Utility of direct susceptibility testing on blood cultures: is it still worthwhile?

Abstract

Earlier targeted therapy for bacteraemia optimizes patient outcomes and reduces broad spectrum antibiotic use. Standardized susceptibility testing results are available at 36-48 h. Direct disc susceptibility testing from blood culture broth reduces time to results but the inoculum is not standardized. No studies have looked at the clinical utility of direct susceptibility results. This retrospective cohort study aimed to assess the correlation between direct and formal testing methods as well as the clinical utility of direct susceptibility results. 160 episodes of bacteraemia with paired direct and formal susceptibility testing were studied. Direct disc testing was performed on blood culture broth. Formal testing was performed on isolates, using automated broth microdilution or Etests. The rate of error was 9.0 % (95 % CI 7.0-11.6 %). In 10 cases (6.3 %, 95 % CI 3.0-11.2 %), inappropriate antibiotics were used due to direct susceptibility results, including two cases with ineffective (as opposed to too broad) antibiotics being used. Antibiotics were changed in 28.1 % of cases once direct susceptibility data was available. There was a decreased time to effective antibiotics in 9.3 % (95 % CI 5.3-15.0 %), and a decreased time to a targeted antibiotics in 14.3 % (95 % CI 9.3-20.8 %) of cases. Despite the error rate, the advantages of earlier times to effective and targeted antibiotics justifies continuing direct testing in bacteraemia episodes with Gram-negative rods. In the Gram-positive group, given the contamination rate, the availability of adjunctive PCR, and the fact that early identification of the isolate could equally influence antibiotic choices, direct susceptibility testing may no longer be warranted.

Rapid antimicrobial susceptibility testing on positive blood cultures through an innovative light scattering technology: performances and turnaround time evaluation

“…The phase following this microbiological performances evaluation would be the introduction of Alfred 60 AST testing in the routine management of positive blood cultures with the assessment of the impact on patient’s outcome. A retrospective cohort study of Menon et al concluded to a speeded-up antibiotic change in 28% of bacteremia cases through the use of susceptibility testing with disk diffusion directly from positive blood cultures versus testing on subcultured colonies [26]. In an interventional study, Verroken et al similarly calculated a time gain of 18.2 h towards optimal antimicrobial treatment with the introduction of a speeded-up positive blood culture workflow including direct MALDI-TOF MS identification, rapid resistance detection testing and direct automated AST [27].…”

Performance and potential clinical impact of Alfred60AST (Alifax®) for direct antimicrobial susceptibility testing on positive blood culture bottles

“…This was also shown by Meda et al [27]. In general, tests that improve time to ID for Gram-positive pathogens and time to AST for Gram-negative organisms have the greatest potential impact in optimizing antibiotic therapy [27,28].…”

Bacteremias por staphylococcus aureus: factores de riesgo asociados a la resistencia a meticilina

“…La identificación del agente causal responsable de bacteriemiasy el estudio de sensibilidad en el laboratorio son esenciales para instaurar un tratamiento antibiótico adecuado y también para detectar precozmente resistencias como las recientemente descritas frente a los glucopéptidos 23,24 .La OMS recuerda que, aunque la resistencia es un proceso natural de adaptación por parte de los microorganismos cuando estos se exponen a los agentes antimicrobianos, se desarrolla mucho más rápidamente por el mal uso y el uso excesivo de estos fármacos. En este sentido, la OMS indica que el uso de antibióticos en los seres humanos ha aumentado en un 36% 13 entre 2000 y 2010, siendo los países desarrollados los que tienen un mayor consumo por persona, aunque el consumo está creciendo rápidamente también en las economías emergentes.…”