Aim
This pilot study assessed if time to positive-blood culture (posBC) isolate identification and antibiotic susceptibility test (AST) availability could be improved by performing a simple subculture at the time of the automated BC flagging at the originating regional pathology laboratory. Results would be compared to posBC subculture on receipt at the specialised (GX) metropolitan Microbiology laboratory. This approach to improving TAT of posBC utilises transport time, as incubation time for subcultures.
Background
The delivery of Microbiological diagnostic services and subsequently patient treatment to regional Hospital patients with bacteraemia is impacted by the time expended in transportation to the GX laboratory (Heidelberg). This leads to delays due to the need to subculture BC broths on receipt at the GX laboratory. We proposed that performing simple subculture onto chocolate blood agar (CBA) at the regional laboratory (in Mildura 600km away; no Microbiology facilities except Bactec-FX and microscopy), would improve the time to identification and AST TATs compared to the subculture performed at the GX laboratory.
Methods
At the regional laboratory, posBC on Bactec-FX were sampled, with one drop of posBC broth inoculated onto pre-warmed CBA, and incubated until courier collection. The subculture (in CO2 culture box), and the posBC bottles(s) were transported to GX laboratory at ambient temperature. If sufficient growth MALDI-TOF and (where indicated) AST (using Vitek 2XL) was initiated. A comparison of time to identification and AST results using regional subcultures was compared to standard GX laboratory methods.
Results
130 posBC from 87 patients were assessed. 90/130 (69%) regional CBA subcultures had sufficient growth to perform MALDI-TOF on arrival at GX laboratory. Identification from regional CBA subcultures was average 6.3 hours earlier than GX subcultures. AST was performed on 32 isolates, and regional CBA AST results were available average 7.9 hours earlier than for GX laboratory. Only 2/130 (1.5%) CBA were contaminated. Insufficient growth on CBA (40/130, 31%) on receipt was generally associated with fastidious organisms including anaerobes.
Conclusions
Implementation of the simple CBA subculture at the regional laboratory enabled earlier identification and AST results of posBC isolates, and potentially resulted in therapy adjustments and improved patient outcomes.