Complex evolutionary trajectories in vivo of two novel KPC variants conferring ceftazidime-avibactam resistance.

More and more ceftazidime-avibactam resistant KPC-producing K. pneumoniae have been reported with its widespread use, and the detection rate of KPC variants has increased dramatically. However, the evolutionary mechanism and fitness effects during KPC mutation remained unknown. Here, we report the complex in vivo evolutionary trajectories of two novel KPC variants, KPC-155 (L169P/GT242A) and KPC-185 (D179Y/GT242A), from Klebsiella pneumoniae in the same patient. The novel variants were shown to confer ceftazidime-avibactam resistance but restore carbapenem susceptibility based on the results of plasmid transformation assays, cloning experiments, and enzyme kinetic measurements. In vitro competition experiments highlighted the adaptive advantage conferred by strains carrying these KPC variants, which could lead to the rapid spread of these ceftazidime-avibactam resistant strains. The growth curve indicated that blaKPC-185 had better growth conditions at lower avibactam concentration compared to blaKPC-155, which was consistent with ceftazidime-avibactam use in vivo. In addition, replicative transposition of the IS26-flanked translocatable unit (IS26-ISKpn6-blaKPC-ISKpn27-IS26) also contributes to the blaKPC amplification and formation of two copies (blaKPC-2 and blaKPC-185), conferring both carbapenem and ceftazidime-avibactam resistance. However, strains with double copies showed reduced competitive advantage and configuration stability. The comparative plasmid analysis of IS26 group (IS26-blaKPC-IS26) and Tn1721 group (Tn1721-blaKPC-IS26) revealed that IS26-insertion could influence the distribution of resistance genes and ability of self-conjugation. The dynamic changes in blaKPC configuration highlight the need for consistent monitoring including antimicrobial susceptibility testing and determination of blaKPC subtypes-during clinical treatment, especially when ceftazidime-avibactam is administered.

Prediction of antimicrobial resistance in Klebsiella pneumoniae using genomic and metagenomic next-generation sequencing data.

OBJECTIVES: Klebsiella pneumoniae is a significant pathogen with increasing resistance and high mortality rates. Conventional antibiotic susceptibility testing methods are time-consuming. Next-generation sequencing has shown promise for predicting antimicrobial resistance (AMR). This study aims to develop prediction models using whole-genome sequencing data and assess their feasibility with metagenomic next-generation sequencing data from clinical samples. METHODS: On the basis of 4170 K. pneumoniae genomes, the main genetic characteristics associated with AMR were identified using a LASSO regression model. Consequently, the prediction model was established, validated and optimized using clinical isolate read simulation sequences. To evaluate the efficacy of the model, clinical specimens were collected. RESULTS: Four predictive models for amikacin, ciprofloxacin, levofloxacin and piperacillin/tazobactam, initially had positive predictive values (PPVs) of 90%, 85%, 84% and 94%, respectively, when they were originally constructed. When applied to clinical specimens, their PPVs increased to 96%, 96%, 95% and 100%, respectively. Meanwhile, there were negative predictive values (NPVs) of 100% for ciprofloxacin and levofloxacin, and 'not applicable' (NA) for amikacin and piperacillin/tazobactam. Our method achieved antibacterial phenotype classification accuracy rates of 96.08% for amikacin, 96.15% for ciprofloxacin, 95.31% for levofloxacin and 100% for piperacillin/tazobactam. The sequence-based prediction antibiotic susceptibility testing (AST) reported results in an average time of 19.5 h, compared with the 67.9 h needed for culture-based AST, resulting in a significant reduction of 48.4 h. CONCLUSIONS: These preliminary results demonstrated that the performance of prediction model for a clinically significant antimicrobial-species pair was comparable to that of phenotypic methods, thereby encouraging the expansion of sequence-based susceptibility prediction and its clinical validation and application.

Dynamic evolution of ceftazidime-avibactam resistance from a single patient through the IncX3_NDM-5 plasmid transfer and blaKPC mutation.

