CRKP is an emerging problem that spreads among our most vulnerable population, children. Previous studies have mostly focused on adults, and molecular epidemiological data on children are limited. The aim of the present study was to describe the microbial resistance characteristics and epidemiological clinical characteristics of CRKP, which may help to prevent CRKP from becoming an epidemic in children. To the best of our knowledge, this is the first report of a small clonal spread of Klebsiella pneumoniae ST716 coproducing KPC-2 and IMP-4 and Klebsiella pneumoniae and ST1140 producing NDM-5 among pediatric patients.
In this study, all 94 CRKPs were multidrug resistant bacteria, but the resistance rate of strains to sulfamethoxazole, tigecycline and colistin was low, which may be due to their side effects; thus, these antibiotics are rarely used in pediatric patients in China. A previous study revealed that colistin in combination with other antimicrobial agents resulted in relatively low nephrotoxicity and a favorable outcome in > 70% of pediatric patients with infections due to carbapenem-resistant bacteria (Antachopoulos et al., 2017). It is worth noting that with the continuous use of colistin in clinical practice, Klebsiella pneumoniae has been reported to be resistant to colistin, and its resistance mechanism is different from previous chromosomal mutations but is caused by the colistin resistance gene (mcr-1) carried by plasmids (Quan et al., 2017). With the limited choice of antimicrobial agents in children, there is an urgent need to take effective infection control measures and strengthen continuous surveillance to prevent further dissemination of CRKPs among pediatric patients.
KPC was previously described as the most common type of carbapenemase in Klebsiella pneumoniae strains in adults (Wang et al., 2018), which is consistent with the current results that the 94 (79.8%) CRKPs collected from children mainly produced the KPC-2 enzyme. In addition, homology analysis showed that KPC-2-producing CRKP ST11 clones were widely spread in multiple departments, mainly in the PICU and CCU. ST11 was the dominant clone of KPC-2-producing CRKP isolates in China. A previous study revealed that ST11 Klebsiella pneumoniae showed a pandrug-resistant phenotype with a high prevalence of virulence factors favoring the binding, biofilm formation, colonization and escape from phagocytosis, which can make clones of this pathogen successfully spread worldwide (Andrade et al., 2014). In this study, NDM-1-producing Klebsiella pneumoniae were identified, accounting for 14.9% of the CRKPs collected. A five-year surveillance of CRKP strains in China revealed that NDM-1 enzymes gradually became the most prevalent type of carbapenemase in children (Dong et al., 2017). The current findings revealed that ST76 and ST20 Klebsiella pneumoniae cause clonal dissemination of NDM-1-producing Klebsiella pneumoniae in our hospital. It has been reported that NDM-1-producing Klebsiella pneumoniae ST76 caused an infection outbreak in the neonatal unit in Shanghai and that NDM-1-producing Klebsiella pneumoniae ST20 caused an infection outbreak in the neonatal unit in Shandong Province, suggesting that ST76 and ST20 are potentially high-risk clones that need more attention (Zhu et al., 2016; Jin et al., 2015). Moreover, NDM-1-producing Klebsiella pneumoniae had different clonal backgrounds, and NDM-1 was also observed in ST17, ST35, ST690 and ST4854 isolates in our study. To our knowledge, ST690 and ST4854 NDM-1-producing Klebsiella pneumoniae have never been reported globally, indicating that the diversity of NDM-1-producing Klebsiella pneumoniae is increasing. The NDM-5 enzyme, first identified in the Escherichia coli strain in the UK, appeared to show increased hydrolytic activity to carbapenems and extended-spectrum cephalosporins (Hornsey et al., 2011; Rahman et al., 2014). Notably, our previous research found that the NDM-5 enzyme was associated with nosocomial outbreaks of ST337 Klebsiella pneumoniae in a neonatal unit in Jiangsu Province (Kong et al., 2019). Our current results show that the first minor clonal spread of blaNDM−5-harboring ST1140 clone strains was identified in the SICU at the Children’s Hospital of Nanjing Medical University, revealing rapid evolution of CRKP strains among pediatric patients.
Notably, two ST716 Klebsiella pneumoniae strains coharboring blaKPC−2 and blaIMP−4 and a novel Klebsiella pneumoniae sequence type 4855 carrying both blaKPC−2 and blaNDM−5 were identified. The KPC enzyme has the ability to hydrolyze monobactam antibiotics but can be inhibited by some β-lactamase inhibitors, such as avibactam. However, avibactam is inactive against metallo-β-lactamase (MBL) producers, including NDM and IMP, and monobactam antibiotics are active against MBL producers (Chiotos et al., 2020). Therefore, the synergistic effects of different carbapenemase classes may lead to higher levels of resistance to carbapenems and other antimicrobials. Due to the limited choice of antibiotics in children, the emergence of these strains brings great challenges to clinical treatment.
Up to now, only one KPC-2 and IMP-4 co-producing CRKP isolate and one strain harbored blaKPC−2 and blaNDM−5 have been identified from children (Tian et al., 2018; Zhou et al., 2020). To our knowledge, this is the first report of a minor clonal dissemination of Klebsiella pneumoniae coproducing KPC-2 and IMP-4 carbapenemases in two PICU patients. Something of concern is that these two pediatric patients died of severe lung infection, which suggests that the Klebsiella pneumoniae isolates coproducing two carbapenemases may pose a significant health risk to pediatric patients. A previous study revealed that Klebsiella pneumoniae coproducing the KPC-2 and NDM-1 enzymes are highly stable, have interhost transmission capacity, and are resistant to the newly marketed ceftazidime-avibactam (Gao et al., 2020). Therefore, effective infection control measures are urgently required to prevent further spread of the strains coproducing two carbapenemases among children.
There are some limitations in this study. First, it was performed at a third-grade children's hospital in Jiangsu province, and molecular epidemiology and drug-resistance mechanisms of CRKP strains in our children may not be generalizable to children patients throughout our country. In addition, the clinical characteristics of patients with CRKP isolates were briefly reviewed in our study, and we did not identify independent risk factors for CRKP strains infections due to a lot of related research has been performed, and our study focused mainly on clinical molecular epidemiology of carbapenem-resistant Klebsiella pneumoniae among pediatric patients.