Polymicrobial Infections and High Resistance Among Gram-Negative Bacteria Are Common in Orthopedic Implant-Associated Infections: A Brazilian Multicenter Study

Orthopedic implants restore mobility and improve quality of life in patients with orthopedic conditions. Despite advances, orthopedic implant-associated infections (OIAI) remain a clinical challenge. This study describes the mono- and polymicrobial microbiological profile and susceptibility profile of OIAI. Retrospective cohort study with 246 OIAI episodes in 210 patients, from November/2021 to February/2024, including fracture-related infection (FRI), periprosthetic infections (PPI), and chronic osteomyelitis (COM). Microbiological analysis was performed on deep tissues and orthopedic implants removed intraoperatively. Susceptibility was assessed by disk diffusion and broth microdilution. Episodes were classified as monomicrobial infection (MMI), polymicrobial infection (PMI), or culture-negative infection (CNI). Qualitative variables were analyzed using chi-square and Fisher’s exact tests, and quantitative variables using Mann–Whitney or Student’s t tests. A total of 164, 70, and 14 episodes of FRI, PPI, and COM, respectively, were included. Frequencies of MMI, PMI, and CNI were 49.2% (121/246), 36.6% (90/246), and 14.3% (35/246). Most FRIs occurred as MMI (71.1%), while in PPI the frequencies of MMI and PMI were similar (23.1% vs 31.1%; p = 0.27; OR = 1.43; 95% CI: 0.74–2.79). A total of 446 microorganisms were isolated, with predominance of Gram-positive cocci (GPC) (66.6%, 297/446). PMI had a higher proportion of Gram-negative bacilli (GNB) compared with MMI (37.7% vs 25.8%; p = 0.033). The main agents were coagulase-negative Staphylococcus (CoNS) (30.5%) and S. aureus (27.1%). Among GNB, Enterobacteriaceae accounted for 23.1%. S. aureus was more frequent in MMI (p < 0.001), while Acinetobacter/Streptococcus spp. were more common in PMI (p < 0.05). Linezolid and sulfamethoxazole + trimethoprim (SMX+TMP) showed the lowest resistance rates for S. aureus (2.0% and 6.0%), while vancomycin was more effective against CoNS (92.0%, p = 0.01). Enterobacteriaceae showed high resistance to ertapenem (70.0%, p = 0.06). Polymicrobial infections are common in OIAI, accounting for nearly half of cases, with high prevalence of GNB and high overall resistance. S. aureus and CoNS predominated and show preserved susceptibility to SMX+TMP, making it a drug of choice for treating OIAI.