Little is known about SARS-CoV-2 evolution under Molnupiravir and Paxlovid, the only antivirals approved for COVID-19 treatment. By investigating SARS-CoV-2 variability in 8 Molnupiravir-treated, 7 Paxlovid-treated and 5 drug-naïve individuals at 4 time-points (Days 0-2-5-7), a higher genetic distance is found under Molnupiravir pressure compared to Paxlovid and no-drug pressure (nucleotide-substitutions/site mean±Standard error: 18.7 × 10−4 ± 2.1 × 10−4 vs. 3.3 × 10−4 ± 0.8 × 10−4 vs. 3.1 × 10−4 ± 0.8 × 10−4, P = 0.0003), peaking between Day 2 and 5. Molnupiravir drives the emergence of more G-A and C-T transitions than other mutations (P = 0.031). SARS-CoV-2 selective evolution under Molnupiravir pressure does not differ from that under Paxlovid or no-drug pressure, except for orf8 (dN > dS, P = 0.001); few amino acid mutations are enriched at specific sites. No RNA-dependent RNA polymerase (RdRp) or main proteases (Mpro) mutations conferring resistance to Molnupiravir or Paxlovid are found. This proof-of-concept study defines the SARS-CoV-2 within-host evolution during antiviral treatment, confirming higher in vivo variability induced by Molnupiravir compared to Paxlovid and drug-naive, albeit not resulting in apparent mutation selection.

Infection prevention and control (IPC) practices are of paramount importance for preventing the spread of multidrug-resistant organisms (MDROs) in hospitals, especially in the intensive care unit (ICU). Whole-genome sequencing (WGS) is seen as a promising tool for IPC, but its employment is currently still limited.

Background: Carbapenem resistant Klebsiella pneumoniae (cr-Kp) causes serious infections associated with a high mortality rate. The clinical efficacy of ceftazidime/avibactam (CZA), meropenem/vaborbactam (M/V), and imipenem/relebactam (I/R) against cr-Kp is challenged by the emergence of resistant strains, making the investigation and monitoring of the main resistance mechanisms crucial. In this study, we reported the genome characterization of a Klebsiella pneumoniae strain isolated from a critically ill patient and characterized by a multidrug resistant (MDR) profile, including resistance to CZA, M/V, and I/R. Methods: An antimicrobial susceptibility test (AST) was performed by an automated system and E-test and results were interpreted following the EUCAST guidelines. Genomic DNA was extracted using a genomic DNA extraction kit and it was sequenced using the Illumina Nova Seq 6000 platform. Final assembly was manually curated and carefully verified for detection of antimicrobial resistance genes, porins modifications, and virulence factors. Results: The K. pneumoniae isolate belonged to sequence type ST512 and harbored 23 resistance genes, conferring resistance to all antibiotic classes, including blaKPC-31 and blaOXA-181, leading to carbapenems resistance. The truncation of OmpK35 and mutation OmpK36GD were also observed. Conclusions: The genomic characterization demonstrated the high resistant profile of new cr-Kp coharboring class A and D carbapenemases. The presence of KPC-31, as well as the detection of OXA-181 and porin modifications, further limit the therapeutic options, including the novel combinations of β-lactam/β-lactamase inhibitor antibiotics in patients with severe pneumonia caused by cr-Kp.

Molnupiravir and Paxlovid are the only antivirals approved for COVID-19 treatment. Previous studies have evaluated their efficacy, tolerability, and viral clearance, but little is known about SARS-CoV-2 evolution under their pressure. Here the dynamics of genomic evolution of SARS-CoV-2 in 8 Molnupiravir-treated, 7 Paxlovid-treated and 5 drug-naïve individuals at 4 time-points (Day 0, Day 2, Day 5 of treatment and Day 7) were in-depth investigated. SARS-CoV-2 strains under Molnupiravir pressure were characterized by a higher genetic diversity compared to Paxlovid and no-drug pressure (mean ± SE: 18.66x10− 4±2.06x10− 4 vs. 3.34x10− 4±0.84x10− 4 vs. 3.10x10− 4±0.84x10− 4, P = 0.0003), with a peak between Day 2 and Day 5. Molnupiravir drove the emergence of more G-A and C-T transitions than other mutations (P = 0.031), regardless of SARS-CoV-2 genes. SARS-CoV-2 under Molnupiravir pressure did not show selective evolution different than that under Paxlovid or no-drug pressure, with the only exception of orf8 (dN > dS, P = 0.001); few amino acid mutations were enriched consistently at specific sites. No evidence of RdRp or Mpro mutations conferring resistance to Molnupiravir or Paxlovid was found. This proof-of-concept study defines the SARS-CoV-2 within-host evolution during antiviral treatment, confirming the higher in vivo variability induced by Molnupiravir respect to Paxlovid and controls, albeit not resulting in selection of resistance mutations.