Characterization of Unexpressed Extended-Spectrum Beta-Lactamase Genes in Antibiotic–Sensitive Klebsiella pneumoniae Isolates

Objective: The current investigation explores whether extended-spectrum β-lactamase (ESBL) genes exist in clinical non-ESBL–producing Klebsiella pneumoniae isolates. Methods: A total of 202 clinical isolates with non-ESBL–producing K. pneumoniae were collected from southern and middle of China. Thirteen β-lactamase genes (blaSHV, CTX-M, TEM, OXA-2, OXA-10, VEB, PER, SFO, GES, CSP, TLA, BEL, and IBC) were screened by PCR and their identity confirmed by sequencing of PCR products. The ESBL-producing phenotype of the isolates that carried ESBL genes was tested and confirmed in 9 of the 18 isolates by a double-disc synergy test. The sequences upstream of ESBL genes of isolates with ESBL-producing genotype (+)/phenotype (−) were also subjected to PCR and sequencing. The ESBL genes and their upstream regions were cloned into Escherichia coli DH5α for functional evaluation. Results: A total of 8.9% (18/202) isolates carried ESBL genes. All of them harbored only one ESBL gene, including 33.3% (6/18) blaSHV and 66...