Antimicrobial susceptibility testing determined by Alfred 60/AST (Alifax®) in a multi-sites lab: performance's evaluation and optimization of workflow

Purpose: New techniques are needed to speed-up the identification and antimicrobial susceptibility testing (AST) of bacteria associated with bloodstream infections. Alfred 60/AST (Alifax (R), Polverara, Italy) performs AST by light scattering directly from positive blood cultures. Methods: We evaluated Alfred 60/AST performances for 4 months. Each new episode of bacteraemia was included and AST were compared to either our rapid automated AST (Vitek (R) 2) or disk diffusion method. The discrepancies were investigated using Etest (R). The time-to-result (TTR) was evaluated by comparing the blood volume inserted into Alfred 60/AST, i.e. 2 versus 7 blood drops. Taking into account the TTR, the workflow of positive blood cultures and the availability of AST results was studied in order to optimize the implementation of Alfred 60/AST. Results: A total of 249 samples and 1108 antibiotics for AST were tested. After exclusion of unavailable results, 1008 antibiotics were analysed. 94.9% (n = 957/1008) of the antibiotics showed categorical agreement. There were 14 very major errors (VME), 24 major errors (ME) and 13 minor errors (mE). The VME were mostly related to clindamycin (64.3%) whereas meropenem and piperacillin-tazobactam constituted the major part (37.5% and 61.5%) of ME and mE respectively. Results were highly reliable for Enterobacterales and enterococci. The mean TTR ranged between 4.3 and 6.3 h and was statistically 20 min faster when applying the 7 blood drops protocol. We showed that Alfred 60/AST could give relievable results within working hours for positive blood culture which are flagged the same day between 12:00 am and 12:00 pm. Conclusion: Our study confirmed that Alfred 60/AST gives reliable AST results in a short period of time, especially for Enterobacterales and enterococci. AST could thus be easily obtained the same day of a positive blood culture. Clinical impact studies are mandatory to validate a 24/24 working.