Dear All (and with thanks to Patricia Bradford for taking the lead on this newsletter): Today, this paper in Nature takes us on a trip to the land of unintended consequences: Turner, A.M., Li, L., Monk, I.R. et al. Rifaximin prophylaxis causes resistance to the last-resort antibiotic daptomycin. Nature 635, 969–977 (2024). https://doi.org/10.1038/s41586-024-08095-4. A wonkish summary is found below our signatures, but here’s the high-level version: Rifaximin is a non-absorbable oral antibiotic used to manage both traveler’s diarrhea and the CNS derangements that can be seen in advanced liver failure (hepatic encephalopathy). See this review (J Antibiotics 2014) and this Medscape summary. Daptomycin is a last-resort antibiotic (WHO AWaRe category of Reserve) used for Gram-positive infections, most notably serious infections due to Staphylococcus aureus and Enterococcus species. It is especially valued for its activity on vancomycin-resistant Enterococcus (Turnidge et al. 2020 CMI, https://doi.org/10.1016/j.cmi.2020.04.027). FDA labeling is here and note also this FDA rationale that extends the breakpoints for Enterococcus species from E. faecalis to also include E. faecium. Daptomycin and rifaximin are totally different classes of antibiotics and would not be expected to have any effects on each other. Daptomycin is a cyclic lipopeptide that acts by binding to (and disturbing) bacterial cell membranes....