Hypervirulent and multidrug resistant Klebsiella pneumoniae strains pose a significant threat to the public health. In the present study, 21 carbapenem-resistant K. pneumoniae isolates (CRKP) were determined by the string test as hypermucoviscous K. pneumoniae (HMKP), with the prevalence of 15.0% (21/140) among CRKP, and 1.1% (21/1838) among all K. pneumoniae isolates. Among them, 7 (33.3%), and 1 (4.76%) isolate belonged to capsular serotype K20 and K2 respectively, while 13 (61.9%, 13/21) weren't successfully typed by capsular serotyping. All the 21 isolates were carbapenemase-producers and were positive for bla_KPC-2. In addition to bla_KPC-2, all the 21 isolates except one harbor bla_SHV-11, and 15 carry extended-spectrum β-lactamase gene bla_CTX-M-65. The virulence-associated genes with more than 90% of positive rates among 21 isolates included ureA (100%, 21/21), wabG (100%, 21/21), fimH (95.2%, 20/21), entB (95.2%, 20/21), ycf (95.2%, 20/21), ybtS (95.2%, 20/21), and iutA (90.5%, 19/21). rmpA and aerobactin were found in 57.1% (12/21) isolates. Five sequence types (STs) were identified by multilocus sequence typing (MLST), including ST11 (11 K-non capsule typable and 5 K20 isolates), ST268 (1 K20 isolate and 1 K-non capsule typable isolate), ST65 (1 K2 isolate), ST692 (1 K-non capsule typable isolate), and ST595, a novel sequence type (1 K-non capsule typable isolate). Pulsed-field gel electrophoresis (PFGE) results showed two major PFGE clusters, of which cluster A accounts for 6 ST11 isolates (28.6%) and cluster B includes 8 ST11 isolates (38.1%, 8/21). Ten and six ST11 isolates were isolated from 2014 and 2015, respectively, while 8 were isolated from the same month of December in 2014. Ten isolates were collected from the intensive care unit (ICU), and all except one belonged to ST11. Additional 4 ST11 isolates were collected from patients in non-ICU wards, who had more than 10 days of ICU stay history in 2014 prior to transfer to their current wards where the isolates were recovered. Taken together, the present study showed a hospital outbreak and dissemination of ST11 HMKP with carbapenem resistance caused by KPC-2. Effective surveillance and strict infection control strategies should be implemented to prevent outbreak by HMKP with carbapenem resistance in hospitals.

A distinctive syndrome caused by hypermucoviscous Klebsiella pneumoniae (HMKP) including pyogenic liver abscess (PLA) is now becoming a globally emerging disease. In the present study, 22.8% (84/369) of K. pneumoniae clinical isolates associated with various types of invasive infections were identified as HMKP, with 45.2% associated with PLA. Multivariate regression analysis showed that male patients with 41-50 years, PLA, diabetes mellitus and hypertension were independent risk factors for HMKP infections. K2 (42.9%, 36/84) was the most common capsular serotype among HMKP isolates, followed by K1 (23.8%, 20/84). 75.0% of K1 HMKP isolates were associated with PLA, while K2 HMKP isolates accounted for more types of invasive infections. The positive rates of iutA, mrkD, aerobactin, iroN and rmpA among HMKP isolates were significantly higher than those among non-HMKP isolates (p<0.05). There was a correlation between magA, ybtS, alls and wcaG and K1 isolates. Interestingly, mrkD was exclusively detected among HMKP (32.1%, 27/84) and K2 isolates (65.9%, 27/41). All K1 and K2 HMKP and non-HMKP isolates were positive for rmpA. aerobactin was found among 95.0% and 97.5% of K1 and K2 isolates. ST23 was found to be the most prevalent ST among 69 HMKP isolates with K1, K2, K5, K20 and K57 (27.5%, 19/69) and was only found among K1 isolates. ST65 was the second most prevalent ST (26.1%, 18/69) and was also only found among K2 isolates. ST23-K1 HMKP isolates (84.2%, 16/19) were associated with PLA, while ST65-K2 isolates were correlated with more types of infections relative to ST23-K1 isolates. PFGE results showed that the homology of 84 HMKP isolates was diverse (Figure 1). Only 5 PFGE clusters with more than 75% similarity accounted for more than 3 isolates. These 5 PFGE clusters only accounted for 35 (41.7%, 35/84) isolates. In conclusion, our study first found that hypertension and male patients with 41-50 years old were independent risk factors. The composition of ST types and PFGE clusters among K. pneumoniae K2 isolates was more diverse than K1 isolates. K1 and K2 HMKP isolates had respective specific profiles of virulence-associated genes.

