Microbiological and inflammatory profiles in diabetic foot infection: A severity-stratified analysis

This study analyzed the bacterial spectrum, antibiotic susceptibility profiles, and serum levels of human neutrophil lipocalin (HNL) and procalcitonin (PCT) in patients with diabetic foot infection (DFI) stratified by infection severity. A retrospective analysis was conducted on clinical data from DFI patients admitted to the Department of Endocrinology and Metabolism at Yan’an University Affiliated Hospital between January 2018 and May 2024. Based on the 2015 Infectious Diseases Society of America/ International Working Group on the Diabetic Foot classification system, patients were classified into mild, moderate, and severe infection groups. Bacterial pathogen distribution, antibiotic susceptibility, and inflammatory markers (HNL [ng/mL] and PCT [ng/mL]) were compared across groups. Among 387 screened patients, 208 (53.8%) had positive bacterial cultures. Monomicrobial infections were identified in 160 cases (77.0%), while polymicrobial infections accounted for 44 (21.2%). Gram-positive (G+) bacteria constituted 58.2% (121/208) of isolates, and Gram-negative (G−) bacteria represented 18.8% (39/208). The predominant Gram-positive (G+) bacteria were Staphylococcus aureus (52.1%), Staphylococcus epidermidis (14.9%), Staphylococcus hominis (5.0%), and Staphylococcus haemolyticus (5.0%), with S aureus being significantly more frequent across all severity groups ( P < .05). Common Gram-negative (G−) isolates included Escherichia coli (28.1%), Klebsiella pneumoniae (15.4%), and Klebsiella oxytoca (10.3%), with no significant differences among groups. Gram-positive (G+) isolates exhibited high susceptibility to gentamicin, vancomycin, oxacillin, and linezolid, with no intergroup differences. Vancomycin susceptibility was significantly higher in moderate and severe groups compared to the mild group ( P < .05). Gram-negative (G−) bacteria showed consistent susceptibility to ampicillin, levofloxacin, ceftazidime, cefoperazone-sulbactam, and meropenem across severity groups. Levels of HNL (ng/mL), PCT (ng/mL), white blood cell count (10 9 /L), neutrophil percentage (%), C-reactive protein (mg/L), and erythrocyte sedimentation rate (mm/h) increased significantly with infection severity ( P < .05). However, high-sensitivity C-reactive protein (mg/L) did not differ significantly among groups. Although polymicrobial infections were increasingly observed in DFI, Gram-positive (G+) bacteria (especially S aureus ) remain predominant. A shift toward Gram-negative (G−) pathogens was associated with higher infection severity. Empirical antibiotic treatment should be guided by local antimicrobial susceptibility patterns. The strong correlation of HNL and PCT with infection severity suggests their potential value in clinical assessment and management.