Emergence of High-Level Colistin Resistance in an Acinetobacter baumannii Clinical Isolate Mediated by Inactivation of the Global Regulator H-NS

Abstract

Colistin is a crucial last-line drug used for the treatment of life-threatening infections caused by multidrug-resistant strains of the Gram-negative bacterium However, colistin-resistant isolates can still be isolated following failed colistin therapy. Resistance is most often mediated by the addition of phosphoethanolamine (pEtN) to lipid A by PmrC, following missense mutations in the operon encoding PmrC and the two-component signal transduction system PmrA/PmrB. We recovered a pair of isolates from a single patient before (6009-1) and after (6009-2) failed colistin treatment. These strains displayed low and very high levels of colistin resistance (MICs, 8 to 16 μg/ml and 128 μg/ml), respectively. To understand how increased colistin resistance arose, we sequenced the genome of each isolate, which revealed that 6009-2 had an extra copy of the insertion sequence element IS within a gene encoding an H-NS family transcriptional regulator. To confirm the role of H-NS in colistin resistance, we generated an deletion mutant in 6009-1and showed that colistin resistance increased upon the deletion of We also provided 6009-2 with an intact copy of and showed that the strain was no longer resistant to high concentrations of colistin. Transcriptomic analysis of the clinical isolates identified more than 150 genes as being differentially expressed in the colistin-resistant mutant 6009-2. Importantly, the expression of, encoding a second lipid A-specific pEtN transferase but not , was increased in the mutant. This is the first time an H-NS family transcriptional regulator has been associated with a pEtN transferase and colistin resistance.

The Concept of Resilience in Ecological Risk Assessment: Scientific and Regulatory Issues

“…Examples of genetic adaptation to stress factors are more common in populations with short life cycle and high mutation and genetic recombination potential, such as bacteria and algae (Lelandais et al 2008). A typical example is the selection of bacterial resistance to antibiotics (Deveson Lucas et al 2018). However, it has also been observed in more complex organisms such as microcrustaceans (Lopes et al 2006).…”

Abundance of Colistin-Resistant, OXA-23- and ArmA-Producing Acinetobacter baumannii Belonging to International Clone 2 in Greece

“…Colistin resistance may also result from the overexpression of etpA, a pmrC homolog. This is mediated by insertional inactivation of a gene encoding an H-NS family transcriptional regulator (Lucas et al, 2018) or by integration of insertion sequence elements upstream of the eptA gene itself (Gerson et al, 2019;Potron et al, 2019;Trebosc et al, 2019).…”

MITE Aba12 , a Novel Mobile Miniature Inverted-Repeat Transposable Element Identified in Acinetobacter baumannii ATCC 17978 and Its Prevalence across the Moraxellaceae Family

“…Two additional examples of IS-mediated disruption of hns in A. baumannii have been recently identified (9, 69). IS Aba12 5 was shown to be responsible in both studies, integrating into the intergenic region downstream of hns (ACICU_00289).…”

“…IS Aba12 5 was shown to be responsible in both studies, integrating into the intergenic region downstream of hns (ACICU_00289). In one case, the last two amino acids of H-NS are altered and the protein extended for an additional three amino acids by the integration of complete and partial copies of the IS Aba12 5 element (69). Collectively, these results infer that H-NS is a hot spot for disruption in A.…”