The effectiveness of prophylactic antibiotics and betadine skin preparation on cranial cutaneous Cutibacterium acnes - A prospective study.

BACKGROUND: Cutibacterium acnes, formerly known as Propionibacterium acnes, is increasingly recognized as a cause of surgical site infection and implant failure despite the use of prophylactic antibiotics and antiseptic surgical preparations. The aim of this study was to investigate whether C. acnes persists in the dermal layer of the skin after standard perioperative antibiotics and skin prepping with alcoholic betadine solution in consecutive patients undergoing a craniotomy. METHODS: A single centre prospective observational study was performed at Flinders Medical Centre. Adult patients undergoing a cranial neurosurgical intervention between October 2019 to March 2021 were eligible for inclusion. After administration of standard preoperative antibiotics (Cefazolin), three swabs were taken for each patient: one before prepping the skin with alcoholic betadine, one after prepping the skin and a dermal swab once the skin was incised. RESULTS: 73 patients were included. Cutibacterium acnes cultures were positive in 61 patients of the "pre-prep" group (83.6%), 12 (16.4%) in the "post-prep" group, and 53 (72.6%) were from dermal swabs There was a significant reduction of positive cultures of the skin after surgical preparation was applied (p < 0.00001). There was a non-significant reduction of positive cultures in the dermal swabs after skin preparation (p = 0.068) CONCLUSIONS: Cutibacterium acnes persists within the dermis of the scalp despite standard prophylactic measures using alcoholic betadine solution and cefazolin.

Antimicrobial Susceptibility Testing for Staphylococcus lugdunensis.

Evaluation of penicillin and oxacillin susceptibility testing was conducted on 200 Staphylococcus lugdunensis isolates. Disc diffusion with penicillin 1 IU (P1, EUCAST) and penicillin 10 IU (P10, CLSI) was compared with nitrocefin discs (Cefinase) and automated broth microdilution (Vitek 2). Oxacillin susceptibility was extrapolated from cefoxitin (FOX; 30 µg) disc diffusion and compared with Vitek 2 results. The reference methods were blaZ and mecA PCR. Penicillin zone diameter and zone edge correlated with blaZ PCR results in all except two P10-susceptible isolates (very major error [VME]) and one P1-resistant isolate (major error [ME]). A total of 148 isolates were blaZ negative, of which 146 and 149 isolates were susceptible by P1 and P10, respectively. A total of 127 were penicillin susceptible by Vitek 2. Vitek 2 overcalled resistance in 21 blaZ-negative, 20 P1-susceptible, and 22 P10-susceptible isolates (Vitek 2 ME rate, 14.2%). Two mecA-positive isolates were oxacillin resistant by FOX disc and Vitek 2 methods (categorical agreement). However, 18 FOX-susceptible mecA-negative isolates tested resistant by Vitek 2. In conclusion, Vitek 2 overestimated penicillin and oxacillin resistance compared with disc diffusion and PCR results. In our study, disc diffusion with zone edge interpretation was more accurate and specific than automated broth microdilution for S. lugdunensis.