The rapid dissemination of carbapenem-resistant Enterobacterales (CRE) especially carbapenem-resistant Klebsiella pneumoniae (CRKP) poses a great threat to global public health. Ceftazidime-avibactam, a novel ß-lactam/ß-lactamase inhibitor combination, has been widely used due to its excellent antibacterial activity against KPC-producing K. pneumoniae. However, several resistance mechanisms have been reported since its use. Here, we conducted a series of in vitro experiments to reveal and demonstrate the dynamic evolution of ceftazidime-avibactam resistance including interspecies IncX3_NDM-5 plasmid transfer between Enterobacter cloacae and K. pneumoniae and blaKPC mutation from blaKPC-2 to blaKPC-33. Through the analysis of conjugation frequency and fitness cost, the IncX3_NDM-5 plasmid in this study showed strong transmissibility and stability in E. coli EC600 and clinical strain K. pneumoniae 5298 as recipient strain. With increasing ceftazidime-avibactam concentration, the conjugation frequency remained at 10-3-10-5, while the mutation frequency of K. pneumoniae 5298 was 10-6-10-8 at the same concentration. Further plasmid analysis (the IncX3_NDM plasmid from this study and other 658 plasmids from the NCBI database) revealed the diverse origin and genetic structure of blaNDM-5 carrying plasmids. E. coli (42.9%), China (43.9%), IncX3 (66.6%) are the most common strains, regions, and Inc types respectively. By analysing of genetic environment detected in IncX3 plasmids, the dominant structures (168/258, 65.1%) were identified: ISKox3-IS26-blaNDM-5-IS5-ISAba125-Tn3000-Tn3. In additon, several structural variations were found in the core gene structure. In conclusion, the high fitness and transmissibility of the IncX3_NDM-5 plasmids were noteworthy. More importantly, the diverse ceftazidime-avibactam resistance mechanisms including blaNDM-5 tranfer and blaKPC-2 mutation highlighted the importance of the continuous monitoring of antimicrobial susceptibility and carbapenemases subtype during ceftazidime-avibactam treatment.

Molecular mechanisms responsible KPC-135-mediated resistance to ceftazidime-avibactam in ST11-K47 hypervirulent Klebsiella pneumoniae.

Ceftazidime-avibactam resistance attributable to the blaKPC-2 gene mutation is increasingly documented in clinical settings. In this study, we characterized the mechanisms leading to the development of ceftazidime-avibactam resistance in ST11-K47 hypervirulent Klebsiella pneumoniae that harboured the blaKPC-135 gene. This strain possessed fimbriae and biofilm, demonstrating pathogenicity. Compared with the wild-type KPC-2 carbapenemase, the novel KPC-135 enzyme exhibited a deletion of Glu168 and Leu169 and a 15-amino acid tandem repeat between Val262 and Ala276. The blaKPC-135 gene was located within the Tn6296 transposon truncated by IS26 and carried on an IncFII/IncR-type plasmid. Compared to the blaKPC-2-positive cloned strain, only the MIC of ceftazidime increased against blaKPC-135-positive K. pneumoniae and wasn't inhibited by avibactam (MIC 32 µg/mL), while clavulanic acid and vaborbactam demonstrated some inhibition. Kinetic parameters revealed that KPC-135 exhibited a lower Km and kcat/Km with ceftazidime and carbapenems, and a higher (∼26-fold) 50% inhibitory concentration with avibactam compared to KPC-2. The KPC-135 enzyme exerted a detrimental effect on fitness relative to the wild-type strain. Furthermore, this strain possessed hypervirulent determinants, which included the IncHI1B/FIB plasmid with rmpA2 and expression of type 1 and 3 fimbriae. In conclusion, we reported a novel KPC variant, KPC-135, in a clinical ST11-K47 hypervirulent K. pneumoniae strain, which conferred ceftazidime-avibactam resistance, possibly through increased ceftazidime affinity and decreased avibactam susceptibility. This strain simultaneously harboured resistance and virulence genes, posing an elevated challenge in clinical treatment.

In vitro mimicry of in vivo KPC mutations by ceftazidime-avibactam: phenotypes, mechanisms, genetic structure and kinetics of enzymatic hydrolysis.

