Effects of Subminimal Inhibitory Concentrations of Chlorhexidine on the Chlorhexidine Resistance and Biofilm Formation in Clinical Drug-resistant Acinetobacter baumannii Isolates

Background and objectives: Multi-drug resistant microorganisms have caused a remarkable increase in hospital-acquired infections (HAI) during the previous few decades. Moreover, microbiological contamination of antiseptics and disinfectants has been recorded in medical settings. Methods:  A total of 61 clinically relevant Acinetobacter baumannii isolates were collected from various clinical specimens in hospitals in Erbil city/Iraq between September 2021 and March 2022. The isolates were identified using VITEK-2 compact system. Antimicrobial susceptibility testing was carried out for a total of 16 different therapeutically relevant antibiotics in accordance with the criteria of the Clinical Laboratory Standards Institute (CLSI) using the above mentioned system. A spectrophotometer was used to determine the optical density at 600 nm (OD600nm) for biofilm evaluation. Wilcoxon signed ranks test used to determine the effect of sub-MIC of CHX on the CHX-MIC and biofilm formation. Results: the study showed that there is a significant difference in CHX-MIC and biofilm formation before and after 7 days of incubation of Acinetobacter baumannii in sub-MIC of CHX (p<0.05). Exposure of Acinetobacter baumannii to sub-lethal CHX concentrations develops inducible resistance to lethal CHX doses. The biofilm formation ability of isolates also increased after using sub-lethal dose of CHX.