Journal article
Shigellosis in Children: Antimicrobial Susceptibility Testing by Automated Instrument vs. Etest Reveals Disagreements
Open forum infectious diseases, v 4(suppl_1), pp S681-S681
01 Oct 2017
Abstract
Abstract
Background
In April 2017, CDC recommended testing Shigella isolates at ciprofloxacin concentration down to 0.12 μg/mL, to detect potential novel resistance in isolates with MICs 0.12–1 μg/mL. The CLSI breakpoint for ciprofloxacin susceptibility (S) is 1 μg/mL and the Vitek®2 system currently tests only down to 0.25 μg/mL. Our objective was to perform S testing by Vitek2 and Etest to assess frequency of ciprofloxacin MIC ≥ 0.12 μg/mL and antibiotic S discrepancies between tests in clinical Shigella isolates.
Methods
Retrospective query of microbiologic data was performed to identify Shigella isolates from 2010 to 2016 to trend epidemiology and antibiotic S by Vitek. Shigella isolates recovered between June and October, 2016 were tested in parallel using Vitek2 and Etest. MIC interpretation disagreements were defined as very major error (S by Vitek2 but resistant [R] by Etest) and major error (R by Vitek2 and S by Etest).
Results
There was marked increase in shigellosis in 2016 (Fig 1). S. sonnei accounted for 90% of sporadic and outbreak isolates. Ampicillin resistance increased over time (21% in 2010, 90% in 2016) (Fig 2). Parallel testing of 36 isolates revealed 7 instances of antimicrobial S discrepancy with 5 very major errors (S by Vitek2 to ampicillin and TMP-SMX, R by Etest) and 2 major errors (R by Vitek2 to TMP-SMX, S by Etest) (Table 1). All 36 isolates were inhibited at the lowest Vitek2 concentration of ciprofloxacin (0.25 μg/mL); Etest confirmed that 34/36 had MIC ≤ 0.12 μg/mL, and 2 had MIC > 0.12 μg/mL (Fig 3).
Conclusion
MIC by Vitek2 and Etest had major discrepancies among 7/36 isolates, for antibiotics other than ciprofloxacin. Etest mirrored Vitek2 for ciprofloxacin testing. Etest revealed that 2/36 isolates with Vitek2 MICs of 0.25 μg/mL (i.e. lowest concentration tested) had MICs greater than 0.12 μg/mL. Vitek2 system adjustments to test ciprofloxacin at lower concentrations would address the CDC advisory. Data are needed to determine clinical relevance of Shigella susceptibility test results.
Table 1.
MIC Disagreements between Vitek2 and Etest
Very major error
Major error
Antibiotic
Patient/Isolate Number
Vitek 2
Etest
Vitek 2
Etest
Ampicillin
23
S ≤ 2
R > 256
25
S 4
R > 256
26
S ≤ 2
R > 256
TMP-SMX
5
S 1/19
R 4/76
29
S 1/19
R 32/608
7
R 8/152
S 2/38
13
R 8/152
S 1/19
Disclosures
All authors: No reported disclosures.
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Details
- Title
- Shigellosis in Children: Antimicrobial Susceptibility Testing by Automated Instrument vs. Etest Reveals Disagreements
- Creators
- Ishminder Kaur - St. Christopher's Hospital for ChildrenEmily Souder - Drexel UniversityJane M Gould - Drexel UniversitySarah S Long - Drexel UniversityAlan T Evangelista - Department of Pathology and Laboratory Medicine, St. Christopher’s Hospital for Children, Drexel University College of Medicine, Philadelphia, Pennsylvania
- Publication Details
- Open forum infectious diseases, v 4(suppl_1), pp S681-S681
- Publisher
- Oxford University Press
- Resource Type
- Journal article
- Language
- English
- Academic Unit
- Pediatrics
- Other Identifier
- 991019335589904721