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.