Detection of "Hidden" Antimicrobial Drug Resistance.

Antimicrobial drug resistance has become a serious public health problem. The current clinical diagnostic methods are turbidity-based assays that have been used for years to track bacterial growth; however, the method is relatively insensitive. To eliminate the new occurrence of drug resistance in infectious bacteria, we developed a highly sensitive EZMTT method for the antibiotic susceptibility test (AST) that magnified the cell growth signal and revealed partial drug resistance (showing 2-20% weak cell growth) that was not detected by the current turbidity assay within 24 h. By simply mixing the EZMTT dye with the bacterial culture and then following the growth by absorbance measurement at 450 nm, the drug-induced proliferation (DIP) rate can be obtained in a high-throughput-screening (HTS) mode with greater than 10-fold better sensitivity than the turbidity assay. The EZMTT-based DIP rate assay of 5 clinically isolated E. coli strains found approximately 30% more partial drug resistance than what was detected in the traditional turbidity-based assay. The observed partial drug resistance was further confirmed by mechanistic analyses. Therefore, a combination of the EZMTT dye and the current clinically used VITEK-type technology has great potential to help understand antimicrobial drug resistance and ultimately provide patients with precise medical care to prevent the occurrence of multidrug resistant bacteria.