Molecular Mechanisms of Colistin Resistance Among Pandrug-Resistant Isolates ofAcinetobacter baumanniiwith High Case-Fatality Rate in Intensive Care Unit Patients

Abstract

Colistin is considered a last-hope antibiotic against extensively drug-resistant isolates of Acinetobacter baumannii. Resistance to colistin has been rarely reported for A. baumannii. Genetic alterations in the PmrA-PmrB two-component system and lipid A biosynthesis genes may be associated with colistin resistance. We investigated molecular mechanisms of colistin resistance in three clinical colistin-resistant (ColR) and two colistin-susceptible (ColS) A. baumannii isolates. A ColR mutant was generated in vitro by repetitive drug exposure. The pmrA, pmrB, lpxA, lpxC, and lpxD genes were amplified and sequenced. To evaluate association between colistin resistance and upregulation of pmrCAB operon, transcriptional level of the pmrC gene encoding for lipid A phosphoethanolamine (PEtN) transferase was quantified by reverse transcription quantitative PCR (RT-qPCR) analysis. All clinical and in vitro-selected ColR isolates harbored at least one point mutation in the pmrB gene, including A142V, P233S, T235I, and A227V substitutions as well as duplication of H325. No alteration was found in the pmrA and other amino acid substitutions identified in the pmrB as well as lpx genes did not seem to be involved in colistin resistance as they were found in both ColS and ColR isolates. RT-qPCR analysis revealed a correlation between colistin resistance and pmrC overexpression. Specific alterations in the PmrB, linked to overproduction of PEtN transferase, triggered colistin resistance in the studied A. baumannii isolates.

Colistin resistance inAcinetobacter baumanniiis driven by multiple genomic traits: Evaluating the role of ISAba1-driveneptAoverexpression among Indian isolates

“…In this study, clinical isolates of CR-ColRAB and CR-ColSAB were characterized for multiple colistin resistance mechanisms. Mutation analysis in lpxACD identified three nonsynonymous mutations; Q4K, V63I and E117K within lpxD in both CR-ColRAB and CR-ColSAB which concurs with previous studies [26,27]. Recent studies report that mutations in pmrB as the major contributor for colistin resistance in A. baumannii [24,26,28,29].The current study identified a non-synonymous mutation, A138T in pmrB while previous studies report other amino-acid substitutions together with A138T which is contrary to the current study [24,26,29].…”

<p>Survey on Genetic Diversity, Biofilm Formation, and Detection of Colistin Resistance Genes in Clinical Isolates of <em>Acinetobacter baumannii</em></p>

“…29,30 Scattered reports of its resistance to the last-line treatment, colistin, have raised further concerns for the medical field. 7,8,23,24 A. baumannii has different mechanisms for resistance to colistin. It is also featured by having ability to produce biofilms, which are very effective in maintaining and retaining this bacterium in hospital environments.…”

“…Biofilm-related genes (bap, ompA, csuE, and bla PER1 ) and colistin resistance-related genes (mcr-1, mcr-2, pmrA, and pmrB) were detected using PCR. [21][22][23] Bacterial DNA extraction was performed in accordance with the boiling method. 24 The PCR assay was carried out in a final volume of 25 μL containing Taq DNA polymerase (1 U; CinnaGen, Iran), dNTPs (100 μM), Taq buffer (5×), DNA template (50 ng), and forward and reverse primers (25 pM).…”

Antibiotic resistance breakers: current approaches and future directions

“…2016; Rapoport et al . 2016; Skov and Monnet 2016; Kluytmans 2017; Haeili, Kafshdouz and Feizabadi 2018) necessitate the development of novel alternatives. Efforts to develop polymyxin derivatives as ARBs to potentiate the actions of antibiotics have been spearheaded in recent decades by Prof. Martti Vaara and co-workers.…”