Retrieving of diguanylate cyclases responsible for biofilm formation and antibiotic resistance in Acinetobacter baumannii

As a common opportunistic nosocomial pathogen, Acinetobacter baumannii has emerged as an increasingly multidrug-resistant threat due to its strong biofilm lifestyle. The GGDEF/EAL domain proteins regulate c-di-GMP metabolism, thereby affecting biofilm formation and antibiotic resistance. Nevertheless, the effects of such proteins on biofilm formation and antibiotic resistance of A. baumannii remain unclear. In this study, we identified and characterized the GGDEF/EAL domain proteins in A. baumannii and evaluated their contributions to biofilm formation and antibiotic resistance. Comparative genomic analysis revealed eleven genes encoding putative proteins that metabolize c-di-GMP in A. baumannii EMB-1. Overexpression of individual putative proteins showed that a diguanylate cyclase DGC8 markedly influenced the colony morphology, surface-associated motility, and biofilm formation of A. baumannii EMB-1. Furthermore, the antibiotic susceptibility test showed that DGC8 enhances the resistance of EMB-1 to four frequently used antibiotics (i.e., ceftazidime, cefepime, levofloxacin, and tigecycline). Importantly, molecular biology evidence suggests that DGC8 regulates biofilm formation through the Csu pili-mediated pathway. Together, our findings provide a basis for understanding the physiology of drug resistance in A. baumannii through the regulation of biofilm formation and surface-associated motility, shedding light on targeting DGC8 as an emerging mitigation strategy to control this pathogen.