Concordance of molecular microbiology and conventional culture techniques for infected diabetic foot ulcer management

Aim

The management of infected diabetic foot ulcers (DFUs) requires balancing the need for timely interventions against the desire for targeted antibiotic therapy, which relies on laboratory results. This study aimed to evaluate concordance between molecular and conventional culture and sensitivity (C&S) methods in identifying bacteria from infected DFUs.

Methods

This study was conducted alongside CODIFI2, a Phase III randomised controlled trial comparing tissue sampling with wound swabbing. It assessed C&S and metagenomic 16S rRNA gene sequencing (M16S) in DFUs with suspected mild or moderate infections using both tissue and swab samples.

Results

In 145 participants, C&S identified 248 microorganisms across 25 genera including eight anaerobic genera. M16S identified a greater number and diversity of microorganisms, detecting 455 across 40 genera, including 173 anaerobes from 15 distinct genera. No bacterial growth was reported in 25.5% (95% CI: 18.0%–32.3%) of C&S samples, whereas M16S identified at least one organism in all samples. While the observed agreement between methods was high (75%), Cohen's Kappa revealed low concordance overall, except for Pseudomonas spp. and Streptococcus spp. (Kappa ≥ 0.5).

Conclusions

M16S detected a broader microbial spectrum, including fastidious anaerobes, but its low concordance with C&S and lack of antibiotic sensitivity data, challenge its suitability as a replacement for C&S in mild or moderate DFU infections. It may offer advantages in infections where increased sensitivity is beneficial, particularly where extended culture approaches are recommended to detect fastidious or low-abundance organisms. For mild to moderate DFU infections, our findings support continued reliance on conventional C&S testing.