Cookies on this website

We use cookies to ensure that we give you the best experience on our website. If you click 'Accept all cookies' we'll assume that you are happy to receive all cookies and you won't see this message again. If you click 'Reject all non-essential cookies' only necessary cookies providing core functionality such as security, network management, and accessibility will be enabled. Click 'Find out more' for information on how to change your cookie settings.

ABSTRACT Nitrofurantoin resistance in Escherichia coli is primarily caused by mutations damaging two enzymes, NfsA and NfsB. Studies based on small isolate collections with defined nitrofurantoin MICs have found significant random genetic drift in nfsA and nfsB , making it extremely difficult to predict nitrofurantoin resistance from whole-genome sequence (WGS) where both genes are not obviously disrupted by nonsense or frameshift mutations or insertional inactivation. Here, we report a WGS survey of 200 oqxAB -negative E. coli from community urine samples, of which 34 were nitrofurantoin resistant. We characterized individual non-synonymous mutations seen in nfsA and nfsB among this collection using complementation cloning and NfsA/B enzyme assays in cell extracts. We definitively identified R203C, H11Y, W212R, A112E, and A112T in NfsA and R121C, Q142H, F84S, P163H, W46R, K57E, and V191G in NfsB as amino acid substitutions that reduce enzyme activity sufficiently to cause resistance. In contrast, E58D, I117T, K141E, L157F, A172S, G187D, and A188V in NfsA and G66D, M75I, V93A, and A174E in NfsB are functionally silent in this context. We identified that 9/166 (5.4%) nitrofurantoin-susceptible isolates were “pre-resistant,” defined as having loss of function mutations in nfsA or nfsB . Finally, using NfsA/B enzyme assays and proteomics, we demonstrated that 9/34 (26.5%) ribE wild-type nitrofurantoin-resistant isolates also carried functionally wild-type nfsB or nfsB / nfsA . In these cases, NfsA/B activity was reduced through downregulated gene expression. Our biological understanding of nitrofurantoin resistance is greatly improved by this analysis but is still insufficient to allow its reliable prediction from WGS data.

Original publication

DOI

10.1128/aac.00242-24

Type

Journal article

Journal

Antimicrobial Agents and Chemotherapy

Publisher

American Society for Microbiology

Publication Date

09/07/2024

Volume

68