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- Title
Short incubation of disc diffusion for Streptococcus pneumoniae and Haemophilus influenzae to reduce time to susceptibility report.
- Authors
Åkerlund, Anna; Serrander, Lena; Sundqvist, Martin
- Abstract
Background Rapidly instituted antimicrobial therapy is important in severe infections, and reduced time to the antimicrobial susceptibility testing (AST) report is thus of importance. Disc diffusion (DD) is a cheap, rapidly adaptable, flexible and comprehensive method for phenotypic AST. Previous studies have shown that early reading of inhibition zones for non-fastidious species is possible. Objectives To evaluate zone reading after short incubation of DD in Haemophilus influenzae (n = 73) and Streptococcus pneumoniae (n = 112). Methods The readability was evaluated and susceptibility interpretation (SIR) was performed, using the EUCAST 18 ± 2 h incubation breakpoint table (version 12.0), after 6 and 8 h of incubation. Categorical agreement (CA) and error rates were calculated using standard DD and broth microdilution as reference. Results The proportion of readable zones in H. influenzae was 19% (6 h) and 89% (8 h). The CA was 98% after 8 h. The corresponding readability in S. pneumoniae was 63%/98% and CA was 95%/97% after 6 and 8 h, respectively. Early reading of the screening discs (benzylpenicillin 1 unit in H. influenzae and oxacillin 1 µg in S. pneumoniae) correctly identified 18/22 of the H. influenzae isolates and all the readable S. pneumoniae isolates with reduced β-lactam susceptibility. For non-β-lactam agents, very major errors were most common for quinolones in S. pneumoniae. Introduction of areas of technical uncertainty (ATUs) reduced the error rate to ≤1.1%. Conclusions We conclude that shortened incubation is feasible for H. influenzae and S. pneumoniae. To reduce the risk of false categorization a buffer zone (i.e. ATU) near the breakpoints must be used.
- Subjects
HAEMOPHILUS influenzae; STREPTOCOCCUS pneumoniae; MICROBIAL sensitivity tests; ERROR rates; PENICILLIN G
- Publication
Journal of Antimicrobial Chemotherapy (JAC), 2023, Vol 78, Issue 10, p2563
- ISSN
0305-7453
- Publication type
Article
- DOI
10.1093/jac/dkad272