Heterogeneity of metallo-β-lactamases in clinical isolates of Chryseobacterium meningosepticum from Hangzhou, China

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Abstract
Objectives: To determine the distribution and heterogeneity of metallo-β-lactamases (MBLs) responsible for imipenem resistance in Chryseobacterium meningosepticum. Methods: Clinical C. meningosepticum isolates (n = 170) were collected from hospitals in Hangzhou, China. Production of MBLs was investigated by determination of imipenem MICs, and by using both a three-dimensional test and a 2-mercaptopropionic acid inhibitory test. Genes encoding BlaB and GOB MBLs were amplified by PCR, sequenced and compared with genes in GenBank. Results: More than 95% of the 170 isolates showed high (MIC > 16 mg/L) or intermediate resistance to imipenem, but only 94 isolates (55%) were shown phenotypically to produce MBLs (imipenem MIC range, 8–256 mg/L), with MBL genes detected in 93 of these. Among them, 83 isolates had blaB alleles and 65 isolates had blaGOB alleles; 38 isolates possessed one MBL gene and 55 isolates contained two genes. The major blaB alleles encoded BlaB-2, -3 and -11, while the major blaGOB alleles encoded GOB-2, -4, -8 and -10. MBLs or their genes were not detected in 76 (45%) isolates, including many that were highly resistant to imipenem. Conclusions: High levels and rates of imipenem resistance in C. meningosepticum from Hangzhou often result from the presence of heterogeneous BlaB and/or GOB MBLs, although undefined carbapenem resistance mechanisms also exist. Susceptibility testing and screening for MBLs should be conducted in order to inform effective treatment for C. meningosepticum infections.

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