Alquethamy, S. F. | Search bioRxiv

bioRxiv2026

Disruption of cAMP Signalling and RNA Regulation Confers Cefiderocol Resistance in Acinetobacter baumannii

Cefiderocol is a siderophore-conjugated cephalosporin used to treat severe multidrug-resistant Gram-negative infections. Its recent prioritisation for US national preparedness underscores its clinical importance, yet resistance can emerge despite apparent in vitro susceptibility. Here, we identify two regulatory routes to cefiderocol resistance in carbapenem-resistant Acinetobacter baumannii (CRAB): mutation of the cAMP-producing adenylate cyclase CavA and truncation of the glycine-rich RNA-binding domain of the post-transcriptional regulator Hfq. These variants occurred in contemporary clinical isolates, conferred resistance in a murine CRAB lung-infection model and imposed minimal fitness costs. In Escherichia coli, deletion of the CavA orthologue cyaA increased competitive fitness during sub-inhibitory cefiderocol exposure. Hfq-CLASH and integrated omics revealed Hfq-dependent regulation of Fur-associated iron homeostasis in A. baumannii. Under iron limitation, truncated-Hfq induced a defence-primed state that attenuated siderophore uptake and reduced cefiderocol activity. These findings identify bacterial regulatory state and iron availability as determinants of cefiderocol susceptibility, with implications for resistance surveillance and susceptibility testing.

microbiology↗

bioRxiv2020

The molecular basis of Acinetobacter baumannii cadmium toxicity and resistance

Acinetobacter species are ubiquitous Gram-negative bacteria that can be found in water, soil and as commensals of the human skin. The successful inhabitation of Acinetobacter species in diverse environments is primarily attributable to the expression of an arsenal of stress resistance determinants, which includes an extensive repertoire of metal ion efflux systems. Although metal ion homeostasis in the hospital pathogen Acinetobacter baumannii is known to contribute to pathogenesis, insights into its metal ion transporters for environmental persistence are lacking. Here, we studied the impact of cadmium stress on A. baumannii. Our functional genomics and independent mutant analyses revealed a primary role for CzcE, a member of the cation diffusion facilitator (CDF) superfamily, in resisting cadmium stress. Further, we show that the CzcCBA heavy metal efflux system also contributes to cadmium efflux. Analysis of the A. baumannii metallome under cadmium stress showed zinc depletion and copper enrichment, which are likely to influence cellular fitness. Overall, this work expands our understanding of the role of membrane transporters in A. baumannii metal ion homeostasis. IMPORTANCECadmium toxicity is a widespread problem, yet the interaction of this heavy metal with biological systems is poorly understood. Some microbes have evolved traits to proactively counteract cadmium toxicity, which includes Acinetobacter baumannii. Here we show that A. baumannii utilises a dedicated cadmium efflux protein in concert with a system that is primarily attuned to zinc efflux, to efficiently overcome cadmium stress. The molecular characterization of A. baumannii under cadmium stress revealed how active cadmium efflux plays a key role in preventing the dysregulation of bacterial metal ion homeostasis, which appeared to be the primary means by which cadmium exerts toxicity upon the bacterium.

microbiology↗