Ceftazidime-avibactam (CZA) is employed for the treatment of infections caused by Klebsiella pneumoniae carbapenemase-producing K. pneumoniae (KPC-KP). Resistance to CZA is frequently linked to point mutations in the blaKPC. We conducted in vitro simulations of in vivo blaKPC mutations using CZA. Four pre-therapy KPC-KP isolates (K1, K2, K3, and K4) were evaluated, all initially exhibited susceptibility to CZA and produced KPC-2. The crucial distinction was that following CZA treatment, the blaKPC-2 mutated in K1, K2, and K3, rendering them resistant to CZA, while K4 achieved microbiological clearance, and blaKPC-2 remained unaltered. The induction assay identified various blaKPC-2 variants, including blaKPC-25, blaKPC-127, blaKPC-100, blaKPC-128, blaKPC-137, blaKPC-138, blaKPC-144 and blaKPC-180. Our findings suggest that the resistance of KPC-KP to CZA primarily results from the emergence of KPC variants, complemented by increased blaKPC expression. A close correlation exists between avibactam concentration and the rate of increased CZA minimum Inhibitory concentration, as well as blaKPC mutation. Inadequate avibactam concentration is more likely to induce resistance in strains against CZA, there is also a higher likelihood of mutation in the blaKPC-2 and the optimal avibactam ratio remains to be determined. Simultaneously, we selected a blaKPC-33-producing K. pneumoniae strain (mutated from blaKPC-2) and induced it with imipenem and meropenem, respectively. The blaKPC-2 was detected during the process, indicating that the mutation is reversible. Clinical use of carbapenems to treat KPC variant strains increases the risk of infection, as the gene can mutate back to blaKPC-2, rendering the strain even more cross-resistant to carbapenems and CZA.

Comparison of three colloidal gold immunoassays and GeneXpert Carba-R for the detection of Klebsiella pneumoniae blaKPC-2 variants.

The increasing use of ceftazidime-avibactam has led to the emergence of a wide range of ceftazidime-avibactam-resistant blaKPC-2 variants. Particularly, the conventional carbapenemase phenotypic assay exhibited a high false-negative rate for KPC-2 variants. In this study, three colloidal gold immunoassays, including the Gold Mountainriver CGI test, Dynamiker CGI test and NG-Test CARBA5, and GeneXpert Carba-R, were used to detect the presence of KPC-2 carbapenemase and its various variants in 42 Klebsiella pneumoniae strains. These strains covered blaKPC-2 (13/42) and 16 other blaKPC-2 variants including blaKPC-12 (1/42), blaKPC-23 (1/42), blaKPC-25 (1/42), blaKPC-33 (6/42), blaKPC-35 (1/42), blaKPC-44 (1/42), blaKPC-71 (1/42), blaKPC-76 (8/42), blaKPC-78 (1/42), blaKPC-79 (1/42), blaKPC-100 (1/42), blaKPC-127 (1/42), blaKPC-128 (1/42), blaKPC-144 (1/42), blaKPC-157 (2/42), and blaKPC-180 (1/42). For KPC-2 strains, all four assays showed 100% negative percentage agreement (NPA) and 100% positive percentage agreement (PPA) with sequencing results. For all 16 KPC-2 variants, GeneXpert Carba-R showed 100% NPA and 100% PPA, and the three colloidal gold immunoassays showed 100% NPA, while the PPAs of the Gold Mountainriver CGI test, Dynamiker CGI test, and NG-Test CARBA5 were 87.5%, 87.5%, and 68.8%, respectively. We also found a correlation between the mutation site in the amino acid of the variants and false-negative results by colloidal gold immunoassays. In conclusion, the GeneXpert Carba-R has been proven to be a reliable method in detecting KPC-2 and its variants, and the colloidal gold immunoassay tests offer a practical and cost-effective approach for their detection. For the sample with a negative result by a colloidal gold immunoassay test but not matching the drug-resistant phenotype, it is recommended to retest using another type of kit or the GeneXpert Carba-R assay, which can significantly improve the accuracy of detection.

Identification of a novel Providencia species showing multi-drug-resistant in three patients with hospital-acquired infection.

