Surgical site infections (SSI) are a severe complication of orthopedic joint implantation. Gram-negative bacteria are increasingly reported, in particular SSI caused by Enterobacterales producing Amp-C cephalosporinase (AmpC-EB). We aimed to describe the characteristics and the management of these AmpC-EB SSI.

We performed a retrospective, observational, monocenter study between January 2019 and March 2025. All patients over 18 yo with arthroplasty, whose perioperative samples were positive with AmpC-EB, were included. Early SSI occurred between one and three months after material implantation. Demographic, clinical, surgical, and microbiological data were collected.

Sixty-six patients presented AmpC-EB SSI during the study period. Mean age was 59.9 ± 20.6yo, 39 (59.1%) patients were male, and 28 (42.4%) were immunocompromised (diabetes, cancer, immunosuppressive treatment).

Sites of infections included 20 (30%) knee, 17 (26%) elbow, 14 (21%) hip, 7 (11%) shoulder, 6 (9%) ankle, 1 spine and 1 wrist.

Fifty-six (84.8%) patients exhibited local signs of infection, 31 (55%) had a fistula and 17 (30%) purulent discharge. Early SSI were reported in 41 (62%) cases.

AmpC-EB involved 56 (85%) Enterobacter cloacae complex , 7 (11%) Serratia marcescens, 1 Providencia stuartii, 1 Hafnia alvei, 1 Citrobacter freundii with different susceptibility profiles: 50 (73.2%) wild cephalosporinase, 16 (22.4%) AmpC derepression showing resistance to cefotaxime, tazocillin and ceftriaxone but susceptibility to cefepime and carbapenems, 2 (3%) expressing extended spectrum beta-lactamase (ESBL). SSI were monomocrobial in 34 (51.5%) cases and polymicrobial in 32 (48.5%) cases, main co-infection observed with S. aureus . Empirical treatment was tazocillin with daptomycine, and was switched to carbapenems in case of ESBL, and to cefepime in case of AmpC derepression.

Early SSI (41 cases (62%)) were primarily treated with DAIR (debridement, antibiotics, and implant retention), whereas infections occurring after three months representing 25 (38%) infections with 9 (36%) required material change and 11 (44%) removal with a revision procedure.

We report a high occurrence of SSI caused by AmpC-EB. These results may highlight an evolution in bacteria involved in SSI. They also urge us to modify our empirical antibiotic treatment tazocillin with daptomycin, for cefepim with daptomycin to cover all AmpC-EB infections.