Carbapenemase-producing Klebsiella pneumoniae (CPKP) strains have emerged as a major problem for healthcare systems. The aim of this study was to determine the circulating clones and analyze the clinical and molecular characteristics of CPKP in our hospital. A total of 74 carbapenemase producers collected from our hospital from 2012 to 2014 were analyzed for the prevalence of extended-spectrum β-lactamase (ESBLs), plasmid-mediated quinolone resistance genes (PMQRs), exogenously acquired 16S rRNA methyltransferase (16S-RMTase), and plasmid-mediated AmpC enzyme (pAmpCs) by PCR and DNA sequencing. The sequence types (STs) of the carbapenemase producers were analyzed by multi-locus sequence typing (MLST). And Pulsed-field gel electrophoresis (PFGE) was performed to investigate the genetic relationship of KPC-2 producing strains. Clinical data were retrieved from the medical records. KPC-2 (n = 72) was the predominant enzyme followed by NDM-1 (n = 2); The genes blaCTX-M, blaSHV, blaTEM-1, blaDHA-1, rmtB, armA, oqxA, oqxB, and qnrB were present in 29 (39.2 %), 27 (36.5 %), 46 (62.2 %), 2 (2.7 %), 25 (33.8 %), 1 (1.4 %), 60 (81.1 %) and 56 (75.7 %), 6 (8.1 %) isolates, respectively. MLST analysis revealed 10 different STs. The most dominant ST was ST11 (78.4 %, 58/74), followed by ST15 (8.1 %, 6/74). PFGE patterns of the KPC-2 producing K. pneumoniae isolates exhibited clonal dissemination of ST11 and ST15 clones as well as a genetic diversity of the remaining strains. The intra- and inter-hospital cross-transmission of KPC-2-producing K. pneumoniae ST11 co-carrying oqxAB and rmtB in our hospital strongly suggested that rapid identification of colonized or infected patients and screening of carriers is quite necessary to prevent a scenario of endemicity.

Klebsiella pneumoniae is a frequent nosocomial pathogen, with the multidrug-resistant (MDR) K. pneumoniae being a major public health concern, frequently causing difficult-to-treat infections worldwide. The aim of this study was to investigate the molecular characterization of clinical MDR Klebsiella pneumoniae isolates. A total of 27 non-duplicate MDR K. pneumoniae isolates with a CTX-CIP-AK resistance pattern were investigated for the prevalence of antimicrobial resistance genes including extended spectrum β-lactamase genes (ESBLs), plasmid-mediated quinolone resistance (PMQR) genes, 16S rRNA methylase (16S-RMTase) genes, and integrons by polymerase chain reaction (PCR) amplification and DNA sequencing. Plasmid replicons were typed by PCR-based replicon typing (PBRT). Multi-locus sequence typing (MLST) and pulsed-field gel electrophoresis (PFGE) were carried out to characterize the strain relatedness. All the isolates co-harbored 3 or more resistance determinants. OqxAB, CTX-M-type ESBLs and RmtB were the most frequent determinants, distributed among19 (70.4%),18 (66.7%) and 8 (29.6%) strains. Fourteen isolates harbored class 1 integrons, with orfD-aacA4 being the most frequent gene cassette array. Class 3 integrons were less frequently identified and contained the gene cassette array of bla_GES-1-bla_OXA-10-aac(6′)-Ib. IncFII replicon was most commonly found in this collection. One cluster was observed with ≥80% similarity among profiles obtained by PFGE, and one sequence type (ST) by MLST, namely ST11, was observed in the cluster. K. pneumoniae carbapenemase (KPC)–producing ST11 was the main clone detected. Of particular concern was the high prevalence of multiple resistance determinants, classs I integrons and IncFII plasmid replicon among these MDR strains, which provide advantages for the rapid development of MDR strains.