Providencia species are important opportunistic pathogens for humans and are associated with several infectious diseases. In this study, we found three clinical strains belonging to a novel Providencia species, namely Providencia huashanensis, including strains CRE-3FA-0001T, CRE-138-0026, and CRE-138-0111. These strains were recovered from three patients, and all of them were associated with nosocomial infections, including incision infection, urinary tract infection, and intracranial infection. The three strains showed high-level resistance to many types of antimicrobials, including amikacin, aztreonam, ceftazidime, cefepime, ciprofloxacin, colistin, polymyxin B, imipenem, meropenem, ceftazidime-avibactam, imipenem-relebactam. Investigation of the resistance mechanism revealed that acquired resistance genes such as blaKPC, blaNDM, blaPER, blaOXA, aac, ant, and qnrD, played an important role in the multidrug-resistant phenotype for the three strains. The phylogenetic trees were reconstructed based on the 16S rRNA gene sequences, multi-locus sequence analysis, and core single nucleotide polymorphisms. The genome sequence of the strains had a range of 83.5%-85.8% average nucleotide identity and 21%-25.5% in silico DNA-DNA hybridization scores with other Providencia type strains. The average nucleotide identity and in silico DNA-DNA hybridization values and the phylogenetic trees indicated that the strains CRE-3FA-0001T, CRE-138-0026, and CRE-138-0111 strains should be considered as a novel species of the genus Providencia, for which the name P. huashanensis sp. nov. is proposed. The type strain is CRE-3FA-0001T = China Center for Type Culture Collection AB 2023186T = Korean Collection for Type Cultures 8373T.

Spread and evolution of blaKPC-plasmid between Serratia marcescens and Klebsiella pneumoniae.

OBJECTIVES: blaKPC-carrying Enterobacterales have post great challenges to global healthcare systems. In this study, we reported the evolution and spread of blaKPC between Serratia marcescens and Klebsiella pneumoniae. METHODS: Four S. marcescens and one K. pneumoniae strains were isolated from the sputum samples of the patient. Antimicrobial susceptibility tests and whole genome sequencing were performed to investigate the phenotype & genotype of strains. Conjugation assays, cloning experiment and kinetic parameters measuring were performed to explore the spread and antimicrobial resistance mechanisms. RESULTS: The evolution and transmission of blaKPC-2 occurred during the treatment of ceftazidime-avibactam and trimethoprim-sulfamethoxazole. Analysis of the antimicrobial susceptibility and genetic profiles of the clinical strains showed that blaKPC-2 evolved into blaKPC-71 and blaKPC-44, together with resistance to ceftazidime-avibactam and carbapenems susceptibility recovery under antimicrobial pressure. Cloning and expression of blaKPC-44 & blaKPC-71 in E. coli DH5α showed that KPC-44 and KPC-71 resulted in a 64∼128-fold increase in the MIC value for ceftazidime-avibactam. Meanwhile, the kinetic assays also showed that the enzyme activity of KPC-44 and KPC-71 towards carbapenems was destroyed and couldn't be inhibited by avibactam. Based on the conjugation assay and whole genome sequence analyses, we provided evolutionary insights into the transmission pathway trace of blaKPC-bearing plasmids between S. marcescens and K. pneumoniae. CONCLUSIONS: Mixed-species co-infection is one of the risk factors leading to the spread of plasmids carrying carbapenem-resistant genes, and increased surveillance of multidrug-resistant Enterobacterales is urgently needed.

Global emergence of a hypervirulent carbapenem-resistant Escherichia coli ST410 clone.

Carbapenem-resistant Escherichia coli (CREC) ST410 has recently emerged as a major global health problem. Here, we report a shift in CREC prevalence in Chinese hospitals between 2017 and 2021 with ST410 becoming the most commonly isolated sequence type. Genomic analysis identifies a hypervirulent CREC ST410 clone, B5/H24RxC, which caused two separate outbreaks in a children's hospital. It may have emerged from the previously characterised B4/H24RxC in 2006 and has been isolated in ten other countries from 2015 to 2021. Compared with B4/H24RxC, B5/H24RxC lacks the blaOXA-181-bearing X3 plasmid, but carries a F-type plasmid containing blaNDM-5. Most of B5/H24RxC also carry a high pathogenicity island and a novel O-antigen gene cluster. We find that B5/H24RxC grew faster in vitro and is more virulent in vivo. The identification of this newly emerged but already globally disseminated hypervirulent CREC clone, highlights the ongoing evolution of ST410 towards increased resistance and virulence.

Klebsiella pneumoniae carbapenemase variants: the new threat to global public health.

