| Antimicrobial resistance phenotypes and SCCmec genotypes of Methicillin-resistant Staphylococcus aureus (MRSA) isolatesObjectiveTo investigate the antimicrobial resistance phenotypes and SCCmec genotypes of 92 MRSA isolates in the first affiliated hospital, Shantou university medical college. Methods1.The bacterial genomic DNA was extracted and polymerase chain reaction (PCR) was used to detect of the mecA gene of MRSA strains.2. The minimum inhibitory concentrations (MICs) of 16 antimicrobial agents against MRSA were testeded by agar dilution method.3. SCCmec types of MRSA isolates were determined by multiplex PCR. Results1. MecA gene was detected in all of 92 MRSA strains.2. More than 80% of MRSA strains were resistant to all of the testedβlactam antibiotics. Most of the strains were resistant to gentamycin, erythromycin and fluoroquinolones while more than half of MRSA strains were susceptible to rifampicin. Chloramphenicol, doxycycline and minocycline still remained a high activity against MRSA isolates. Vancomycin resistant Staphylcoccus aureus was not found in this study.3. SCCmecIII and IIIA were predominant types among the cilinal MRSA isolates. This result was consistent with previous reports that SCCmec III and IIIA types were predominant in most Asian countries.Conclusions1. Antimicrobial resistance of MRSA isolates in the first affiliated hospital, Shantou University Medical college are multidrug resistant. However, chloramphenicol, semi-synthetic tetracyclines and vancomycin are highly effective against MRSA isolates.2. SCCmecIII and IIIA were predominant types among the MRSA isolates suggesting that most of the MRSA isolates in this study may have originated from HA-MRSA. Mechanism of synergic effect between baicalein andβlactams against MRSAObjectiveTo investigate the mechanisms of synergic effects of baicalein in combination withβlatams against MRSA. Methods1. The minimum inhibitory concentrations (MICs) of baicalein alone and in combination withβlactams against MRSA isolates were determined by agar dilution method and microdilution checkboard method.2. Global transcriptional response of Staphylococcus aureus to baicalein was analysed by AFFX GeneChips and confirmed by real time PCR.3. Western blot was performed to dectect the expression of PBP2a produced by MRSA isolates affected by baicalein. Fluroimage was used to analyse the production and binding ability of PBPs of MRSA after treated with baicalein.4. Crude autolysis enzyme and cell wall were extracted. MRSA autolysis profile and activity were analysed by SDS-PAGE electrophoresis.5. Activity ofβ-lactamase inhibited by baicalein was detected by microplate reader.6. The activity ofβ-lactamase was not significantly inhibited by baicalein. Reusults1. The MICs of baicalein alone against MRSA isolates ranged from 64 to 128μg/ml. 32μg/ml baicalein remarkablely reduced the MICs of cefazolin, oxacillin and ampicillin against MRSA and ATCC25923 with FIC index range from 0.266 to 0.75. These results revealed the synergism of cefazolin, oxacillin and ampicillin against MRSA in combination with 32μg/ml baicalein.2. The results of GeneChips showed that 164 genes were remarkably upregulated by baicalein, 53 of which were identified genes. 332 genes were downregulated, 64 of which were identified genes. The functions of these differentially expressed genes were involved in basic metabolism, gene transcription regulation, transporter, DNA repair and replication,autolysin and methylation. The results of real– time PCR were in consistent with those of Genechips.3. The results of Western blot revealed that PBP2a expression of MRSA did not decrease significantly when treated with baicalein. Fluorescence image resulte showed that the baicalein did not either induce the production of PBPs or interfere with the affinity between PBPs and Bocillin - FL .4. Baicalein increased the uptake of cafazolin into MRSA.5. Baicalein increased the expression of autolytic system or induced the activity of autolysin.ConclusionThere is a synergic effect between baicalein andβlactam antibiotics against MRSA. Baicalein significantly decreases the MICs ofβlactam antibiotics against MRSA isolates. The following factors may involve in the mechanisms of the restoration of susceptibily of MRSA toβlactams by baicalein.1. Bacalein may inhibit expression of multidrug-resistant transporter, which increases the concentration of the antibiotic uptake and enhances the susceptibility ofβlactams of MRSA.2. Baicalein probably interferes with the process of DNA replication and repair, and therefore increases the toxic effects of antibiotics against MRSA.3. The expression of some methylase and ribosomal protein may be inhibited by baicalein so that hinder the normal process of protein synthesis.4. Baicalein triggers the autolysis system of MRSA, which may also involve in the mechasnims of enhanced antibacterial effects ofβlactam antibiotics.
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