| Streptococcus suis is a Gram-positive cocciand, frequently found in the tonsil and nasal cavity. The generally clinical symptoms of pigs infected with S.suis are meningitis, septicemia, arthritis and pneumonia. S.suis infection has been one of the major problems, causing severe economic losses in the swine industry worldwide. In this study, drug resistance of S.suis clinical isolates in China were evaluated, and quinolone-resistant isolates were used for study on fluoroquinolone-resistant mechanism. Besides, study on Characteristics of S.suis isolates from nasal cavity of healthy swine were performed. Data in the present study was expected to be in help of future study on S.suis diagnosis prevention, and control.1. Study on drug resistance of Streptococcus Suissusceptibility testing of S.suis on 126 isolates from diseased pigs and 23 isolates from nasal cavity of healthy swine were carried out with Streptococcus drug susceptibility testing board (MICroSTREP plus (?) 1 Panel).The results showed that all the 149 isolates were sensitive to meropenem, vancomycin, P-lactams and fluoroquinolones, but strong resistance to tetracycline, macrolides, Lincosamide et al. were frequently observed from these isolates. Of the 149 isolates,109 strains (73.2%) were not sensitive to more than four antibiotics. By comparing spectrum, isolates from healthy pigs showed significantly higher-level resitance toβ-lactams, macrolides, Chloromycetin, fluoroquinolones and Sulfonamides than isolates from diseased pigs. The certain correlation of S.suis serotype 2 and resistance were observed after statistical snalysis(P<0.01), but no correlation was observed in other serotypes (p>0.05). The results provided reference data for clinical treatment for S.suis.2. Study on characterization of fluoroquinolone resistance in Streptococcus SuisThe drug susceptibility test was performed for 149 S.suis isolates from China,11 isolates were selected as quinolone resistance and 2 isolates showed intermediate multi-drug resistance, tolerant to more 5 antibiotics. Furthermore, of the 13 isolates resistant to fluoroquinolone, most showed virulence genotype of ef-/sly-/mrp-, except one strain with sly+/mrp*+. These findings suggest that quinolone resistance of S.suis might affect the sensitivity to other antibiotics and loss of virulence factors.Mutation in parC, pare, gyrA and gyrB were observed in quinolone-resistant isolates after sequence analysis, and some novel mutations were confirmed. The results showed mutation at Ala552-Thr of ParE in combination with mutation at Ala427-Thr of GyrB was more frequent than mutations in ParC and GyrA, which may a first-class mutation leading to reduced susceptibility to gatifloxacin. Findings suggest mutation at Ser79-Tyr of ParC might lead to gatifloxacin resistance. It was demomstrated that parC was the first target of fluoroquinolones. S.suis developed gradually reduced sensitivity to fluoroquinolones with the increase of mutations. Mutations in ParC and GyrA were the critical factors for development of fluroquinolone resistance in S.suis, Results from phenogenetic analysis showed fluoroquinolone resistance in S.suis was not due to clonal spread of resistant strains or horizontal gene transfer with other bacteria, but due to gene mutations. We also confirmed the great relationship between S.suis multidrug resistance and the quinolone-resistance, and the existence of efflux pump in S.suis with the efflux pump inhibitors. It was demonstrated that multidrug resistance and fluoroquinolone resistance were related to the interaction of related resistance gene and efflux pump.3. Characteristics of Streptococcus Suis isolates from healty pigs240 isolates were identified as S.suis from 398 nasal swabs collected from healthy pigs in Shandong, Hunan, Hubei and Jiangxi provinces. One of the isolates was serotype 2 strain. Results of serotyping showed as follows,61 strains of all agglutination,42 strains of multi-agglutination and 33 strains of serotype 21/29. The dominant pathogenic serotype followed by 16 strains of S.suis Serotype 7,3 strains of Serotype 4 and 2 strains of Serotype 8. Interestingly,2-4 serotype strains were isolated from one nasal swab.Fingerprint polymorphism in S.suis from healthy pigs gene was observed after ERIC-PCR analysis. The band spectral similarity from 76% of the isolates was from 50% to 100%, and can be grouped into 29 clusters, but 24% isolates could not be clustered. The band spectral similarity of isolates from the same area were more than 70%.MLST typing showed that SDJA6 strain belongs to ST7, and XJ12 strain belongs to ST14, and the rest 14 strains could not be typed, and their genotypes belong to 12 kinds of new STs. The results suggest that the S.suis had different clones co-existing in healthy pigs. Some STs originated from different genetic background and serotypes, but some strains of the same serotype blonged to different STs, suggesting serotyping might be a poor indicator of genetic relationship between S.suis isolates. In combination with the results of serological typing and fingerprinting, these findings suggest that capsular genes may be moving horizontally through the S.suis population. |
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