Klebsiella pneumoniae carbapenemase (KPC) variants, which refer to the substitution, insertion, or deletion of amino acid sequence compared to wild blaKPC type, have reduced utility of ceftazidime-avibactam (CZA), a pioneer antimicrobial agent in treating carbapenem-resistant Enterobacterales infections. So far, more than 150 blaKPC variants have been reported worldwide, and most of the new variants were discovered in the past 3 years, which calls for public alarm. The KPC variant protein enhances the affinity to ceftazidime and weakens the affinity to avibactam by changing the KPC structure, thereby mediating bacterial resistance to CZA. At present, there are still no guidelines or expert consensus to make recommendations for the diagnosis and treatment of infections caused by KPC variants. In addition, meropenem-vaborbactam, imipenem-relebactam, and other new ß-lactam-ß-lactamase inhibitor combinations have little discussion on KPC variants. This review aims to discuss the clinical characteristics, risk factors, epidemiological characteristics, antimicrobial susceptibility profiles, methods for detecting blaKPC variants, treatment options, and future perspectives of blaKPC variants worldwide to alert this new great public health threat.

Emergence of KPC-134, a KPC-2 variant associated with ceftazidime-avibactam resistance in a ST11 Klebsiella pneumoniae clinical strain.

The emergence of various new Klebsiella pneumoniae carbapenemase (KPC) variants leading to ceftazidime-avibactam treatment failure is a new challenge in current clinical anti-infection treatment. Here, we report a ceftazidime-avibactam-resistant K. pneumoniae 1072-2 clinical strain carrying a novel KPC variant, KPC-134, which differs from KPC-2 by both single mutation (D178A) and 8-amino acid insertions (asp-asp-asn-arg-ala-pro-asn-lys). The results of antimicrobial susceptibility testing showed that the isolate was resistant to meropenem (MIC = 4 mg/L), ceftazidime (MIC ≥ 32 mg/L), cefepime (MIC ≥128 mg/L), aztreonam (MIC ≥128 mg/L), and ceftazidime-avibactam (MIC ≥128 mg/L) but sensitive to imipenem (MIC = 0.5 mg/L), imepenem-relebactam (MIC = 0.5 mg/L), meropenem-vaborbactam (MIC = 2 mg/L), and aztreonam-avibactam (MIC = 4 mg/L). The plasmid containing blaKPC-134 was isolated from K. pneumoniae, and the blaKPC-134 gene was cloned into plasmid pHSG398 and transformed into an Escherichia coli DH5α to observe changes in antimicrobial resistance. The results indicated that the transformant was positive for blaKPC-134 and increased MICs of ceftazidime-avibactam, ceftazidime, cefepime, and aztreonam by 512-fold, 256-fold, 16-fold, and 4-fold, respectively, compared with the recipient. The results of third-generation sequencing showed that the blaKPC-134 gene was carried by a 133,789 bp IncFII-IncR plasmid, and many common resistance genes (including blaCTX-M-65, blaTEM-1B, blaSHV-12, rmtB, and catB4) along with the IS26, tnpR, ISkpn8, ISkpn6-like, and Tn1721 elements were identified. IMPORTANCE The emergence of various new KPC variants leading to ceftazidime-avibactam treatment failure is a new challenge for clinical anti-infection treatment. Here, we describe the characterization of a ceftazidime-avibactam-resistant blaKPC-134-positive Klebsiella pneumoniae clinical strain for the first time. K. pneumoniae bearing with KPC variant often mislead clinical anti-infection treatment because of their unique antimicrobial susceptibility profile and the tendency of conventional carbapenemase assays to give false negative results. Therefore, timely identification of KPC variants and effective anti-infective therapy are key to saving infected patients.

In Vivo Development of Aztreonam Resistance in Meropenem-Resistant Pseudomonas aeruginosa Owing to Overexpression of the blaPDC-16.

