Multidrug-resistant (MDR) Staphylococcus spp. and Enterococcus spp. are pathogens frequently identified in fracture-related infections (FRI), and may be associated with unfavorable outcomes. This study aims to evaluate the prevalence, the susceptibility profile to beta-lactams, and the presence of resistance genes in these pathogens from patients included in the multicenter FRIDAY project (Fracture-Related Infection Clinical and Microbiological Data Analysis Study).

Microorganisms previously isolated in conventional culture media, originating from eleven Brazilian hospitals, were identified at the Laboratório Especial de Microbiologia Clínica (LEMC-UNIFESP) by mass spectrometry (MALDI-TOF MS). Isolates with a phenotypic resistance profile to beta-lactams were submitted to DNA extraction from colony-forming units (CFU) in broth and analyzed by conventional single PCR for detection of the genes mecA, vanA and vanB, with subsequent agarose gel electrophoresis.

Among the 202 patients evaluated and 312 microorganisms identified, Gram-positive bacteria were found in 186 isolates (59.6%). Among the total pathogens identified, Staphylococcus spp. accounted for 152 (48.7%) and Enterococcus spp. 19 (6.1%). Of the 85 Staphylococcus spp. isolates, the mecA gene was detected in 44 (51.8%), and 36 of these also proved resistant to cefoxitin in the phenotypic test, representing a genotype–phenotype concordance rate of 81.8%. Among the 41 isolates negative for mecA, 37 were also susceptible to cefoxitin. For Enterococcus spp., 13 isolates were tested for vanA and vanB, with three (23.1%) positive for vanA and none with detection of vanB.

There was high genotype–phenotype concordance using conventional PCR in the detection of the mecA gene in Staphylococcus spp. and the vanA gene in Enterococcus spp. The data reinforce the relevance of molecular analyses in the genotypic characterization of the resistance profile, providing support for rapid diagnosis and for earlier guidance of antimicrobial therapies in complex orthopedic infections, contributing to more assertive clinical decisions in high-complexity services.