The microcolony detection method (MCD), a simple and rapid screening test for antimicrobial resistance bacteria on positive blood cultures

Rapid detection of antibiotic-resistant bacteria in blood cultures is critical for the timely treatment of patients with sepsis. The aim of this study was to develop a simple method for the rapid detection of drug-resistant bacteria from blood cultures and to evaluate its performance. We developed an optical microscopy-based microcolony detection method (MCD) for the rapid detection of antibiotic-resistant bacterial colonies in media. This method was tested using staphylococci resistant to methicillin and gram-negative bacilli resistant to third-generation cephalosporins and carbapenem. The results of the investigations of clinical samples using this method were compared with the drug susceptibility testing results for each of the 457 isolates, which included 134 staphylococci and 323 g-negative bacilli. The MCD was successful in detecting antibiotic-resistant bacterial growth from culture-positive blood samples in approximately 3 h. The sensitivity/specificity for methicillin-resistant staphylococci was 100%/97.2%. In the case of gram-negative bacilli, the sensitivity/specificity values for bacteria resistant to ceftriaxone, ceftazidime, and carbapenem were 100%/98.7%, 100%/89.3%, and 100%/90.9%, respectively. Therefore, MCD is a clinically useful screening method for the efficient and rapid detection of antibiotic-resistant bacteria and can be easily implemented in laboratories.