ABSTRACT
Objective To evaluate the feasibility of matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS) for identification and cluster analysis of Streptococcus suis. Methods Eighteen clinical isolates biochemically identified as Streptococcus suis were pre-treated by smearing formic acid method and formic acid-acetonitrile extraction method. The identification results and protein profiles of MALDI-TOF-MS method were analyzed and compared. A self-constructed database of profiling with better pretreatment method was established, and cluster analysis was performed on the 18 strains of Streptococcus suis. At the same time, PFGE homology analysis was performed to compare the results of the two genotyping. Results Both pretreatment methods could accurately identify Streptococcus suis with scores above 2.1. The protein fingerprint of formic acid and acetonitrile extraction method had a smoother baseline, fewer miscellaneous peaks and more identifiable ion peaks. Comparison of the results of homology typing showed that the homology results of MALDI-TOF-MS were significantly different from those of PFGE. Conclusion MALDI-TOF-MS can accurately identify Streptococcus suis for the strains pre-treated with formic acid method or formic acid-acetonitrile extraction method, and the formic acid-acetonitrile extraction method can obtain a better protein mapping. MALDI-TOF-MS can play a certain role in typing, but it still has some limitations and cannot completely replace the PFGE.
ABSTRACT
Objective To study the biological characteristics of clinical isolates of human infected Streptococcus suis type 2 in Zhongshan City from 2016 to 2019 and classify the strains using pulse-field gel electrophoresis (PFGE), and to provide a scientific basis for clinical prevention and treatment of porcine streptococcus suis disease. Methods Twelve strains of Streptococcus suis type 2 were collected from 2016 to 2019 and identified by automatic bacterial identification instrument. The carrying status of five major virulence genes of Streptococcus suis was detected by nucleic acid and protein analyzer, including capsular polysaccharide (cps2J), lysozyme-releasing protein (mrp), hemolysin (sly), glutamate dehydrogenase (gdh), and extracellular factor (ef). The susceptibility of Streptococcus suis to 12 kinds of commonly used antibiotics was determined by the broth microdilution method, and the homology analysis was carried out by PFGE method. Results Twelve strains of Streptococcus suis type 2 were divided into four virulence genotypes, mainly mrp-/sly+/ef+/cps2J+/gdh+ (6strains) and mrp-/sly-/ef+/cps2J+/gdh+(4strains). Drug susceptibility test results showed that 12 strains of Streptococcus suis type 2 were resistant to erythromycin, tetracycline and clindamycin, and they all were multi-resistant strains. According to the classification results of PFGE, the 12 strains were classified into 7 PFGE types based on 100% similarity coefficient. The PFGE band types of Streptococcus suis in the same year had high homology. Conclusion The virulence genotypes of 12 clinical isolates of human infected type 2 Streptococcus suis in Zhongshan from 2016 to 2019 are diverse, and the strains are resistant to multiple antibiotics. Most strains in the same year are the same clone strains. PFGE genotypes are not correlated with virulence genotypes and drug resistance spectrum.