ITC Entropy Dominance (DeltaH/DeltaG < 0.3) as a Pre-Treatment Screening Criterion to Select Fever-Robust Phages, With Receptor Downregulation Captured as a Parallel Assay

Phage therapy is a medical approach that uses viruses — called bacteriophages, or 'phages' — to hunt and destroy bacterial infections. It's a promising alternative (or complement) to antibiotics, especially as antibiotic resistance grows. Meanwhile, isothermal titration calorimetry, or ITC, is a lab technique from biophysics that precisely measures how strongly two molecules bind to each other, and crucially, *why* they bind — whether the attraction is driven by energy (enthalpy) or by disorder (entropy). This hypothesis proposes connecting these two worlds in a clever way. The core idea is that not all phages grip their bacterial targets equally well when a patient has a fever. When body temperature climbs from normal to feverish (~39°C), the binding chemistry between a phage and its docking site on a bacterium can weaken — but only for certain phages. The hypothesis argues that ITC can predict which phages will hold their grip at fever temperatures. Specifically, phages whose binding is driven more by entropy (molecular disorder) than by direct energy transfer are predicted to stay effective at fever. A ratio called ΔH/ΔG below 0.3 is proposed as a screening cutoff. A companion test would also check whether the bacterium's docking protein changes in abundance under heat stress — it may actually *increase* at fever, which would be a bonus for phage effectiveness. In plain terms: before treating a feverish patient with phage therapy, you'd run a quick lab screen to pick phages that won't lose their potency precisely when the patient needs them most. It's the difference between sending soldiers to battle in gear that works in heat versus gear that melts.

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