Phenotypic and molecular characterization of CTX-M-14 extended-spectrum β-lactamase and plasmid-mediated ACT-like AmpC β-lactamase produced by Klebsiella pneumoniae isolates from chickens in Henan Province, China.

Extended-spectrum β-lactamases (ESBLs) and AmpC β-lactamases produced by a clinical isolate of Klebsiella pneumoniae from chickens were detected with confirmatory phenotypic tests of the Clinical and Laboratory Standards Institute. The minimum inhibitory concentrations of 18 antibacterial drugs against K. pneumoniae were determined by the 2-fold microdilution method. The genotype and subtype of the ESBL-producing and AmpC β-lactamase-producing K. pneumoniae isolate were identified by PCR amplification of the enzyme-encoding genes followed by DNA sequencing analysis. K. pneumoniae K(1) isolate was an ESBL-producing and AmpC β-lactamase-producing bacteria with high resistance to β-lactam antibiotics, such as penicillins, third-generation cephalosporins, fluoroquinolones, and aminoglycosides. The sequence analysis showed that K. pneumoniae K(1) harbored TEM-type, SHV-type, CTX-M-type, and ACT-type AmpC β-lactamase nucleotide sequences. The TEM-type sequence was designated as TEM-1; the SHV-type sequence was designated as SHV-11; the CTX-M-type sequence was designated as CTX-M-14. Compared with the ACT-like sequence (EF078894), the ACT-type sequence was characterized by 8 nucleotide mutations (A(75)G, C(84)G, T(90)C, A(105)G, G(213)A, G(246)A, C(309)T, and T(315)C). Only one mutation at position 75 led to an amino acid substitution (Asn28Lys). The bla(ACT) type was an ACT-like derivative.