Study On The Effect Of Macrolides And β-Lactams Against Streptococcus Suis Biofilm In Vitro

Swine streptococcicosis is an important zoonotic disease caused by Streptococcus suis. It can lead to the symptom of swine meningitis, arthrophlogosis, endocarditis, septicemia in swine. Streptococcus suis serotype2not only is the most pathogenic, but also leads to the infection and death in particular community, that brings about greatly influence to public hygiene and human life. Once the bacteria have formed biofilm, it greatly increases the resistance and pathogenicity of bacteria. In the experiment, the antibacterial activities of macrolides and β-lactams antibacterials against streptococcus suis and biofilms were determined. And the activity of the macrolides alone or combined with β-lactams in the treatment of biofilms were determined. This experiment will provide useful experimental reference for further basis on the drug resistance to biofilms and the treatment of biofilms infection.By the United States Committee for Clinical Laboratory Standards (NCCLS), Minimum inhibitory concentration (MIC) of4strains of Streptococcus suis serotype2to macrolides and P-lactams antibacterials were tested. The result showed that, the resistance of Streptococcus suis against macrolides and β-lactams were100%and0%respectively.Biofilms were cultivated with Calgary biofilm device (CBD). The formation of biofilms was examined by crystal violet assay and scanning electron microscope (SEM). The results showed that the biofilms formed in vitro after72h. The minimal biofilm inhibitory concentration (MBIC) and minimal biofilm eradication concentration (MBEC) of macrolides and β-lactams to biofilms were determined. The results revealed that the MBIC and MBEC to biofilms were higher than the MIC to corresponding planktonic, but the MBEC to biofilms were>1024μg·mL-1.In the experiment of the effect of macrolides to the formation of biofilms, using bacterial suspension containing macrolides with OMIC,1/4MIC,1/16MIC cultivate biofilms, after72h observed with SEM, and tested contents of competence-stimulating peptide (CSP) with high performance liquid chromatograph (HPLC). The results showed that the structure of disposed of biofilms by erythrocin (ERY) and azithromycin (AZI) was inexistence. The concents of CSP disposed by ERY and AZI were degraded than the blank (P<0.01), while it is insignificant between1/4MIC and1/16MIC antimicrobial agents group (P>0.05), and it independed on the concentration of the antimicrobial agents. But such effects could not be seen for tylosin (TYL). In the experiment of the effect of macrolides to the elimination of mature biofilms, the mature biofilms was influenced by OMIC,1/4MIC,1/16MIC macrolides. The morphological change of the biofilms and the contents of CSP were detected with SEM and HPLC, respectively. The results revealed that the structure of disposed of biofilms was non-integrity, finely broken and irregular, and the contents of CSP disposed by ERY and AZI were degraded than the blank (P<0.01), while it is insignificant between1/4MIC and1/16MIC antimicrobial agents group (P>0.05), and it independed on the concentration of the antimicrobial agents. But it is insignificant between TYL group and0MIC group (P>0.05).Finally, the MBIC and MBEC of β-lactams to disposed of biofilms by OMIC,1/4MIC,1/16MIC ERY and AZI were determined. The results showed that the MBIC and MBEC of β-lactams to disposed of biofilms by1/4MIC,1/16MIC ERY and AZI were degraded than the OMIC group (P<0.01), which revealed that ERY and AZI had synergistic action to P-lactams, but it is insignificant between1/4MIC and1/16MIC antimicrobial agents group (P>0.05), which revealed that it independed on the concentration of the antimicrobial agents.