Fosfomycin Resistance Mechanisms: Metabolic States Drive Bacterial Regrowth

Fosfomycin Resistance Mechanisms and Metabolic Blind Spots

Bacterial metabolic shifts can override antibiotic lethality. Specific gene knockdowns in Escherichia coli allow populations to survive and regrow after fosfomycin exposure. Fosfomycin acts as a sniper, targeting MurA to halt cell wall synthesis. While transporter loss is a documented issue, the influence of cellular metabolism on fosfomycin resistance mechanisms has remained obscure. This gap leaves clinicians blind to why treatment fails despite apparent susceptibility. This study utilised a CRISPR interference library to screen 1,515 metabolic genes, aiming to identify which metabolic activities dictate drug efficacy.

The Regrowth Phenotype

Disruption of ATP synthase and pyruvate kinase creates a survival window. Researchers observed that silencing these genes, particularly pykF, causes an initial die-off followed by robust recovery. This phenomenon is known as heteroresistance. It allows a fraction of the bacterial population to persist under pressure. Population analysis profiles confirmed that this is not uniform resistance but a dynamic adaptation. The bacteria are not simply enduring the attack; they are changing their internal environment to mitigate it.

Mechanics of Survival

The survival strategy is dual-layered. First, whole-genome sequencing of the pykF strain identified a specific mutation in ibaG, a gene located directly upstream of the drug's target, murA. Second, the metabolic shift alters the chemical battlefield. Metabolome analysis measured distinct accumulation of phosphoenolpyruvate (PEP) in the regrowing cells. PEP is the natural substrate for MurA. By flooding the enzyme with its natural fuel, the bacteria likely prevent fosfomycin from attaching. The drug is physically crowded out. Transcriptome analysis further revealed the upregulation of cpxP, a cell envelope stress response regulator. This suggests the bacteria actively repair envelope damage while the drug is competitively inhibited.

Strategic Implications

Metabolic dormancy or alteration is an active route to evolution. The study suggests that transient metabolic states provide the necessary time for bacteria to develop permanent genetic resistance. Standard susceptibility testing often misses these transient states. If clinical isolates exhibit low ATP synthase activity, standard fosfomycin courses might fail. Future therapies may require metabolic adjuvants to ensure total eradication, preventing the 'bunker mentality' that allows resistance to fester.