Geographical patterns of in vitro susceptibilities to tigecycline and colistin among worldwide isolates of Acinetobacter baumannii, Escherichia coli and Klebsiella pneumoniae: Data from the Antimicrobial Testing Leadership and Surveillance (ATLAS) programme, 2016–2021

This study aimed to investigate the geographical trends of minimum inhibitory concentrations (MICs) for tigecycline and colistin in Acinetobacter baumannii, Escherichia coli, and Klebsiella pneumoniae isolates which were collected for the Antimicrobial Testing Leadership and Surveillance (ATLAS) programme from 2016–2021. MICs of the isolates were determined using the broth microdilution method. In the study period, there was an increase in MIC₅₀ and MIC₉₀ values in Asia for tigecycline MICs in A. baumannii isolates, and the geometric mean of MICs increased significantly from 0.51–0.96 (R² value of 0.912). The isolates in Europe and Latin America also showed an increase in the geometric mean, but the percentage of MIC values ≤ 2 mg/L decreased from 99.7% to 86.7% in Asia. Among the Asian countries studied, China (90.9%), Thailand (94.3%), and Malaysia (95.5%) showed the lower percentages of tigecycline MIC values ≤0.5 mg/L for E. coli isolates. In terms of colistin susceptibility among A. baumannii isolates, there was no increase in MIC₅₀/ MIC₉₀ or the geometric mean from 2016–2021. Compared to other continents, A. baumannii isolates in Europe had the highest MIC₅₀ (0.5 mg/L), MIC₉₀ (2 mg/L), and geometric mean (0.55 mg/L). For E. coli, the percentage of colistin MIC values ≤2 mg/L was consistently >98% in the study areas from 2016–2021. Among K. pneumoniae isolates, Europe and Latin America had higher geometric means of MICs (0.41 and 0.4 mg/L, respectively) and lower percentages of colistin MICs ≤2 mg/L than those in the other continents.