| Streptococcus suis(S.suis)is the main pathogen,especially Streptococcus suis type 2,which is the most virulent serotype of 35 serotypes of Streptococcus suis,for the pig breeding industry,posing a huge threat to the development of pig industry and human security.However,at present,the epidemiological distribution data of Streptococcus suis virulence factors is very scarce in domestic and abroad,and the pathogenic mechanism of many virulence factors is still unclear.In addition,as the irregular use of antibiotics in our country results in drug abuse,the sensitivity of Streptococcus suis to antibiotics continues to decrease,causing great obstacles to the clinical treatment with the first-line drug in the pig breeding industry.Thus,this study aimed to investigate the prevalence of Streptococcus in pig farms in five provinces,and to determine the resistant phenotypes,virulence factors and virulence phenotype of isolates,and then to illuminate the resistance,virulence distribution,as well as the resistance possessed different virulence levels,so as to provide basic data for the control of swine streptococcosis.In this study,163 samples from lung,trachea,brain,joint fluid,heart,liver and spleen of sick pigs were collected from pig farms in Hunan,Fujian,Guangdong,Anhui and Jiangsu,respectively.A total of 65 strains were identified as Streptococcus suis using selective medium and 16 s molecular biological method,and the total isolation rate was39.88%.In terms of origin of isolates,Anhui has the highest separation rate of 66.57%(10/15),while Fujian has the lowest rate of 13.33%(2/15).From the separation site,the lung isolation rate was the highest,the separation rate was 57.69%(30/52),and the separation rate of the liver was 25%(1/4).Further,65 strains of Streptococcus suis were obtained for MLST typing.Except 8 strains,other strains were successfully typed,and 16 ST types were obtained.The most popular one was ST242(27/65),followed by ST117.(6/65)and ST1(5/65).Using the cps-2J gene to identify type 2 Streptococcus suis,a totalof 37 strains of cps-2J gene were detected,yielding the 53.85% detection rae of type 22 pig chain the detection rate of type 22 pig chain was 53.85%.The susceptibility of 65 strains of Streptococcus suis to 14 antimicrobial agents was determined by broth dilution method.The highest resistance rate of ciprofloxacin was95.38%,followed by compound sulfamethoxazole and gentamicin,respectively.93.85%and90.77%;followed by erythromycin,chlortetracycline and tetracycline,both close to 90%.In addition,the resistance rate of amikacin is also higher and it's at 78.46%,The resistance to levofloxacin,linezolid and cefotaxime.were relatively low and they are 23.08%,16.92%and 12.31%,respectively,and the resistance to other antimicrobial agents were lower(<10%).By the analysis of strain resistance spectrum,65 strains of Streptococcus can be grouped into 30 patterns,of which AMK-GEN-CETE-CIP-SXT-FFC-ERY-TET resistance spectrum is the most popular spectrum,accounting for 32.31%,followed by AMK-GEN-CETE-CIP-SXT-FFC-ERY,accounting for 10.77%.Further analysis of the multi-drug resistance of the strains revealed that all the strains were resistant to the four or more antimicrobial agents tested,while the number of strains resistant to more than seven antimicrobial agents was 57,accounting for 87.69%(57/65).It is suggested that the strains show serious multi-drug resistance.Detection of virulence factors of 65 Streptococcus suis strains by PCR,including 89 k virulence island virulence-related factors(1/2,3/4,5/6,1/6,943,944),non-virulence island virulence-related factors(epf,mrp,sly),and virulence factors such as sao.It was found that the detection rate of sly was the highest among the non-virulence island virulence-related factors(61.54%(40/65)).followed by epf and sao,55.38%(36/65)and 53.85%(35/65),respectively,and mrp(12.31%(8/65))was the lowest.Among the 89 k virulence island virulence-related factor,the detection rate of 1/6 was the highest,which was 55.38%(36-65),the second was 1/2 and 5/6,which were 21.54%(14/65)and 29.23%(19/65),respectively,the detection rate of 3/4 gene was 1.54%(1-65),while 943 and 944 were not detected.The virulence of the strain was further tested using mouse infection model.Among the 65 strains of Streptococcus tested,10 strains were highly virulent,with the mortality rate of mouse was 100%,and 13 strains were moderately virulent,with the mortality rate of mouse was 75% to 87.5%,20 strains were weakly virulent,and themortality rate of mouse reached 12.5% to 62.5%;22 strains were non-virulent and the mortality rate was 0.The drug resistance of Streptococcus suis type 2 and non-type 2 was compared and analyzed.It was found that Streptococcus suis type 2 was more resistance to ampicillin,but less resistance to penicillin,levofloxacin and vancomycin,there was no significant difference in susceptibility to other drugs.Further analysis of the drug resistance of different virulent strains showed that the strains with high mortality in mice were resistant to penicillin,ampicillin,cefotaxime and levofloxacin.The drug resistance rates of vancomycin and linazolamide were lower than those of the strains with low mortality,while the resistance to erythromycin was higher than that of the strains with low mortality in mice.In summary,the isolation rate of streptococcus is relatively high in sick pigs,especially streptococcus type 2.In addition,ST242 is the most popular ST type.Among the strains,the detection rate of 89 k Virulence Island was relatively high,meanwhile,the proportion of strains with moderate virulence was also high.These strains were highly resistance to various of antibiotics,and were only sensitive to a few drugs such as ampicillin,penicillin,florfenicol and vancomycin,and the multidrug resistance is serious.However,the strains with high mortality in mice showed relatively low resistance to antibiotics as a whole.The link between virulence and drug resistance of Streptococcus suis needs further investigation,which provides a reference for the effective prevention and control of swine streptococcosis. |
PDF Full Text Request