ArticleThe Journal of antimicrobial chemotherapy2025
Validation of a modified rapid test to detect the cefazolin inoculum effect in methicillin-susceptible Staphylococcus aureus from bloodstream infections in hospitals from North and Latin America.
Article in The Journal of antimicrobial chemotherapy, 2025. The graph could read no effect estimate from its abstract, so it casts no vote on the map. Cited by 3 papers.
What it found
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The abstract states no effect estimate the extractor could read, or names no intervention and outcome on the map, so this paper lights no cell and moves no belief. It is still indexed, cited and linked below.
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Trials whose registry record cites this paper, or whose number appears in the abstract. A trial that started after this paper was published is citing it as background, not reporting it.
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Who cites it
3 citing papers in PubMed.
- Development of a rapid diagnostic test for the cefazolin inoculum effect in methicillin-susceptible Staphylococcus aureus: Cefinase disk direct (CDD) test.European journal of clinical microbiology & infectious diseases : official publication of the European Society of Clinical Microbiology · 2026Article
- The inoculum effect of methicillin-susceptibleMicrobiology spectrum · 2026Article
- The Cefazolin Inoculum Effect: An Underappreciated Factor in MSSA Treatment Strategies.Infectious diseases and therapy · 2026Review
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Authors and funding
19 authors.
Funding
Abstract
backgroundThe cefazolin inoculum effect (CzIE), defined here as a cefazolin MIC at high inoculum (107 colony-forming units/mL) ≥16 mg/L in MSSA, has been associated with less favourable clinical outcomes. However, detection of this phenotype is challenging in the clinical microbiology laboratory. We previously described modification of a rapid nitrocefin test using ampicillin disks rather than ampicillin powder for induction of the Staphylococcus aureus β-lactamase (BlaZ).
objectiveEvaluate the performance of the modified rapid nitrocefin test in a blinded fashion using MSSA isolates recovered from patients with bacteraemia.
methodsWe evaluated 200 MSSA isolates recovered from Latin American (LA) and North American (NA) hospitals (67 and 133 from NA and LA, respectively). The CzIE was determined using the modified rapid nitrocefin test with ampicillin disks and compared with MIC determination at high inoculum (gold standard). All isolates were subjected to whole-genome sequencing on an Illumina Hi-Seq platform. Performance metrics were calculated for the complete dataset and according to specific BlaZ types.
resultsThe prevalence of the CzIE was 53% (105/200). Compared with the gold standard, the modified nitrocefin rapid test had a sensitivity of 96% and a specificity of 91.6%, with an overall accuracy of 94%. There were no false-positive results among blaZ-negative MSSA strains.
conclusionsThe modified nitrocefin rapid test exhibited a robust performance to detect the CzIE in isolates from the Americas. This methodology is inexpensive and can be implemented in clinical microbiology laboratories around the world, including those with limited resources.
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