The rapid acquisition of antibiotic resistance of Pseudomonas aeruginosa has been a complex problem in clinics. Two meropenem-resistant P. aeruginosa isolates were collected from the same patient on May 24, 2021, and June 4, 2021, respectively. The first was susceptible to aztreonam, while the second displayed resistance. This study aimed to identify the genetic differences between two P. aeruginosa isolates and uncover alterations formed by the within-host bacterial evolution leading to aztreonam resistance during therapy. Strains were subjected to antimicrobial susceptibility testing using the broth microdilution method. Genomic DNAs were obtained to identify their genetic differences. The relative mRNA levels of ß-lactam-resistance genes were determined by real-time PCR. Both isolates belonged to ST 773 high-risk clones with the same antibiotic resistance genes, eliminating the possibility of horizontally obtaining resistance genes. Reverse transcription (RT)-PCR results showed that the blaPDC-16 mRNA level in the second one was about 1,500 times higher than that in the first one. When 3-aminophenyl boronic acid was added, the second strain recovered its susceptibility to aztreonam, which confirmed that the overexpression of blaPDC-16 was the main reason for the isolate's resistance to aztreonam. Compared to the first strain, the second showed a single amino acid substitution in AmpR located upstream of blaPDC-16, which may contribute to the upregulation of blaPDC-16 and lead to aztreonam resistance. AmpR plays an essential role in regulating antibiotic resistance in P. aeruginosa, and there is a need to be alert to clinical treatment failures associated with mutations in ampR. IMPORTANCE Pseudomonas aeruginosa is notorious for being highly resistant to antimicrobial agents. In this study, two P. aeruginosa strains isolated from the same patient with different susceptibility to aztreonam were used to illustrate the within-host resistance evolution process of P. aeruginosa. Both isolates, which belonged to a ST773 high-risk clone, had the same ß-lactam resistance genes (blaPDC-16, blaIMP-45, blaOXA-1, and blaOXA-395), which means the second isolate might have been derived from the first isolate by gaining aztreonam resistance via mutations associated with aztreonam resistance relative genes. Subsequently, we found that mutation in ampR may be the cause of aztreonam resistance in the second isolate. Mutation in ampR leads to its loss of control over blaPDC-16, allowing overexpression of blaPDC-16 and further resistance to aztreonam. This study revealed that ampR plays an essential role in regulating antibiotic resistance in P. aeruginosa. There is a need to be alert to clinical treatment failures associated with mutations in ampR.

A Nationwide Genomic Study of Clinical Klebsiella pneumoniae Carrying blaOXA-232 and rmtF in China.

OXA-232 carbapenemase is becoming a threat in China due to its high prevalence, mortality, and limited treatment options. However, little information is available on the impact of OXA-232-producing Klebsiella pneumoniae in China. This study aims to characterize the clonal relationships, the genetic mechanisms of resistance, and the virulence of OXA-232-producing K. pneumoniae isolates in China. We collected 81 OXA-232-producing K. pneumoniae clinical isolates from 2017 to 2021. Antimicrobial susceptibility testing was performed using the broth microdilution method. Capsular types, multilocus sequence types, virulence genes, antimicrobial resistance (AMR) determinants, plasmid replicon types, and single-nucleotide polymorphism (SNP) phylogeny were inferred from whole-genome sequences. OXA-232-producing K. pneumoniae strains were resistant to most antimicrobial agents. These isolates showed partial differences in susceptibility to carbapenems: all strains were resistant to ertapenem, while the resistance rates to imipenem and meropenem were 67.9% and 97.5%, respectively. Sequencing and capsular diversity analysis of the 81 K. pneumoniae isolates revealed 3 sequence types (ST15, ST231, and one novel ST [ST-V]), 2 K-locus types (KL112 and KL51), and 2 O-locus types (O2V1 and O2V2). The predominant plasmid replicon types associated with the OXA-232 and rmtF genes were ColKP3 (100%) and IncFIB-like (100%). Our study summarized the genetic characteristics of OXA-232-producing K. pneumoniae circulating in China. The results demonstrate the practical applicability of genomic surveillance and its utility in providing methods to prevent transmission. It alerts us to the urgent need for longitudinal surveillance of these transmissible lineages. IMPORTANCE In recent years, the detection rate of carbapenem-resistant K. pneumoniae has increased and represents a major threat to clinical anti-infective therapy. Compared with KPC-type carbapenemases and NDM-type metallo-ß-lactamases, OXA-48 family carbapenemases are another important resistance mechanism mediating bacterial resistance to carbapenems. In this study, we investigated the molecular characteristics of OXA-232 carbapenemase-producing K. pneumoniae isolated from several hospitals to clarify the epidemiological dissemination characteristics of such drug-resistant strains in China.

Performance of Ceftazidime-Avibactam 30/20-µg and 10/4-µg Disks for Susceptibility Testing of Enterobacterales and Pseudomonas aeruginosa.

