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Poloxamer dilution as an on-demand alternative to agar dilution-based antimicrobial susceptibility testing
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DOI：10.1128/jcm.01822-25.png)
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Abstract
En 中文
Agar dilution is a reference susceptibility testing method uniquely or preferentially recommended for certain antimicrobials. However, the effort required to pour individual agar plates spanning a doubling dilution range precludes its practical implementation in hospital clinical laboratories. Here, we describe an on-demand replacement for agar dilution, specifically substituting Poloxamer 407 (also known as Pluronic F-127) for Bacto agar as the solidifying agent. Notably, 20% Poloxamer 407 solutions (e.g., with Mueller-Hinton broth) remain liquid at refrigerated temperatures but solidify upon warming, enabling facile setup of poloxamer dilution testing in Petri dish or microwell format. For fosfomycin susceptibility testing, poloxamer dilution and reference agar dilution showed excellent categorical agreement (CA) and essential agreement (EA) for Escherichia coli (100% and 87%, respectively, n = 31). For other Enterobacterales, excluding Klebsiella spp., CA and EA were both 82% (n = 17, respectively). For Pseudomonas aeruginosa, CA and EA were 60% and 100% (n = 10), respectively, with the lower CA reflecting the large number of strains tested with minimal inhibitory concentrations near categorical breakpoints. There were no very major errors, while major errors were only observed for Klebsiella spp. Additionally, poloxamer dilution substantially reduced the number of skipped dilutions sixfold for E. coli (P < 0.0001) and inhibited swarming of Proteus spp. We conclude that poloxamer dilution and agar dilution, an imperfect gold standard, have essentially equivalent practical performance and that poloxamer dilution can therefore serve as an on-demand alternative testing methodology in clinical laboratories for fosfomycin testing of gram-negative pathogens. A broader exploration of poloxamer dilution's utility is thus warranted.
Keywords:
Poloxamer 407
Pluronic F-127
agar dilution
antimicrobial susceptibility testing
fosfomycin
Mueller-Hinton medium
gram-negative bacteria
Enterobacterales
Pseudomonas aeruginosa
clinical microbiology laboratory
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