The aim of this study was to investigate the genomic epidemiology of MRSA in China to identify predominant lineages and their associated genomic and phenotypic characteristics. In this study, we conducted whole-genome sequencing on 565 MRSA isolates from 7 provinces and municipalities of China between 2014 and 2020. MRSA isolates were subjected to MLST, spa typing, SCCmec typing, analysis of virulence determinants and antimicrobial susceptibility testing. Among 565 MRSA isolates tested, clonal complex (CC) 59 (31.2%), CC5 (23.4%) and CC8 (13.63%) were the major lineages, and the clonal structure was dominated by ST59-t437-IV (14.9%), ST239-t030-III (6.4%) and ST5-t2460-II (6.0%), respectively. Of note, CC8, the predominant lineage in 2014–2015, was replaced by CC59 after 2016. Interestingly, the extension and unstable structure of the CC5 population was observed, with ST5-t311-II, ST764-t1084-II, ST5-t2460-II and ST764-t002-II existing complex competition. Further analysis revealed that virulence determinant profiles and antibiograms were closely associated with the clonal lineage. The CC59 MRSA was less resistant to most tested antimicrobials and carried fewer resistance determinants. But rifampicin resistance and mupirocin resistance were closely linked with CC8 and CC5, respectively. MRSA isolates conservatively carried multiple virulence genes involved in various functions. PVL encoding genes were more common in ST338, CC30, CC398, ST8 and CC22, while tsst-1 was associated with ST5. In conclusion, the community-associated CC59-ST59-t437-IV lineage was predominant in China, with diverse clonal isolates alternately circulating in various geographical locations. Our study highlights the need for MRSA surveillance in China to monitor changes in MRSA epidemiology.

Staphylococcus aureus, particularly methicillin-resistant S. aureus (MRSA), is an important human pathogen that causes both hospital- and community-acquired infections worldwide [ 1 x 1 Takano, T, Saito, K, Teng, LJ, and Yamamoto, T. Spread of community-acquired methicillin-resistant Staphylococcus aureus (MRSA) in hospitals in Taipei, Taiwan in 2005, and comparison of its drug resistance with previous hospital-acquired MRSA. Microbiol Immunol. 2007; 51: 627–632 Crossref | PubMed | Scopus (20) | Google Scholar See all References , 2 x 2 Tacconelli, E, Pop-Vicas, AE, and D'Agata, EM. Increased mortality among elderly patients with meticillin-resistant Staphylococcus aureus bacteraemia. J Hosp Infect. 2006; 64: 251–256 Abstract | Full Text | Full Text PDF | PubMed | Scopus (43) | Google Scholar See all References , 3 x 3 Vandenesch, F, Naimi, T, Enright, MC et al. Community-acquired methicillin-resistant Staphylococcus aureus carrying Panton—Valentine leukocidin genes: worldwide emergence. Emerg Infect Dis. 2003; 9: 978–984 Crossref | PubMed | Scopus (1363) | Google Scholar See all References ]. The resistance of MRSA to β-lactam antibiotics is associated with penicillin-binding protein 2a, encoded by the mecA gene. This gene is located on a mobile element, the staphylococcal cassette chromosome mec (SCCmec), with at least five different types of SCCmec having been reported [ 4 x 4 Ito, T, Ma, XX, Takeuchi, F, Okuma, K, Yuzawa, H, and Hiramatsu, K. Novel type V staphylococcal cassette chromosome mec driven by a novel cassette chromosome recombinase, ccrC. Antimicrob Agents Chemother. 2004; 48: 2637–2651 Crossref | PubMed | Scopus (498) | Google Scholar See all References , 5 x 5 Ma, XX, Ito, T, Tiensasitorn, C et al. Novel type of staphylococcal cassette chromosome mec identified in community-acquired methicillin-resistant Staphylococcus aureus strains. Antimicrob Agents Chemother. 2002; 46: 1147–1152 Crossref | PubMed | Scopus (457) | Google Scholar See all References ]. Hospital-acquired MRSA (HA-MRSA) isolates harbour mainly SCCmec types I, II and III, whereas SCCmec types IV and V are found mainly in community-acquired MRSA (CA-MRSA) isolates [ 4 x 4 Ito, T, Ma, XX, Takeuchi, F, Okuma, K, Yuzawa, H, and Hiramatsu, K. Novel type V staphylococcal cassette chromosome mec driven by a novel cassette chromosome recombinase, ccrC. Antimicrob Agents Chemother. 