ACT-6, a novel plasmid-encoded class C β-lactamase in a Klebsiella pneumoniae isolate from China

Abstract

The purpose of this study was to investigate the phenotypic and molecular characterization of a novel plasmid-mediated AmpC-type b-lactamase in Klebsiella pneumoniae E701 isolated from Anhui province in China. In comparison with the ACT-1, sequence analysis revealed that there were 43 point mutations in the coding gene, and 10 of which led to amino-acid substitution. Resistance could be transferred by conjugation or transformation with plasmid DNA into E. coli JM109, which was due to the production of a b-lactamase with an isoelectric point of 8.4 named ACT-6. Cloning, expression, purification and kinetics were carried out to study the characterization of the novel AmpC-type b-lactamase. The results of MIC determinations and substrate profiles showed there was no significant difference in the activities of the novel enzyme and ACT-1. Moreover, the class 1 integron and the whole open reading frame of the novel AmpC-type b-lactamase from K.pneumoniae E701 were detectable in the same size plasmid. This is the first report on the emergence of the novel ACT-6 type b-lactamases in K. pneumoniae.

Characterization and identification of a novel chromosomal class C β-lactamase, LAQ-1, and comparative genomic analysis of a multidrug resistance plasmid in Lelliottia amnigena P13

“…The purified β-lactamase LAQ-1 showed the highest catalytic efficiency for piperacillin ( k cat / K m of 107.68) and showed moderate catalytic efficiency against first- (cefazolin, k cat / K m of 39.88) and second-generation cephalosporins (cefoxitin, k cat / K m of 16.92), and penicillins (ampicillin, k cat / K m of 20.96). It demonstrated low catalytic efficiencies against the third-generation cephalosporin (such as ceftazidime with a k cat / K m of 4.58) and the extended-spectrum cephalosporins (such as cefepime, with a k cat / K m of 8.18; Table 4 ), which is similar to the values for other chromosome- or plasmid-encoded class C β-lactamases, such as ACT-6 ( Zhu et al, 2011 ) and CMY-2 ( Bauernfeind et al, 1996 ). LAQ-1 was more active against cefazolin and cefoxitin than ACT-6 ( Zhu et al, 2011 ) because of its much higher k cat , which was partially compensated by its higher K m values ( Table 4 ).…”

“…It demonstrated low catalytic efficiencies against the third-generation cephalosporin (such as ceftazidime with a k cat / K m of 4.58) and the extended-spectrum cephalosporins (such as cefepime, with a k cat / K m of 8.18; Table 4 ), which is similar to the values for other chromosome- or plasmid-encoded class C β-lactamases, such as ACT-6 ( Zhu et al, 2011 ) and CMY-2 ( Bauernfeind et al, 1996 ). LAQ-1 was more active against cefazolin and cefoxitin than ACT-6 ( Zhu et al, 2011 ) because of its much higher k cat , which was partially compensated by its higher K m values ( Table 4 ). However, the enzyme kinetic hydrolytic activities were not completely consistent with the changes in the MIC levels of the recombinant clone (pUCP24- bla LAQ-1 /DH5α).…”

“…However, the recombinant clone harboring bla LAQ-1 did not show any change in MIC levels to carbapenems. bla LAQ-1 conferred resistance to fourth-generation cephalosporins, unlike ACT-6 ( Zhu et al, 2011 ) and CMY-2 ( Bauernfeind et al, 1996 ). Classic class A β-lactam inhibitors, such as clavulanic acid and sulbactam, had poor inhibitory effects on the activity of LAQ-1 ( Table 3 ).…”

Antimicrobial resistance determinants in silage

“…ACT-17 from E. hormaechei was also predicted to have plasmid origins. Members of the ACT beta-lactamases, also known as AmpC beta-lactamases, are normally encoded by genes located on the chromosomes 13 , but recently have also been found on plasmids 125,126 . Furthermore, E. hormaechei had regulator gene baeR associated to a plasmid.…”