Characterization of serotypes, antibiotic resistance, and bla-TEMgene of Glaesserella parasuis in large-scale pig farms in 5 southern provinces of China during 2017–2019

Abstract:

[Objective] To analyze the serotypes, antibiotic resistance, and resistance genes of 21 isolates of Glaesserella parasuis in large-scale pig farms.[Methods] Serotypes were identified by PCR and the resistance to 25 antibiotics with the K-B disk diffusion method. Seven resistance genes, including bla-_TEM, bla-_NDM, and bla-_CTX, were detected by PCR. Then chi-square test and Fisher's exact test were used to analyze the association between resistance phenotypes and genotypes. The β-lactam resistance gene bla-_TEM was sequenced and the sequences of amino acids encoded by bla-_TEM from different isolates were compared. Finally, the relationship between the differential sites of the amino acids and antibiotic resistance was analyzed by CLC Sequence Viewer. [Results] The isolates were dominated by serotypes 4 and 12. They showed high rate (61.9%, 13/21) of resistance to β-lactam antibiotic oxacillin and 90.5% (19/21) of the isolates demonstrated multi-antibiotic resistance. bla-_TEMwas identified in 52.4% (11/21) of the isolates, which was significantly correlated with the resistance phenotype of penicillin G, oxacillin, and cefradine. There were mutations of the amino acids encoded by bla-_TEM among isolates, which may be related to the antibiotic resistance of the isolates.[Conclusion]Multi-antibiotic resistance of G. parasuis isolates is prevalent in large-scale pig farms, and the high rate of β-lactam resistance is attributed to the inborn resistance gene bla-_TEM. The conclusion lays a theoretical basis for surveillance of antibiotic resistance of G. parasuis in large-scale pig farms.