Balancing mcr-1 expression and bacterial survival is a delicate equilibrium between essential cellular defence mechanisms

Abstract

MCR-1 is a lipid A modifying enzyme that confers resistance to the antibiotic colistin. Here, we analyse the impact of MCR-1 expression on E. coli morphology, fitness, competitiveness, immune stimulation and virulence. Increased expression of mcr-1 results in decreased growth rate, cell viability, competitive ability and significant degradation in cell membrane and cytoplasmic structures, compared to expression of catalytically inactive MCR-1 (E246A) or MCR-1 soluble component. Lipopolysaccharide (LPS) extracted from mcr-1 strains induces lower production of IL-6 and TNF, when compared to control LPS. Compared to their parent strains, high-level colistin resistance mutants (HLCRMs) show reduced fitness (relative fitness is 0.41–0.78) and highly attenuated virulence in a Galleria mellonella infection model. Furthermore, HLCRMs are more susceptible to most antibiotics than their respective parent strains. Our results show that the bacterium is challenged to find a delicate equilibrium between expression of MCR-1-mediated colistin resistance and minimalizing toxicity and thus ensuring cell survival.

Compensatory mutations modulate the competitiveness and dynamics of plasmid-mediated colistin resistance in Escherichia coli clones

“…However, a demonstrable loss of electron density and significant impaired cell wall integrity were observed in both MCR-3.1-and MCR-3.5-producing E. coli TOP10 cells ( Supplementary Fig. 2), which is consistent with our previous findings with mcr-1 expression [8].…”

“…Two variants of mcr-3 (mcr 3.1 and mcr 3.5) are now highly prevalent in South East Asia (unpublished data), but despite their clinical importance, the impact of mcr-3 expression on bacterial fitness is still unknown. To test the impact of mcr-3 expression on bacterial fitness, we cloned mcr-3 into an inducible expression vector using a strategy as previously described to measure the cost of mcr-1 [8] (details of strains and plasmids are listed in Supplementary Table 1). Consistent with our previous work, induction of mcr expression slowed the growth of E. coli Top10 relative to uninduced controls, demonstrating a fitness cost by mcr expression ( Fig.…”

<b><i>Pseudomonas aeruginosa</i></b> and <b><i>Klebsiella</i></b> <b><i>pneumoniae</i></b> Adaptation to Innate Immune Clearance Mechanisms in the Lung

“…Whether or not these mutations carry a high fitness cost is not well established in humans. In a Galleria mellonella infection model, MCR-1-mediated resistance was associated with decreased fitness and attenuated cytokine production [100]. How the alterations in the structure of LPS affect immune cell recognition and subsequent immunogenicity has not been published to date.…”

Development of a pig infection model with colistin-resistant Escherichia coli

“…The transconjugant obtained in vitro from E. coli 13-220 acquired resistance to colistin, tetracycline, sulfamethoxazole and trimethoprim. Different studies have shown that the in vitro acquisition of an mcr-1-containing plasmid does not lead to a considerable fitness cost in E. coli as measured by growth kinetics, cytotoxicity, and virulence in a Galleria mellonella model (Tietgen et al, 2018;Zhang et al, 2017), but a high level of mcr-1 expression compromises growth rate, fitness, and the membrane's structural integrity while increasing cellular death (Yang et al, 2017). In our experiment, most isolates from samples collected from the E. coli 13-220 M-inoculated pigs shared the characteristics of this strain, suggesting that the commensal strains which had acquired the mcr-1 gene were perhaps not as competitive as E. coli 13-220 M.…”

“…Furthermore, it has been shown that acquisition and expression of the mcr-1 gene in a E. coli cell may result in gross morphological changes, including cell membrane impairment, and reduced fitness and attenuated virulence in a Galleria mellonella model. Moreover the mcr-1 mediated LPS modification reduces the stimulation of macrophages, and a lower production of IL-6 and TNF was induced with LPS extracted from mcr-1 strains compared to control LPS (Yang et al, 2017). Thus because of these potential differences of susceptibility and virulence of mcr-1 strains, we decided to develop an experimental model of colibacillosis in weaned piglets using multi-drug-resistant E. coli strains isolated from clinical cases and carrying the mcr-1 gene.…”