Prediction of nitrofurantoin resistance among Enterobacteriaceae and mutational landscape of in vitro selected resistant Escherichia coli.

Nitrofurantoin (NIT) has long been a drug of choice in the treatment of lower urinary tract infections. Recent emergence of NIT resistant Enterobacteriaceae is a global concern. An ordinal logistic regression model based on PCR amplification patterns of five genes associated with NIT resistance (nfsA, nfsB, ribE, oqxA, and oqxB) among 100 clinical Enterobacteriaceae suggested that a combination of oqxB, nfsB, ribE, and oqxA is ideal for NIT resistance prediction. In addition, four Escherichia coli NIT-resistant mutants were in vitro generated by exposing an NIT-susceptible E. coli to varying concentrations of NIT. The in vitro selected NIT resistant mutants (NI2, NI3, NI4 and NI5) were found to have mutations resulting in frameshifts, premature/lost stop codons or failed amplification of nfsA and/or nfsB genes. The in vitro selected NI5 and the transductant colonies with reconstructed NI5 genotype exhibited reduced fitness compared to their parent strain NS30, while growth of a resistant clinical isolate (NR42) was found to be unaffected in the absence of NIT. These results emphasize the importance of strict adherence to prescribed antibiotic treatment regimens and dosage duration. If left unchecked, these resistant bacteria may thrive at sub-therapeutic concentrations of NIT and spread in the community.