Objective: In total, 97 carbapenem-resistant Enterobacteriaceae (CRE) were collected from 17 hospitals located in Nanjing, Southeast China, and analyzed for epidemiological characteristics. Methods: Antimicrobial susceptibility was determined; followed by determination of the prevalence of resistance determinants, including extended-spectrum β-lactamase (ESBLs), plasmid-mediated AmpC enzyme (pAmpCs), plasmid-mediated quinolone resistance genes (PMQRs), fosfomycin resistance gene and exogenously acquired 16S rRNA methyltransferase (16S-RMTase) using PCR and DNA sequencing. The sequence types (STs) of CRE were determined by multi-locus sequence typing (MLST). The plasmid profiles were detected by PCR-based replicon typing (PBRT). Results: All the CRE strains displayed high MIC₅₀ and MIC₉₀ for nearly all clinical available antibiotics, except for aztreonam/avibactam, minocycline, ceftazidime/avibactam, tigecycline, and colistin. KPC-2 (79.4%) and NDM (19.6%) were the main carbapenemases, CTX-M (76.3%) and SHV (60.8%) were the predominant ESBLs. In addition, oqxAB (70.1%) and qnr (63.9%) were the major PMQRs; rmtB (47.4%) was the main 16S-RMTase; fosA (76.3%) and fosA3 (37.1%) were the fosfomycin resistance gene. PBRT analysis showed presence of IncR (66.0%) and IncFII (64.9%) replicon types in the majority of the isolates, followed by IncFIB (46.4%) and IncX3 (16.5%). The IncFII and IncR replicon-types were found mainly in K. pneumoniae (68.8%), whereas the IncX3 replicons dominated in E. coli isolates (100.0%). The three dominating MLST-types ST11, ST15 and ST268 comprised 68.0% of the 77 K. pneumoniae. Seven distinct STs were identified among 8 E. coli. Conclusions: The treatment for infections caused by CRE isolates is challenged by the presence of multiple resistance determinants and plasmid replicons. Our results highlighted the expansion of blaKPC-2 carrying K. pneumoniae ST11, the new emergency of single blaNDM-5 carrying K. oxytoca ST36, as well as blaIMP-4 and blaNDM-1 co-carrying E. cloacae ST418, which alert us on the urgency for antimicrobial resistant surveillance, to prevent dissemination of these highly transmissible and dangerous lineages.

The waning humoral immunity and emerging contagious severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants resulted in the necessity of the booster vaccination of coronavirus disease 2019 (COVID-19). The inactivated vaccine, CoronaVac, is the most widely supplied COVID-19 vaccine globally. Whether the CoronaVac booster elicited adaptive responses that cross-recognize SARS-CoV-2 variants of concern (VoCs) among 77 healthy subjects receiving the third dose of CoronaVac were explored. After the boost, remarkable elevated spike-specific IgG and IgA responses, as well as boosted neutralization activities, were observed, despite 3.0-fold and 5.9-fold reduced neutralization activities against Delta and Omicron strains compared to that of the ancestral strain. Furthermore, the booster dose induced potent B cells and memory B cells that cross-bound receptor-binding domain (RBD) proteins derived from VoCs, while Delta and Omicron RBD-specific memory B cell recognitions were reduced by 2.7-fold and 4.2-fold compared to that of ancestral strain, respectively. Consistently, spike-specific circulating follicular helper T cells (cTfh) significantly increased and remained stable after the boost, with a predominant expansion towards cTfh17 subpopulations. Moreover, SARS-CoV-2-specific CD4⁺ and CD8⁺ T cells peaked and sustained after the booster. Notably, CD4⁺ and CD8⁺ T cell recognition of VoC spike was largely preserved compared to the ancestral strain. Individuals without generating Delta or Omicron neutralization activities had comparable levels of CD4⁺ and CD8⁺ T cells responses as those with detectable neutralizing activities. Our study demonstrated that the CoronaVac booster induced broad and potent adaptive immune responses that could be effective in controlling SARS-CoV-2 Delta and Omicron variants.