Phenotypic and genotypic characterization of β-lactam resistance in Klebsiella pneumoniae isolated from swine

Little is known about the antimicrobial resistance mechanisms in Klebsiella pneumoniae from swine in China. Thus, this paper aims to demonstrate the β-lactam resistance phenotypes and genotypes of K. pneumoniae isolates from swine in southwestern China, detect possible new β-lactamase variants, and determine whether or not the variants differ in their antibiotic resistance. Isolates from 58 unrelated diseased swine were collected from 61 pig farms in southwestern China from 2007 to 2009. Among the 58 isolates, 75.8-100% were resistant to β-lactam, 62.0-68.97% to fluoroquinolone, 44.8-46.55% to aminoglycoside, and 8.62-17.24% to β-lactam inhibitors. PCR amplification and DNA sequencing showed that blaTEM-1 was detected in 100% (n = 58) of the isolates, blaSHV in 82.76% (n = 48), blaCTX-M in 39.66% (n = 23), and blaOKP in 17.24% (n = 10). The blaSHV types included blaSHV-1, blaSHV-11, blaSHV-12, and blaSHV-27. None of the isolates harbored blaKPC, blaLEN, or blaGES gene. Four novel variants (blaOKP-A-13, blaOKP-A-14, blaOKP-A-15, and blaOKP-A-16) were identified among the 10 OKP β-lactamase-producing K. pneumoniae isolates resistant to ampicillin, amoxicillin, oxacillin, cefalexin, and cefadroxil. Plasmid analysis and PCR amplification indicated that blaTEM-1 genes were detected in the total plasmid. Molecular typing by pulsed-field gel electrophoresis revealed the presence of 10 distinct pulsotypes of OKP producer isolates. Plasmid DNA digested with XbaI yielded two to six bands of ca. 0.15-30 kb. Transformants of the 10 OKP producer isolates showed no differences in their antibiotic susceptibility, except for the pulsotype B transformant, which carried blaCTX-M. In China, β-lactam resistance appeared to be common among K. pneumoniae isolates from swine, suggesting that K. pneumoniae may be a reservoir for the dissemination of β-lactam resistance among Chinese pig farms.