Aurélie Jayol

Polymyxins: Antibacterial Activity, Susceptibility Testing, and Resistance Mechanisms Encoded by Plasmids or Chromosomes

SUMMARY Polymyxins are well-established antibiotics that have recently regained significant interest as a consequence of the increasing incidence of infections due to multidrug-resistant Gram-negative bacteria. Colistin and polymyxin B are being seriously reconsidered as last-resort antibiotics in many areas where multidrug resistance is observed in clinical medicine. In parallel, the heavy use of polymyxins in veterinary medicine is currently being reconsidered due to increased reports of polymyxin-resistant bacteria. Susceptibility testing is challenging with polymyxins, and currently available techniques are presented here. Genotypic and phenotypic methods that provide relevant information for diagnostic laboratories are presented. This review also presents recent works in relation to recently identified mechanisms of polymyxin resistance, including chromosomally encoded resistance traits as well as the recently identified plasmid-encoded polymyxin resistance determinant MCR-1. Epidemiological features summarizing the current knowledge in that field are presented.

Genetic Features of MCR-1-Producing Colistin-Resistant Escherichia coli Isolates in South Africa

ABSTRACT A series of colistin-resistant Escherichia coli clinical isolates was recovered from hospitalized and community patients in South Africa. Seven clonally unrelated isolates harbored the mcr-1 gene located on different plasmid backbones. Two distinct plasmids were fully sequenced, and identical 2,600-bp-long DNA sequences defining a mcr-1 cassette were identified. Promoter sequences responsible for the expression of mcr-1, deduced from the precise identification of the +1 transcription start site for mcr-1, were characterized.

Heteroresistance to Colistin in Klebsiella pneumoniae Associated with Alterations in the PhoPQ Regulatory System

ABSTRACT A multidrug-resistant Klebsiella pneumoniae isolate exhibiting heteroresistance to colistin was investigated. The colistin-resistant subpopulation harbored a single amino acid change (Asp191Tyr) in protein PhoP, which is part of the PhoPQ two-component system that activates pmrHFIJKLM expression responsible for l-aminoarabinose synthesis and polymyxin resistance. Complementation assays with a wild-type phoP gene restored full susceptibility to colistin. Then, analysis of the colistin-susceptible subpopulation showed a partial deletion (25 bp) in the phoP gene compared to that in the colistin-resistant subpopulation. That deletion disrupted the reading frame of phoP, leading to a longer and inactive protein (255 versus 223 amino acids long). This is the first report showing the involvement of mutation(s) in PhoP in colistin resistance. Furthermore, this is the first study to decipher the mechanisms leading to colistin heteroresistance in K. pneumoniae.

Rapid Detection of Polymyxin Resistance in Enterobacteriaceae.

The test is inexpensive, easy to perform, sensitive, specific, and can be completed in <2 hours.

A Universal Culture Medium for Screening Polymyxin-Resistant Gram-Negative Isolates

ABSTRACT The colistin-containing SuperPolymyxin medium was developed for screening polymyxin-resistant Gram-negative bacteria. It was evaluated with 88 polymyxin-susceptible or polymyxin-resistant cultured Gram-negative isolates. Its sensitivity and specificity of detection were ca. 100%. The SuperPolymyxin medium is the first screening medium that is able to detect intrinsic and acquired polymyxin-resistant bacteria.

Modulation of mgrB gene expression as a source of colistin resistance in Klebsiella oxytoca

Gene modifications in the PmrAB and PhoPQ two-component regulatory systems, as well as inactivation of the mgrB gene, are known to be causes of colistin resistance in Klebsiella pneumoniae. The objective of this study was to characterise the mechanism involved in colistin resistance in a Klebsiella oxytoca isolate. A K. oxytoca clinical isolate showing resistance to colistin was recovered in Cali, Colombia. The pmrA, pmrB, phoP, phoQ and mgrB genes were amplified and sequenced. Wild-type mgrB genes from K. pneumoniae and K. oxytoca were cloned, and corresponding recombinant plasmids were used for complementation assays. By analysing the mgrB gene of the K. oxytoca isolate and its flanking sequences, an insertion sequence (IS) of 1196bp was identified in its promoter region. The insertion was located between nucleotides -39 and -38 when referring to the start codon of the mgrB gene, thus negatively interfering with expression of the mgrB gene by modifying its promoter structure. This IS was very similar to ISKpn26 (99% nucleotide identity) belonging to the IS5 family. Complementation assays with mgrB genes from wild-type K. pneumoniae or K. oxytoca restored full susceptibility to colistin. In conclusion, here we identified the mechanism involved in colistin resistance in a K. oxytoca isolate. Modulation of mgrB gene expression was the key factor for this acquired resistance to colistin.

