Trade-Offs between Antibacterial Resistance and Fitness Cost in the Production of Metallo-β-Lactamases by Enteric Bacteria Manifest as Sporadic Emergence of Carbapenem Resistance in a Clinical Setting

Abstract

Meropenem is a clinically important antibacterial reserved for treatment of multi-resistant infections. In meropenem-resistant bacteria of the family Enterobacterales, NDM-1 is considerably more common than IMP-1, despite both metallo-β-lactamases (MBLs) hydrolysing meropenem with almost identical kinetics. We show that blaNDM-1 consistently confers meropenem resistance in wild-type Enterobacterales, but blaIMP-1 does not. The reason is higher blaNDM-1 expression because of its stronger promoter. However, the cost of meropenem resistance is reduced fitness of blaNDM-1 positive Enterobacterales. In parallel, from a clinical case, we identified multiple Enterobacter spp. isolates carrying a plasmid-encoded blaNDM-1 having a modified promoter region. This modification lowered MBL production to a level associated with zero fitness cost but, consequently, the isolates were not meropenem resistant. However, we identified aKlebsiella pneumoniae isolate from this same clinical case carrying the same blaNDM-1 plasmid. This isolate was meropenem resistant despite low-level NDM-1 production because of a ramR mutation, reducing envelope permeability. Overall, therefore, we show how the resistance/fitness trade-off for MBL carriage can be resolved. The result is sporadic emergence of meropenem resistance in a clinical setting.

A novel magnetic bead-based extraction method for the isolation of antimicrobial resistance genes with a case study in river water in Malawi

“…By contrast, a greater number of ESBL resistance genes were detected post incubation than direct from water filter. There has been an increase in data surrounding the relative fitness costs on bacteria that harbour resistance markers in the absence of selection pressure, notably those associated with large mobile plasmids (Cheung et al, 2021; Huang et al, 2013; Melnyk et al, 2015). We hypothesise that the loss here is due to carbapenemases being less stable within bacteria than ESBLs, similar to outcomes observed by Cheung et al, (2021).…”

“…There has been an increase in data surrounding the relative fitness costs on bacteria that harbour resistance markers in the absence of selection pressure, notably those associated with large mobile plasmids (Cheung et al, 2021; Huang et al, 2013; Melnyk et al, 2015). We hypothesise that the loss here is due to carbapenemases being less stable within bacteria than ESBLs, similar to outcomes observed by Cheung et al, (2021). However, more extensive research is needed to both further our understanding of AMR as well as guide laboratory practice.…”

Deciphering the evolution of metallo-β-lactamases: A journey from the test tube to the bacterial periplasm

“…NDM-1 is more prevalent than IMP-1 in carbapenem-resistant Enterobacterales despite exhibiting similar activities in vitro (15,17). Avison and coworkers (84) have shown that this is due to higher expression levels of NDM-1, since the blaNDM-1 gene is found downstream an ISAba125 insertion sequence which provides a conserved strong promoter. In contrast, blaIMP-1 genes are located downstream of variable promoter sequences with different strengths, resulting in lower protein levels and, consequently, reduced resistance (84).…”

“…Avison and coworkers (84) have shown that this is due to higher expression levels of NDM-1, since the blaNDM-1 gene is found downstream an ISAba125 insertion sequence which provides a conserved strong promoter. In contrast, blaIMP-1 genes are located downstream of variable promoter sequences with different strengths, resulting in lower protein levels and, consequently, reduced resistance (84). An E. coli isolate carrying the blaIMP-6 gene was shown to be susceptible to imipenem and meropenem, as the result of the transcriptional repression of blaIMP-6.…”

“…The finding of a strong promoter can account for the higher frequency of NDM-1 in Enterobacterales based on genetic determinants (84). However, this cannot explain why some blaMBL genes are confined to one host, while others can adapt to a wide variety of bacteria (Table 1).…”