Ceftazidime-avibactam, a new ß-lactam-ß-lactamase inhibitor combination, is active against multidrug-resistant Enterobacterales and Pseudomonas aeruginosa isolates and has became available for clinical use in China in the latter half of 2019. In this study, we evaluated the performance of the disk diffusion test with ceftazidime-avibactam 10/4-µg and 30/20-µg disks, compared with the reference broth microdilution method, with a collection of 467 Enterobacterales and 182 P. aeruginosa nonduplicate clinical isolates. The results of antimicrobial susceptibility testing indicated that the categorical agreement (CA) of ceftazidime-avibactam 10/4-µg disk testing for all tested Enterobacterales isolates was 99.8%, with 0.5% very major errors (VMEs) and no major error (ME). The CA of ceftazidime-avibactam 10/4-µg disk testing for all tested P. aeruginosa isolates was 87.9%, with 15.5% MEs and no VME. The CA of ceftazidime-avibactam 30/20-µg disk testing for all tested Enterobacterales isolates was 99.4%, with 1.5% VMEs and no ME. The CA of ceftazidime-avibactam 30/20-µg disk testing for all tested P. aeruginosa isolates was 91.8%, with 2.5% VMEs and 9.9% MEs. Overall, ceftazidime-avibactam 10/4-µg disk testing showed superior performance and was more suitable for assessment of the susceptibility of Enterobacterales and P. aeruginosa isolates. IMPORTANCE Multidrug-resistant Enterobacterales and P. aeruginosa strains have become a global public threat, with the emergence and prevalence of plasmid-mediated extended-spectrum ß-lactamases (ESBLs), AmpC cephalosporinases, and carbapenemases disseminated worldwide. Ceftazidime-avibactam, which is commercially available, has shown excellent in vitro activity against multidrug-resistant and carbapenem-resistant Enterobacterales and P. aeruginosa isolates. Moreover, ceftazidime-avibactam has shown promise in treating infections caused by multidrug-resistant and carbapenem-resistant isolates. The disk diffusion test for ceftazidime-avibactam is the most common antimicrobial susceptibility testing method in most laboratories in China. The accurate detection of ceftazidime-avibactam susceptibility is of great significance for the rational clinical application of drugs. Here, we evaluated the performance of the ceftazidime-avibactam 10/4-µg and 30/20-µg disk diffusion tests, compared with the reference broth microdilution method, with clinical Enterobacterales and P. aeruginosa isolates.

Identification of KPC-112 from an ST15 Klebsiella pneumoniae Strain Conferring Resistance to Ceftazidime-Avibactam.

Ceftazidime-avibactam is an effective antibiotic combination of a ß-lactam and a ß-lactamase inhibitor against Klebsiella pneumoniae-carbapenemase (KPC)-producing Enterobacterales. Despite a relatively low resistance rate, reports of resistance to ceftazidime-avibactam mainly caused by the mutations in KPC have increased in recent years. Here, we report a ceftazidime-avibactam-resistant and carbapenem-susceptible Klebsiella pneumoniae strain carrying a novel KPC variant, KPC-112, which differs from KPC-2 by 4-amino-acid deletions at Ambler positions 166L/167E and 242G/243T. The isolate was identified as K. pneumoniae by a Vitek mass spectrometer (bioMérieux, France). The MICs of antimicrobial agents were determined using broth microdilution susceptibility method. The result showed that the isolate was resistant to ceftazidime-avibactam (MIC = >128 mg/L) but susceptible to imipenem (MIC = 0.5 mg/L), meropenem (MIC = 1 mg/L), and tigecycline (MIC = 2 mg/L). The carbapenemase genes were confirmed by PCR-based sequencing. Plasmid transformation assay showed that the blaKPC-112-positive transformant increased MICs of ceftazidime-avibactam, ceftazidime, and cefepime by at least 256-fold, 128-fold, and 128-fold, respectively, compared with the recipient Escherichia coli DH5α. According to the whole-genome sequencing analysis, many common resistance genes were identified, including blaKPC-112, blaOXA-1, blaCTX-M-15, blaTEM-1B, blaSHV-28, aac(6')Ib-cr, aac(3)-IId, qnrS1, catA2, catB4, and fosA6, and mutations of GyrA (GyrA-83F and GyrA-87A) and ParC (ParC-80I) were also found. Overall, our study highlights the importance of monitoring susceptibility during ceftazidime-avibactam treatment and accurate detection of KPC variants. IMPORTANCE Carbapenem-resistant Enterobacterales (CRE) are one of the most serious antimicrobial resistance problems in the world, listed as an "urgent" threat by the U.S. Centers for Disease Control and Prevention. Among CRE, K. pneumoniae-carbapenemase-producing Klebsiella pneumoniae (KPC-KP) has become a significant health threat due to its rapid transmissibility and high mortality. With the wider clinical use of ceftazidime-avibactam, reports of resistance have increased in recent years even though the overall resistance rate remains relatively low. Among the reported resistance mechanisms are mainly mutations derived from the blaKPC-2 or blaKPC-3 gene. Here, we describe the characterization of a ceftazidime-avibactam-resistant blaKPC-112-positive K. pneumoniae clinical isolate for the first time. A number of Enterobacteriaceae isolates producing these kinds of KPC variants might be missed by conventional antimicrobial susceptibility testing (AST) methods and lead to irrational drug use. So, this study of KPC-112 will help to establish the diversity of KPCs and remind researchers of the challenge of drug resistance and detection brought by the KPC variants.

