In vitro Combined Inhibitory Activities of β-Lactam Antibiotics and Clavulanic Acid Against bla(KPC-2)-Positive Klebsiella pneumoniae

BACKGROUND: The spread of KPC-producing Enterobacteriaceae has triggered a global public health concern, with KPC-2-positive strains being the most prevalent in China. We hereby studied the in vitro combined inhibitory activities of three kinds of β-lactam antibiotics and clavulanic acid at different concentrations against bla(KPC-2)-positive Klebsiella pneumoniae to explore the antimicrobial characteristics of these combinations and alternative therapeutic regimens for infections caused by bla(KPC-2)-positive K. pneumoniae strains. MATERIALS AND METHODS: In this study, 153 clinically isolated bla(KPC-2)-positive K. pneumoniae strains from 19 provinces in China were collected from 2016 to 2018. Antimicrobial susceptibility testing of imipenem/clavulanic acid, meropenem/clavulanic acid, ceftazidime/clavulanic acid, and each antimicrobial agent alone was performed by broth microdilution technique according to the CLSI guidelines. The concentration ratios of β-lactam antibiotics to clavulanic acid were as follows: 1:1, 1:2, 1:4, 1:8, 1:16, 1:32. The antimicrobial susceptibility of the combinations was determined according to the breakpoints of Imipenem, meropenem, and ceftazidime established by the CLSI directives for Enterobacteriaceae. RESULTS: The MICs of all three combinations gradually declined with increments in the proportion of clavulanic acid in the regimens, and the most significant decline in the MIC(50) and MIC(90) was seen in combinations at the concentration ratio of 1:1 (also 1:2 for meropenem/clavulanic acid). When the concentration of clavulanic acid was restricted to 4 mg/L, the susceptibility of more than 70% of the isolates to the regimens could be restored with imipenem MIC 2–4 mg/L, meropenem MIC 2–8 mg/L or ceftazidime MIC 8mg/L. However, the percentage decreased to 30 to 40% when the initial MIC level was higher. CONCLUSION: The highest combined inhibitory activity of β-lactam antibiotics/clavulanic acid at low concentration ratios against bla(KPC-2)-positive K. pneumoniae may offer a new way to optimize the effects of these antimicrobial regimens.