Pathogen Profiling in Reverse Total Shoulder Arthroplasty: Virulence Traits of Clinical Isolates Before and After Intraoperative Povidone–Iodine Irrigation

Background/Objectives: Reverse total shoulder arthroplasty (RTSA), a commonly performed procedure in elderly patients with osteoarthritis, is frequently complicated by postoperative infections-primarily caused by Cutibacterium acnes and coagulase-negative staphylococci (CoNS)-which remain a major clinical challenge. While standard antiseptic skin protocols can reduce the bacterial load at the surgical site, they often fail to achieve complete eradication, particularly with C. acnes, a resident species of the shoulder microbiome. Recent evidence indicates that intraoperative povidone-iodine irrigation is effective in significantly decreasing microbial burden; however, a thorough characterization of the virulence factors of the isolated strains remains essential. Methods: A total of 187 clinical strains isolated immediately after RTSA were characterized with respect to their antibiotic resistance profiles and biofilm-forming capacity, and the impact of intraoperative povidone-iodine irrigation on the reduction in bacteria that express these virulence traits was evaluated. Results: Of the 120 C. acnes isolates, 97.67% were susceptible to the tested antimicrobial agents, while only 3.33% exhibited resistance, specifically to clindamycin. In contrast, 53% of CoNS isolates were classified as susceptible, whereas the remaining 47% demonstrated multidrug resistance. Biofilm production was detected in 24% (29/120) of C. acnes and 39% (25/64) of CoNS isolates, with a statistically significant reduction observed after irrigation only for C. acnes. No association was found between biofilm formation and clindamycin resistance in C. acnes, likely due to the low number of resistant isolates. Conversely, among CoNS, a correlation was observed, with the 17.2% of biofilm-producing strains also exhibiting resistance to antimicrobial agents. Conclusions: Notwithstanding the presence of these virulence factors, povidone-iodine irrigation proved effective in substantially reducing the number of bacterial isolates recovered at the surgical site without selecting for strains with enhanced pathogenicity. Notably, the majority of resistant bacteria were detected prior to intraoperative irrigation. This intraoperative procedure may be a key approach to reducing prosthetic joint infections frequently caused by more virulent pathogens, which are unlikely to be selected following this disinfection strategy.