First Report of bla CTX-M-167, bla SHV-1, and bla TEM-1B Carrying Klebsiella pneumonia Showing High-Level Resistance to Carbapenems.

The prevalence of carbapenem-resistant Klebsiella pneumoniae is increasing. Although carbapenemase production is the main resistance mechanism of K. pneumonia to carbapenems, there are still some reports of non-carbapenemase-producing K.pneumoniae showing high-level resistance to carbapenems. In this study, we had also isolated a carbapenemase-negative carbapenem-resistant K. pneumoniae L204 from a patient with an asymptomatic urinary tract infection. Species identification was performed using MALDI-TOF MS, and carbapenemase-encoding genes were detected using both NG-test carba-5 and whole-genome sequencing. Antimicrobial susceptibility testing was performed by the broth microdilution method according to CLSI guidance. The results of antimicrobial susceptibility testing indicated that K. pneumoniae L204 was resistant to meropenem (MIC = 16 mg/L) and imipenem (MIC = 4 mg/L), but susceptible to ceftazidime-avibactam (MIC = 8 mg/L). Through whole-genome sequencing, several resistance genes had been identified, including bla TEM-1B, bla CTX-M-167, bla SHV-1, aac(6')-1b-cr, qnrS, aadA16, tet(A), fosA, sul1, and mph(A). The efflux pump inhibition testing showed that the efflux pump was not involved in the resistance mechanism to carbapenems. The result of the conjugation experiment indicated that the plasmid with bla CTX-M-167 and bla SHV-1 was transferrable. The sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) demonstrated that K. pneumoniae L204 only contained outer membrane porin OmpK35.

Antimicrobial activities of sitafloxacin and comparators against the clinical isolates of less common nonfermenting Gram-negative bacteria.

OBJECTIVES: To evaluate in vitro activities of sitafloxacin and comparators against the clinical isolates of less common nonfermenting Gram-negative bacteria (NFGNB). METHODS: The isolates of less common NFGNB were collected during a long period spanning five years from 2016 to 2020 in Huashan Hospital, Fudan University in Shanghai. A broth microdilution method was used to determine the minimum inhibitory concentrations (MICs) of sitafloxacin and comparators. RESULTS: In terms of MIC50/90 values, sitafloxacin was highly active against Stenotrophomonas maltophilia (0.25/1 mg/L), Burkholderia cepacia complex (0.25/2 mg/L), Achromobacter xylosoxidans (0.25/1 mg/L), and Chryseobacterium gleum (1/2 mg/L), but less active for Elizabethkingia (1/8 mg/L) and Chryseobacterium indologenes (16/32 mg/L). Sitafloxacin was more active than other fluoroquinolones against these NFGNB except Chryseobacterium. CONCLUSION: The results are helpful for clinicians to be aware of the role of sitafloxacin in managing the infections caused by these NFGNB.

Ceftazidime-Avibactam in Combination with Imipenem as Salvage Therapy for ST11 KPC-33-Producing Klebsiella pneumoniae.

A 22-year-old man, after a hematopoietic stem cell transplant, suffered long-term pneumonia caused by blaKPC-2-positive K. pneumoniae and blaKPC-33-positive K. pneumoniae alternately and finally achieved pathogenic clearance and improvement of clinical infectious conditions after using ceftazidime-avibactam in combination with imipenem as salvage therapy. This case provides a reference for treating infection caused by K. pneumoniae with a KPC variant in countries lacking new antimicrobial agents.