| Objective: The aim of this work was to characterize the cross-resistance mediated by three kinds of antimicrobial reagents(chlorhexidine,antibiotics and Traditional Chinese medicine(TCM))and to analyze the intrinsic mechanisms of the emergency on antimicrobial resistance.Moreover,this work may give an outline and profound knowledge to the development of new antimicrobial agents,and provide theoretical perspectives about systematical and standardized ways to use antimicrobial drugs,and this was of great significance for the long-term development of TCMs.Methods: 1.The sub-lethal dose of chlorhexidine diacetate(CHX),tetracycline(TET),Rhizoma Coptidis extract(RCE)and three antibacterial Chinese patent medicines involving Gengen Qinlian pill(GGQL),Xiang lianwan pill(XLW)and Shuang Huanglian oral liquid(SHL)were used for continuous cultivation of one reference strain(ATCC 25923)and 2 clinical isolates(SA hzj and SA ljb)for 12 days,respectively.The selection assays were carried out three times repeatedly.The susceptibility change was determined by analysis of the minimum inhibitory concentration(MIC)after drug-selection.The trained strains were reverted by drug-free agar for 10 days.`2.After that,the physiological and biochemical characteristics of mutant strains were tested,and the 16 S r DNA was used to identified the strains.Then the expression of aac(6`)/aph(2`)、aph(3`)-IIIa and ant(4`)-Ia were examined by the PCR approach.Results: 1.After CHX selection,the susceptibility to RCE was decreased(MIC increased by 4-16 fold).However,the results was indicated that the resistance to TET(8-512 fold increased MIC),gentamicin(GEN)(16-512 fold increased MIC),amikacin(AMK)(16-512 fold increased MIC)and cefepime(FEP)(4-16 fold increased MIC)was increased.2.After exposure of TET,the sensibility to RCE and CHX was lowered,but the resistance to other antibiotics was raised.However,there was an emergency of increased susceptibility to AMK(MIC decreased by 8 times).3.It seemed there was a tendency of cross-resistance to TET,AMK and FEP(MIC increased by 4-64 fold)rather than to ciprofloxacin(CIP),GEN and meropenem(MEM)after TCMs treatment.Also,TCMs could increase the susceptibility of AMK(MIC decreased by 4-8 times).4.The results of detection of AMK resistance showed that the aac(6`)/aph(2`)gene was found in: SA hzj and SA ljb(before and after RCE selection),aph(3`)-IIIa gene was found in: SA hzj(after RCE selection)and SA ljb(before and after RCE selection),ant(4`)-Ia gene was found in: SA hzj(before and after the RCE selection(in the last examination)).Nevertheless,all the antimicrobial genes of AMK were not found in ATCC 25923 before and after RCE exposure.Conclusion: 1.The results indicated that no matter selected by biocides,antibiotics or TCM reagents could result in less susceptibility or cross-resistance to the other two reagents in SA.There may be some same antimicrobial mechanisms in these three antimicrobial agents.However,TCMreagents could increase susceptibility of SA to chlorhexidine and antibiotics.2.Not only the single herb such as RC or Chinese patent medicine containing RC could arouse cross-resistance,but the Chinese patent medicine not including RC could also lead to increase resistance or cross-resistance.3.The emergency of cross-resistance was not inevitable after these drug-selections.The probability seemed to be basically unpredictable.4.It seemed there was prone to occur in some kind of antibiotics.The results implied that SA was much more likely to be cross-resistant to TET,AMK and FEP rather than CIP,GEN and MEM after selected by TCM reagents.5.The aac(6`)/aph(2`),aph(3`)-IIIa and ant(4`)-Ia gene of AMK resistance was detected in the strains after RCE selection. |
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