Determination of antibiotic sensitivity of bacteria by flow cytometry method

Introduction and Aim: The aim of this study was to determine the in vitro antibiotic susceptibility of gram-positive and gram-negative bacteria by using flow cytometry method and to shorten the delivery time. Material and Method: Six standard strains and 11 clinical isolates were examined in this study. Antibiotic susceptibility of all strains; was tested with VITEK 2 automated system, liquid microdilution and flow cytometric method. Antibiotic dilutions were determined according to the current EUCAST guidelines. Antibiotic dilutions were determined according to the current EUCAST guidelines. Prior to flow cytometric analysis, bacterial suspensions in the microplate were incubated at 120 rpm and 35-37 ° C for 2 hours. The suspension in each well was transferred to 100μl reading tubes. Then, 10 Syl Syto 9 and 10 Propl Propidium iodide dye were added to each tube and incubated for 15 minutes in dark. In flow cytometric analysis, growth control wells and antibiotic wells were compared by overlay on the FL1-H graph and a growth control wells in bacterial count of at least 55% in antibiotic wells was accepted as the sensitivity criterion. Results: Antibiotic susceptibility determined by flow cytometric method with BMD and VITEK 2 system were found to be as follows; two E. coli strains (92.3%, 84.6%), four K. pneumoniae strains (88.7%, 81.8%), two P. aeruginosa strains (73%, 73%), two A. baumannii complex strains (81.8%, 81.8%), two S. aureus strains (86.1%, 81.2%), three Enterococcus spp. strain (81.8%, 88.8%). Conclusion Antibiotic susceptibility studies with flow cytometric method showed a high level of agreement between BMD and VITEK 2 system. In gram negative bacteria, flow cytometry and other methods were found to be more compatible than gram positives. Antibiotic susceptibility tests shorten the delivery time of 12-14 hours. However, it has not yet been standardized to be used in all laboratories. More detailed and comprehensive studies are needed to determine antibiotic susceptibility by flow stiometry. Keywords: Flow cytometri, antimicrobial suscecbility, MIC, EUCAST