Study On The Resistance Of Streptococcus Pneumoniae Induced By Erythromycin In Vitro

S.pneumoniae is a common cause of otitismedia, sinusitis, bronchitis, community-acquired pneumonia, and an important cause of human death. Antibiotics are used to treat this kind of infection. However for the use of antibiotics, the phenomenon of resistance becomes seriously. So the researchs of mechanism of resistance are very important. Now the major researchs of mechanism alway through the contradistinction between isolates from clinic to standard strain,but about the researchs through the contradidtinction between strain after inducting with antibiotic to initial strain had not been found.This study was used agar dilution method to determinate Streptococcus pneumonia's MICs and then obtain the strains which were sensitive to erythromycin.Streptococcus pneumonia tigr4 and two clinical sensitive isolates C1,C2 were induced by erythromycin with the method of increasing drug concentration,getting the drug resistant strains and determinating their MICs. Culturing the drug resistant strains on blood agar medium for twenty generations consecutively to detect the stability of drug resistance. Comparing the character of colony,appearance under microscope and the sensitivety to Optochin of S.pneumoniae before and after induction; Balb/c mouse were used to detect the change of virulence before and after induction. the rplD,rplV genes and 23S rRNA in sensitive and resistant strains were amplified by PCR and RT-PCR.The products of PCR and RT-PCR were sequenced. CPHmodels-2.0 and PyMOL were used to predict the spatial structures of ribosomal protein L4 and L22 which were coded by the rplD and rplV genes.The MICs of test strains were 0.0312mg/L totally.After induction,The MIC of Streptococcus pneumonia tigr4 was increased from 0.0312 mg/L to 256mg/L, the MICs of two clinical isolates were increased from 0.0312 mg/L to 32mg/L,but no changes of Streptococcus pneumonia R6. After culturing the resistant strains on blood agar medium for twenty generations consecutively,the MICs had no changes. There were no visible changes of the character of colony,appearance under microscope and the sensitivety to Optochin after induction; In comparison with the primal strains,There were no visible changes of virulence after induction (P>0.05). The Streptococcus pneumonia tigr4 had the amino acid change of V32A in ribosomal protein L4,D35G in ribosomal protein L22,and two clinical isolates had amino acid changes of 67QK68 to 67RE68 in ribosomal protein L4. The ribosomal protein L22 and ribosomal protein L4 had visible changes in spatial structures for the D35G and Q67R,K68E mutations respectively. In summary, Streptococcus pneumonia can be induced to resistant to erythromycin in vitro,and the acquired drug-resistance had good stability; S.pneumoniae had no visible changes on biochemics and virulence after induction. The mechanisms of resistance relate to the new mutations in the binding domain of erythromycin is one of the mechanism of S.pneumoniae resistant to macrolide.