emphasizes an urgent need for more intensive surveillance and precaution measures to prevent the CERC spread.

Synergetic Effects of Combined Treatment of Colistin With Meropenem or Amikacin on Carbapenem-Resistant Klebsiella pneumoniae in vitro

The purpose of this study was to investigate the synergistic and bactericidal effects of combinations of colistin with meropenem or amikacin in vitro and provide laboratory data needed for development of therapeutic strategies for the treatment of carbapenem-resistant Klebsiella pneumoniae (CRKP) infection. We found that minimum inhibitory concentration (MIC) of colistin, meropenem and amikacin were 2~32, 4~256, and 1~16384 μg/ml, respectively. The minimum bactericidal concentration of the antibiotics was either 1× or 2×MIC. Treatments of 6 CRKP isolates at 1 μg/ml colistin completely killed 2 of them and suppressed 4 others growth. 4 CRKP isolates at 16 μg/ml meropenem or amikacin completely killed and suppressed 2 others growth. 2 CRKP isolates showed synergic effects in all colistin combination and 3 CRKP isolates showed synergic effects in part of colistin combination. Our data suggest that colistin in combination with either meropenem or amikacin could be a valid therapeutic option against colistin-resistant CRKP isolates. Moreover, the combination of colistin-amikacin is less expensive to treat CRKP infections in Eastern Heilongjiang Province.

The in vitro activity of polymyxin B and tigecycline alone and combination with other antibiotics against carbapenem-resistant Enterobacter cloacae complex isolates, including high-risk clones

Background

The emergence of carbapenem-resistant Enterobacteriaceae (CRE) has become a significant problem for global public health. Currently, treatments program is minimal. This study aimed to evaluate the molecular mechanisms of carbapenem-resistant Enterobacter cloacae complex isolates (CREC) infections. Methods: Resistance genes were detected using PCR with specific primers. Multilocus sequence typing (MLST) was also performed. Furthermore, we evaluated the effects of polymyxin B (PMB) and tigecycline (TGC) antibiotics (Abs) alone and in combination with meropenem (MEM), amikacin (AMK), and levofloxacin (LEV) against CREC isolates. The results were then compared with in vitro synergy testing results obtained from time-kill assays (TKAs), and the microdilution checkerboard method.

Results

The synergistic efficiency of PMB + TGC was also evaluated. Abs use clinically achievable concentrations to determine the antibacterial effects of the Ab. Similar sequence type (ST) classifications had a comparably resistant phenotype; PMB-based combination therapy is better than TGC-based combination therapy.

Conclusions

we found that the combination of PMB + AMK is promising for the treatment of AMK-sensitive CREC. The high-risk ST93 carrying the bla _KPC-2 gene should be monitored.