2004; 48: 2637–2651 Crossref | PubMed | Scopus (498) | Google Scholar See all References , 5 x 5 Ma, XX, Ito, T, Tiensasitorn, C et al. Novel type of staphylococcal cassette chromosome mec identified in community-acquired methicillin-resistant Staphylococcus aureus strains. Antimicrob Agents Chemother. 2002; 46: 1147–1152 Crossref | PubMed | Scopus (457) | Google Scholar See all References ]. In addition, CA-MRSA isolates often produce Panton—Valentine leukocidin (PVL), encoded by two co-transcribed genes, lukS-PV and lukF-PV (lukS/F-PV) [ 1 x 1 Takano, T, Saito, K, Teng, LJ, and Yamamoto, T. Spread of community-acquired methicillin-resistant Staphylococcus aureus (MRSA) in hospitals in Taipei, Taiwan in 2005, and comparison of its drug resistance with previous hospital-acquired MRSA. Microbiol Immunol. 2007; 51: 627–632 Crossref | PubMed | Scopus (20) | Google Scholar See all References , 2 x 2 Tacconelli, E, Pop-Vicas, AE, and D'Agata, EM. Increased mortality among elderly patients with meticillin-resistant Staphylococcus aureus bacteraemia. J Hosp Infect. 2006; 64: 251–256 Abstract | Full Text | Full Text PDF | PubMed | Scopus (43) | Google Scholar See all References , 3 x 3 Vandenesch, F, Naimi, T, Enright, MC et al. Community-acquired methicillin-resistant Staphylococcus aureus carrying Panton—Valentine leukocidin genes: worldwide emergence. Emerg Infect Dis. 2003; 9: 978–984 Crossref | PubMed | Scopus (1363) | Google Scholar See all References , 4 x 4 Ito, T, Ma, XX, Takeuchi, F, Okuma, K, Yuzawa, H, and Hiramatsu, K. Novel type V staphylococcal cassette chromosome mec driven by a novel cassette chromosome recombinase, ccrC. Antimicrob Agents Chemother. 2004; 48: 2637–2651 Crossref | PubMed | Scopus (498) | Google Scholar See all References , 5 x 5 Ma, XX, Ito, T, Tiensasitorn, C et al. Novel type of staphylococcal cassette chromosome mec identified in community-acquired methicillin-resistant Staphylococcus aureus strains. Antimicrob Agents Chemother. 2002; 46: 1147–1152 Crossref | PubMed | Scopus (457) | Google Scholar See all References , 6 x 6 Diep, BA, Sensabaugh, GF, Somboona, NS, Carleton, HA, and Perdreau-Remington, F. Widespread skin and soft-tissue infections due to two methicillin-resistant Staphylococcus aureus strains harboring the genes for Panton—Valentine leucocidin. J Clin Microbiol. 2004; 42: 2080–2084 Crossref | PubMed | Scopus (215) | Google Scholar See all References ]. S. aureus isolates producing PVL have been associated predominantly with severe skin infections and necrotising pneumonia [ 6 x 6 Diep, BA, Sensabaugh, GF, Somboona, NS, Carleton, HA, and Perdreau-Remington, F. Widespread skin and soft-tissue infections due to two methicillin-resistant Staphylococcus aureus strains harboring the genes for Panton—Valentine leucocidin. J Clin Microbiol. 2004; 42: 2080–2084 Crossref | PubMed | Scopus (215) | Google Scholar See all References , 7 x 7 Gilbert, M, Gregson, D, Gillespie, J et al. Clinical features of community-acquired methicillin-resistant S. aureus (CAMRSA) skin and soft tissue infections (SSTI) in an outbreak in persons with histories of drug use, homelessness or incarceration. Can J Infect Dis Med Microbiol. 2005; 16: 109 Google Scholar See all References , 8 x 8 Gillet, Y, Issartel, B, Vanhems, P et al. Association between Staphylococcus aureus strains carrying gene for Panton—Valentine leukocidin and highly lethal necrotising pneumonia in young immunocompetent patients. Lancet. 2002; 359: 753–759 Abstract | Full Text | Full Text PDF | PubMed | Scopus (1095) | Google Scholar See all References , 9 x 9 Gonzalez, BE, Martinez-Aguilar, G, Hulten, KG et al. Severe staphylococcal sepsis in adolescents in the era of community-acquired methicillin-resistant Staphylococcus aureus. Pediatrics. 2005; 115: 642–648 Crossref | PubMed | Scopus (281) | Google Scholar See all References ]. The prevalence of PVL genes among clinical isolates of S. aureus in China is not known. The aim of the present study was to investigate the prevalence of the PVL genes and the molecular characteristics of S. aureus isolates from hospitalised patients in a teaching hospital in China.