Rapid and simple detection of extended spectrum β-lactamase, metallo β-lactamase, and AmpC β-lactamase using drug susceptibility testing microfluidic (DSTM) method and its applicability for blood culture specimens

Abstract

Background

The recent global increase in the prevalence of antibiotic-resistant bacteria and the lack of development of new antimicrobials emphasize the importance of rapid antimicrobial selection for the treatment of infections. Matsumoto et al. (2016) proposed an innovative rapid method for drug susceptibility testing for Pseudomonas aeruginosa that provides results in 3 h. Subsequently, in a similar Drug Susceptibility Testing Microfluidic device (DSTM), we developed a rapid method to detect extended-spectrum β-lactamase, metallo β-lactamase, and AmpC β-lactamase simultaneously.

Methods

When three types of inhibitors (clavulanic acid, EDTA, and cloxacillin) were combined with β-lactamase sensitive substrate, e.g., ceftriaxone together, strains that produce any of these three classes of β-lactamases become susceptible and when one of the three is missing, only strains producing β-lactamase sensitive to the missing inhibitor grow normally. Susceptibilities were microscopically evaluated from elongated cell shapes. Enzyme classes were identified by testing to determine which inhibitors the strains were resistant to when deficient.

Results

Multiple enzyme producers were easily identified by this method. Twenty-one genome-sequenced strains of carbapenem-resistant Escherichia coli were tested, and it was confirmed that chromosomal AmpC was not involved in E. coli's carbapenem resistance. Direct blood culture testing was possible by a simple pretreatment of the culture.

Conclusion

Rapid detection of β-lactamases via this method could be useful for the infectious treatment approach.