Relationship Between Resistance And Pathogenicity Of Streptococcus Strains And The Effect Of The Infection On The Activity Of Liver Drug-Metabolizing Enzymes

1 A number of 108 strains were surveyed for in vitro minimal inhibitory concentration (MIC) to 30 drugs by microdilution test to find out the resistance present situation among Streptococcus isolated from veterinary clinic. Staphylococcus aureus ATCC25923 was used as reference strains for MIC quality control and clinical categorization of isolates as susceptible or resistant was based on MIC interpretative standards of the National Committee for Clinical Laboratory Standards(NCCLS). None of the strains were susceptible to all antimicrobial compounds tested and most strains(91.64 %) were multidrug-resistant. High level resistance to streptomycin was also detected. Resistance to sulfonamides(83.3-91.7%) , aminoglycosides (85.2-88%), lincosamides (52.8-59.3 %) , tetracyclines (74.1%) and macrolides(36.1 -69.4%) were most frequent, then P-lactam(9.3~47%) and quinolones(36.1 -61 %) resistance, while 90.7% strains were susceptible to florfenicol,53.7% strains were susceptible to taimulin. All resistant strains to β-lactam were tested for β-lactamase production and the results were negative. There were cross-resistance between penicillin, ceftiofur, erythromycin, enrofloxacin, sulfamethoxazole, streptomycin, tiamulin,florfenicol , lincomycin and doxycycline,the cross-resistance rate were 18.9%, 97.3%,89.2%, 94.6%, 94.6%, 59.5%,21.6% ,94.6% and 91.9% respectively. In conclusion,the study demonstrated a significant increase in resistance to most commonly used antimicrobial agents among Streptococcus strains isolated from veterinary and the resistant alert must be paied attention to the veterinary clinic.2 To investigate the mechanisms of erythromycin-resisant streptococcus isolated from animals, the minimal inhibitory concentrations(MICs) of pencillin, erythromycin and clindamycin against Streptococcus isolates were detected by agar two-fold dilution,the resistance phenotypes of erythromycin-resistant streptococcus were determined by the double disk test and the presence of mefA, erm B genes were determined by PCRamplification. The results showed that of 108 strains studied, the rate of resistance to penicillin, erythromycin and clindamycin were 34.3%, 69.4%, 52.8%,respectivery. By the double disk test, of 75 erythromycin-resistant isolates,55 isolates (73.3%) were assigned to the cMLS_B phenotype, 5 isolates (6.7%) were M phenotype and 15 isolates (20%) were inducible resistant, expressly the iMLS_B phenotype. The mefA gene was present in all of the strains showing the M-resistance phenotype. Some isolates expressing a cMLSb phenotype and iMLS_B phenotype were confirmed genotypically by the presence of the ermB gene, but 6 isolates were detected none of the ermB and mefk gene. Genes coding for both resistance mechanisms were found in one strain. No amplification was detected in all the erythromycin susceptible isolates.The correspondence rate of phenotypes and genotypes was 92%. In conclusion,erythromycin resistant Streptococcus isolated from animals mediated by ermB was predominance in China. The PCR amplification can be a useful method to quickly detect the erythromycin resistant isolates.3 To identify if there was the mechanism of active efflux in erythromycin resistant Streptococcus strains isolated from veterinary with mefA gene.Several erythromycin resistant strains with mefA gene,ermB gene and several susceptibal strains were selected in this test.Chess method was used to deterimining the effect of carbonylcyanidem chlorophenylhydrazone (CCCP) on the MIC of erythromycin,azithromycin,timilcosin and penicillin against Streptococcus isolates.SDS -PAGE method was used to analyzing the membrane protein profile between erythromycin resistant Streptococcus strains and other strains.The uptake of the ~14C-erythromycin in all the strains and the effect of CCCP, a proton conductor, on the accumulation were assayed by intact cells. The results showed that CCCP can obviously reduce the MIC of erythromycin and azithromycin against erythromycin resistant strains with mefA gene,but can not reduce the MIC of timilcosin and penici...