“Antimicrobial susceptibility of carbapenem-resistant Acinetobacter baumannii against tetracycline, doxycycline, tigecycline, minocycline and colistin: experience from a tertiary care hospital in Karachi”

In recent years, Acinetobacter baumannii has become a notorious hospital-acquired pathogen, particularly in critical care settings, due to its rapid development of resistance to even broad-spectrum antibiotics, including carbapenems. Amid the growing problem of antimicrobial resistance, carbapenem-resistant A. baumannii (CRAB) has been designated a critical global priority organism. Therefore, we aimed to evaluate the in vitro effectiveness of alternative agents, specifically tetracycline and its derivatives (doxycycline and minocycline), along with colistin, particularly in regions with a high CRAB burden, limited therapeutic options, and epidemiological data. Carbapenem-resistant Acinetobacter baumannii (CRAB) isolates from various clinical samples, excluding blood specimens, were included in this study. Antimicrobial susceptibility testing for tetracycline, doxycycline, tigecycline, and minocycline was performed using the disk diffusion method, while the broth microdilution method was employed for colistin. Interpretation of clinical breakpoints for all antibiotics was performed in accordance with the Clinical and Laboratory Standards Institute (CLSI) M100 guidelines. During the study period, 207 Acinetobacter baumanii isolates were characterized as CRAB. Most were isolated from male patients (58%) aged 0–25 (38%). Pneumonia was the most common clinical diagnosis (51%), followed by skin and soft tissue (31%) and urinary tract infection (7%). Tigecycline demonstrated the highest susceptibility (99%), followed by colistin (98%), minocycline (92%), and doxycycline (86%). Tetracycline exhibited the lowest susceptibility among the isolates (28%). Tigecycline, colistin, and minocycline demonstrated the highest efficacy. These findings are crucial for optimizing treatment strategies, enhancing surveillance of multidrug resistance, and reinforcing infection prevention, control, and antimicrobial stewardship programs.