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

Abstract

Ceftazidime-avibactam is an effective antibiotic combination of a β-lactam and a β-lactamase inhibitor against Klebsiella pneumoniae-carbapenemase (KPC)-producing <i>Enterobacterales</i>. 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 <i>bla</i>_KPC-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 <i>bla</i>_KPC-112, <i>bla</i>_OXA-1, <i>bla</i>_CTX-M-15, <i>bla</i>_TEM-1B, <i>bla</i>_SHV-28, <i>aac(6')Ib-cr</i>, <i>aac(3)-IId</i>, <i>qnrS1</i>, <i>catA2</i>, <i>catB4</i>, and <i>fosA6</i>, 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. <b>IMPORTANCE</b> Carbapenem-resistant <i>Enterobacterales</i> (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 <i>bla</i>_KPC-2 or <i>bla</i>_KPC-3 gene. Here, we describe the characterization of a ceftazidime-avibactam-resistant <i>bla</i>_KPC-112-positive K. pneumoniae clinical isolate for the first time. A number of <i>Enterobacteriaceae</i> 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.