Microbiology of Pressure Ulcers: A Systematic Review

Pressure ulcers are complex wounds frequently complicated by infection. This review aims to characterize the distribution of microorganisms in pressure ulcers and secondarily to assess heterogeneity across studies and compare yields between invasive (biopsies) and noninvasive (swabs/irrigation-aspiration) sampling techniques with implications for antimicrobial management. PubMed, Embase, and the Cochrane Library were searched up to 1 January 2025. Original research articles reporting microbiological data from pressure ulcers were included. Studies were excluded if data were incomplete, combined with other wound types, or derived from non-ulcer sampling sites. Risk of bias was assessed using Risk of Bias in Non-randomized Studies - of Interventions (ROBINS-I) V2, ROBINS-E, and RoB 2 frameworks. Data were synthesized descriptively and statistically. Twenty-eight studies (1,473 patients, 1,682 pressure ulcers, and 4,231 microbial isolates) were included. The most frequently isolated microorganisms were Staphylococcus aureus (39.7% of ulcers), Corynebacterium spp. (28.8%), Escherichia coli (23.1%), Proteus spp. (23.1%), Streptococcus spp. (22.7%), coagulase-negative Staphylococcus (21.6%), Enterococcus spp. (20.7%), Pseudomonas spp. (17.8%), and Bacteroides spp. (16.0%). On average, 2.5 isolates were reported per ulcer (range: 0.5-4.8). Significant heterogeneity was observed across studies for nearly all major organisms (global heterogeneity: χ² = 1958.4, df = 405, p < 0.001). Swabs more frequently yielded Providencia spp., Pseudomonas spp., Proteus spp., and Enterobacter spp., whereas biopsies more frequently yielded Streptococcus spp., Enterococcus spp., and Klebsiella spp. Comparability was limited by the inclusion of diverse populations treated across 14 different countries over the past 50 years. Methodological inconsistencies in sampling and reporting (particularly regarding contaminants, duplicates, and anaerobes) further complicated interpretation and underscore the need for standardized protocols. Nevertheless, findings consistently confirmed a polymicrobial flora dominated by a small group of recurrent species. The ulcer microenvironment is dynamic and distinct from culture media, complicating both diagnosis and treatment. Despite marked heterogeneity, the consistent predominance of Staphylococcus aureus, Enterobacteriaceae, Streptococcus spp., Enterococcus spp., Pseudomonas spp., and Bacteroides spp. provides a valuable framework for empiric therapy. The potential benefits of short perioperative courses of broad-spectrum antibiotics targeting these pathogens warrant further investigation, and prospective controlled trials are urgently needed. The study protocol was registered in PROSPERO (CRD420251076473) and is available at https://www.crd.york.ac.uk/PROSPERO/view/CRD420251076473.