Multiple Novel Ceftazidime-Avibactam-Resistant Variants of bla(KPC-2)-Positive Klebsiella pneumoniae in Two Patients

As the first-line antimicrobial agent for the infection caused by carbapenem-resistant Enterobacterales, ceftazidime-avibactam develops drug resistance during its ever-growing clinical use. In this study, we report multiple novel variants in bla(KPC-2)-positive Klebsiella pneumoniae from two separate patients during their exposure to ceftazidime-avibactam. For one patient, the bla(KPC-2) gene carried by K. pneumoniae mutated into bla(KPC-35), bla(KPC-78), and bla(KPC-33) over the same period, while that for the other patient mutated into bla(KPC-79) and further evolved into bla(KPC-76) to enhance resistance level, among which bla(KPC-76) and bla(KPC-79) were reported for the first time. In contrast with bla(KPC-2), the emergent mutations within the Ω-loop conferred high-level resistance to ceftazidime-avibactam with a sharp reduction of carbapenemase activity. These bla(KPC)-positive K. pneumoniae isolated from sputum (both patients) and cerebrospinal fluid (patient 2) belonged to ST11 and ST859, respectively. All strains located bla(KPC) alleles on IncFII/IncR plasmids, except one on an IncFII plasmid. Such bla(KPC-2) variants first appeared after 9 to 18 days of ceftazidime-avibactam usage, but the lack of its feasible detection method often led to the assumption of ceftazidime-avibactam sensitivity resulting in clinical incorrect usage. Subsequent substitution of ceftazidime-avibactam with carbapenems also failed, because the bla(KPC-2)-containing K. pneumoniae dominated again. Ultimately, treatment failed even with the therapeutic regimen of ceftazidime-avibactam combined with carbapenems, because of the inadequate concentration of avibactam in infection sites and decreased drug sensitivity of strains caused by increased expression of bla(KPC) and point mutation of ompK35 and ompK36. As novel KPC variants conferring resistance to ceftazidime-avibactam are constantly emerging worldwide, quick and efficient laboratory detection and surveillance are urgently needed for infection control. IMPORTANCE Carbapenem-resistant K. pneumoniae which was classified as the most urgent threat by World Health Organization, is the most critical public health concern due to its high mortality rate. Recently, the rapid mutation of bla(KPC) has occurred during anti-infective therapy, which posed an unexpected challenge for both the diagnostic laboratory and clinical practice.