Abstract
ABSTRACTExtended-spectrum β-lactamases (ESBLs) which predominantly encoded by plasmids can spread among different bacterial strains through conjugative dissemination of ESBL-encoding plasmids. With this, bacteria acquire additional resistance and generate multidrug resistance. ESBLs are predominantly derived from plasmid-mediated TEM- or SHV-type β-lactamases through one or more point mutations that lead to a large number of TEM or SHV derivatives causing serious drug resistance issue. To explore the molecular mechanism concerning multidrug resistance, we adopt an antimicrobial sensitivity testing method to analyze the resistance phenotypes that expressed from multidrug resistant isolates collected in northern Taiwan. We found that 70% of these isolates were ESBLs strains and all of them were resistant to β-lactam antibiotics (ampicillin, piperacillin, cefazolin, cefuroxime, cefotaxime and aztreonam), but most of them were sensitive to another kind of β-lactam antibiotics—cephamycin (cefoxitin and flomoxef). We also analyzed TEM and SHV genotypes and their distribution in order to understand the correlations between resistance genotypes and phenotypes. We found that the TEM and SHV isolates collected in this study contain multiple point mutations and most of the TEM isolates belong to the TEM-1b (57%) and another TEM-A (28%) types, however, most of SHV-12 isolates were the SHV-type (63%). According to the available TEM and SHV genotypes, we designed a gene chip that can detect most of the genotypes of TEM and SHV-ESBLs in clinical isolates, because gene chip has the advantage of detecting single nucleotide mutation. For the purpose of clinical diagnostics, we optimized the hybridization and washing conditions, and also probe design. Gene chips are suitable for use in clinical diagnosis because of the advantage of detecting many resistance strains at the same time. It is likely, in the future, that clinical diagnostic gene chip will be able to make up a deficiency of existing diagnostic system and help us to choice correct antibiotics, then avoid bacteria producing drug resistance.