Rapid screening of positive blood cultures for extended-spectrum β-lactamases and metallo-β-lactamases using a drug susceptibility testing microfluidic method

Objectives: An increasing number of drug-resistant bacteria have been identified recently. In particular, drug- resistant bacteria have been linked to unfavorable prognoses in patients with bacteremia, highlighting the need for rapid testing. Our previous studies have focused on the utility of a drug susceptibility testing micro- fluidic (DSTM) method using microfluidic channels. A system with this DSTM method for screening for beta-lactamases can rapidly detect extended-spectrum beta-lactamases (ESBLs) and metallo-beta-lactamases (MBLs). In this study, we have evaluated the clinical utility of pre-treatment for screening positive blood cultures using the DSTM method. Methods: A total of 178 positive blood cultures and five simulated samples of MBL-producing bacteria were prepared at Kochi University Hospital, Japan. The pretreatment consisted of a two-step centrifugation. The obtained sediments were screened with the DSTM method for the production of beta-lactamase based on morphological changes in the bacteria after 3 h of incubation. Results: The pretreatment functioned properly for all samples. Of the 25 ESBL samples, 21 were positive for ESBLs. Four false-negative samples, all obtained from the same patient, contained CTX-M-2 enzyme-producing Proteus mirabilis and showed insusceptibility to an ESBL inhibitor. The simulated samples prepared for MBL screening were positive for MBLs. Conclusions: When combined with a method for rapidly identifying bacterial species, DSTM may enable patients with bloodstream infections to start receiving appropriate treatment within 4 h after positive blood cultures are screened.