National survey of colistin resistance among carbapenemase-producing Enterobacteriaceae and outbreak caused by colistin-resistant OXA-48-producing Klebsiella pneumoniae , France, 2014

From January 2014 to December 2014, 972 consecutive non-replicate carbapenemase-producing Enterobacteriaceae isolates from colonised or infected patients were collected at the Associated French National Reference Centre as part of the French national survey on antimicrobial resistance. It included 577 Klebsiella spp. (59%), 236 Escherichia coli (24%), 108 Enterobacter spp. (11%), 50 Citrobacter spp. (5%), and a single Salmonella spp. isolate (0.1%). Of 561 K. pneumoniae isolates, 35 were found to be resistant to colistin (6.2%). PFGE analysis revealed a clonal outbreak involving 15 K. pneumoniae isolates belonging to sequence type ST11, recovered in a single hospital in the Picardie region in northern France. Those clonally related isolates showed variable levels of resistance to colistin, ranging from 4 to 64 mg/L. They harboured the blaOXA-48 carbapenemase gene and the blaCTX-M-15 extended-spectrum beta-lactamase gene. Among the 91 Enterobacter cloacae isolates, seven were resistant to colistin and produced different types of carbapenemases. Surprisingly, none of the E. coli and Citrobacter spp. isolates showed resistance to colistin. This national survey including carbapenemase-producing isolates recovered in 2014 reported a high rate of colistin resistance in K. pneumoniae and E. cloacae (6.2% and 7.7%, respectively) in France.

Failure to detect carbapenem-resistant Escherichia coli producing OXA-48-like using the Xpert Carba-R assay®.

J.-W. Decousser, L. Poirel, M. Desroches, A. Jayol, E. Denamur and P. Nordmann 1) Department of Virology, Bacteriology— Infection Control, ParasitologyMycology, Assistance Publique-Hopitaux de Paris (AP-HP), University Hospital Henri Mondor, Creteil, 2) IAME, UMR 1137, INSERM, F-75018 Paris, France, 3) Medical and Molecular Microbiology Unit, Department of Medicine, Faculty of Science, University of Fribourg, Fribourg, Switzerland, 4) INSERM U914 “Emerging Antibiotic Resistance”, 5) Centre National Associe—Centre de Reference des Resistances aux Antibiotiques, K.-Bicetre, France and 6) Hopital Fribourgeois—hopital Cantonal, Fribourg, Switzerland

Acquisition of broad-spectrum cephalosporin resistance leading to colistin resistance in Klebsiella pneumoniae

ABSTRACT An extended-spectrum β-lactamase (ESBL)-producing and colistin-resistant Klebsiella pneumoniae clinical isolate was recovered from a patient who was treated with cefotaxime. This isolate harbored a blaCTX-M-15 ESBL gene that was associated with an ISEcp1 insertion sequence. Transposition of that tandem occurred within the chromosomal mgrB gene, leading to inactivation of the mgrB gene and consequently to acquired resistance to colistin. We showed here a coselection of colistin resistance as a result of a broad-spectrum cephalosporin selective pressure.

Prevalence of faecal carriage of colistin-resistant Gram-negative rods in a university hospital in western France, 2016

Plasmid-mediated and chromosomally-encoded colistin resistance is increasingly being reported worldwide. We aimed to determine the prevalence of faecal carriage of colistin-resistant Gram-negative rod isolates in a university hospital in western France. From February to May 2016, rectal swabs from 653 patients hospitalized in various clinical settings were recovered and subsequently screened for colistin resistance using the SuperPolymyxin medium. Antimicrobial susceptibilities were determined according to EUCAST guidelines. Genetic detection of plasmid-mediated colistin resistance was performed by PCR. The faecal carriage with intrinsic colistin-resistant isolates was high (23 %), while the faecal carriage with Gram-negative rods showing acquired resistance was low (1.4 %). No isolate carried the plasmid-mediated mcr-1/mcr-2 genes. It was noteworthy that none of the patients carrying isolates with acquired colistin resistance had previously received a colistin-based treatment, while these isolates were not multidrug resistant.