Characterization of Two Macrolide Resistance-Related Genes in Multidrug-Resistant Isolates.

In analyzing the drug resistance phenotype and mechanism of resistance to macrolide antibiotics of clinical isolates, the agar dilution method was used to determine the minimum inhibitory concentrations (MICs), and PCR (polymerase chain reaction) was applied to screen for macrolide antibiotics resistance genes. The macrolide antibiotics resistance genes were cloned, and their functions were identified. Of the 13 antibiotics tested, strains showed high resistance rates (ranging from 69.5-82.1%), and MIC levels (MIC90 > 256 μg/ml) to macrolide antibiotics. Of the 131 known macrolide resistance genes, only two genes, and , were identified in 262 clinical isolates. Four strains (1.53%, 4/262) carried both the and genes, and an additional three strains (1.15%, 3/262) harbored the gene alone. The cloned and genes conferred higher resistance levels to three second-generation macrolides compared to two first-generation ones. Analysis of MsrE and MphE protein polymorphisms revealed that they are highly conserved, with only 1-3 amino acids differences between the proteins of the same type. It can be concluded that even though the strains showed high resistance levels to macrolides, known macrolide resistance genes are seldom present in clinical strains, demonstrating that a mechanism other than this warranted by the and genes may play a more critical role in the bacteria's resistance to macrolides.