J Med Microbiol. 2021 Apr;70(4). doi: 10.1099/jmm.0.001347.
Introduction. Nitrofurantoin is one of the preferred antibiotics in the treatment of uropathogenic multidrug-resistant (MDR) infections. However, resistance to nitrofurantoin in extensively drug-resistant (XDR) bacteria has severely limited the treatment options.Gap statement. Information related to co-resistance or collateral sensitivity (CS) with reference to nitrofurantoin resistant bacteria is limited.Aim. To study the potential of nitrofurantoin resistance as an indicator of the XDR phenotype in Enterobacteriaceae.Methods. One hundred (45 nitrofurantoin-resistant, 21 intermediately resistant and 34 nitrofurantoin-susceptible) Enterobacteriaceae were analysed in this study. Antibiotic susceptibility testing (AST) against nitrofurantoin and 17 other antimicrobial agents across eight different classes was performed by using the Vitek 2.0 system. The isolates were screened for the prevalence of acquired antimicrobial resistance (AMR) and efflux pump genes by PCR.Results. In total, 51 % of nitrofurantoin-resistant and 28 % of intermediately nitrofurantoin resistant isolates exhibited XDR characteristics, while only 3 % of nitrofurantoin-sensitive isolates were XDR (P=0.0001). Significant co-resistance was observed between nitrofurantoin and other tested antibiotics (β-lactam, cephalosporin, carbapenem, aminoglycoside and tetracycline). Further, the prevalence of AMR and efflux pump genes was higher in the nitrofurantoin-resistant strains compared to the susceptible isolates. A strong association was observed between nitrofurantoin resistance and the presence of bla PER-1, bla NDM-1, bla OXA-48, ant(2) and oqxA-oqxB genes. Tigecycline (84 %) and colistin (95 %) were the only antibiotics to which the majority of the isolates were susceptible.Conclusion. Nitrofurantoin resistance could be an indicator of the XDR phenotype among Enterobacteriaceae, harbouring multiple AMR and efflux pump genes. Tigecycline and colistin are the only antibiotics that could be used in the treatment of such XDR infections. A deeper understanding of the co-resistance mechanisms in XDR pathogens and prescription of AST-based appropriate combination therapy may help mitigate this problem.