ramR Deletion in an Enterobacter hormaechei Isolate as a Consequence of Therapeutic Failure of Key Antibiotics in a Long-Term Hospitalized Patient

Abstract

Genome changes are central to the adaptation of bacteria especially under antibiotic pressure. The aim of this study was to report phenotypic and genomic adaptation undergone by Enterobacter hormaechei clinical strain that became highly resistant to key antimicrobials during a four months period in a patient hospitalized in intensive care unit (ICU). All six clinical E. hormaechei strains isolated in one ICU-hospitalized patient have been studied. MICs regarding 17 antimicrobial molecules have been measured. Single nucleotide polymorphism (SNP), was determined on the sequenced genomes. The expression of genes involved in antibiotic resistance among Enterobacter cloacae complex strains were determined by qRT-PCR. All the strains belonging to the same Sequence-Type 66 and were distant by a maximum of nine SNP. After three months of hospitalization, three strains presented a significant increase in MICs regarding ceftazidime, cefepime, temocillin, ertapenem, tigecycline, ciprofloxacin and chloramphenicol. Those resistant strains did not acquire additional antibiotics resistant genes but harbored a 16 bp deletion in the ramR gene. This deletion led to the up expression of RamA, AcrA, AcrB, TolC and the down expression of OmpF. The ΔramR mutant harbored the same phenotype as the resistant clinical strains regarding tigecycline, chloramphenicol and ciprofloxacin. The increased expression of RamA due to partial deletion in the ramR gene led to a cross resistance phenotype by an increase of antibiotics efflux through the AcrAB-TolC pump and the decrease of antibiotics permeability by porin OmpF. ramR appears to be an important adaptative trait for E. hormachei strains.

Multiple Mechanisms of Tigecycline Resistance in Enterobacteriaceae from a Pig Farm, China

“…We did not identify tmexCD1-toprJ1 or any genes belonging to the tet (X) family in the six E. hormaechei isolates. Compared to the E. hormaechei isolates showing susceptibility to tigecycline in this study, strain FY01 obtained from a patient in France ( 15 ), and E. cloacae NCTC9394 (GenBank accession no. FP929040 ), no amino acid changes within the genes ramR , ramA , marA , marR , acrA , acrB , or tolC possibly associated with tigecycline were identified (Table S2 in the supplemental material).…”

Phenotypic and Genotypic Characterization of Multidrug-Resistant Enterobacter hormaechei Carrying qnrS Gene Isolated from Chicken Feed in China

“…The E. hormaechei strain E70 carrying pE70 was isolated from a patient’s urine sample. Previous reports show that the isolation of E. hormaechei are mainly focused on clinical samples ( 2 , 62 , 63 ). In this study, the E. hormaechei strain M1 strain was isolated from chicken feed, which is a new source.…”

Studies on the Transmission of a Tigecycline Resistance-Mediating tet (A) Gene Variant from Enterobacter hormaechei via a Two-Step Recombination Process

“…The AcrAB mutant efflux pump was the major mechanism of tigecycline resistance among Gram-negative bacteria, including Klebsiella pneumoniae and Enterobacter cloacae ( 9 , 10 ). In recent years, it was reported that in Klebsiella pneumoniae , Enterobacter cloacae and Salmonella Typhimurium, the mutation of the ramR gene leaded to the increased expression of AcrAB efflux pump, which enhanced the resistance to various drugs, including tigecycline ( 11 – 13 ). In 2010, it was discovered in Salmonella that a variant of the efflux gene tet (A) can lead to low-level tigecycline resistance ( 14 ).…”